U.S. Department of 

Transportation Human Factors Guidance for Intelligent 

Transportation Systems at the Highway-Rail Federal Railroad 

Administration Intersection 

Office of Research 

and Development 

Washington, DC 20590 

DOT/FRA/ORD-06/26 Final Report This document is available to the 

December 2006 U.S. public through the National 

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Springfield, VA 22161. 
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Human Factors Guidance for Intelligent Transportation Systems at the Highway-Rail 

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James W. Jenness, Neil D. Lerner, Robert E. Llaneras, Jeremiah P. Singer, and Richard W. Huey

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13. ABSTRACT (Maximum 200 words)

This document provides guidance recommendations and supporting material to assist designers and implementers of intelligent 

transportation system (ITS) applications related to highway-rail intersections (HRI). The guidance focuses specifically on 

roadway user human factors requirements associated with ITS as applied to HRIs. The guidance is intended to be of immediate 

help to practitioners but also to serve as a resource and impetus toward the development of consensus standards and other more 

formal guidance or specification. The document has four parts. Part I describes the purpose and scope and provides a human 

factors conceptualization of the roadway user. Part II provides an overview of ITS applications that have been implemented at 

HRIs. Part III presents general human factors guidance that cuts across various specific HRI applications, for topics such as 

message factors, roadside displays, in-vehicle displays, and displays for pedestrians. Part IV presents guidance for specific HRI 

applications, including train arrival warnings, advance information about the HRI, enforcement and control of vehicles, and light 

rail transit. Each guidance chapter provides background on the topic, an explicit statement of the major human factors issues, and 

a set of guidance recommendations (with accompanying rationale for each). This report includes over 130 guidance 

recommendations.

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202

14. SUBJECT TERMS

Human factors, intelligent transportation systems (ITS), highway-rail intersection (HRI), grade 

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ii
Contents 

Preface and Acknowledgements............................................................................................... vii

Executive Summary ................................................................................................................... 1

Part I: Introduction.................................................................................................................... 3

1. Purpose and Scope................................................................................................... 5

1.1 Purpose ....................................................................................................................5

1.2 Scope of the Guidance..............................................................................................5

1.3 Human Factors Resources Related to ITS and to Road User Behavior......................6

1.4 Organization of the Report .......................................................................................8

2. Conceptualizing the Roadway User ........................................................................10

2.1 Need for a User-Centered Design Perspective ........................................................10

2.2 Selected Characteristics of HRI Road Users...........................................................11

2.3 Summary................................................................................................................15

Part II: Overview of ITS Implemented at the Highway-Rail Intersection ..................................17

3. Implemented Systems.............................................................................................19

3.1 Information About Arriving Trains.........................................................................19

3.2 Multiple Train Warnings........................................................................................27

3.3 Vehicle Control and Automated Enforcement ........................................................32

3.4 Summary of Lessons Learned.................................................................................35

Part III General Human Factors Considerations for Application of ITS to Highway-Rail

Intersections .................................................................................................................41

4. Message Factors .....................................................................................................43

4.1 Background............................................................................................................43

4.2 Key Human Factors Issues and Need for Guidance ................................................43

4.3 Recommendations..................................................................................................48

5. Roadside Displays ..................................................................................................75

5.1 Background............................................................................................................75

5.2 Key Human Factors Issues and Need for Guidance ................................................79

5.3 Recommendations..................................................................................................81

6. In-Vehicle Displays................................................................................................93

6.1 Background............................................................................................................93

6.2 Key Human Factors Issues and Need for Guidance ................................................94

6.3 Recommendations..................................................................................................96

7. Displays for Pedestrians .......................................................................................109

7.1 Background..........................................................................................................109

iii 
7.2 Key Human Factors Issues and Need for Guidance ..............................................110

7.3 Recommendations................................................................................................112

Part IV: Human Factors Requirements for Specific ITS Applications.....................................117

8. Warnings about Train Arrival ...............................................................................119

8.1 Background..........................................................................................................119

8.2 Key Human Factors Issues and Need for Guidance ..............................................119

8.3 Recommendations for Train Arrival Warnings.....................................................122

8.4 Specific Recommendations for MTWs.................................................................133

9. Advance Information about the HRI and Dynamic Route Guidance......................143

9.1 Background..........................................................................................................143

9.2 Key Human Factors Issues and Need for Guidance ..............................................144

9.3 Recommendations................................................................................................145

10. Enforcement and Control of Vehicles ...................................................................157

10.1 Control of Vehicles ..............................................................................................157

10.2 Automated Enforcement.......................................................................................158

11. Light Rail Transit .................................................................................................161

11.1 Background..........................................................................................................161

11.2 Key Human Factors Issues and Need for Guidance ..............................................162

11.3 Recommendations................................................................................................165

References .............................................................................................................................173

Appendix. List of Recommendations......................................................................................185

Acronyms and Abbreviations ..................................................................................................191

iv 
Illustrations 

Figure 1. Scope of the project.....................................................................................................6

Figure 2. Guidance chapters (Chapters 4-11) and their interrelationship .....................................9

Figure 3. Rail View online user interface..................................................................................21

Figure 4. Rail Monitoring System online user interface ............................................................22

Figure 5. Advance signs with train-activated flashing lights in Laredo, Texas ..........................23

Figure 6. In-vehicle HRI display for school buses ....................................................................25

Figure 7. Advisory in-vehicle warning system..........................................................................26

Figure 8. LACMTA MTW for pedestrians installed at Vernon Avenue grade crossing.............28

Figure 9. Los Angeles Metropolitan Transportation Authority MTW display (prototype) .........29

Figure 10. Timonium Road crossing site with MTW ................................................................30

Figure 11. Maryland MTA MTW display.................................................................................31

Figure 12. Prototype GRIP signs, AVV Test Centre .................................................................76

Figure 13. Kiama, NSW, Australia curve warning sign.............................................................77

Figure 14. Collision warning signs for the major leg (left) and minor leg (right) of the

intersection .............................................................................................................78

Figure 15. Information handling zones (from Lerner et al., 2002)...........................................126

v 
Tables 

Table 1. Highway-rail intersection warnings and enforcement projects.....................................37

Table 2. List of recommendations for message factors..............................................................49

Table 3. General advantages and disadvantages of message display modes ..............................60

Table 4. Driver performance variability factors (adapted from Lerner et al., 1995) ...................68

Table 5. Recommendations for roadside displays .....................................................................81

Table 6. List of recommendations for in-vehicle displays .........................................................96

Table 7. Recommendations for pedestrian displays.................................................................112

Table 8. Recommendations for warnings about train arrival ...................................................123

Table 9. Message characteristics for information handling zones............................................125

Table 10. Proposed message content for CMS displays at the HRI .........................................128

Table 11. Recommendations for message content and message comprehension for MTWs ....133

Table 12. Recommendations for advanced information about the HRI....................................146

Table 13. Information needed by drivers in advance of the HRI .............................................156

Table 14. Recommendations for LRT.....................................................................................165

vi 
Preface and Acknowledgements 

This document, Human Factors Guidance for Intelligent Transportation Systems at the 

Highway-Rail Intersection, provides guidance recommendations and supporting material to assist 

designers and implementers of intelligent transportation system applications related to highwayrail grade crossings. The document was developed under Federal Railroad Administration 

(FRA) contract DTFR53-00-R-00017. A final project technical report, Human Factors 

Guidelines for Intelligent Transportation Systems at the Highway-Rail Intersection: Final 

Project Technical Report, documents the primary activities and findings of the project. The 

technical report is available upon request from the project’s sponsor, Dr. Thomas Raslear 

(thomas.raslear@fra.dot.gov). 

This document is a revision that incorporates the comments of reviewers on an earlier draft. The 

project technical report includes a summary overview of the general findings of the reviewers. 

This version of the guidelines includes revisions in response to selected reviewer comments. It 

also includes footnotes that present selected reviewer opinions that may be of interest to readers. 

The project team would like to thank Dr. Raslear and the staff of the FRA Office of Research 

and Development for support, guidance, and critical review throughout the course of this work. 

Important contributions were also made by the outside reviewers of the initial draft of this 

document. Reviewers were recruited from a range of technical disciplines and stakeholder 

groups. We thank these organizations for helping to distribute the request for reviewers: 

 Transportation Research Board (Technical committees AHB15, AHB60, AND10,

AND20)

 ITS America 

 Association of American Railroads 

 Operation Lifesaver 

 Human Factors and Ergonomics Society (Surface Transportation Technical Group) 

 American Association of State Highway and Transportation Officials 

 American Traffic Safety Services Association 

 Transport Canada 

We gratefully acknowledge the outside reviewers who gave their time in reviewing all or 

portions of the document and provided many insightful comments. This acknowledgement 

should not be taken to imply that any individual reviewers endorse, approve, or agree with the 

contents of this document. The reviewers include: 

 Patricia DeLucia, Texas Tech University 

 Joanne Harbluk, Transport Canada 

 Joe Jeffrey, Road-Tech Safety Services, Inc. 

 Steve Laffey, Illinois Commerce Commission 

 Kumar Manjunathan, Montana State University, Western Transportation Institute 

vii 
 William McShane, Polytechnic University 

 Gina Melnik, Volpe National Transportation Systems Center 

 David Miller, Cornell University 

 Bill Petit, Safetran Systems 

 Dick Raub, Raub Associates 

 Victor Riley, User Interaction Research and Design 

 Thomas Smith, University of Minnesota 

 Heather Stoner, Aptima Inc 

 Arnand Tharanathan, Texas Tech University 

 Eric Wigglesworth (retired, Australia) 

 Ken Wood, Federal Highway Administration 

 Anonymous reviewers 

viii 
Executive Summary 

Intelligent transportation systems (ITS) technology can be applied to many transportation 

applications to improve safety and operations. Among the current and potential ITS applications 

are services related to the highway-rail intersection (HRI). The HRI is a point of potential 

conflict between rail and roadway traffic and, as such, is an important safety and operational 

concern. If ITS is to fulfill its promise, however, it is essential that the systems be designed with 

the human user in mind. The field of human factors specifically addresses issues of human 

interaction with systems. Although considerable human factors research and guidance for some 

ITS services has occurred, this has not been the case for HRI applications. No systematic effort 

to provide human factors standards or guidance for HRI ITS applications exists. 

This document, Human Factors Guidance for Intelligent Transportation Systems at the 

Highway-Rail Intersection, provides human factors guidance recommendations and supporting 

material to assist designers and implementers of ITS applications related to HRIs. The guidance 

has a very specific focus on roadway user requirements that emerge for human factors issues 

associated with ITS as applied to HRIs. The guidance is intended for practitioners. However, 

the guidance may also be used as a basis for consensus standards and other more formal human 

factors guidance such as approved practices, industry guidelines, design specifications, 

regulatory policy, model applications, and so forth. Therefore, another purpose of this document 

is to serve as a resource and impetus for subsequent standardization, industry consensus, and 

formalization. 

A set of key human factors issues was defined based on an extensive review of technical 

literature, expert contacts, reports of implemented systems, and analysis of guidelines in related 

fields. Guidance for the issues and applications was structured into a draft version of this 

document. A multidisciplinary group of potential users of the guidelines, stakeholder groups, 

and experts in relevant disciplines reviewed the guidance. Reviewers rarely disagreed with the 

guidance content. Revisions were made based on review comments and the document now 

includes selected reviewer comments as footnotes. These provide opinions and perspectives that 

may be of interest to readers. 

The document has four parts. Part I (Introduction) consists of two background chapters. 

Chapter 1 covers the purpose of the document and scope of the guidance. Chapter 2 helps 

conceptualize the roadway user so that a proper perspective may be brought to human-centered 

design of ITS applications. 

Part II, Overview of ITS Systems Implemented at the HRI, is a single chapter (Chapter 3) that 

describes the features and performance of ITS applications that have been implemented (usually 

as demonstration projects) at HRIs. 

Part III, General Human Factors Considerations for Application of ITS to HRIs, and Part IV, 

Human Factors Considerations for Specific Applications, present the actual human factors 

recommendations. Part III (Chapters 4–7) presents general human factors guidance that cuts 

across various specific HRI applications, for topics including message factors, roadside displays, 

in-vehicle displays, and displays for pedestrians. Part IV (Chapters 8–11) presents guidance for 

specific HRI applications, warnings about train arrival, advance information about the HRI and 

dynamic route guidance, enforcement and control of vehicles, and light rail transit (LRT). In all, 

this report includes more than 130 guidance recommendations. 

1
Each of the guidance chapters (Chapters 4–11) has a similar structure. The Background section 

describes the application and the relevant safety and operational concerns, and it reviews relevant 

research, practice, and field experience. The Key Human Factors Issues and Need for Guidance 

section identifies the major human factors issues of particular concern for the application and 

why guidance is needed. The Recommendations section provides the actual guidance statements 

with supporting discussions and rationales, as well as cross references to other sections of the 

guidelines and citations of key documents, where appropriate. 

2
Part I: Introduction 

3

1. Purpose and Scope 

1.1 Purpose 

ITS technology holds the promise of improved safety and operations for many transportation 

applications. The National ITS Architecture identifies more than 30 of these interrelated 

applications as user services, among which is the HRI User Service. Among the many listed 

elements and requirements of ITS for HRI in the architecture are those that require some form of 

communication with and management of the range of roadway users approaching and crossing 

the HRI. These road users include motor vehicle operators, bicyclists, and pedestrians. 

Researchers and developers of ITS have clearly recognized that if ITS is to fulfill its promise and 

find public acceptance, it is essential that the systems be designed with the human user in mind. 

Products and systems that are not well understood, readily usable, and acceptable to the roadway 

users who encounter them can put the ITS enterprise at risk. A considerable amount of human 

factors research and guidance related to a number of ITS user services has occurred. This, 

however, has not been the case for the HRI, which was identified in the National ITS 

Architecture somewhat later than many other user services. Various specific ITS applications 

have been deployed, demonstrated, or proposed for the HRI. Where evaluations have been done, 

however, there frequently has not been a strong human factors component. No systematic effort 

to provide human factors standards or guidance for the HRI ITS user service has occurred. 

The purpose of this document

1

 is to identify the major roadway user human factors issues related 

to the use of ITS at HRI and to provide guidance for dealing with these issues. This guidance is 

designed for immediate use by practitioners. However, it is also seen a step toward the 

development of consensus standards. The recommendations and principles put forward here can 

provide a basis from which standards organizations, regulatory agencies, and a broad range of 

concerned stakeholders can work together to devise and promote standards. In fact, this 

document identifies, but does not address, some important human factors requirements. For 

example, one guideline recommends that the same standard icon be used to denote an HRI in all 

in-vehicle displays. The guidance identifies some of the attributes such a standardized icon 

should have. In the absence of a general industry practice or conclusive research studies, 

however, it would not be appropriate to promote a specific icon because the very point of the 

recommendation is that the stakeholder community comes to agree on a single icon. To identify 

the key human factors issues and develop recommendations, this work has made use of research 

studies, field evaluations, existing guidelines from other applications, and a range of expert 

contacts. This document attempts to provide whatever guidance the current state of knowledge 

and consensus permits while also indicating where critical gaps in knowledge and needs for 

subsequent consensus standards development exist. 

1.2 Scope of the Guidance 

The scope of this effort is restricted to the conjunction of the areas of human factors, HRI, and 

ITS (Figure 1). The human factors issues of concern in this document are those related to the 

roadway user, including passenger vehicle and motorcycle operators; operators of large vehicles, 

1 This document incorporates revisions in response to selected reviewer comments on an initial draft. It also includes 

footnotes that present selected reviewer opinions that may be of interest to readers. 

5
such as buses and tractor trailers; bicyclists; and pedestrians. Issues related to traffic control 

center/rail operations center, train crew, communications protocols, and maintenance operations, 

are not within this scope, but treatments exist elsewhere (e.g., Askey & Sheridan, 1996; Multer, 

Rudich, & Yearwood, 1998; Oriol, Sheridan, & Multer, 2004). 

HF ITS 

HRI 

Figure 1. Scope of the project 

Having recognized that this report focuses on the human factors of ITS applications for the HRI, 

it must be acknowledged that some human factors principles may be broadly important for all 

ITS applications, not just the HRI. These must be addressed to some degree, or this document 

will not serve its purpose of providing immediate guidance for HRI ITS designers and 

implementers. Such issues as display location, choice of modality, and so forth must be dealt 

with for any ITS application. While this document is not intended to be a general reference for 

human factors design, it discusses general principles to some degree. 

Many human factors concerns are related to road user safety at the HRI, independent of any ITS 

component. A variety of reports and research studies over the past 25 years have addressed these 

concerns (e.g., Lerner, Ratte, & Walker, 1989; Mortimer, 1988; Dewar, 2001). Consensus 

standards groups and regulatory agencies have considered many of these issues in the 

development of current practice. The factors addressed by current standards and practice may be 

important to HRIs with ITS elements but not because of the ITS element. For example, features 

of automatic gates (markings, timing, etc.) should meet human factors concerns, regardless of 

whether the HRI is traditional or incorporates ITS. In this document, some unique aspect of the 

ITS application must exist in order to provide guidance here. General practices for HRI, which 

already reflect consensus or regulation, are not revisited in this document. 

In summary, the scope of the recommendations provided in this report encompasses human 

factors requirements for road users related to ITS applications at HRIs. User-centered design is 

important for all types of HRI and for all human users within all component elements of ITS 

systems, but such general concerns are beyond this project’s scope. 

1.3 Human Factors Resources Related to ITS and to Road User Behavior 

Although not a great deal of human factors research and guidance is directly related to ITS at the 

HRI, the human factors of other ITS applications have received more substantial resources. 

These are generally in the form of research findings or recommended practices, rather than as 

specific consensus standards. Because of interrelationships between user services and because 

6
shared design issues exist, these sources may also prove useful for HRI applications. The 

recommendations in this report draw upon human factors research from a variety of ITS 

applications and can also serve as direct references for the interested reader. 

Two primary consensus standards organizations develop guidance for human factors issues in 

ITS. Established in 1991 to develop vehicle-related ITS standards, the Society of Automotive 

Engineers (SAE) Standards Division is responsible for developing industry consensus standards. 

SAE is involved in various ITS standards projects intended to produce standards and 

recommended practices that support system architecture, in-vehicle systems interface, advanced 

traveler information systems, and commercial vehicle operations, among other areas. Specific 

standards developed to date or currently under development include ITS In-Vehicle Message 

Priority; Operating Characteristics and User Interface for Adaptive Cruise Control; Operating 

Characteristics and User Interface Requirements for Forward Collision Warning Systems; 

Integration of ITS In-Vehicle User Interfaces; Navigation and Route Guidance Function 

Accessibility While Driving; and In-Vehicle ITS Display Legibility. 

The International Organization for Standardization’s (ISO) Technical Committee 204 is the lead 

international organization responsible for developing and harmonizing ITS standards across a 

broad range of ITS applications. ISO was founded in 1946 by 25 national standards 

organizations to bring together producers and users in the development of voluntary international 

standards. ISO has parallel efforts to develop standards related to transportation information and 

control systems, as well as road vehicle standards for ITS systems. 

Research studies funded by National Highway Traffic Safety Administration (NHTSA), Federal 

Highway Administration (FHWA), and various States produced various guideline documents. 

These include the following: 

 Human Factors Design Guidelines for Advanced Traveler Information Systems (ATIS) 

and Commercial Vehicle Operations (CVO) (Campbell et al., 1998) 

 Preliminary Human Factors Design Guidelines for Driver Information Systems (Green et 

al., 1995) 

 Preliminary Human Factors Guidelines for Crash Avoidance Warning Devices (Lerner et 

al., 1996) 

 In-Vehicle Display Icons and Other Information Elements: Final In-Vehicle Symbol 

Guidelines (Campbell, Richman, Carney, & Lee, 2002) 

 Driver Information Demand Guidelines (Lerner & Llaneras, 2000) 

 Guidelines for Changeable Message Sign Messages (Dudek, 2002) 

 Developing Standards and Guidance for Changeable Message Signs in the Manual on 

Uniform Traffic Control Devices, Final Report (Dudek, 2003) 

 The Development of Traffic-Information Web-Site Design Guidelines (Nowakowski, 

Lenneman, Kojima, & Green, 1999) 

7
In addition to these guidance documents, useful books on the human factors of driver behavior 

are also available, including some focused on ITS. Among these are the following: 

 Human Factors in Traffic Safety (Dewar & Olson, 2001) 

 Human Factors for Highway Engineers (Fuller & Santos, 2002) 

 A Policy on Geometric Design of Highways and Streets (AASHTO, 2001; particularly 

Chapter 2, “Design Controls and Criteria”) 

 Driving Future Vehicles (Parkes & Franzen, 1993) 

 Human Factors in Intelligent Transportation Systems (Barfield & Dingus, 1998) 

 Ergonomics and Safety of Intelligent Driver Interfaces (Noy, 1997) 

Two broad reviews of driver behavior at the HRI appeared in the late 1980s: 

 Driver Behavior at Rail-Highway Grade Crossings (Lerner, Ratte, & Walker, 1989) 

 Human Factors in Highway-Railroad Grade Crossing Accidents (Mortimer, 1988) 

More recent, but narrower, reviews of specific HRI issues have appeared since these reports, but 

the fundamental human factors concerns remain the same. Westat (1999) provided a recent 

update of post-1989 literature specifically relevant to passive crossings and concluded that the 

issues remain largely the same and not much better understood. 

1.4 Organization of the Report 

Chapter 2 provides some context for considering the roadway user in the design of devices and 

systems for application at the HRI. A user-centered perspective is fundamental to good human 

factors design. Chapter 2 discusses some attributes of the road user that should be kept in mind 

for any application of ITS at the HRI. 

Following Chapter 2, three general sections (parts) comprise the remainder of the document. 

Part II, Overview of ITS Implemented at the HRI, provides a brief review of ITS applications at 

the HRI with respect to Implemented Systems (Chapter 3). Part III, General Human Factors 

Considerations for Application of ITS to HRIs, identifies concerns and provides guidance for 

issues that may be related to a range of possible ITS applications for HRI. These considerations 

are organized under the headings of Message Factors (Chapter 4), Roadside Displays (Chapter 

5), In-Vehicle Displays (Chapter 6), and Displays for Pedestrians (Chapter 7). These chapters 

address human factors concerns that must be confronted, whatever the specific application. 

Part IV, Human Factors Requirements for Specific ITS Applications, identifies human factors 

concerns related to Warning About Train Arrival (Chapter 8); Advance Information About HRIs 

and Dynamic Route Guidance (Chapter 9); Enforcement and Control of Vehicles (Chapter 10); 

and Light Rail Transit (Chapter 11). Finally, the appendix lists all of the recommendations from 

Chapter 4 through Chapter 11. 

Within these chapters, the general structure is to provide some background discussion on a given 

topic or application, followed by an explicit statement of the major human factors issues and 

need for guidance. This is then followed by specific guidance recommendations. Sometimes 

these recommendations can be quite specific. At other times, they can at this point only provide 

8
a general principle or set of limits. An accompanying Rationale Statement supports each 

recommendation.. 

Figure 2 shows the overall structure and interrelationships between guidance Chapters 4-11. The 

chapters are grouped into a rough hierarchy according to the level of generality and content of 

the recommendations. Chapters containing more widely applicable recommendations are 

positioned at levels closer to the top of the figure. The bi-directional arrows connecting the three 

levels indicate that similar or related recommendations in different chapters are cross referenced. 

Within the chapters, related recommendations in other chapters are within brackets; for example, 

the note [Also see: Recommendation 6-2] refers to Recommendation #2 in Chapter 6. 

Figure 2. Guidance chapters (Chapters 4-11) and their interrelationship 

9
2. Conceptualizing the Roadway User 

2.1 Need for a User-Centered Design Perspective 

The field of human factors addresses the interaction of devices or systems and their human users 

as these users engage in various tasks. Good human factors design requires an understanding of 

the characteristics of the users and the tasks in which they are engaged. ITS devices and 

systems, as with any application, should be designed in a manner consistent with the capabilities 

and behaviors of the range of people that will be using them. Furthermore, although the designer 

of the ITS device or system may have a specific purpose in mind, realization of that objective 

through design should be consistent with the road user’s task as the road user understands it. The 

user-centered design philosophy is that an effective, safe, and accepted product is designed 

around the user. It takes into account not only physical and perceptual capabilities (such as 

reaction time or visual acuity) but also behaviors, knowledge, motivations, and attitudes. A good 

overview of the application of human factors in highway and vehicle applications may be found 

in Human Factors and Traffic Safety (Dewar & Olson, 2001), which also contains a chapter 

specifically on railroad grade crossings. 

The behavior of roadway users is often complex and difficult to predict. They may not always 

respond to ITS information related to the HRI in the manner in which the designer intended that 

information to be used. Proper responding by road users requires that they do the following: 

 Notice the display, in a reliable and timely manner 

 Process the information being presented 

 Comprehend the intended message and all of its implications 

 Accept the validity and personal relevance of the message 

 Choose to respond to the message, given the full range of (sometimes conflicting) tasks 

and motivations with which they are dealing 

 Have the ability to execute the desired behavior in a safe and timely manner 

This list of required steps is not meant to imply that the mental process underlying road user 

behavior necessarily runs off in this sequence. Real human cognition is much more complex and 

this is not intended to represent a model of road user cognition. The point is that each of the 

requirements above must be accomplished for the road user to ultimately act in the desired 

manner. The designer of an ITS device or system needs some understanding of the road users 

who deal with the HRI and who will be encountering the ITS display. Fundamental human 

attributes in perception and cognition that are relevant for the design of any display may be 

found in basic human factors references and are reflected in many of the ITS guidance 

documents cited in Section 1.3. Equally important, however, are the characteristics of roadway 

users that relate to their driving behavior, risk perception, and decisionmaking. 

This chapter highlights some characteristics of the road user that are important for maintaining a 

proper perspective in the design of ITS and HRI applications. These characteristics may be 

incorporated in the guidance that is found in Parts III and IV of this document. It is also useful, 

however, to make these characteristics explicit, so that ITS developers can properly 

conceptualize the road users for whom they are designing. 

10
2.2 Selected Characteristics of HRI Road Users 

 System context. When developing an ITS traffic control device (TCD) or road user 

information system, a natural tendency to focus specifically on the interaction of the road 

user with the device exists. But this narrow focus is not necessarily how the world looks 

from the road user’s perspective. For example, drivers may be concerned with 

maintaining the vehicle’s path, monitoring other road users, monitoring other TCDs, 

searching for a landmark or sign, determining what lane they should be in, and so forth. 

They may also be attentive to non-driving features, such as looking at the surrounding 

area, conversation with passengers, attending to the sound system, and many other 

possible activities. An encounter with an ITS display is not an isolated event but occurs 

within the continuous flow of driving, where things may be constantly changing. The 

road user is always operating in a system with many demands and distractions, and no 

reason exists to assume that one particular device or display has a unique status. An ITS 

display has to function effectively within the system of roadway information, activities, 

and goals that characterize the road user. Research on driver behavior at the HRI 

suggests that road users often give little attention to the HRI in the context of normal 

driving. ITS displays, like other roadway-related devices, must be designed and 

evaluated for use as just one element in the system with which the road user is dealing. 

 Understanding of the HRI. Roadway users do not always understand the meaning or 

implications of an HRI-related traffic control device, nor do they always understand their 

responsibilities at the HRI (e.g., Dewar, 2001; Lerner et al., 1989). Numerous examples 

of misunderstandings that can contribute to inappropriate behavior exist. These include 

the following: 

 Not understanding the specific meaning of such TCDs as the railroad advance 

warning sign, the railroad crossing sign (Crossbuck), various pavement markings, 

flashing lights, and automated gates. The public has a general understanding that 

these TCDs have something to do with the HRI, but the more specific meanings of 

devices are often not understood. Road users may also not fully comprehend the 

meaning of storage space signing and delineation near intersections or dynamic 

envelope delineation around the clearance zone of the tracks. 

 Poor appreciation of the different levels of protection at HRIs (gates, signals, passive) 

and misunderstanding of the level of protection at a particular crossing. 

 Inadequate understanding of the responsibilities of the road user at various types of 

HRI. These include the responsibility to search for conflicting rail traffic, the 

requirement to yield to trains in hazardous proximity, and the actions required, 

permitted, or prohibited by specific TCDs (gates, signals, stop signs, Crossbuck). 

Road users may not understand the responsibility to keep their vehicles out of 

potential conflict zones, such as storage space and dynamic envelope areas. 

 Poor appreciation of sight distance limitations and associated vehicle approach speed 

requirements, in general and for a specific HRI. 

 Limited understanding of the risk factors at the HRI. For example, many road users 

do not appreciate the limits to a train’s ability to stop or the implications of multiple 

tracks. They may not recognize variations in train speed. They may also not 

11
recognize limitations to the reliability and accuracy of their own visual and auditory 

capabilities (e.g., judging speed and distance, hearing train horns). 

 Levels of the driving task. Driving is not a unitary task but a collection of many different 

activities that the motorist must coordinate. Theorists who model or describe the driving 

task have conceptualized it in many ways, but a number of these models have agreed in 

characterizing driving task demands as falling into three hierarchical levels. Using the 

terminology of the Positive Guidance model (Lunenfeld & Alexander, 1990; Post, 

Alexander, & Lunenfeld, 1981), these levels are termed control, guidance, and 

navigation. Control tasks are related to basic driver control of the vehicle and its relation 

to the roadway and obstacles; this involves immediate control of speed, path, and 

direction. Guidance tasks are those tasks related to a driver’s selection and maintenance 

of safe speed and path. While the control level deals with the driver’s interaction with 

the vehicle, the guidance level is more related to decisionmaking and involves judgments 

and predictions about the upcoming situation. The navigation level involves planning 

and executing a trip, from its origin to its destination. In the Positive Guidance Model, 

these three task levels form a hierarchy based on the primacy of the information (that is, 

its priority for being dealt with). The control level has the highest primacy, and the 

navigation level has the lowest primacy. When providing ITS information or any form of 

information to drivers, it is important to design and locate the information display so that 

it is consistent with primacy requirements. Drivers who are dealing with time-critical 

demands for high-primacy actions must have those demands satisfied before they are 

confronted with lower primacy needs. This has implications for where information 

should be placed, how it should be sequenced, how it should be spread out, and how it 

should be related to roadway features. 

 Handling information. Several aspects of handling information should be noted. These 

include coping with the information load, integrating information sources, and the timing 

of information needs. Motorists often have to cope with a great deal of information while 

they are driving. This may include formal driving-related or HRI-related information 

from signs, signals, markings, and other displays. It may also include many other sorts of 

information, such as the features of the roadway; the features of the HRI, the actions of 

other traffic, and in-vehicle information displays; and information from many possible 

sources unrelated to driving. Processing this information—sorting it, attending to it, and 

interpreting it—takes time and effort. A road user must have sufficient time to process 

and respond to the information in an ITS display, under the real-world information 

environment in which it occurs. Some ITS displays have the potential to contribute to 

information overload for the road user. When motorists receive more information than 

they can process in the time available, various things can happen: “they may decelerate 

severely or drive too slowly, make late or erratic maneuvers, take an improper route 

alternative, ignore crucial information, fail to monitor other traffic, or have excessive 

episodes of eyes-off-the-road time” (Lerner, Llaneras, McGee, Taori, & Alexander, 

2003). Information overload is a joint product of the demands of the information and the 

time available for dealing with it. Therefore, the designer of an ITS application must 

consider the demands of processing the information in the ITS display and how this fits 

within the general driving and information context in which it will be presented. Another 

aspect of information handling is the road user’s integration of all sources of information. 

12
The designers of an ITS display may consider their device to provide the information to 

which the road user should respond. To the road user, however, this may be only one of 

various sources of information. This information may come not just from TCDs, but 

from what is implied to the motorist by the appearance of the roadway, the appearance of 

the HRI, the actions of other traffic, and personal history and beliefs. The weight given 

to an ITS message will be influenced by how the road user perceives its accuracy and 

personal validity. Various studies have shown that user compliance with ITS information 

degrades as the accuracy and timeliness of the message declines (e.g., Kantowitz, 

Hanowski, & Kantowitz, 1996). Furthermore, people recognize that the assumptions or 

objectives of the designer may not be consistent with their personal situation, as they 

perceive it. For example, a driver may feel that a warning is based on the capabilities of 

less capable drivers or that the safety cushion is more extreme than necessary. Dynamic 

ITS displays based on real-time data therefore must protect their validity and convey a 

believable message to individual road users. 

 Expectancies. People do not only respond to what is physically present at the moment, 

but also to what they expect the situation to be. Expectancies are based on long-term 

general experience (e.g., history of what a driver has encountered at HRIs), long-term 

specific experience (e.g., what a driver has encountered at a particular HRI in the past, 

what a driver has encountered from a particular device in the past), and short-term 

experience (e.g., characteristics of the road the driver has just been operating over). 

When the actual situation is consistent with the road user’s expectancy, the way the road 

user responds tends to be quick and accurate. When a road user’s expectancy is 

inaccurate, the way the road user responds tends to be slow and error-prone, and 

information may lack credibility. The implications of this are that the designer should (1) 

try to create the proper expectancy in the road user; (2) design the system to be 

compatible with likely road user expectancies; and (3) where inaccurate user expectancy 

is likely to occur, take additional measures to overcome this. 

 Personal optimization. The designer of an ITS application will have the goal of 

optimizing safety and operational efficiency for train operations and/or roadway traffic. 

This is not the perspective of individual road users. They focus on their own goals, 

which may seem trivial when viewed from the designer’s perspective. Time saving, 

impatience, frustration, and convenience may all drive individual decisions, even if the 

potential safety consequences would appear to be more critical concerns. This is 

sometimes referred to as personal utility. Optimization of individual concerns might 

influence how road users react to such factors as gate down time, preemption, or route 

recommendations. 

 Risk perception and risk management. Road users base their actions on their perceived 

risk, which is not necessarily an accurate reflection of actual risk. Safety information 

about the HRI will be interpreted and evaluated based on the road user’s personal feelings 

about risk and the quality and validity of the ITS information relative to other sources of 

belief. Furthermore, the road user’s goal is typically not to minimize personal risk but 

rather to optimize all personal benefits, based on their personal criteria; safety is only one 

element of this equation. Another important aspect of risk behavior is that people often 

adapt their behavior to some potential safety benefit in a way that lets them take more 

risk. This phenomenon is termed risk compensation. For example, if drivers had an in13
vehicle warning about the presence of approaching trains at an HRI, they might 

compensate for this safety enhancement by driving faster through the site and engaging in 

a less visual search for trains. For this reason, the realized benefits of new roadway 

safety technologies are often not as great as research studies or initial evaluations suggest 

they would be. 

 Social context. Although driving is an individual activity, road use does occur in a social 

context. The presence of other people can facilitate or inhibit various behaviors in road 

users. For example, if vehicles queue up behind a driver at an HRI, the driver may feel 

pressured to cross the tracks, even if he or she is unsure of the safety of the situation. If a 

driver prefers to slow adequately to search for trains while other vehicles do not, the 

driver may be made to feel overly cautious or as if he or she is a traffic obstruction. 

When some road user violates a TCD (e.g., going around a gate), this may facilitate 

similar behavior by subsequent road users. In some cases, local norms of behavior 

emerge (e.g., everyone knows you don’t really stop at that particular HRI). One 

particular concern for ITS applications may be when partial penetration of an in-vehicle 

system in the vehicle fleet occurs. Some of the aspects of social interaction may be 

exacerbated if various road users are getting different information. 

 Attention and distraction. A person’s ability to simultaneously pay attention to different 

features of the environment is limited. This is a concern for all types of roadway users, 

although the problem is most acute for motor vehicle operators because of their higher 

travel speeds and greater stopping requirements. Different aspects of the driving task and 

various sources of information may compete for the driver’s limited attention. The 

allocation of attention to different activities may be influenced by the momentary 

demands of the driving task, the timeliness and urgency of the information, and personal 

motivations. ITS displays ideally should be timed so that they are compatible with other 

driver information needs and do not mutually interfere with other driving task demands. 

Furthermore, drivers are often not fully attentive to the driving task itself. The ITS 

device and system developer should not work from the assumption that the driver is 

necessarily focused on the driving task. Recent research on driver distraction 

demonstrates that distraction is not unusual but rather quite typical of normal driving. 

For example, a recent study (Stutts et al., 2003) instrumented the personal vehicles of 70 

volunteer drivers and videotaped their behavior for up to 10 hours of actual driving time. 

The experimenters recorded many different categories of potentially distracting activities 

such as eating, drinking, using a cell phone, and attending to things inside the vehicle. 

This study found that some distracting activity was going on nearly one-third of the time 

while the vehicle was in motion. About one-half of this distracted time was attributable 

to conversation with a passenger, while the rest was distributed across many types of 

distractions. The actual degree of distraction was not measured in this study, so these 

events may best be described as potential distractions. Nonetheless, this study indicates 

how common overtly observable behaviors with distraction potential, unrelated to 

driving, occur during typical travel. Of course, unobservable distractions (such as 

daydreaming or thinking about personal concerns) also occur and would add to this 

distracted time. No reason exists to assume this potential for distraction would be any 

less in the vicinity of an HRI. ITS design must therefore recognize that users of the 

14
device or system are quite likely to have their attention directed to unrelated aspects of 

the driving task and to non-driving activities. 

 Range of driver and vehicle capabilities. Road users represent an extremely diverse 

population. First, the mode of transport varies, from pedestrians to bicyclists, 

motorcyclists, passenger vehicle drivers, and operators of large vehicles, such as buses 

and tractor trailers. These different classes of road user vary drastically in travel speed, 

stopping ability, acceleration, viewer’s eye position, visibility of the roadway, noise 

environment, and driving task demands. Human factors aspects of ITS displays must 

encompass the full range of road user categories for which the application is intended. 

Second, within any of these groups, people will differ radically in terms of capabilities, 

knowledge, and experience. With the exception of commercial or public vehicle 

operators, only minimal constraints exist on who is allowed to use the roadway. Road 

users, therefore, vary widely in visual capabilities of many sorts (e.g., acuity, night 

vision, peripheral field, glare susceptibility, color vision), auditory perception (e.g., 

detection threshold, localization, speech perception), information processing ability, 

psychomotor skills, anthropometric characteristics, health pathologies, transient 

debilitations (fatigue, alcohol, drugs, emotional state), training, literacy, and driving 

history. The need to encompass this range of roadway users is not unique to applications 

of ITS at the HRI; it is important for any TCD application. However, because some 

innovative ITS technologies may lack the history of field application experience 

associated with traditional signs and signals, established criteria for broadly usable 

devices may be lacking. The designer should avoid a preconceived notion of the typical 

user of the technology and remain cognizant of the range of capabilities among road 

users. 

2.3 Summary 

Designing an effective ITS device or system for the HRI requires an appreciation of the 

capabilities, behaviors, motivations, and attitudes of the range of roadway users who may 

encounter the ITS display. The human factors aspects of design cannot be treated as a simple 

and direct transaction between the device and the road user, with the road user responding 

automatically in the manner envisioned by the designer. Road user behavior is more complex 

than that. There exist numerous models of various sorts that attempt to describe some aspect of 

driver behavior. However, no broadly accepted and sufficiently detailed model of the driver or 

other road user serves as an integrative scheme for characterizing the roadway user. This chapter 

highlighted some of the important behavioral characteristics of HRI road users as an aid in 

conceptualizing the target of ITS device and system design. ITS applications developed around 

an appropriately understood concept of the road user are more likely to be effectively used and 

accepted. 

15

Part II: Overview of ITS Implemented at the HRI 

17

3. Implemented Systems 

This chapter briefly describes several ITS applications for HRIs that have been implemented in 

the United States. The chapter groups the applications under three headings: Information About 

Arriving Trains (Section 3.1), Multiple Train Warnings (Section 3.2), and Vehicle Control and 

Automated Enforcement (Section 3.3). In compiling this information, the focus is on 

applications that are targeted to the information and safety needs of roadway users. In several 

cases, lessons learned from the operation of these systems have shaped the human factors 

guidance given in the remainder of this document. Table 1, at the end of this chapter, highlights 

several key pilot studies and operational field tests of advance alert and warning systems, as well 

as other ITS implementations that support law enforcement and traffic control at HRIs. 

3.1 Information About Arriving Trains 

Advance information about approaching trains can be delivered to motorists through a variety of 

means, including in-vehicle systems (e.g., navigation units, stand-alone devices, highway 

advisory radio (HAR)), roadside changeable message signs (CMS), kiosks, Web sites, personal 

digital assistants, and cell phones. Information about train movements can also be incorporated 

into Traffic Management Center operations, enabling operators to alleviate effects of train 

activity on traffic by adjusting signal phasing and timing, dynamically implementing lane use or 

turn restrictions, recommending alternate routes via CMS, and coordinating with emergency 

services. Much of the work in this area has focused on enabling advance train detection 

(developing the technology and making it reliable, accurate, and feasible to implement). 

A number of proof-of-concept studies examining alternative techniques, configurations, and 

architectures have been performed. Most notably, the Federal Railroad Administration (FRA) 

has sponsored a series of performance-based engineering evaluations of vehicle proximity alert 

systems that alert drivers to the presence of a train approaching the HRI (Carroll, Passera, & 

Tingos, 2001). The goal of the research program was to assess the feasibility and effectiveness 

of these systems for detecting trains at passive crossings. Test results showed that some system 

designs were able to reliably detect train direction and speeds, and they pointed to additional 

design issues and concerns to be addressed in future development efforts. This includes work to 

increase system reliability, reduce false alarms, tune the warning zone around the HRI to prevent 

nuisance alarms, design user interfaces, and develop human factors standards. 

A number of systems designed to warn or alert motorists of approaching trains or trains 

occupying the HRI have been developed and field tested. Although these have varied along a 

number of key factors (type of information presented to motorists, the means through which 

information is communicated, size and scope, and the target users, etc.), these systems are 

generally designed to provide unique information beyond what is currently available at HRIs. 

Most of these systems have emphasized presentation of dynamic train information (train 

approaching, or at the HRI, train speed and direction, etc.). The following describes these 

systems. 

3.1.1 Train Detection and Reporting Systems in Texas—College Station, Sugar 

Land, and Laredo 

The Texas Department of Transportation (DOT) and Texas Transportation Institute (a research 

center of Texas A&M University) have collaborated to develop innovative systems to detect 

19
train movements and to report and predict HRI status information to transportation researchers 

and officials, emergency response services, and roadway users. Three such systems are Rail 

View in College Station, Rail Monitor in Sugar Land, and an unnamed rail monitoring system in 

Laredo. 

Rail View was implemented along the Wellborn Corridor in College Station, Texas (Texas 

Transportation Institute, 1999; Trans-Link Train Monitoring Project, 2002). The primary 

purpose of this system is to provide real-time train movement information to emergency service 

providers, traffic management operators, and traffic signal controllers. Researchers also use Rail 

View data to improve traffic control systems near HRIs. The data provided by the system 

include train location, direction, speed, estimated times of arrival and clearance at downstream 

HRIs, and the duration that the train will occupy the HRI. This information is especially useful 

to emergency service providers who can use the Rail View information to choose a route that 

will not be blocked by a train. Real-time crossing information is available to firefighters on instation laptops. The Rail View technology would also allow crossing information to be 

presented to emergency responders through in-vehicle computers, though this has not been 

attempted. Data are also available to the general public on Texas A&M University’s Web site 

and through Web-enabled cell phones, though these media provide limited benefits to motorists 

and may cause driver distraction if used within the vehicle. Figure 3 shows the online user 

interface. At the lower left of the display is a low frame rate video image of one HRI on the 

corridor (video display is blank in Figure 3), and at the far right is a map of grade crossings in 

the vicinity. When a train is present in the rail corridor, the display also presents the train 

location, length, and speed, along with the estimated time of the train’s arrival at upcoming grade 

crossings and the estimated time of the train’s departure from grade crossings that it has passed. 

No train is present in the example shown in Figure 3. Rail View data can also be made available 

to motorists using CMSs and in-vehicle devices, though no such motorist information systems 

have yet been implemented or investigated. 

The Texas DOT also implemented a train detection and reporting system in Sugar Land, Texas 

(Goolsby, Vickich, & Voight, 2003). The system monitors 6.4 miles of rail, which includes 

eight HRIs. Approximately 30 trains travel this corridor every day. The primary goal of the Rail 

Monitor system is to provide HRI status information to police, fire, and emergency medical 

services (EMS) to allow responders to avoid unnecessary delays at train-occupied HRIs. 

Information kiosks were provided for police and fire dispatch and for individual stations. The 

same information was also available to the public through the Houston Transtar Web site 

(http://traffic.houstontranstar.org/rail/). Train status information is updated in near real-time. As 

shown in Figure 4, the system information includes a graphic representation of HRIs along the 

rail line with icons to represent train presence and direction, train speed, length, and estimated 

time of arrival and clearance at downstream HRIs. Interviews with dispatchers and fire station 

officials indicated that these users found the system helpful and had confidence in its reliability. 

Like the Rail View system described earlier, Rail Monitor is not currently designed to aid typical 

roadway users, but future enhancements may make the HRI information available to 

20
Figure 3. Rail View online user interface 

roadway users using CMSs, HAR, or mobile wireless technologies, such as cell phones and 

pagers. Future enhancements may also include integration of train information with nearby 

traffic signals to improve signal timing and preemption. 

In Laredo, Texas, drivers on Mines Road (FM 1472) often face long delays and heavy traffic as a 

result of frequent train crossings; each train may occupy the HRI for as long as 7 minutes (Texas 

Transportation Institute, 2001; L. Ruback, Texas Transportation Institute, personal 

communication, February, 2004). An existing system at the HRI used flashing lights on static 

signs to inform drivers in advance if a train was present at the HRI, but it did not provide drivers 

with any additional information. The new system still uses advance signs with flashing lights to 

alert drivers to train presence (see Figure 5), but it also triggers an automated message to play 

through an HAR frequency. The HAR message reports whether a train is present at the HRI, 

how long it has been present, and the direction it is traveling. Each message is about 10 seconds 

long and repeats continuously. The message is updated every 3 minutes, and messages are 

automatically generated from a prerecorded set of information. Despite the designers’ goal of 

providing a bilingual message to accommodate the large Spanish-speaking population in the 

area, limitations of the existing hardware prevented this. Drivers can use the HAR information 

to choose a route that will not be blocked by the train, though the HAR message does not specify 

alternate routes. Designers envisioned the system as primarily benefiting commercial drivers, 

but other motorists may take advantage of the advance information as well. No evaluation has 

been conducted to assess the system’s effectiveness. 

21
Figure 4. Rail Monitoring System online user interface 

3.1.2 Advance Warning to Avoid Railroad Delays (AWARD)—San Antonio, Texas 

The AWARD system uses ITS technology to detect and predict train arrival and HRI information 

(Federal Highway Administration, 2000, 2001; Carter et al., 2000). The information is also 

delivered directly to traffic management operators and emergency service providers, as well as 

being available to the public on the Web. This information is also presented to motorists via 

advance CMSs. The CMSs are intended to inform motorists traveling on the freeway when a 

train occupying an HRI near an upcoming exit is causing traffic backups. This allows drivers to 

select alternate exits to avoid delays. The system detects the presence of trains operating in 

affected areas and predicts the time and duration of the blockage of HRIs at or near freeway exits 

22
Figure 5. Advance signs with train-activated flashing lights in Laredo, Texas 

and entrances. Information is also presented using Advanced Traveler Information Systems 

(kiosks, Web, in-vehicle navigation systems, Traffic Management Centers, etc.) incorporated 

into the effort as part of the Metropolitan Model Deployment Initiative. Unfortunately, the 

system was never fully deployed, making it difficult to assess user satisfaction and system 

effectiveness, though subsequent simulation models estimate that travel time delays could be 

reduced nearly 20 percent for drivers who reroute around blocked HRIs. The Texas DOT 

continues to operate the AWARD system at six HRIs. 

3.1.3 Moorhead Area Integrated Train Detection and Traffic Control System—

Moorhead, Minnesota 

The Minnesota DOT and the City of Moorhead, Minnesota, cooperated to develop this system 

that tracks train movements through the downtown Fargo-Moorhead area. Rail traffic on the 

Burlington Northern Santa Fe Railroad averages 50 trains per day through this area. The purpose 

of the system is to reduce motorist delay and improve emergency vehicle response (SRF 

Consulting Group, Inc., 2000). Initially, the system used video-based sensing, but, in a 

subsequent phase of the project, microwave-based sensors were added to detect train presence, 

speed, length, and direction. Train movements are predicted, and dispatchers can use this 

information to estimate time of arrival at each HRI. Traffic signals in the area were programmed 

with a train present timing plan in an effort to reduce traffic delays associated with train 

movements through HRIs. An independent evaluation did not find evidence for significant 

reductions in traffic delays following system implementation (Advanced Traffic Analysis Center, 

2003). Some problems, however, exist with this analysis. Various technological problems 

caused a delay in the timeline for implementing the system, and this resulted in the before and 

after evaluation periods being spaced several months apart. The evaluators noted that traffic 

patterns changed during the study period, and the small amount of data collected limited the 

statistical power of the analysis. Despite problems with the evaluation, system implementers 

agreed that they did not realize substantial overall reduction in traffic delays. Problems with 

transitioning the traffic signal controllers to normal synchronization following the train present 

timing sequence diminished the potential benefits of the system on traffic flow. The train 

detection system is no longer connected with the traffic signal system (E. Minge, personal 

23
communication, August, 2004). In the future, the system may provide real-time train 

information to motorists, as well as emergency vehicle and transit operators and dispatchers. 

Motorists may be notified of delays associated with train movements through CMS located in 

advance of affected HRIs. These signs may display information such as the number of minutes 

that the nearest HRI would be blocked. (Results of a survey of area drivers suggested that a 

substantial percentage of drivers (74 percent) would re-route to avoid a 10-minute delay.) 

3.1.4 Intelligent Grade Crossing—New Hyde Park, New York 

The intelligent grade crossing (IGC) was developed by New York State DOT and Alstom 

Signaling (Chappell & Carroll, 2000; Federal Highway Administration, 2001; Grade crossing 

system tested at New Hyde Park, 2001). Although never actually implemented for use, system 

features were simulated at one HRI on the Long Island Railroad. This HRI has heavy rail traffic, 

typically more than 200 trains per day. Combined with heavy roadway traffic, trains can cause 

substantial delays for motorists. The IGC uses advanced train detection, vehicle detection, and 

communication equipment to improve roadway traffic flow, provide information to motorists, 

and enhance communications between train crews and the HRI. The system activates HRI lights 

and gates based on train speed and location and thus can provide a constant warning time of 27 

seconds. This can result in an overall decrease in gate-down time and a subsequent reduction of 

motorist delays. The system also includes CMSs upstream of the HRIs to inform motorists of 

train status and, in conjunction with a queue detection system, to inform motorists not to cross 

the tracks if the queue is in danger of extending back onto the tracks. System descriptions, 

however, did not address specific messages. When long queues do accumulate, the IGC can turn 

the downstream traffic signal green to release the queue. If the system detects a vehicle stopped 

on the tracks, approaching trains are brought to a stop. The IGC also reduces gate-down time by 

allowing gates to remain up when trains are stopped at a station adjacent to the roadway. In the 

case of multiple train events, the enhanced train detection capabilities also prevent gates from 

beginning to rise after the first train passes, only to begin descending again once the second train 

enters the activation zone. By keeping the gates down during the entire multiple train event and 

providing a second train coming message on CMSs, drivers may be less likely to attempt to cross 

the tracks after the first train passes. The IGC also has a unique feature to accommodate 

emergency vehicles. While most ITS systems provide train movement information to emergency 

personnel to allow them to reroute, the IGC actually allows emergency personnel to 

communicate with the IGC and, if there is enough time, automatically bring the train to a stop 

before it obstructs the HRI. 

3.1.5 In-Vehicle Signing System for School Buses at Highway-Rail Grade 

Crossings—Glencoe, Minnesota 

This in-vehicle signing system presented alerts and warnings to bus drivers approaching HRIs 

(SRF Consulting Group, Inc., 1998). The system was installed on 29 buses in a Minnesota 

school district and was functional at 5 HRIs. The system provided two types of information: (1) 

a crossing alert, indicating proximity to an at-grade rail crossing and alerting drivers to the 

presence of the HRI and (2) a train warning indicating whether or not a train is present or near 

the HRI (approaching train warning). Alerts were presented in vehicles using icons, light 

emitting diodes (LEDs), and warning tones. The icons were meant to represent standard warning 

signs currently present at all HRIs. Presence of an HRI was communicated using the Manual on 

Uniform Traffic Control Devices for Streets and Highways (MUTCD) standard W-10 advance 

24
warning sign icon with two small yellow LEDS mounted in the upper and lower quadrants 

defined by the “x” of the sign (see Figure 6, left panel). Once the system detected an HRI, the 

yellow LEDS flashed in unison at a rate of four times per second, and an auditory tone was 

issued (runs 200 milliseconds (ms) of 1300 Hz tone, followed by 200 ms of silence, then 200 ms 

tone). Two repetitions of the tone were presented at initial detection. When the system detected 

an approaching train or one occupying the HRI, it issued a train warning via the standard 

Crossbuck sign graphic that included two red LEDs under the graphic (see Figure 6, right panel). 

The red LEDs flashed in alternation at a rate of 500 ms and were accompanied by an auditory 

signal (1900 Hz tone) that cycled 500 ms on, 200 ms off, 200 ms on, 200 off. The system 

emitted eight repetitions of the tone upon initial detection. After that, LEDs continued to flash, 

but the tones were silenced. Tones were repeated for each additional train warning signal 

(second train). The system was mounted in the center of the dashboard above the steering 

column to avoid obstructing the driver’s view of the dash controls, gauges, or mirrors. 

Figure 6. In-vehicle HRI display for school buses 

The system provided a minimum of 250 feet of advanced warning (grade crossing/train 

presence) and possessed several unique features, including compensation for ambient noise to 

automatically adjust the volume over the surrounding in-vehicle environment and the ability to 

discern the direction the bus is traveling relative to the HRI. This avoids nuisance warnings 

when the vehicle is within the vicinity of the HRI but not intending to cross the tracks. In other 

words, the system was designed not to activate unless the vehicle’s direction of travel would take 

it through the HRI. A blue LED in the lower right corner indicated normal operation; the light 

flashed when the vehicle was in the presence of a transmitter signal. This feature enabled drivers 

to discern equipped HRIs from those not possessing this advance warning capability. 

An evaluation studied the impact of the warning system on bus driver behavior (approach 

speeds, scanning behavior, etc.) and perceptions of the system (awareness of tracks, presence of 

train, driver confidence in system). Because of the small scale of the deployment, no actual 

crash data could be studied. No significant differences were found across these measures for 

performance with the system compared to baseline performance levels. Drivers were concerned 

that false alarms (alerts issued when not in proximity of an HRI or in the presence of a train) 

could erode driver confidence in the system. Interviews with bus drivers revealed that 80 percent 

of drivers believed that the system provided useful warning information, but only 15 percent of 

drivers felt that their driving behavior actually changed as a result. Interviews with train 

engineers suggest that the system may be more useful in commercial trucks than in cars because 

there appears to be more of a concern on their part for collisions with large commercial vehicles 

than passenger cars. All in-vehicle and trackside equipment is removed after the evaluation 

period, and the system is no longer in use. 

25
3.1.6 Advisory On-Board Warning Systems at Railroad Grade Crossings—MetraMilwaukee North Line 

The Illinois DOT piloted an in-vehicle warning system designed to alert drivers of a train 

approaching or occupying an HRI (Benekohal, Aycin, Sikaras, Jonak, & Kennedy, 2000; Aycin 

& Benekohal, 2002). The Advisory On-Board Warning system was deployed at five actively 

controlled crossings along the Metra-Milwaukee North line. The deployment phase of the pilot 

study spanned 9 months and included more than 270 vehicles equipped with a commercially 

available in-vehicle receiver and display unit developed by Cobra Electronics. Study sites had 

moderately heavy train activity (between 70 and 115 trains daily) with commuter, Amtrak, and 

freight train movements. Drivers from 38 organizations participated in the study that included 

school buses, emergency, fleet, and commercial vehicles. The system was designed to 

supplement existing HRI warning systems (lights, gates, etc.) by providing an advisory warning 

of a train approaching or occupying the HRI and featured a warning zone range between 800 and 

1,200 feet. 

The in-vehicle unit (see Figure 7), installed within the driver’s forward field of view, was 

capable of providing audio and visual warning messages. The form of the alert was varied as 

part of the pilot test and included audio only, visual only, or combination audio and visual 

modes. In the visual-only mode, text messages indicating “Caution” or “Warning Train” were 

issued in the presence of a train approaching or occupying the HRI (the caution message was 

only issued in situations where the unit was not 100 percent certain of a train event). In the 

audio-only mode, the system presented warning signals (beeps and tones) in the presence of a 

train approaching or occupying the HRI. The volume of the audio warning message was 15–35 

decibels (dB) above the ambient noise level. In the combined audio and visual mode, drivers 

received both audible warning signals and text messages. The system continuously issues 

warnings for the duration of the train event and terminates once the train cleared the HRI and the 

active crossing controls (gates and flashers) ceased operation. Drivers also received training on 

how to operate the unit and interpret system messages. Results of the pilot showed promise, but 

a more reliable operating system is required for future deployments. 

Figure 7. Advisory in-vehicle warning system 

Summary: Information About Arriving Trains 

Relatively little empirical data have been collected to assess impacts of train arrival warning 

systems on driver behavior and acceptance. Current evidence indicates that drivers prefer 

advance information that provides unique train status information (e.g., estimated arrival time, 

expected delay associated with train crossing) as opposed to systems that merely provide 

26
redundant information currently available at HRIs (signage and active traffic control device 

treatments). Furthermore, although status information is valuable to waiting motorists, the 

ability to re-route and avoid delays is an important benefit provided by these types of systems 

(see Chapter 9). Data also suggest that directionally sensitive systems (those capable of issuing 

warnings to approaching motorists only) may be better accepted than global systems that 

broadcast messages indiscriminately because they limit nuisance alarms; this is particularly 

crucial for in-vehicle systems. System reliability is a major factor for all types of 

implementations. To instill trust and have roadway users act on the information provided, 

systems must be perceived as accurate and reliable. 

3.2 Multiple Train Warnings 

A special need for train arrival warning occurs when more than one arriving train presents a 

hazard to the roadway user. This situation can be particularly dangerous because the first train 

may reduce the likelihood that the roadway user will be aware of the second train. The first train 

may block the view of the second train. It may mask the sound of the second train. It may draw 

the road user’s attention away from the approaching second train. In many cases, drivers may 

not be expecting a second train event, making it even more challenging for them to detect and 

respond to the unexpected event. ITS technologies that provide specific information about train 

movements can be incorporated into systems that alert roadway users to the presence of multiple 

trains. A warning device used to alert roadway users to the presence of another train is known as 

a second train warning, or more generally, a multiple train warning (MTW). MTWs may be 

designed for motorist and pedestrian applications, typically for actively controlled grade 

crossings where multiple train events occur frequently with significant potential for collisions. 

Other considerations for the application of MTWs include traffic and pedestrian volumes, crash 

data or observations of risky behaviors, public comment, high train speeds and/or limited sight 

distances, mixed rail traffic (with varying speeds), the number of tracks, and geometry of the 

HRI. 

No common practice has emerged for MTW implementation. While some signs are text only 

(Calgary Transit in Canada, San Jose LRT in California, and Joint Powers Board and Union 

Pacific lines in California), others are graphic only (Los Angeles Metro Blue Line (MBL) in 

California), or they include both text and graphics (Maryland Mass Transit Administration 

(MTA)). British Rail (Railtrack) combines a passive warning sign with a two-pitched auditory 

warning. When the second train approaches the HRI, the auditory warning increases in pitch to 

indicate that another train is coming. The passive sign is intended for motor vehicle operators 

and pedestrians, but the auditory signal is intended primarily for pedestrians. 

For most of the MTW applications noted, the choice of display modality was apparently based 

on implementer preference or budget limitations, or at best limited to informal in-house testing 

with employees. Empirical testing with appropriate user groups was not part of sign 

development. Likewise, in most cases no reported followup studies to assess system 

effectiveness or message comprehension occurred. The systems implemented by the Los 

Angeles County Metropolitan Transportation Authority (LACMTA) and the Maryland MTA, 

however, did include such evaluations. The following sections summarize both demonstration 

projects. 

27
3.2.1 Second Train Warning Sign Demonstration Project—Los Angeles, 

California 

The LACMTA implemented an MTW at the Vernon Ave HRI on the MBL (PB Farradyne, 2002; 

Khawani, 2001; V. Khawani, Los Angeles County Metropolitan Transportation Authority, 

personal communication, December 2001). Figure 8 shows the HRI, with the warning display 

visible in the upper center of the photograph and a train entering from the right. This MTW is 

specifically intended for pedestrians. Track geometry, frequent multiple train events 

(approximately 25 per day), and large volumes of pedestrians contributed to make the Vernon 

Avenue HRI one of the most hazardous on the MBL for pedestrians. Multiple train events were 

factors in a number of vehicle-train and pedestrian-train collisions. Though no MTW was 

provided to motor vehicle operators, there were active warnings, including gates that minimized 

the potential for multiple train-related collisions on the roadway. 

Figure 8. LACMTA MTW for pedestrians installed at Vernon Avenue grade crossing 

The particular graphic signs used in this field test were selected following a series of 

development activities that included an expert workshop and field surveys with local area 

pedestrians. Graphic signs were better understood than the text-only signs, possibly because the 

text signs were presented in English despite a majority of Spanish-speaking respondents. The 

final graphic sign chosen (Figure 9) was a two-part display that, when activated, showed a 

simple line illustration of the HRI from the pedestrian’s perspective. The first phase of the 

display showed an LRT train on the top track on the right-hand side of the display with an arrow 

pointing from the person to the train. The second phase of the display showed an LRT train on 

the bottom track on the left-hand side of the display with an arrow pointing from the person to 

the train. The sign is mounted on a standard mast arm on a platform between sets of tracks and 

28
(Note: Actual sign has amber legend on black background.) 

Figure 9. LACMTA MTW display (prototype) 

is visible from both directions of approach. When no train is coming, the sign remains dark. 

A survey of pedestrians near the HRI found that although 77 percent recalled seeing the sign, 

only 4 percent understood that more than one train was approaching. However, 92 percent 

interpreted that caution was necessary. The frequency of risky acts performed by pedestrians 

was compared before and after sign installation. The before period was the 11 weeks 

immediately preceding sign installation. The 9-week after period was spread out due to technical 

problems. Data were collected for 5 weeks beginning about 5 weeks after sign installation. Data 

were collected for another 4 weeks beginning more than 11 months after sign installation. Risky 

acts were defined as occasions in which pedestrians crossed the tracks with less than 15 seconds 

before a train arrived. The comparison found that risky acts decreased by 14 percent after sign 

installation. The decrease became more apparent when limiting analysis to risky crossings below 

6 seconds (32-percent decrease) and risky crossings below 4 seconds (73-percent decrease), 

though there were only 19 total observations in the latter category. The assessment of sign 

effectiveness indicates that the MTW sign does reduce the likelihood of train-pedestrian 

collisions, but lack of understanding of the sign’s meaning may limit the sign’s potential to 

improve pedestrian safety. 

Although the MTW remains operational, LACMTA has not implemented the sign at other HRIs 

(V. Khawani, LACMTA, personal communication, December 2001). The agency has installed 

pedestrian gates and swing gates that provide a physical barrier, as opposed to a sign, which it 

feels can be ignored more easily. However, on a case-by-case basis, it may consider 

circumstances that warrant a second train sign as a supplement to the gates. The agency feels 

there is a need for caution about providing too many signs, active displays, and other equipment 

at an HRI because it might result in confusion for the pedestrian or motorist. 

3.2.2 Second Train Coming Warning Sign Demonstration Project—Timonium, 

Maryland 

The Maryland MTA implemented an MTW at the Timonium Road HRI of the Baltimore Central 

Rail Line in Baltimore County (Maryland Mass Transit Administration and Sabra, Wang, & 

Associates, Inc., 2001; V. Hartsock, Maryland MTA, personal communication, December 2001). 

Unlike the sign in Los Angeles, the Maryland sign is primarily intended for use by motor 

vehicles, though standard incandescent Walk/Don’t Walk signals were installed to aid pedestrian 

crossing the tracks. Though no serious collisions have occurred at the Timonium Road HRI, 

heavy roadway traffic and numerous daily multiple train events (approximately 10 per day) 

resulted in the location for sign implementation. Figure 9 shows the implementation, which 

29
supplements existing train-activated lights and gates.. The warning display, which remains blank 

unless a multiple train event is detected, is visible on the cantilever arm that supports the flashing 

signal lights (highlighted by a dashed circle in Figure 10), and a normal pedestrian crossing 

signal is visible at the sidewalk to the left. 

Figure 10. Timonium Road crossing site with MTW 

Principles developed by MTA and the Federal Transit Administration (FTA) regarding legibility, 

message content, message clarity, and sign location guided the design and implementation 

process. Based on these criteria, an FTA report on LRT signage, and the prototype signs 

developed by the LACMTA for the Vernon Avenue crossing, a committee of Maryland MTA 

experts developed three prototype displays for consideration. Two were three-phase displays 

with text and animation; the only difference between the two was the order of the phases. The 

third was a single animation incorporating both text and graphics. MTA managers were shown 

all three signs as they would appear on the final sign, and they showed a strong preference for 

the three-phase display shown in Figure 11: 

 Phase 1: Flashing “WARNING” text for 2.5 seconds 

 Phase 2: Steady “2nd TRAIN COMING” text for 2.5 seconds 

 Phase 3: Simple graphic display of HRI (roadway intersecting with tracks from vehicle 

operator’s perspective) with animation of two trains crossing road from opposite 

directions for 4 seconds 

30
Figure 11. Maryland MTA MTW display 

The total duty cycle of the sign is 9 seconds. The sign remains active from the moment that a 

second train activates the HRI warning devices until at least one full cycle has been completed 

and all trains have cleared the gate activation circuits. Two signs were installed, one for each 

direction of traffic. Each sign was installed on a cantilever arm overhanging the roadway. An 

amber beacon was installed adjacent to each sign. When the MTW sign is activated, the beacon 

flashes to draw motorists’ attention to the sign. 

Investigators measured the frequency of various specific risky behaviors performed by vehicles 

and pedestrians in the month immediately before sign installation, and these data were compared 

to similar measurements collected during the 2 months immediately following sign installation 

The risky behaviors encompassed a range of driver and pedestrian actions of varying severity, 

including motorists who initially crossed the plane of the gate but then reversed behind this line, 

pedestrians that crossed Timonium Road in front of the lowered gate, vehicles stopping beyond 

the plane of the gate arm or inside of the gate, and vehicles that began to move forward after the 

first train passed but then stopped. 

Investigators found small reductions in unsafe behaviors though the total number of observations 

for each specific type of behavior was often very small. Overall, the frequency of risky 

behaviors decreased from 25.9 per 100 multiple train events before sign installation to 20.4 per 

100 multiple train events in the first month after sign installation. This frequency decreased 

again to 16.7 per 100 multiple train events in the second month after installation, which may 

reflect increased driver awareness and comprehension through exposure, publicity, and word of 

mouth. 

The apparent decrease in risky acts after sign installation may be somewhat misleading because 

it is based on the assumption that all risky behaviors are equally dangerous. In fact, an increase 

occurred in the number of drivers who crossed the gate line before realizing that a second train 

was coming and subsequently reversed to avoid the gate crashing on their vehicles. Though the 

number of observations of this incident type is too small to make a definitive judgment, it raises 

the possibility that the presence of an MTW may result in a dilemma situation for drivers who 

notice the MTW after beginning to cross the tracks. Though many factors may contribute to this 

phenomenon, the simplest countermeasures are to (1) improve the conspicuity of the MTW to 

ensure that the sign immediately draws the attention of motorists before they attempt to cross the 

tracks and (2) design phased displays in a way that the multiple train event and the need to 

remain stopped behind the gates are explicitly expressed in the first phase. 

31
Summary: Multiple Train Warnings 

Only two formal evaluations of MTW systems have been conducted, and both of these were 

limited in scope. Despite some notable safety improvements, the results of the demonstration 

projects in Los Angeles and Maryland indicate that the MTWs were less than optimal. For 

example, although more than 90 percent of pedestrians who viewed the Los Angeles sign in 

action interpreted that caution was necessary, only 4 percent specifically identified it as an 

MTW. Though comprehension might increase over time and with publicity campaigns, the 

initial lack of understanding is a significant concern. The feedback from pedestrians at this site 

indicated that the graphic signs conveyed the need for caution, but the specific reason for caution 

may be unclear. Investigators did not specifically assess road users comprehension of the 

Maryland MTA MTW. Maryland MTA selected the message to install by showing the three 

prototype messages to a group of MTA managers and having them complete a survey. Though 

the respondents’ preference for the final sign was overwhelming, Maryland MTA did not survey 

the intended users of the sign (e.g., motor vehicle operators and pedestrians). Unlike MTA staff, 

roadway users would be naive to the purpose of the sign, and their impressions may have 

differed for that reason. After implementation, Maryland MTA conducted a mail survey to 

assess sign effectiveness. The sign received largely favorable impressions, but the survey did not 

assess sign comprehension. The before and after observations revealed some decrease in risky 

behaviors, but drivers still attempted to proceed across the tracks as the gates ascend, despite the 

active MTW. It is not clear whether drivers fail to see the sign, fail to comprehend the message, 

or simply choose to ignore the warning. In summary, the reduction in certain undesirable road 

user behaviors suggests the benefit of MTWs, but various user-centered concerns remain for 

optimal design. 

3.3 Vehicle Control and Automated Enforcement 

Vehicle control systems prevent collisions with trains by creating a physical barrier to prevent 

roadway users from entering the track area when a train is approaching. Typical stop arm gates 

provide a barrier, but drivers can often pass around these gates or even break through them, 

either unintentionally or intentionally. Although a number of novel and promising systems have 

been developed to reduce the ease and likelihood of thwarting gates, few can be described as 

ITS. Examples of such non-ITS systems include the StopGateTM Crashworthy Highway 

Railroad Intersection Barrier and four-quadrant gates. 

Automated enforcement has been applied to a number of applications, including red lightrunning, speeding, and HRI applications. Automated enforcement is a controversial issue that 

often raises issues of privacy, constitutionality, and accuracy. Turner and Polk (1998) provide an 

overview of major issues in automated enforcement and how to go about establishing a 

successful automated enforcement program. Important aspects include informing the public of 

the effort, involving the judiciary, and passing enabling legislation. Additional concerns that 

must be addressed are citizens’ concerns for privacy, concerns that the system is primarily for 

revenue generation, and the process and penalties associated with the citation process. 

32
Automated enforcement has been implemented at a number of HRIs in the United States. These 

systems discourage drivers from driving around active crossing gates at HRIs and to deliver 

citations to violators. Although specific methods vary, these systems use sensors to determine 

when a rail crossing violation occurs and record images to support prosecution. Applied image 

capture technologies include both wet film 35mm requiring digitization with manual citation 

preparation and digital images with video transmitted to a local police department for citation 

generation. Some of the systems had sensors that were linked to the railroad circuitry while 

others were stand alone. The following provides brief descriptions of these systems. 

3.3.1 Dragnet Vehicle Arresting Barrier (VAB) System—McLean, Illinois 

Illinois DOT implemented the Dragnet VAB at three locations on the proposed Chicago-St. 

Louis high-speed corridor (Coleman & Venkataraman, 2001). The VABs essentially consisted 

of a net suspended above the roadway that can be lowered during train approach. When a 

vehicle strikes the net, it is quickly brought to a stop with minimal vehicular damage. The 

University of Illinois evaluated the systems. The evaluation period was 10 months, but, for a 

variety of reasons, including malfunctions and road construction, the system was operational for 

less than one-half of the days of the evaluation. VABs were installed at three HRIs, but 

sufficient data were only collected at one site: US-136 in McLean, which has average daily 

traffic of 2,800 vehicles per day and a speed limit of 45 mph. Two VABs were mounted at this 

site, one for each direction of traffic. VABs consisted of two towers, one on each side of the 

roadway. A net was suspended between the two towers perpendicular to the roadway. For 

eastbound traffic, the VAB was located 27.7 meters from the HRI stop gate. For westbound 

traffic, the VAB was located 46.2 meters from the stop gate. While no trains are approaching, 

the net is suspended over the roadway, above passing vehicles. System deployment occurs as 

follows (timings are approximate): 

 55 seconds before train arrival: pairs of red lights on the VABs begin flashing 

 27 seconds before train arrival: railroad lights and gates activate 

 13 seconds before train arrival: VAB nets and railroad gates are fully deployed 

Fixed signs upstream of the VABs instructed drivers to stop at the VAB when the red lights are 

flashing. Investigators found that 83 percent of drivers complied. All of the noncompliant 

drivers passed under the VAB before the railroad lights and gates activated. However, data 

indicated a trend over time where violations were becoming more frequent and more dangerous 

(closer to the point of train arrival), though interruptions to data collection prevented statistical 

confirmation of this trend. Unfortunately, this study did not make any comparisons to standard 

active grade crossings, though the increase in violations over time seems to indicate that the 

VAB did not have an ideal impact on driver behavior. Researchers cite a number of human 

factors problems with the system, including driver distraction caused by the large towers, the 

peripheral location of the flashing lights on the towers and cross bracing, and the fact that the 

VAB lights activate about 18 seconds before the railroad lights and gates activate. The Illinois 

DOT removed the VAB system after the evaluation period because frequent malfunctions made 

it unreliable and costly to maintain. 

33
3.3.2 Automated Enforcement Demonstration Project—Jonesboro, Arizona 

The first application of automated enforcement at an HRI was a joint venture of the city of 

Jonesboro and Burlington Northern & Santa Fe Railroad (BNSF) (Lammert, 1999). The site had 

a high rate of train-vehicle collisions and frequent damage to the gate arms caused by 

noncompliant motorists. An image capture system, which Science Applications International 

Corporation (SAIC) provided, used an infrared beam to detect violations, a camera to capture the 

violation, and telephone wire to transmit the data to police. No signs were used to inform drivers 

of the enforcement system. Officials estimate that an average of only two violations occurred 

per month with the enforcement system active and that the frequency of violations decreased 

during the first year of use. Investigators provided no data, however, on violation frequency 

before enforcement. Gate damage was also reported to be less frequent than it was before the 

enforcement phase. The system was in operation from 1991 to 1995, when it began to 

malfunction. It has remained offline ever since. 

3.3.3 MBL Grade Crossing Safety Program—Los Angeles, California 

LACMTA implemented an automated enforcement program on the MBL as part of a larger 

project intended to increase safety at HRIs on the MBL (Lammert, 1999). A number of 

problems, including HRI geometry and roadway user misunderstandings, contributed to a high 

rate of pedestrian and vehicle collisions with trains. In 1992, MTA responded by increasing 

police presence and ticketing at HRIs. Though successful, the program was too expensive to 

maintain. In the same year, MTA initiated a project to demonstrate the use of automated 

enforcement at two gated HRIs. Cameras were installed overlooking the HRIs. The cameras 

were not hidden, and nearby signs warned roadway users of their presence in English and 

Spanish. The signs had a small picture of two video cameras facing an MUTCD standard W-10 

advance warning sign icon. The text messages below the icons were “PHOTO CITATIONS 

ISSUED” and “INFRACCIONES REGISTRADAS FOTOGRAFICAMENTE.” U.S. Public 

Technologies manufactured the camera systems. Photos generated by the system included a data 

overlay that included a timestamp and violation-specific data. Difficulties due to sun glare, 

missing license plates, and unmatched license plates resulted in citations being issued to only 

about one-half of recorded violators. Despite ticketing difficulties, gate-running violations 

decreased by 92 percent at one site and 68 percent at the other. Encouraged by this high rate of 

success, MTA added additional cameras at other HRIs along the MBL and reported a 70-percent 

reduction in trains colliding with vehicles at these HRIs. 

3.3.4 Automated Enforcement at Highway-Rail Grade Crossings—Ames, Iowa 

Officials in the city of Ames decided that an improvement was needed at one HRI that 

experienced an unusually high number of train-vehicle collisions. The officials decided to install 

an automated enforcement system (Lammert, 1999). Fixed signs were installed upstream of the 

HRI to inform motorists of the system. The message on the signs was “RR XING 

SURVEILLANCE SYSTEM” (Fitzpatrick, Bartoskewitz, & Carson, 1997). System designers 

chose to use the same SAIC system that was used in Jonesboro, Arizona. Two cameras were 

installed at the HRI; one facing each direction of traffic. Cold weather, however, interfered with 

the infrared detectors, which were subsequently replaced by loop detectors. Even with the 

detection upgrade, limitations still prevented citations from being issued. Photos taken at night, 

because of the brightness of the flash on the retro-reflective license plates often had unreadable 

34
license plate numbers.. Laws required violators to be personally identifiable, but the camera 

images rarely achieved this level of resolution. Citation notices were also required to be 

delivered in person, which substantially reduced the efficiency of the process. Because of these 

difficulties, the definition of a violation was scaled back to exclude the least egregious violators; 

rather than issuing punitive citations, officials chose to issue warnings instead. 

3.3.5 Automated Railroad Crossing Enforcement System (ARCES)—DuPage 

County, Illinois 

Beginning in 1999, the Illinois Commerce Commission conducted an evaluation of the 

effectiveness of ARCES at three HRIs in DuPage County (Illinois Commerce Commission, 

2002). The HRIs chosen represent a cross-section of features, including a suburban downtown 

HRI, a four-lane urban HRI, and a two-lane rural HRI. A fourth site was added in 2002 but was 

not part of the initial investigation. Each location tested a slightly different type of photo 

enforcement system, including systems from ACS State and Local Solutions (formerly Lockheed 

Martin IMS), SAIC, Nestor Traffic Systems, and Proscan. Although questions regarding the 

legality of photo enforcement prevented sufficient data from being collected at one site, beforeand-after comparisons showed gate violation reductions of 47 percent and 87 percent at the other 

two sites. Although collisions with trains were too rare at these sites to make a statistical 

comparison, the annual rate of collisions has been below average since ARCES implementation. 

The investigators conclude that automated enforcement is an effective means to reduce gate 

violations, but that the high cost of system installation, maintenance, and the citation process are 

likely to preclude broad implementation. If only implemented at high-risk HRIs that have a high 

number of violations, however, automated enforcement systems may generate sufficient revenue 

to recoup their cost within a few years of use. 

Summary: Vehicle Control and Automated Enforcement 

Results from field evaluations indicate that VABs, of the type described above, suffer from poor 

operational reliability and motorist noncompliance. On the other hand, automated enforcement 

can be an effective method to reduce the frequency of gate violations at HRIs. However, a 

number of issues, including privacy concerns and legal arguments, must be overcome before 

automated enforcement can be successful. Additionally, the system must be reliable and 

adequately maintained to ensure that violating vehicles can be identified. Previously 

implemented systems suffered from malfunctions. These problems were compounded in cases 

where no agency was clearly responsible for system maintenance and repair. Although none of 

the current systems appeared to cause detrimental behaviors among drivers (e.g., violating 

drivers becoming disoriented by a camera flash), implementers should consider the possibility of 

such effects. Another issue to consider is the extent of public outreach. Polk (n.d.) recommends 

a campaign to inform the public of the system’s existence but not to publicize the exact 

locations. One possibility is to place camera housings at many HRIs and to rotate a small 

number of cameras between these sites. Finally, because of restrictive costs, it is important to 

choose sites for installation based on crash likelihood and frequency of violations. 

3.4 Summary of Lessons Learned 

Lessons learned from these deployments and demonstration projects suggest that advance alert 

and warning systems have the potential to provide safety and operational benefits, although 

technological and political challenges (i.e., DOT-Rail-community cooperation) often hamper, the 

35
development and successful implementation of these systems. Although most of the systems 

discussed in this chapter function at gated HRIs, they may also be applicable at passive HRIs 

where no active warning devices exist, in situations with reduced visibility, and at other high-risk 

locations. Nevertheless, no uniform system architecture or standardized set of messages has 

been adopted. Systems have varied in design and with regard to the types of information 

communicated to drivers, as well as the form in which the information is communicated to 

drivers. Two basic system distinctions have emerged: systems that provide additional 

information to drivers for the sake of better informed decisions (e.g., in-vehicle alerts and 

multiple train warnings) and systems that actively prevent or discourage undesirable behavior 

(e.g., vehicle control and automated enforcement). The majority of systems were implemented 

as demonstration projects and then removed soon after evaluation was complete. While some 

provided useful data on their effectiveness, others demonstrated the use of a new system without 

conducting any evaluation. 

36
Draft

Table 1. Highway-rail intersection warnings and enforcement projects

System Name Agency/Organization Implementation Description Information Communicated 

Information About Train Arrival 

Rail View Texas DOT, Texas 

Transportation Institute 

College Station, 

Texas 

Provides real-time train 

movement information to 

emergency service providers, 

traffic management operators, 

and traffic signal controllers 

 Train location 

 Train speed & direction 

 Estimated time of arrival 

at downstream HRIs 

 Duration that the train 

will occupy the HRI 

Rail Monitor Texas DOT, Texas 

Transportation Institute 

Sugar Land, Texas Provides HRI status 

information to police, fire, 

and EMS to allow responders 

to avoid unnecessary delays 

at train-occupied HRIs 

 Train location 

 Train speed and direction 

 Train length 

 Estimated time of arrival 

and clearance at HRIs 

Train Presence 

Information by 

HAR 

Texas DOT, Texas 

Transportation Institute 

Laredo, Texas Uses HAR to broadcast 

automated messages and 

fixed flashing signs upstream 

of the HRI to warn drivers 

 Intersection blocked 

 How long intersection has 

been blocked 

before they reach the HRI 

(“Train When Flashing,” 

“Expect Delays”) 

 Train direction 

37
Draft 

Table 1. Highway-rail intersection warnings and enforcement projects (continued) 

System Name Agency/Organization Implementation Description Information Communicated 

AWARD Texas DOT, San Antonio, Texas Advises motorists and 

TransGuide, Part of the emergency responders of 

Metropolitan Model delays resulting from railroad 

Deployment Initiative blockages using changeable 

message signs posted near 

freeway exits 

IGC New York State DOT, New Hyde Park, Uses train detection, vehicle 

Alstom Signaling New York detection, and 

communication equipment to 

improve roadway traffic flow, 

provide information to 

motorists, and enhance 

communications between 

train crews and the HRI 

In-Vehicle Signing Minnesota DOT, 3M, Glencoe, Minnesota In-vehicle signing installed in 

System for School Dynamic Vehicle Safety 29 school buses; provides 

Buses at Railroad- Systems drivers with two types of 

Highway Grade information: (1) crossing 

Crossings alert and (2) train warning. 

Icons represent external RRX 

signs. Visual and audible 

alerts provide a minimum of 

250 feet of warning time 

(equivalent to 6.8 seconds at 

25 mph and 3.8 seconds at 45 

mph) 

 Traffic delay due to train 

 Alternate route 

 Constant warning time 

 Emergency vehicle 

accommodation 

 Vehicle detection 

 Crossing status 

 Crossing alert 

 Train warning 

38
Draft

Table 1. Highway-rail intersection warnings and enforcement projects (continued)

System Name Agency/Organization Implementation Description Information Communicated 

Integrated Train 

Detection and 

Minnesota DOT, 

Minnesota Guidestar, 

Moorhead, 

Minnesota 

Three-phased project. No 

communication to motorists 

Future: 

 Traffic Control 

System 

SRF Consulting at this time, only system 

development and testing. 

Future plans include using 

CMSs and linked database to 

(CMS) Number of 

minutes nearest HRI will 

be blocked 

 Train estimated time of 

provide emergency vehicle 

dispatchers with train data 

arrival at each HRI 

Advisory On-Board 

Warning 

Illinois DOT, University 

of Illinois at UrbanaChampaign, Raytheon 

Systems 

Metra-Milwaukee 

North Line 

A pilot study with a 9-month 

operational phase involving 

more than 270 equipped 

vehicles. System provides invehicle warnings (text/audio) 

that a train is approaching or 

at the HRI. Uses two 

 Caution or warning 

(indicates train 

approaching or at HRI) 

different system messages: 

caution and warning 

Multiple Train Warnings 

Pedestrian Second LACMTA Los Angeles, Warns pedestrians that trains  Multiple trains arriving at 

Train Warning California are approaching on more than HRI 

one track at a pedestrian 

crossing area 

Second Train Maryland MTA Timonium, Warns motorists at a gated  Multiple trains arriving at 

Warning Sign Maryland LRT HRI that trains are HRI 

approaching on both tracks 

39
Draft

Table 1. Highway-rail intersection warnings and enforcement projects (continued)

System Name Agency/Organization Implementation Description Information Communicated 

Vehicle Control and Automated Enforcement 

Dragnet VAB Illinois DOT, University McLean, Illinois Physically stop intruding 

of Illinois vehicles by using nets 

Automated City of Jonesboro, Jonesboro, Detection and image capture 

Enforcement BNSF Arkansas system designed to 

Demonstration automatically photograph and 

Project cite drivers who cross tracks 

while gates are down 

MBL Grade LACMTA Los Angeles, CA Detection and image capture 

Crossing Safety system designed to 

Program automatically photograph and 

cite drivers who cross tracks 

while gates are down 

Automated Ames, Iowa Detection and image capture 

Enforcement at system designed to 

Highway-Rail automatically photograph and 

Grade Crossings cite drivers who cross tracks 

while gates are down. 

System used same hardware 

as Jonesboro application 

ARCES Illinois Commerce DuPage, Illinois Detection and image capture 

Commission system designed to 

automatically photograph and 

cite drivers who cross tracks 

while gates are down 

 Warning (indicates train 

approaching or at HRI) 

 Citations mailed to 

owners of violating 

vehicles 

 Citations mailed to 

owners of violating 

vehicles 

 Nonpunitive warnings 

hand delivered to 

violators at home 

 Citations mailed to 

owners of violating 

vehicles 

40
Draft 

Part III: General Human Factors Considerations for Application of ITS 

to HRIs 

41

4. Message Factors 

4.1 Background 

This chapter deals with the general attributes of ITS messages related to the HRI. The purpose 

of ITS messages presented to a road user is to bring about some desired behavior in the road 

user. This chapter will identify attributes of messages that promote appropriate behavior for the 

range of intended users. The chapter deals with general message attributes, such as information 

content, format, and timing, rather than details of the display itself. It also encompasses system 

considerations (i.e., general concerns for ITS HRI messages as elements of the broader contexts 

in which road users encounter them). 

This chapter is closely related to Chapter 5, Roadside Displays; Chapter 6, In-Vehicle Displays; 

and Chapter 7, Displays for Pedestrians. To some extent, different considerations and different 

available options for roadside messages and in-vehicle messages exist. Therefore, these 

subsequent chapters deal in greater detail with a number of message factors. In Chapter 4, the 

concern is with the broader attributes of messages that are relevant to both roadside and invehicle displays. Many recommendations, however, are closely related to recommendations 

given in other chapters. Cross references are given in the text. 

Getting the human user to respond appropriately to warnings and alerts has been an issue in 

many different domains of activity, including workplace safety, consumer product use, medical 

device use, control rooms, and aviation. Road user behavior is not unique in this regard. It is 

often difficult to get people to notice warning information, even when it is plainly visible, and 

difficult to get them to respond as desired, even when the message is noticed. Research and 

experience across these many applications, as well as work specifically on TCDs or ITS, has 

pointed to some of the attributes that an effective message should possess. For example, 

research and guidance on ITS messages exists for advanced traveler information systems 

(Campbell, Carney, & Kantowitz, 1998), driver route guidance (Lerner & Llaneras, 2000), and 

in-vehicle information systems (Driver Focus-Telematics Working Group, 2003). Research and 

guidance on TCD messages includes warning signs (Lunenfeld & Alexander, 1990) and variable 

message displays (Dudek, 2003). Examples of research and guidance from other domains 

include consumer product instructions and warnings (Singer, Balliro, & Lerner, 2003), advanced 

traffic management centers (Sobhi & Kelly, 1999), and nuclear power plant control rooms 

(O’Hara, Higgins, Persensky, Lewis, & Bongarra, 2004). Broad reviews and integrations of the 

range of literature on warning effectiveness have occurred (e.g., Miller, Lehto, & Frantz, 2001). 

The discussion and recommendations in this chapter make use of the broader literature on 

warnings, as well as specific information in highway safety and ITS literature. 

4.2 Key Human Factors Issues and Need for Guidance 

4.2.1 Issue: Distinguishing Different Types of Messages 

Many different types of information may relate to the presence or status of HRIs. Some 

messages concern safety issues while others concern non-safety issues, such as travel 

information and route selection. A particular ITS display device—such as a CMS or an invehicle information interface—may display safety and non-safety messages at various times and 

may not be dedicated specifically to HRI information. Some messages may be urgent and 

require immediate driver response while others can be processed more leisurely or even safely 

43
ignored. Safety-critical messages must be immediately distinguishable from other messages and 

must have attributes that ensure they are responded to quickly and reliably. 

Traditional fixed roadway signing has various color and shape conventions so that motorists can 

immediately recognize the category of information being communicated. The effectiveness of 

this coding—whether most motorists actually understand and respond to the code as well as 

might be desired—is somewhat questionable, but it is seen as a critical aspect of the sign and 

marking system. The MUTCD (Federal Highway Administration, 2003) in Section 1A.12 

defines the general meaning of reserved colors (e.g., with background sign colors of yellow 

indicating warning, white indicating regulation, and green indicating direction guidance). Active 

TCDs also have conventions (e.g., red flashing lights for stop messages on intersection traffic 

signals and at HRIs). No convention exists for ITS applications related to HRIs to make various 

message types distinguishable. For CMSs, there is typically no use of color, shape, or other 

coding occurs, even though current technologies permit this (Lerner, Singer, & Huey, 2004). For 

in-vehicle systems, no accepted convention exists. 

4.2.2 Issue: Requirements for Effective Warning Messages 

Warnings are the most critical type of message. As this term is used here, a warning is a timecritical message that informs the road user of a hazard or required action of which he/she may be 

unaware. A substantial human factors literature exists on warning effectiveness across a range of 

domains (transportation safety, product warnings, workplace warnings, instructional materials, 

control rooms, and medical devices). This literature has identified a number of necessary stages 

that must be successfully met if a warning is to be effective. The following lists these general 

stages: 

 Notice the display 

 Comprehend the message 

 Accept the validity of the message (credibility) 

 Comply with the message 

Noticing has to do with the conspicuity and salience of the display. This is primarily related to 

display features rather than message features. Conspicuity is dealt with only generally in this 

chapter and more specifically in Chapter 5 for roadside displays and Chapter 6 for in-vehicle 

displays. Comprehension includes such concerns as the legibility or audibility of the message, 

standardization of message components, and the user’s mental model of the system. Message 

credibility can be a particular concern for real-time ITS displays. It is related to factors such as 

accuracy, timeliness, nuisance warnings, consistency with expectancies, and the perceived 

motives of the message provider. Compliance is important to focus on because even when 

messages are understood and perceived as credible, they may not be complied with. 

Noncompliance may be intentional on the road user’s part because of the desire to save time, 

following the example of other road users, or other motivations. Noncompliance may also be 

unintentional, if the road user is not capable of responding in time or with accuracy. This relates 

to factors of message timing, workload, consistency of operation, and risk perception. For 

traditional TCDs (in general and for HRI devices in particular), standards and practice have 

already helped establish the conspicuity, comprehensibility, and credibility of the message, 

although perhaps not always optimally. For example, drivers do not always understand what to 

44
do at a signalized HRI, and many are skeptical of the timing of signals and gates (e.g., Lerner, 

Ratte, & Walker, 1989). For innovative ITS HRI applications, road users do not bring a history 

of familiarity with the device, and guidance for system developers is limited. 

4.2.3 Issue: Unintended Consequences 

ITS information can have unintended consequences that are problematic. For example, a display 

might draw attention away from other important driving cues or add to the driver’s mental 

workload. Messages can be intrusive or annoying, leading to poor acceptance or defeat of the 

system. Research has found that nuisance speech messages are more annoying to drivers than 

tonal signals (Lerner, Dekker, Steinberg, & Huey, 1996). Road users might also use ITS 

information in ways unintended by the designer. For example, information about train arrival 

time might lead some drivers to speed to beat the train, or information about a delay at an HRI 

could lead to illegal or inappropriate lane changes or U-turns. Another potential unintended 

consequence is automation complacency (e.g., Endsley, 1996). This is a general phenomenon 

seen in systems where part of the operator’s task is automated. Vigilance and situation 

awareness may be reduced, and the user may just assume that system status is proper. Applied to 

the HRI situation, an example might be drivers that fail to search at a passive crossing because 

they expect to get an alert from a train-based warning system. Related to automation 

complacency is the phenomenon that has been termed risk compensation or behavior feedback 

(e.g., Evans, 1991). Various analyses of highway safety improvements have shown that the 

improvement does not simply overlay some benefit on current driver behavior. Rather, the new 

feature leads to a change in driver behavior, which can reduce or even eliminate the potential 

benefit. Rather than passively accepting the improvement as simply a safety enhancement, 

drivers may trade off all or part of the safety benefit for some other perceived benefit. A classic 

example is a Swedish study (Rumar et al., 1976) that found that drivers equipped with studded 

tires drove at higher speeds than other traffic on icy roads, giving back a portion of the safety 

benefit for the convenience of faster travel. ITS applications for HRIs might result in similar 

effects. For example, if drivers anticipate receiving in-vehicle alerts from train-based systems, 

they may approach HRIs at higher speeds. While the possible effects of HRI ITS treatments may 

be speculative, the various unintended consequences of ITS messages are well established as 

possibilities to which the designer must be alert. 

4.2.4 Issue: Message Design for Specific Roadway Users 

ITS messages should consider the needs of specific road users. Two general aspects to this exist. 

One is to take advantage of ITS capabilities so that the message can be optimized for a particular 

individual motorist and vehicle receiving the message. The other is to ensure that the message is 

appropriate for particular groups within the broader population of road users. 

Fixed highway signs, signals, and markings provide the same message all the time, without 

regard to the user, the vehicle, and current traffic and environmental conditions. As a 

consequence, features of the message (content, location, timing, appearance) must be designed 

based on certain assumptions, which may not always be appropriate. The criteria are often based 

on a conservative (less capable) design driver (e.g., 85th percentile on some attribute), which 

makes the assumptions too conservative for the majority of drivers and yet may still fail to 

adequately address the more extreme drivers. This mismatch can weaken the message. ITS 

capabilities offer the possibility of recognizing specific aspects of the situation and tailoring the 

45
message for the road user. For example, the timing or content of a message about an HRI ahead 

might be modified based on the vehicle’s speed, vehicle size and braking capability, roadway 

surface conditions, visibility conditions, whether there is a queue of traffic, or individual driver 

attributes, such as reaction time or local familiarity. 

Among the population groups that must be considered in the design of ITS messages are the nonEnglish-literate and older people. Although various current in-vehicle products may offer a 

language option for the display, providing a menu of language options is not possible for 

roadway-based signs (although sometimes a message may be presented in two languages, as in 

Section 3.3.3). Unlike much fixed signage, which uses graphical elements such as icons, shapes, 

and colors, current roadway signs for ITS messaging generally use text messages on CMS 

displays. Therefore the non-English-literate may not receive useful information. For older road 

users, important considerations include poorer vision, slower information processing, and longer 

perception-reaction times. Various studies have also shown age differences in how drivers 

comprehend the meaning of different signs and symbols. Older drivers will comprise an 

increasingly greater portion of the driving population as the baby boom generation ages, and 

messages must be usable by this group. Another segment of the population that must be 

considered for pedestrian-related displays is those with disabilities. Mobility characteristics 

(e.g., wheel chair use) may influence the optimal timing or content of messages for pedestrians. 

Sensory impairments (visual or auditory) also influence message criteria. The Americans with 

Disabilities Act (ADA) Accessibility Guidelines for Buildings and Facilities (1998) is specifically 

referenced in the MUTCD (Federal Highway Administration, 2003), and ADA requirements are 

a general issue for roadway design, operations, and displays. Persons with disabilities likewise 

should be considered in the design of ITS messages intended for pedestrians. Chapter 7, 

Displays for Pedestrians, deals further with some of these concerns. 

4.2.5 Issue: Modes of Display 

One issue facing the designer of ITS displays is the choice of mode(s) in which to present the 

message. The predominant mode today is visual, in either text or pictorial/symbolic form. 

Acoustic messages are increasingly common for in-vehicle ITS applications and may be in the 

form of speech or non-speech signals (earcons). Acoustic signals are integral parts of the 

traditional (non-ITS) HRI system through bells at active crossings and train horns. Haptic and 

tactile signals can be used in vehicles for alerting; examples include vibration of the steering 

wheel or pedals, or counterforces in the steering wheel or accelerator pedal. Haptic and tactile 

signals are present on the roadway in the form of rumble strips and raised pavement markers but 

only as fixed roadway features and not as controllable ITS messages. The choice of mode may 

be quite application-specific and will have different considerations for in-vehicle and roadwaybased devices. Therefore further discussion will primarily be in other chapters (Chapters 5, 6, 7). 

Some general human factors considerations related to the mode of display, however, are 

appropriately considered for any application. 

4.2.6 Issue: System Considerations 

In designing ITS displays for HRI applications, it is essential to approach the problem from a 

systems perspective. The message about the HRI is presented to the roadway user in a complex, 

real-world context. Although the designer of the application may be specifically focused on 

some HRI information, the roadway user who receives that information is not so narrowly 

46
focused. Drivers must attend to the full array of information presented to them while dealing 

with vehicle control and traffic events, and the ITS information about the HRI is but one element 

in this array. Therefore, if the ITS application is to be successful, it must communicate 

effectively within the information environment in which the road user operates. 

Various system contexts exist in which ITS messages about the HRI must operate. These 

contexts include those listed below. 

 ITS services context. ITS information and services that are present in addition to the 

specific HRI message of interest. For example, an in-vehicle system might provide 

information related to other ITS user services, such as en-route driver information, route 

guidance, traveler services information, and collision avoidance. Messages related to 

HRI information must function effectively within this broader ITS system. 

 Roadway information system. The road user is confronted with information from traffic 

control devices of all sorts, including signs, signals, and markings. Information from less 

formal sources also exist, such as the surrounding environment, tree lines, and road 

geometry. This information system includes information that may be related to the ITS 

information about the HRI, as well as information about unrelated aspects of the road. 

All of this information must function in a mutually compatible way. The content, timing, 

location, appearance, and density of the various information sources must work in a 

complementary manner and not generate confusion or unreasonable demands on the road 

user. 

 Traffic operations environment. The ITS message about the HRI will occur while the 

driver is coping with all of the other things a motorist must contend with, such as 

navigating, dealing with other traffic, selecting the proper path and speed, and monitoring 

the entire situation for possible hazards. The ITS message will have to function 

effectively within this context and should not lead to driver problems in dealing with 

other critical aspects of the driving task at that time. 

 Roadway and railway network. The road user encounters an ITS application at a 

particular HRI within the context of a network of roads and HRIs. The road user’s 

experience with the network will influence expectancies and behaviors at particular sites. 

For example, the characteristics of the network will influence whether the drivers expect 

to encounter an HRI, whether they anticipate an active or passive crossing, and whether 

they expect high-speed trains. The use of ITS within this system may influence the 

response to an ITS message at any one location. For example, if an ITS system that 

transmits an in-vehicle warning about arriving trains is operational at some HRI in a 

region but not others, drivers may have an inaccurate expectation about whether they will 

receive a warning; or if installations at different HRIs have different operational features 

(e.g., different algorithms for when to initiate a message), the road user’s mental model of 

what the TCD does may be inaccurate. 

The ITS HRI application is only one component of each of these systems. Good human factors 

design must include consideration of how the specific application functions within these systems 

because the roadway user encounters the application within these more general contexts. 

Numerous aspects to these system considerations exist, including the following: 

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 Uniformity and compatibility of messages and display features from application to 

application. 

 Integration of ITS functions. Prototype applications involving ITS at the HRI typically 

have been developed and evaluated as stand-alone devices or services. As ITS services 

proliferate, however, individual applications will not perform optimally if they are not 

systematically integrated with other ITS information. This is particularly a concern for 

in-vehicle systems. 

 Management of driver workload. Drivers must simultaneously deal with various aspects 

of the driving task (e.g., maneuvering, watching for hazards, speed monitoring, lane 

keeping, navigating) and with various sources of information (signs, markings, traffic, 

roadside, in-vehicle sources). When the demand on the driver is excessive, information 

gets missed and driving performance deteriorates. Therefore ITS messages about the 

HRI must be considered in terms of how they contribute to driver workload as well as in 

terms of how they will function in the context of the pre-existing driver workload. 

 Development of road user expectancies about a given situation based on his/her 

experience with the entire system. For example, if an ITS warning system is installed at 

some HRIs in an area, a road user might incorrectly anticipate that the system is 

operational at all HRIs in the area. 

 Compatibility of ITS HRI messages with the roadway traffic control system. 

4.3 Recommendations 

Recommendations for message factors are grouped under nine topics, in the box provided on the 

next page. For each topic, the individual recommendation statements are given. 

4.3.1 Factors to Ensure Message is Noticed 

Recommendation 4-1: Ensure adequate conspicuity of the message 

Locate visual displays near the road user’s probable line of site, within 20 degrees if possible. 

Consider message modes (acoustic, tactile) or alerting cues that do not require the driver to be 

oriented toward the message. For visual displays, conspicuity can be enhanced by size, contrast, 

color, and movement (flashing, animation). Conspicuity enhancements must be considered 

along with potential negative consequences, such as driver distraction, annoyance, intrusiveness, 

esthetics, and interference and incompatibility with other roadway communication elements. 

Specific recommendations for conspicuity depend on the particular ITS application. 

[Also see: Sections 5.2.2, 8.2.4, 11.2.1 and Recommendations 5-3 through 5-9, 6-6, 6-8 through 

6-13, 7-1, 7-4, 8-10, 11-6] 

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Table 2. List of recommendations for message factors 

Factors to ensure message is noticed 

1. Ensure adequate conspicuity of the message. 

2. Limit displays to needed messages. 

Factors to improve comprehension of message 

3. Ensure legibility and audibility under probable operating conditions. 

4. Make the desired road user action explicit and unambiguous. 

5. Use standard or common wording, abbreviations, images, and formats. 

6. Test for road user comprehension. 

7. Promote compatibility with the road user’s mental model of how the system works. 

Factors to improve credibility of message 

8. Ensure that information is accurate and timely. 

9. Minimize the frequency of all categories of nonuseful alerts. 

10. Consider road user perceptions about motivations and criteria of traffic-rail authorities. 

Factors to improve compliance with the message 

11. Provide adequate response time, consistent operation, and controlled workload. 

12. Avoid excessively conservative criteria. 

13. Provide road user feedback regarding noncompliance and unsafe behaviors. 

Distinguishing safety-critical messages 

14. Design safety-critical messages to be immediately recognizable as urgent safety alerts and 

discriminable from other messages. 

Choice of message display mode 

15. Consider the advantages and disadvantages of alternative display modes. 

Unintended consequences of the message 

16. Avoid driver distraction. 

17. Consider the potential effects of automation complacency and risk compensation (behavioral 

adaptation). 

18. Minimize annoyance. 

19. Anticipate road user misuse of information. 

Message appropriateness for specific road users 

20. Customize ITS messages for the current situation. 

21. Devise messages for effective communication with non-English-literate road users. 

22. Devise messages for effective communication with older road users. 

23. Devise messages for effective communication with road users having disabilities. 

System considerations 

24. Provide uniform messages and displays across information sources and sites. 

25. Provide compatible message timing among information sources. 

26. Manage information demand and driver workload. 

27. Integrate ITS functions. 

28. Avoid the development of inappropriate road user expectancies about the roadway and railway 

network. 

29. Integrate ITS HRI displays and controls with the roadway traffic control system. 

Rationale 

The road user cannot receive a message unless he/she is aware of the presence of the message 

display. The message must be conspicuous enough that it is detected by the road user in a 

reliable and timely way. This is especially so for time-critical warning messages. Therefore, the 

physical aspects of the message display must make the display stand out to the driver when and 

where the information is needed. Because visual messages depend on the road user’s eyes being 

oriented toward the display, conspicuity is enhanced if the visual display can be located near 

where the gaze is likely to be directed and if the display includes those factors that increase 

conspicuity, particularly if the display is initially outside of foveal (central) view. Some 

conspicuity enhancements, however, may lead to distraction or annoyance and so should be used 

49
only with caution [Also see: Recommendations 4-17, 4-18]. For example, animated CMS 

displays can be very attention-getting yet raise real questions about appropriateness (Lerner et 

al., 2004), and the MUTCD (Federal Highway Administration, 2003) includes prohibitions 

against the use of animation for certain applications. Acoustic signals have the advantage of 

remaining detectable wherever the road user’s gaze is directed. This is also true for tactile 

signals although they have been used minimally to date. Brief acoustic signals can help to alert 

the driver to the presence of a visual message, or the message itself may be in acoustic (speech or 

non-speech) mode. When messages are not useful to the road user (false alarms, overly 

conservative, information is already known), however, acoustic signals (and especially speech 

messages) may be more annoying and less acceptable to users. 

While the general principle of conspicuity in this guideline is common to all ITS displays for the 

HRI, the specific means of meeting conspicuity needs will depend on whether the ITS display is 

within the vehicle, on the road and intended for motorized traffic, or on the road and intended for 

pedestrians. 

Recommendation 4-2: Limit displays to needed messages 

Warnings, alerts, and other messages not directly requested by the road user should be limited in 

number and should meet a specific user need. Ideally, the ITS display will remain dark (for 

visual) or silent (for acoustic) when no need is present. This recommendation applies to 

messages that are intended to alert the road user, in contrast to information about conditions that 

the road user is actively seeking. For example, a route guidance display is appropriately 

maintained as long as the driver seeks to use it. 

Rationale 

It is easier to detect the presence versus absence of a display rather than a change from one 

display to another. Therefore the attention-getting value of a particular message about the HRI 

will be enhanced if the display field (sign panel, in-vehicle display, and acoustic and speech 

communications) is only active when messages are required. Furthermore, the frequent 

presentation of messages can reduce the salience of the existence of a message. This problem of 

overuse is a general concern for highway safety messages of any type. For example, the 

MUTCD (FHWA, 2003) in Section 2A.04, Excessive Use of Signs, states that regulatory and 

warning signs “should be used conservatively because these signs, if used in excess, tend to lose 

their effectiveness.” 

One caveat to this recommendation concerns failure modes, particularly for warning systems. 

Existing active HRI warning systems maintain a standby power system and can operate in 

warning mode when a power failure or other system failure occurs. If a warning system fails, the 

system should be able to operate in a failure mode in which the warning message is displayed for 

the duration of the failure, even though the system may be incapable of detecting threats. 

50
4.3.2 Factors to Improve Comprehension of Message 

Recommendation 4-3: Ensure legibility and audibility under probable operating 

conditions 

Rationale 

Even if the driver notices the display, the display can only communicate a message if it is legible 

(visual messages) or audible (acoustic non-speech and speech messages). While this is evident, 

the important point in this recommendation is to determine the likely range of real-world 

operating conditions. For roadway visual displays, this includes weather-related visibility 

conditions, such as rain, snow, fog, and spray; lighting-related concerns, such as veiling glare, 

disability glare from oncoming traffic, poor illumination or retro reflectance at night; and 

obscuration by objects, such as truck traffic or vegetation. In-vehicle displays may also suffer 

glare, and acoustic displays may be degraded by engine noise, wind, conversation, and 

entertainment systems. Specific criteria for legible or audible messages are distinct for roadway 

displays and in-vehicle displays. Therefore Chapters 5 and 6 provide more specific 

recommendations. 

Recommendation 4-4: Make the desired road user action explicit and 

unambiguous 

While it is important to convey the nature of the hazard or other specific information about the 

situation, this information alone may not be adequate to ensure a proper and timely response. 

Part of the message conveyed to the road user should be a clear sense of what action to take. 

This does not necessarily have to be stated explicitly, but if it is implied, confirm that the road 

users make the proper inferences. 

Rationale 

Road users may understand the general nature of a message, but this does not mean that they 

fully comprehend the appropriate action they should take in response to that information. 

Examples of this may be seen in current fixed HRI signing. For example, the Number of Tracks 

Sign (R15-2) may fully convey the message that there are a certain number of tracks at that HRI, 

but road users may have no idea why this is useful information and how it should affect their 

actions. Similar lack of full understanding might occur with ITS messages. For example, if an 

in-vehicle system provides an indication that there is an HRI ahead, the road user may not know 

if this means he/she should slow down immediately or take some other action. If an HRI 

employs an advance barrier system, the road user may not understand where to stop. Although 

making the user response unambiguous is desirable for any sign, this is a particular concern for 

HRI ITS messages because the applications are unfamiliar and not standardized, so the road user 

does not have previous experience. 

Recommendation 4-5: Use standard or common wording, abbreviations, images, 

and formats 

Display elements should be familiar to the road user and have their understandability established. 

Sharing common elements also contributes to display uniformity throughout the information 

system [Also see: Recommendation 4-24]. Ideally, key aspects of the message wording and 

51
other display elements should be standardized. In the absence of consensus practices, where 

possible, use established conventions from related applications. 

Rationale 

Displays for roadway and in-vehicle ITS applications do not have the advantage of established 

practices or standards for the content of the display. Developers of prototype or demonstration 

systems may use different words or images for the same concept. Designers should take 

advantage of previous research and other applications for determining the components of their 

messages. For example, abbreviations

2

 used for CMS are based on research, and their 

subsequent use in various applications promotes comprehension when used for the HRI 

application. Furthermore, if new displays are developed without regard to common usage, this 

results in a lack of uniformity throughout the information system. Recommendation 4-24 

discusses the need for uniformity further. Wording, icons, and other display elements can be 

adapted from fixed roadway signs that are already familiar to road users. Chapter 5 discusses 

some proposed ITS messages and sets of abbreviations which the designer should consider. In 

the absence of consensus practices, designers should take advantage of existing conventions and 

resources where possible and use message elements with which road users are likely to be 

familiar. 

Recommendation 4-6: Test for road user comprehension 

For novel displays, confirm that the intended message is fully conveyed to the range of intended 

users. This is particularly necessary for pictorial, diagrammatic, or symbolic displays, but 

misunderstanding can still occur even with text or speech messages. Comprehension tests should 

include a representative range of road users, including older people. 

Rationale 

In the area of TCDs, many examples of signs, signals, and markings exist that are poorly 

comprehended, even after many years of use (Knoblauch & Pietrucha, 1985). This includes 

signs associated with the HRI in particular (Lerner et al., 1989). Road user experience and 

public education are unlikely to overcome poor communication. It is important to confirm that a 

new display actually conveys the intended message. Comprehension testing has been lacking in 

various ITS applications. Many ITS implementations reviewed in this project did not include 

adequate comprehension testing before activation. Many displays were chosen by the designer 

or an internal committee that is not representative of the range of road users. While it may be 

evident that road users may misinterpret icons, symbols, color codes, or other nonlinguistic 

elements, even word messages may not convey the meaning intended by the designer (Dewar & 

Olson, 2001). 

Although comprehension testing may sound straightforward, a number of complexities and 

issues actually exist. Various techniques exist, none of which is routinely accepted, and there is 

no consensus criterion for acceptability. Findings may be influenced by the context in which the 

displays are presented, and by whether multiple choice, short answer, or behavioral methods are 

used to measure comprehension. Images can be displayed with various degrees of sophistication, 

2 A reviewer who teaches message creation for CMSs emphasized that before using an abbreviation, developers 

should try to find a simpler way to say the same thing without abbreviating. 

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from dynamic display in a simulator setting to paper images. Comprehension testing methods 

must, therefore, be carefully thought out so that the findings are meaningful for the particular 

application. 

However the testing is done, it is important to look not only at the frequency of correct 

understanding but also at the nature of misunderstandings. Misunderstandings may provide 

clues as to how to improve the display. Additionally, certain misunderstandings, termed critical 

confusions, may be very dangerous since the viewer interprets the message in a manner that 

might lead to an inappropriate action. For example, if a display at an HRI showed the remaining 

time until a train clears the HRI, but a road user interpreted this as showing the time until a train 

arrives at an HRI, a driver might believe an opportunity to cross exists when in fact there is none. 

When testing comprehension, it is important to use a test population that is generally 

representative of road users. Convenience samples drawn from the system developer’s staff or 

clients may bring different levels of sophistication about displays, HRIs, and safety problems. In 

addition, certain population groups may have different levels of comprehension. In particular, 

many studies have found poorer comprehension of signs and symbols among older drivers. 

Recommendation 4-7: Promote compatibility with the road user’s mental model 

of how the system works 

Inappropriate behaviors may occur when the road user’s conception of how the information or 

warning system operates conflicts with the actual manner of operation. Ideally, the system 

developers should understand the road user’s perspective and design the system to be compatible 

with it. Otherwise, some remedial action may be required. Focus groups or indepth interviews 

of road users may be very helpful for addressing this, in both the design stage and after 

implementation. Simple survey questionnaires or limited testing of message comprehension may 

not be adequate to uncover subtle but possibly important misconceptions in the road user’s 

mental model of the system [Also see: Recommendation 4-28]. 

Rationale 

The user of an ITS system will have some conception of how the system works, what 

information it provides, how it responds, how accurate it is, the conditions under which it works, 

and so forth. This mental model of the system may or may not be accurate. Where the road user 

has an inaccurate mental model, a potential for acting inappropriately based on a misconception 

exists. For example, consider a train-based system that transmits a signal to activate in-vehicle 

or roadside messages at a passive HRI. If this system only activates in response to higher speed 

trains, road users may not realize this; in their mental model, the system will activate in response 

to all trains. Therefore, they may fail to engage in proper search at the HRI; or road users may 

believe the system is implemented at all HRIs in a corridor, whereas in fact it may only be 

installed at problem HRIs. System designers, engineers, and other rail or highway authorities 

may bring very different knowledge and experience to the situation, in contrast to typical road 

users. Things that may appear obvious to them may not be recognized by many road users. In 

devising message systems for the HRI, it is essential to try to think like a road user. It may be 

very helpful to conduct focus groups or interviews with road users to get insights into their 

interpretation of how the system works. To uncover these user perceptions, however, there must 

be an opportunity to probe for subtle misconceptions and to give the respondents opportunities to 

raise issues that the designer may not have considered. For this reason, simple survey questions 

may not be very revealing. The issue also goes beyond simply determining whether the road 

53
user understands a display. For instance, in the example above, a driver may understand the 

meaning of the train approaching display perfectly well, yet have an important misunderstanding 

of how the warning system is implemented. 

4.3.3 Factors to Improve Credibility of Message 

Recommendation 4-8: Ensure that information is accurate and timely 

The perceived credibility of ITS information and road user satisfaction with ITS systems are 

sensitive to the accuracy of the information. Information may be inaccurate due to limited data, 

infrequent updates, the accuracy of predictive algorithms, or system failure modes. 

Rationale 

ITS systems lose credibility if the information provided is inaccurate or outdated (Campbell et 

al., 1998; Lerner & Llaneras, 2000). Sometimes the system designer is faced with the trade-off 

between providing the road user with more and better information versus introducing the 

possibility of inaccurate information. For example, an ITS system may inform a driver about the 

probable delay at the HRI and propose an alternate route. While this is useful information, the 

accuracy of the prediction about a time delay depends on the estimation of train arrival time and 

traffic conditions. The farther in advance the information is provided (allowing drivers to select 

alternate routes), the more the prediction is subject to error. Road users will tolerate some 

inaccuracy in the system. Research (e.g., Kantowitz, Hanowski, & Kantowitz, 1997) has found 

that, while relatively small levels of inaccuracy have a deleterious effect on driver trust and 

satisfaction with the system, effects on actual compliance with the information are not substantial 

until a greater degree of inaccuracy occurs. 

Guidelines produced for traffic routing information (Lerner & Llaneras, 2000) include the 

following recommendations: update information frequently and time-stamp traffic information; 

supplement current information with predictive information; and be conservative and accept 

some delay in providing information to avoid disseminating erroneous information. 

Recommendation 4-9: Minimize the frequency of all categories of nonuseful 

alerts 

Warning messages lose their credibility when they occur frequently. Any warning that is not 

perceived as relevant by the road user can damage credibility. Consider the following types of 

nonuseful warning messages: 

 Warnings triggered by inappropriate stimuli 

 Warnings triggered by inaccurate and unreliable information 

 Warnings initiated because the system cannot discriminate among threatening and nonthreatening scenarios (e.g., stationary versus moving trains) 

 Warnings that are redundant because the road user is already aware of the situation 

 Warnings that occur too early to be relevant 

 Warnings that occur too late to be helpful 

 Warnings not relevant for this particular road user [Also see: Recommendation 4-23] 

54
Non-useful messages can have negative effects on credibility for the particular HRI application, 

as well as for the ITS system of which the application may be a part. 

Rationale 

Research has shown that inappropriate messages not only reduce the perceived credibility (or 

trust) of an automated system (e.g., Parasuraman, 1997), but that nonuseful alerts also result in 

slower and less reliable responding to the signal (e.g., Chugh & Caird, 1999) and greater user 

annoyance with the system (e.g., Lerner et al., 1996). While nearly all design guides provide a 

recommendation to limit nuisance warnings, it is very difficult to quantify this requirement, and 

tolerable limits are no doubt quite situation-specific. Any warning that is not useful to the road 

user can damage the credibility of the warning system, but no research compares the effects of 

the various categories of non-useful warnings. For example, it may be the case that an alarm 

triggered by an inappropriate, but visible, stimulus is less damaging to credibility than an alarm 

that is generated by no apparent event. Similarly, little is known about the acceptability of nonuseful alarm rates for an application that is part of a larger system. For example, if a train 

warning function is part of a larger in-vehicle ITS warning system, how is the credibility of the 

HRI-related warning affected by nuisance alarm rates for other applications in the system (e.g., 

rear-end collision warnings)? While data are lacking, it would be reasonable to assume that the 

overall performance of the system influences the user of an ITS system in any individual 

application. 

Recommendation 4-10: Consider road user perceptions about the motivations 

and criteria of traffic-rail authorities 

Rationale 

Road users will consider a message credible to the extent they perceive it is intended for their 

benefit. They may question the intent of the authorities who operate an ITS service. Possible 

examples include the following: 

 Alternative route recommendations are based on consideration of neighborhood residents 

or to optimize the performance of an entire roadway system, rather than to optimize the 

trip of the particular road user 

 Cautionary messages are there to protect the operational authorities from liability but are 

not really necessary 

 Messages are intended for other road users (less familiar, less skillful) but not for more 

competent users 

 Regulatory controls or automated enforcement are there for revenue-generating purposes 

and are not really safety relevant 

Perceptions such as these, whether accurate or not, can result in the road user rejecting the 

message as irrelevant. To the extent possible, the perceived personal benefits of compliance 

should be made as evident as possible. It may be difficult to do this within the constraints of a 

traffic control device display. Therefore, the perceived relevance of the system may need to be 

addressed through public education or enforcement activities. 

55
4.3.4 Factors to Improve Compliance with the Message 

Recommendation 4-11: Provide adequate response time, consistent operation, 

and controlled workload 

Rationale 

Even if road users comprehend and accept the credibility of an ITS message, they may fail to 

comply with the message due to the difficulty of performing the correct action. Factors that 

cause difficulty include the following: 

 Unclear what the proper response is, multiple response options 

 Insufficient time to execute the desired response 

 Inconsistency in operational aspects (e.g., message location, timing) 

 Competing demands (high driver workload) 

Response time and distance requirements for driving situations are frequently based on the 

concepts of driver perception-reaction time (PRT) and maneuver time or distance (AASHTO, 

2001). The conceptual model is a sequential one, where the PRT process generates a selected 

driving maneuver that then begins at the completion of the PRT period. Highway design 

equations use PRT and maneuver time and distance to determine sight distance requirements. 

PRT is the time it takes for a driver to recognize a situation, determine the driving response, and 

initiate the maneuver. This mental process may feel nearly instantaneous to the driver but is 

frequently (depending on the situation) on the order of seconds. For example, 2.5 seconds is the 

PRT used for stopping distance requirements, and, at highway speeds, the distance traveled while 

making a decision can be hundreds of feet. Driver PRT is related to the simplicity of the 

response and the number of alternatives (AASHTO, 2001; Pline, 2001). 

Inconsistency in operational aspects affects the road user’s ability to comply through its effect on 

driver expectancy. Road users will have some expectancy about probable messages and message 

formats, such as where the message should be located, how it is timed, how much time they have 

to respond, and so forth. If these characteristics vary from system to system or site to site, road 

users may have inaccurate expectancies. When road users’ expectancies are violated, their 

responses may be slow and error prone. 

Driver workload is a result of a variety of factors beyond the ITS HRI message itself. 

Recommendation 4-16 addresses workload aspects of the HRI message. But workload is also 

related to other driving and non-driving tasks that a motorist may be engaged in. Many nondriving activities (e.g., cell phone use, entertainment system use) may be beyond the control of 

the ITS system operator or traffic engineer. Other aspects of the roadway or roadside or vehicle, 

however, are either predictable or controllable and should be considered when evaluating driver 

workload. ITS HRI display location should not conflict with high demand situations. These 

include roadway geometric features (e.g., curves, intersections, lane drops), traffic interactions 

(e.g., merges, driveways, lane changing, pedestrian activity), roadway information sources (e.g., 

signs, signals, markings), off-road facilities and activities (e.g., advertising signs, commercial 

activity), and in-vehicle displays and controls (e.g., other roadway information, use of navigation 

systems). Recommendation 4-26 provides further discussion of driver workload. 

56
Recommendation 4-12: Avoid excessively conservative criteria 

Warnings and displays that are unnecessary from the perspective of the individual driver can 

increase noncompliance. Overly conservative criteria for displays and algorithms can result in 

unnecessary delays and increases in noncompliant, risky behaviors.

3 

Rationale 

Road users at an HRI may not comply with a warning if they do not perceive it to be reasonable 

(Lerner et al., 1989). In an effort to maximize safety, algorithms for initiating an ITS warning 

may be based on very conservative assumptions and large margins of safety. This may have the 

counter-effect of degrading respect for the system and increasing noncompliance. One means for 

dealing with this is to use ITS capabilities to customize messages for the immediate situation; 

Recommendation 4-20 addresses this. 

Recommendation 4-13: Provide road user feedback regarding noncompliance 

and unsafe behaviors 

Road users may have very poor awareness of the potential consequences of unsafe and 

noncompliant behaviors in response to ITS or other HRI messages. The normal driving 

experience rarely provides them with feedback that they have committed an unsafe act. 

Feedback can be provided through traditional or automated enforcement, public education, or 

intelligent feedback from roadside devices. 

Rationale 

Road users might engage in noncompliant and unsafe behaviors and never realize they did 

something potentially dangerous. For example, drivers may not engage in proper visual search at 

a passive crossing; but because train arrival is a relatively rare event, they may not experience 

any sense that they acted dangerously; or a driver may cross in front of an approaching train 

despite an ITS warning and not realize how close the event was or what the potential variance in 

crossing times might be. This lack of feedback results in what has been termed benign 

experience, where the driver’s perception of the event reinforces the belief that the behavior was 

safe. Because the normal driving experience typically does not provide feedback about the 

actual risk of the behavior, some other means of conveying this must be sought. Enforcement is 

one strategy. This may not only enhance driver perception of crash risk, it also adds the 

likelihood of another risk (enforcement action) that may actually be more significant to the 

driver. Enforcement at HRIs is typically very limited, but automated enforcement technologies 

provide a means to implement enforcement through ITS. Public education is another way to 

provide feedback. Although organizations already exist to educate the public (e.g., Operation 

Lifesaver), more can be done to provide information about HRI safety. Finally, ITS technology 

suggests that it may be possible to provide direct feedback to drivers through sensing and 

communications. ITS technologies could sense unsafe vehicle actions and provide appropriate 

messages to drivers. A review of current systems, however, revealed no such ITS applications. 

3 While agreeing with this general point, one reviewer pointed out that highway-rail grade crossings generate a 

“substantial amount of litigation and accidents resulting from less than conservative criteria may prevent suppliers 

from entering the market.” 

57
4.3.5 Distinguishing Safety-Critical Messages 

Recommendation 4-14: Design safety-critical messages to be immediately 

recognizable as urgent safety alerts and discriminable from other messages 

Safety-critical messages will not be effective unless they quickly and reliably draw attention and 

are immediately recognizable to the road user as being urgent and requiring immediate attention. 

To retain effectiveness, road users must be able to distinguish them from other types of displays 

(e.g., traveler information) and from other signals that might occur in the road users environment 

(e.g., cell phone ring). The best way to ensure a recognizable and discriminable format for 

safety-critical messages is through development of consensus standards. In the absence of 

standards, use warning elements familiar to road users through other applications, and select 

display parameters associated with high perceived urgency. Text warning messages, especially 

if they are presented in display locations that are used for other types of messages (CMS panels, 

in-vehicle consoles), are not adequate for urgent safety messages unless additional features exist 

to ensure immediate recognition of the safety urgency (e.g., color coding, acoustic alert). 

Rationale 

Considerations for safety-critical displays for roadside and in-vehicle ITS may be somewhat 

different (see Chapters 5 and 6), but they share this common requirement. Road users potentially 

encounter a range of messages from many different sources, and they will only respond quickly 

to these messages if the messages are clearly related to safety. A standard display, dedicated 

solely to urgent safety messages, is the ideal way to ensure road user recognition and to protect 

the message from confusion with other sources of signals and information. Although experts 

have stated the need for a consensus standard for ITS crash warnings (e.g., Lerner et al., 1996), 

no standards or regulatory body has proposed a standard, and no consensus practice is emerging. 

Consensus display aspects for the various modes of ITS message display should include color,

4 

shape, icon, wording, dynamic elements (e.g., flash rate), acoustic signal/earcon, voice 

characteristics, and tactile attributes. 

In the absence of consensus display features for safety-critical messages, consider using display 

elements that may already be familiar to road users. Fixed highway sign characteristics are 

obvious candidates. For example, road users are familiar with the black-on-yellow convention 

for warning signs and symbols for rail crossings. Current full-matrix CMS technology allows for 

color, icons, and movement in CMS signs, so that these do not need to be limited to 

monochromatic, all-text display. 

Some signal parameters can help to convey a sense of urgency for visual and acoustic displays. 

Stimuli that are effective in conveying urgency, however, also tend to contribute to annoyance if 

there are false warnings [Also see: Recommendation 4-18] or to distraction [Also see: 

Recommendation 4-16]. Campbell et al.(2002) developed a useful set of guidelines for ITS invehicle visual and auditory displays. 

4 A reviewer cautioned against the use of red; in this person’s experience, red messages can cause undesirable 

slowing of traffic. Unless slowing is desired, this reviewer suggests the use of amber displays. 

58
4.3.6 Choice of Message Display Mode 

Recommendation 4-15: Consider the advantages and disadvantages of 

alternative display modes 

The factors that relate to the choice of the mode of display—visual, auditory nonspeech, auditory 

speech, haptic, and tactile—are application-specific and are addressed in more detail in 

subsequent chapters. General advantages and disadvantages associated with each mode exist 

however, and these should be considered, whatever the application. Because each display mode 

has certain limitations, some redundancy should be provided in display modes, particularly for 

time-critical or safety-critical messages. 

Rationale 

Table 3 provides a general summary of the advantages and disadvantages of each mode. Visual 

and auditory modes are well researched. Relatively little research or experience with haptic 

signals to drivers has occurred. However, research (e.g., Lee, Hoffman, & Hayes, 2004) 

suggests that under at least some conditions, haptic signals can be rapidly responded to and may 

be less annoying than auditory signals. The importance of a given advantage or disadvantage, or 

the ability of the designer to overcome the disadvantage, is application-specific. Options for invehicle systems are generally greater than for roadway-based systems, which are largely limited 

to visual displays. ITS technologies, however, may be able to make greater user of other modes 

even for roadway displays. Chapters 5 and 6 provide further detail on display modes and 

characteristics for roadway-based and in-vehicle systems. 

4.3.7 Unintended Consequences of the Message 

Recommendation 4-16: Avoid driver distraction 

Message displays should not require long-glance durations, excessive numbers of glances, long 

task completion times, or high cognitive demand. The amount of information that the driver 

must process should be easily dealt with in the time available under actual driving conditions. 

Specific considerations for distraction differ somewhat for in-vehicle and roadside displays; 

further recommendations are in appropriate chapters. 

59
Table 3. General advantages and disadvantages of message display modes 

Message Mode Potential Advantages Potential Disadvantages 

Visual  Message detail 

 Complex information 

 Can show spatial relationships 

 Can simultaneously provide 

multiple units of information 

 Message can remain as needed, 

no memory requirement 

 User control of information 

sampling 

 Color, shape, and icons can be 

language-free 

Auditory  No receptor orientation is 

Nonspeech required 

 Rapid reaction time 

 Can be directional 

 Orienting response 

Speech  No receptor orientation is 

required 

 Message specificity 

 Numerous different messages 

can be readily discriminated 

 Does not require learning of 

meaning 

Haptic or Tactile  No receptor orientation is 

required 

 Response compatibility (natural 

association) 

 Little used information channel 

 Eyes must be oriented toward 

display to detect 

 Limited foveal vision requires 

directed looks (visual 

distraction) 

 Susceptible to interference by 

glare, intervening objects 

 Effectiveness can be degraded 

by visual clutter (vision is a 

highly used information channel 

during driving) 

 Text messages require language 

literacy, reading takes time 

 Intrusive, annoying 

 Startle 

 Masking by environmental 

noise 

 Impinges on others 

 Ineffective for hearing impaired 

 Only general messages 

 Limited number of readily 

discriminated and remembered 

sounds 

 More annoying than nonspeech 

 Time required to speak message 

 Intelligibility suffers in noise 

background 

 Impinges on others 

 Ineffective for hearing impaired 

 Ineffective for nonspeakers of 

the language 

 Only general messages 

 Little experience or research on 

effectiveness, design parameters 

60
Rationale 

Distraction may be a problem for all roadway users. Distraction caused by focusing attention on 

a message display, however, is a particular concern for motorized traffic at the HRI because of 

the higher speeds of traffic. Displays that demand too much attention result in driver distraction, 

which results in deteriorated driving performance during the distraction episode. Such attentiondemanding events also contribute to high driver workload. Driver distraction and workload may 

be related but are distinct issues. Distraction refers to the fact that road user attention can be 

devoted to some feature or event to such an extent that the road user does not devote adequate 

attention to all aspects of the driving task. High workload refers to the situation where a driver 

has too much information and/or too many requirements to be able to respond in the time 

available. Driver distraction and workload are concerns for ITS research and practice in general 

and are not specific to HRI applications. 

Driver distraction problems are not limited to distraction by tasks or events unrelated to the 

driving task (such as cell phone use or roadside activity). Even driving-related tasks can be 

distracting if they require too much attention, depriving other driving-related activities of their 

required attention. While the designer of an ITS HRI display (or any other ITS display) wants to 

attract road user attention, the message should not require or encourage long glances or an 

excessive number of glances. For example, animated displays can be very attention-getting, but 

they can be captivating, and if duty cycles are long, viewers may be drawn to them for extended 

periods. Although a value of two seconds has sometimes been used to define the limit of an 

acceptably long glance (e.g., Driver Focus-Telematics Working Group, 2003), various factors 

may determine what is allowable. For example, if an in-vehicle ITS system presents some 

advance information that takes 2 seconds to process, users can time the moment to initiate the 

glance and may even be able to acquire the information with multiple, briefer glances. In 

contrast, if a roadway-based display requires 2 seconds of looking time, users have much less 

flexibility in when to look at the display. They may not be able to defer looking at the message, 

even if driver workload is high at the time the information is available. 

Displays that present an amount of information that is excessive for the time available to process 

the information contribute to information overload. Some suggested criteria exist for CMS 

displays and in-vehicle displays, and these are considered in Chapters 5 and 6. Workload, 

however, is not entirely an attribute of a given display and task but rather includes the context in 

which the display occurs. For this reason, workload is a system concern, and Recommendation 

4-26 further discusses this issue. 

Recommendation 4-17: Consider the potential effects of automation 

complacency and risk compensation (behavioral adaptation) 

The support provided to road users by an ITS application may result in undesirable changes in 

road user behavior that reduce (or even eliminate) the predicted safety benefits of the system. 

Two categories of behavioral changes occur as a result of experience with a system. One is a 

loss of vigilance and awareness as a result of over-reliance and trust in automation (automation 

complacency). The second (risk compensation) is where road users take advantage of increased 

safety provided by the system to engage in less safe behaviors (higher speeds, distracting 

activities). The ITS designer should analyze changes to the road user’s task from the road user’s 

perspective, with consideration of the potential motivations of the road user that might result in 

undesired behavioral changes. Post-implementation evaluations of actual driver behavior should 

61
be considered, including long-term evaluation to identify changes that may occur after extended 

experience with the system. 

Rationale 

Automation complacency is a clearly demonstrated effect but one that remains difficult to predict 

and quantify. Automation complacency refers to the case where a user over-relies on some 

automated aspect of the system, which can result in a failure to monitor the system, a failure to 

properly monitor the external environment, poor situational awareness, and poor decision 

making (Parasuraman, 1997; Endsley, 1996). Because the user takes a more passive role, 

benefits of automation that are intended by the designer as supplements to normal user vigilance 

instead serve to replace that vigilance. For example, an in-vehicle system that alerts motorists to 

approaching trains at a passive crossing may result in the drivers failing to search for 

approaching trains; if a system error occurs, the user’s trust in the automated detection can result 

in a collision that might not otherwise occur. As a consequence of automation complacency 

drivers may be generally less aware of conditions at the HRI, such as the appropriateness of their 

approach speed, geometric demands, or the actions of other vehicles. The design challenge is to 

get road users to maintain normal alertness to the environment even though they have automated 

aids. 

Another outcome of presumed safety improvements in the highway safety field is risk 

compensation (also termed behavioral adaptation and behavior feedback). This refers to the 

finding that road users give back part (or even all) of a safety benefit in return for some other 

perceived advantage. For this reason, the actual observed benefits of some safety technology 

frequently have not been as great as was predicted based on engineering analyses. Safety 

advances that have led to risk compensation behaviors include antilock brakes, center high 

mounted brake lights, studded tires, and improved lane delineation. Evans (1991), Smiley 

(2000), and Elvik (2004) address risk compensation issues. For ITS applications, considerable 

concern about potential changes in driver behavior has existed, but there has been little 

operational experience to assess these changes. For HRI applications, if drivers receive warnings 

about approaching trains, they may be more willing to approach HRIs at higher speeds, engage 

in other distracting tasks (e.g., cell phone use), or follow other vehicles more closely (with 

potential for vehicle-vehicle collisions). 

The essential point about automation complacency and risk compensation is that road users may 

change their behavior if a change in the task or the information environment occurs. The ITS 

message provider cannot think in terms of a fixed driver behavior that the new information is 

being added to. Driver behavior will change in response to the new information, and this change 

may be undesirable from the public safety standpoint. 

Recognizing the potential for automation complacency and risk compensation, how can the 

developer of an ITS HRI system predict and control these effects? Some detailed treatments of 

the effects of automation and variables related to it (e.g., Parasuraman, 1997) exist, but there is 

little systematic practical guidance for the ITS HRI developer. Some have suggested that risk 

compensation effects will be less pronounced if the safety benefit is transparent to the road user 

(e.g., Elvik, 2004), but this is often not feasible. Some have suggested the need for driving 

simulator or test track studies during system development to search for behavioral effects. These 

methods, however, may not be particularly practical and effective if complacency and adaptation 

develop over extended time and experience. Perhaps the most pragmatic recommendation is to 

62
recognize that these effects may occur and then to analyze the proposed message and display 

from the road user’s perspective, considering the range of motivations that road users may have. 

These behavioral phenomena also suggest the need for both short- and long-term evaluation of 

driver behavior after implementation of an ITS system for HRI application. 

Recommendation 4-18: Minimize annoyance 

System designers should minimize annoyance while maintaining message effectiveness. 

Unfortunately, many of the attributes that contribute to display effectiveness (conspicuity, 

urgency) also are associated with annoyance. The use of graded warnings may help mitigate 

annoyance effects. 

Rationale 

Messages intruding on the road user have the potential to cause annoyance. Annoyance may 

lead to poor public acceptance of an ITS system, nonuse or system defeat, and degraded 

responding to messages. Message content, physical attributes of the display, and social and 

psychological factors may influence the annoyance of a message. The designer of an ITS 

message related to the HRI must consider trade-offs with annoyance while trying to achieve 

display conspicuity, comprehensiveness (to cover all users and situations), and completeness of 

information. 

Road users may be annoyed by a message if they deem its content useless. Recommendation 4-9 

describes various categories of nonuseful warnings. Research exists on the effects of false 

alarms (e.g., Chugh & Caird, 1999) or unreliable information (e.g., Campbell, Carney, & 

Kantowitz, 1998). Most existing research, however, has focused on how these attributes relate to 

driver behavior (e.g., response time, route decisions) and with few exceptions (e.g., Lerner, 

Dekker, Steinberg, & Huey, 1996) has not focused on annoyance and user acceptance. In 

general, a very thorough understanding of what is acceptable and how road users react to various 

categories of nonuseful messages is not available. 

The same physical attributes that can make a message attention-getting can also make it more 

intrusive and annoying. For visual displays, these features include brightness and dynamic 

change (flashing, animation). For acoustic displays, these features include loudness, dynamic 

change, abruptness, and tonal attributes. In general, acoustic signals are more intrusive than 

visual signals, and speech messages tend to annoy drivers more than nonspeech signals (Lerner 

et al., 1996). Some indication also exists that users may respond to qualities of the voice, such as 

intelligibility, naturalness, and the apparent gender of the speaker. For example, a German 

carmaker reportedly had to change the voice providing navigation information because “many 

men refused to take directions from ‘a woman’” (Vedantam, 2004). 

The message parameters that relate to signal effectiveness tend to be correlated with annoyance 

as well Some limited research, however, has attempted to identify acoustic signal features that 

differentially effect annoyance and perceived urgency (e.g., Edworthy, Loxley & Dennis, 1991; 

Marshall, Lee, & Austria, 2001; Tan & Lerner, 1995). Because the qualities of conspicuity and 

urgency that contribute to a good warning display also may contribute to annoyance, one method 

to address this problem is to use graded warnings (e.g., Lee & Hoffman, 2004; Lerner et al., 

1996). In this approach, the urgency of the warning message increases in stages or as a 

continuously graded signal. The most urgent (and potentially annoying) signal occurs only in the 

final, most critical stage. Therefore this imminent crash signal occurs rarely and briefly. An 

63
example of a multistage warning is a case where a visual display informs a driver if he/she is 

approaching an HRI at too great a speed, but an acoustic alarm is sounded only if the driver fails 

to respond and must make a severe braking action. Another possibility is to continuously 

increase the loudness and pulse frequency of an acoustic signal as the driver approaches the HRI 

at too high a speed. 

Another aspect that may make a message annoying is that it may occur in the presence of other 

people and so a social aspect influences the driver’s reaction. For example, a voice message to 

slow down will be heard by other passengers in the vehicle, and this could be embarrassing or 

aggravating to the driver and make the passengers uncomfortable. In an early application of 

collision avoidance technologies, a vehicle headway warning system was installed on a bus fleet. 

Bus drivers did not like that passengers were able to hear these audible warnings. Social 

concerns suggest the advantage of display modes that communicate more specifically to the 

intended recipient of the message. Haptic and tactile signals might be especially promising in 

this regard, although they are at this point little researched. 

Roadway-based systems may have the potential to cause annoyance among people other than the 

road user for whom the message is intended. Sounds or lights may affect residents, businesses, 

or others in the area. 

Recommendation 4-19: Anticipate road user misuse of information 

Information presented to the road user for one purpose may be used for another purpose and may 

result in undesirable behaviors. Operational features of the system may also provide information 

that the road user responds to with undesirable behavior. Consider how the information content 

and operation of a message relates to individual user motivations. If the message is likely to 

induce unsafe behaviors, consider revising the message or discouraging the undesired behavior. 

Rationale 

Some road users may attempt to optimize their trips, even if they must perform illegal or risky 

acts. ITS information that is intended to assist the driver in making decisions about normal 

driving behaviors may instead be used as a cue that an inappropriate behavior may help to avoid 

some delay. For example, countdown displays that indicate the time to train arrival might tell 

drivers that they can beat the train if they speed sufficiently. Displays that inform waiting 

motorists of the remaining time until the train clears might lead to vehicles breaking out of a 

queue and making illegal turns. Operational features, beyond message content itself, may also 

induce unsafe actions. For example, some traffic signal pre-emption schemes may imply to 

turning traffic that they will lose their permissive turn phase and so induce erratic actions by 

impatient drivers. Vehicle-responsive barrier systems could motivate some drivers (particularly 

teens) to “play chicken” with the system or even try to trigger an activation. It may be difficult 

to predict the likelihood of some of these driver behaviors, but they nonetheless should be 

considered and dealt with before problems occur. 

4.3.8 Message Appropriateness for Specific Road Users 

Recommendation 4-20: Customize ITS messages for the current situation 

Use available ITS information to adapt the message content, features, and algorithms to the 

current situation. Non-ITS messages and displays are necessarily based on assumptions about 

64
the road user, vehicle, environment, and other factors. If specific information on the actual 

situation can be used in place of assumptions, the message can be made more effective and 

credible. 

Rationale 

Many aspects of non-intelligent HRI displays are based on design assumptions, including vehicle 

characteristics (e.g., current speed, size, braking distance, clearance), driver characteristics (e.g., 

acuity, hearing, reaction time, alertness, familiarity with the area or particular HRI), 

environmental conditions (e.g., visibility conditions, weather and road surface, surrounding 

activity), and traffic characteristics (e.g., prevailing speeds, queues). For any given road user 

who encounters the display at a given time, many of these assumptions may be inappropriate. 

Often the necessary conservativeness of design assumptions will mean that warnings are overly 

conservative, reducing the credibility of the system. Warnings and other messages may be 

displayed at points in time that are not optimal for the specific road user. Message content may 

not be suited to the road user’s information needs. On the other hand, under some conditions 

(e.g., poor visibility, queued traffic), even relatively conservative design assumptions may not be 

adequate to cover the requirements of a particular road user at a given time. Intelligent systems 

at the HRI may be able to collect relevant information (e.g., vehicle speed) as part of the system 

design or make use of information collected by other sources (e.g., roadside weather stations, 

traffic monitoring systems). Future systems may make more use of communication between the 

vehicle and the information system, so that the system may recognize the particular vehicle or 

driver. 

For in-vehicle systems, current efforts also exist to develop technologies to sense driver 

distraction and alertness, to learn and adapt to individual driver behavior and capabilities, and to 

allow driver customization of display attributes. With better use of information, ITS HRI 

messages can avoid unnecessary warnings, provide more urgent alerts when needed, or give 

more specific information. For example, if the system recognizes vehicle attributes it could alert 

low clearance trucks to a low ground clearance (humped) crossing without subjecting other 

traffic to an unnecessary warning. If the system senses vehicle speed, a warning about an 

approaching train could be optimally timed for the driver, and, for drivers at higher speeds or 

projected collisions, the warning could be more extreme. If the HRI component of an ITS 

system communicates with a driver’s route guidance system, the system could provide 

information about delays at upcoming HRIs only when the projected route would encounter that 

delay. Situation-specific messages may be advantageous in many other applications. Another 

important consideration, however, must also be taken into account. There may be system-level 

effects of customizing the message. For example, message customization may disrupt the 

consistency of content and location of ITS messages with traditional fixed roadway signing or 

traffic interaction effects might occur if different drivers get different messages. 

Recommendations 4-24 and 4-25 include further discussion of these system considerations. 

Recommendation 4-21: Devise messages for effective communication with nonEnglish-literate road users 

Non-English-literate road users may be accommodated by presenting the message in languagefree form, supplementing a text or spoken message with additional language-free elements, or 

(for in-vehicle ITS) providing an option for alternative languages. 

65
Rationale 

To accommodate multiculturalism and illiteracy, pictorial or symbolic highway signs are often 

used instead of text signs, particularly for regulatory and warning messages. Many in-vehicle 

ITS displays rely on visual icons instead of or in addition to word messages. Roadway-based 

ITS displays, however, often use CMSs with text messages. This fails to take advantage of the 

capabilities of current full-matrix CMS technologies to use icons or shape and color coding. The 

general point is that whether in-vehicle or roadway-based, ITS HRI messages must communicate 

to the general driving public just as broadly as traditional fixed signing does.

5 

Recommendation 4-22: Devise messages for effective communication with older 

road users 

Many age-related changes in perception and cognitive capabilities are significant for the design 

of ITS messages. These may relate to display factors, such as choice of mode, visual display 

attributes, acoustic attributes, message format, display location, timing of messages, and amount 

of information. It is essential that message displays be appropriate for older drivers because they 

represent a significant and growing proportion of drivers and because older drivers may be more 

dependent than others for support from TCDs. The age at which certain perceptual or cognitive 

changes become significant in the driving population varies for different attributes, with some 

(e.g., accommodation, glare sensitivity) emerging meaningfully in the mid-50s and others (e.g., 

cataracts, reduced walking speed) typically emerging considerably later. However, a substantial 

drop in driving performance occurs, as indicated by crash experience as well as driver 

performance research studies, by the mid-70s (although this may not be so for any individual 

driver). Therefore, the capabilities of road users in their 60s and older should be considered in 

devising messages and displays, and those in their mid-70s may be at special risk and should be 

explicitly considered. 

Rationale 

Demographic changes in the population, as well as ever-increasing driving rates among older 

people, have focused concern on older drivers as a group. In 2002, 16 percent of the driving age 

population in the United States was 65 or older; by 2030, this group is projected to represent 25 

percent of the driving age population and account for 25 percent of fatal crash involvements 

(Lyman, Ferguson, Williams, & Braver, 2001). With advancing age, crash involvement rates (on 

a per mile driven basis) increase, and fatal crash rates increase even more dramatically (Massie 

& Campbell, 1993). While fatal crash involvement is about 1.5 crashes per 100 million driving 

miles for those in their 40s and 50s, it is 2.5 crashes per 100 million driving miles for those aged 

70–74 and 4.2 crashes per 100 million driving miles for those aged 75–79 (Insurance Institute for 

Highway Safety, 2005). For those 85 or older, the rate is 14.5 crashes per 100 million driving 

miles or about 9 times the rate of middle-aged drivers. Older drivers are, therefore, an important 

group to consider in the design of any highway safety system. Lerner, Ratte, and Walker (1989) 

reported that the overrepresentation of older drivers in grade crossing fatal accidents was quite 

similar to that (actually a little higher than) for fatal crashes as a whole. Particular concerns may 

5 One reviewer commented on his experience with the use of graphics on portable CMS displays. Because of the 

“coarseness” of the image, symbols (such as standard MUTCD graphics) that may be well understood on static signs 

may not be well understood in the CMS display. 

66
exists for ITS applications because these are unfamiliar to the older motorist, have typically been 

developed without adequate regard to older users, and because older people are sometimes less 

willing to accept new technologies. 

The list of factors that change with age is quite extensive, and the significance of any particular 

factor depends on the particular application. Table 4, adapted from Lerner, Benel, and Dekker 

(1995), lists driver performance variability factors associated with vision, audition, attention and 

cognition, anthropometry, psychomotor skills, body senses, and health status. Most of these 

factors have some association with age. 

Staplin, Lococo, Byington, and Harkey (2001a, 2001b) developed a set of highway design 

guidelines and recommendations to accommodate older drivers and pedestrians. Although these 

recommendations do not encompass ITS, the documents contain extensive background and 

supporting rationale sections that show how age-related capabilities may be incorporated into 

highway practice. 

Recommendation 4-23: Devise messages for effective communication with road 

users with disabilities 

Adopt a universal design approach that respects the needs of all road users and encompasses 

their capabilities and limitations. Pedestrian traffic in particular may include individuals with a 

wide range of sensory or mobility impairments. Designers of ITS displays should anticipate the 

requirements of these road users and ensure that the systems are safe and usable for the entire 

population. This may require redundant modes of display to serve those users with either visual 

or auditory disabilities. The timing of messages, as well as physical aspects of the HRI, should 

include consideration of those with mobility limitations. Chapter 7 deals with design for 

pedestrian populations in further detail. Disabilities are of less concern in design for motor 

vehicle users because licensing requirements and visual and motor demands of the driving task 

exclude those with severe uncompensated impairments from the driving population. The 

primary concern is that the message display takes consideration of hearing impaired drivers and 

does not rely solely on acoustic messages. 

Rationale 

In recent years, designers of products and systems have increasingly recognized the need to 

accommodate the full range of potential users. The set of users may include persons with 

various disabilities or constraints, such as visual impairments, motor difficulties, or need for 

mobility aids. The transportation community has recognized the need to accommodate such 

users in the design of transportation facilities. This is reflected in various sections of the 

MUTCD (Federal Highway Administration, 2003), in other guidelines (U.S. Access Board, 

2004), and from Barlow, Bentzen, and Tabor (2003). ITS HRI message design must consider the 

full range of users for appropriate visual attributes, acoustic attributes, display location, and 

temporal parameters. While this principle is true for any ITS HRI display, the diversity of the 

potential user population is a much greater concern for pedestrian applications. Chapter 7, 

Displays for Pedestrians, provides further discussion. 

Universal design is an approach that begins the design process with recognition of the broad 

range of users and capabilities and integrates the features required for making the product or 

system accessible for everyone. This integrated quality distinguishes the approach from one that 

67
Table 4. Driver performance variability factors (adapted from Lerner et al., 1995) 

Dr

aft 

68

Attention, Cognition, Health Status/ Vision Audition Higher Order Anthropometrics Psychomotor Skills Body Senses Pathologies Perception 

Spatial light perception Tone perception Perceptual Judgment Body Dimensions Response Time Mechanoreceptive/touch Functional age 

 Contrast sensitivity Loudness perception  Spatial/temporal Eye height (seated)  Simple reaction Proprioceptive/position Dementia, Alzheimer’s 

 Static visual acuity Speech perception judgment Dynamic eye position time in space Depression 

Temporal light Frequency  Time Functional reach  Complex/ Kinesthetic/movement Level of fitness 

perception discrimination  Distance Mobility and Strength disjunctive reaction Vestibular/balance Chronic stress 

 Adaptation Intensity discrimination  Speed/velocity Overall range of motion time Alcoholism 

 Dynamic scene Temporal discrimination  Relative speed (flexibility/dexterity)  Decision/choice Drug addiction 

perception Sound localization  Trajectory Head/neck mobility reaction time Cardiovascular 

Color perception Detection thresholds estimation Foot/leg mobility  Control lag time condition 

Movement perception Auditory adaptation Perceptual organization Hand/arm mobility Movement Capabilities Cerebrovascular 

 Dynamic visual Noise tolerance and flexibility Hand dexterity  Movement speed condition 

acuity Otiological conditions Perceptual construction Grip strength (dominant/  Movement Arthritis 

 Peripheral motion  Conduction Field dependence nondominant hand) precision Osteoporosis 

detection deafness Risk perception Limitations of  Movement ballistics Diabetes mellitus 

 Search/scanning  Nerve deafness Attention movement/flexibility  Continuous tracking 

Seizures, epilepsy 

capabilities  Tinnitus  Selective attention Limitations of strength Limb loss/paralysis 

Handedness  Preferred force/ Other specific diseases/  Looming (motion  Presbycusis  Divided attention effort combinations of diseases in depth)  Vigilance/level of  Maximal force/ Other neurological Night vision attention effort 

 Night myopia  Attention impairments 

 Glare switching 

 Dark adaptation  Attentional field/ 

Depth perception useful field of 

Accommodation view 

Peripheral field loss Information processing 

Ophthalmic conditions Information processing 

 Corneal damage rate 

 Senile miosis  Problem-solving 

 Myopia/Hyperopia skills 

 Astigmatism  Learning 

 Presbyopia capabilities 

 Cataract  Reading speed 

 Glaucoma  Reading accuracy 

 Macular  Cognitive style 

degeneration Memory 

 Diabetic  Primary/short-term 

retinopathy  Secondary/long­

 Detached retina term 

 Retinitis  Iconic 

pigmentosa 
later adds additional features to accommodate certain users, after an initial design for typical 

users. Integration of concerns for all users from the beginning frequently results in designs that 

are better for everyone and may be more cost effective (and less stigmatizing) than adding on 

features later in the process. A good general resource for information on universal design is The 

Center for Universal Design, a clearinghouse operated through the College of Design at the 

North Carolina State University (http://www.design.ncsu.edu/cud/index.html). 

4.3.9 System Considerations 

Recommendation 4-24: Provide uniform messages and displays across 

information sources and sites 

Information about the HRI coming from various sources should display the information in 

similar ways. This means that the display should be similar for HRI roadway messages at all 

locations and for in-vehicle systems from all providers. It also means that in-vehicle and 

roadway messages should be related, although they do not need to be identical. Visual messages 

should be uniform in terms of wording, icons, color, and shape. Acoustic messages should be 

uniform in terms of spectral characteristics, earcons, voice characteristics, and temporal patterns. 

Consensus standards or practices are required to insure uniformity across all systems, but these 

do not currently exist. 

Rationale 

Uniformity in displays is important to ensure comprehension, promote a rapid response, and 

minimize confusion. Standardization of wording, images, shape, and color are well established 

for fixed roadway signage, primarily through the MUTCD. Uniformity (treating similar 

situations in a similar way) is an explicit principle for traffic control devices (Section 1A.06). It 

serves to simplify the task of the road user because it promotes “recognition and understanding, 

thereby reducing perception and reaction time.” Various current vehicle console displays and 

controls are likewise standardized through SAE, ISO, and others. Displays for roadway and invehicle ITS applications do not have the advantage of such uniformity. The development of 

consensus standards is strongly recommended. In the absence of consensus practices, designers 

or operators of HRI systems must take steps to promote uniformity for their users. 

The uniformity of the display can be considered among roadway sites, among in-vehicle 

products, and between roadway and in-vehicle information sources. For roadway-based HRI 

displays, the appearance of the display should be similar at every site. Given the prototype 

nature of many ITS HRI applications, little similarity for similar cases may exist. For example, 

the second train warning displays in Section 3.2 portray a similar message in quite different 

ways. Even where the message is not identical, common message components should be 

similarly conveyed. For example, the means of indicating that the message is related to an HRI 

ought to share similar elements for various messages. For in-vehicle ITS displays, the 

appearance of the display should be similar for all products and vehicles. One barrier to 

consistency for in-vehicle displays is that manufacturers are concerned about product 

differentiation and want their systems to have a look and feel that is distinct from competing 

products. The variability of displays for similar messages is very evident in current in-vehicle 

ITS products for navigation systems and intelligent cruise control (e.g., Llaneras & Singer, 

2002). For the HRI application, where time-critical safety warnings may exist, this 

nonuniformity may be more significant. Uniformity also relates to the relationship between 

69
roadway displays (whether fixed signing or ITS) and in-vehicle displays for the same message. 

Because of the very different viewing conditions and display alternatives, displays that are 

optimal for one application may not be ideal for the other. Nonetheless, the displays should be 

closely related to the extent possible. For example, Section 8B of the MUTCD (Federal 

Highway Administration, 2003) shows a number of text warning signs (e.g., NO GATES OR 

LIGHTS). An in-vehicle voice warning system should use consistent wording, unless a very 

strong case can be made for an alternative. Likewise, similar visual icons or colors should be 

used, unless a strong case exists for some alternative design. Uniformity is an important 

consideration for minimizing confusion and clutter, and the ITS developer should carefully 

consider this. Because standards already exist for fixed roadway signing, it is suggested that the 

features of these signs be considered as a starting point. 

Uniformity refers not just to the specific message wording or icon but also to coding 

conventions. For example, in the visual mode, fixed signing uses color and shape to distinguish 

different types of warning, regulatory, and informational signs. Acoustic messages also might 

have similar coding conventions. For example, the same voice or alerting tone might be used for 

all safety-critical messages to distinguish these from other types of messages. 

Recommendation 4-25: Provide compatible message timing among information 

sources 

The timing of messages from multiple sources (e.g., in-vehicle ITS display and fixed roadway 

sign) of related information should be compatible. Compatible, however, does not necessarily 

mean at the same time. The optimal relationship may depend on various factors, including the 

type of message, the degree of redundancy, the amount or complexity of information, and the 

benefits of customization of the ITS message [Also see: Recommendation 4-20]. For ITS 

informational (notification) messages that are not safety-critical and that are highly redundant 

with roadway signs, presentation of messages from both sources at about the same time and 

place is advantageous. For other situations with urgent messages, complex messages, different 

message content, high workload, or major effects of customization, other timing relationships 

may be preferable. No straightforward guidance exists, and the decision must be based on a 

careful consideration of information processing demands and driver behavioral requirements. 

Rationale 

If two sources of information provide related or redundant information about some aspect of the 

HRI, it might seem reasonable to present that information from both sources at the same point in 

time. The situation, however, is more complex than that, and very little research on how to 

optimize the relationship between on-road and ITS messages has occurred. Campbell et al. 

(1998) provide the following guidance: “Notification messages presented on an ATIS should be 

paired with redundant roadway sign information.” This guidance was based on driving simulator 

research and is carefully worded to constrain the scope of the recommendation. “‘Notification 

messages’ are those that simply inform drivers and allow them to decide on the appropriate 

action on their own” (pp. 7-12). This is in contrast to command style messages that suggest a 

particular action to take. Research has found benefits to simultaneous presentation only for the 

notification messages. The guidance also specifically states redundant information. 

Simultaneous timing might not be ideal if the messages are complex because the driver might 

have difficulty processing and comparing both messages. If the messages are somewhat 

70
different in content but simultaneous, this might also be difficult to process. For example, a 

fixed sign message might indicate that a certain feature ahead, and, an ITS message might tell 

drivers to slow down if their speed is too high to deal with that feature. Simultaneous messages 

could conceivably slow responding to urgent messages, particularly if the two messages are in 

different forms. Furthermore, as noted in Recommendation 4-20, fixed signing must be located 

based on fixed design assumptions while ITS message timing can be customized for the current 

situation. This may result in differences in message timing between information sources but 

more optimal timing. Minimal research or operational experience exists to guide the 

consideration of timing of messages from multiple sources. It should not be assumed, however, 

that simultaneous timing is optimal for all situations. 

Recommendation 4-26: Manage information demand and driver workload 

The ability of a driver to respond to a particular message is a function of the amount and 

complexity of the information in that message, the time available to process and act on the 

information, and the other simultaneous demands on the driver from other information sources 

and other aspects of the driving task. ITS information about the HRI will not be fully effective if 

it occurs under high workload conditions and/or contributes substantially to high workload. 

Coordinating HRI information with other in-vehicle ITS information and in-vehicle tasks is a 

matter of systems integration [Also see: Recommendation 4-27]. Coordinating HRI information 

with roadway-based information displays and with the demands of the driving task requires a 

systematic analysis of driving task demands and information density. While no established, 

comprehensive format exists for such an analysis, the concept of information spreading in the 

Positive Guidance model (Alexander, n.d.; Lunenfeld & Alexander, 1990; Alexander & 

Lunenfeld, 1998) provides one framework for this. A simple computational model for driver 

information overload (Lerner et al., 2003) is also available as an aid to evaluating information 

load and comparing alternatives for display location and timing. 

Rationale 

Dealing with information intake, decisionmaking, navigating, maneuvering, scanning for 

hazards, and doing other tasks, while traveling at highway speeds, can be very demanding. The 

problem of high driver workload is an issue from two perspectives. First, displays of ITS 

messages about the HRI can contribute to high workload at certain locations. Second, displays 

of HRI messages may not be effective if workload from other sources is already high. Therefore, 

the demands imposed upon the driver by an ITS HRI message must be considered in the context 

of other information and other tasks that the driver must also deal with. Managing driver 

workload requires adapting the timing, location, and/or message content of the HRI display to 

the driver’s information environment and operational environment. 

An analytic approach known as Positive Guidance provides some systematic procedures for 

analyzing driver information requirements and “giving drivers the information they need to avoid 

hazards, when and where they need it, in a form they can best use it” (Mortimer, Blomberg, 

Alexander, & Vingilis, 2004). Although the procedure was not developed for ITS applications, it 

still provides a useful analytic framework. Lunenfeld and Alexander (1990), Alexander (n.d.), 

and Alexander and Lunenfeld (1998) describe Positive Guidance procedures. 

Lerner et al. (2003) developed a simple conceptual model of driver information load that 

incorporates a weighting of four factors: (1) sign array information demand; (2) local 

71
information density in the region around the sign; (3) roadway demand (based on the presence of 

various roadway features); and (4) maneuver proximity (workload ramps up as the driver 

approaches choice points and areas where maneuvers are required). This model was based on 

empirical studies of fixed freeway signs (non-ITS) and generates quantitative, though crude, 

estimates of information load. It allows comparison of alternatives for locating messages. The 

computational model may help identify driver information load problems, but the model is 

limited for direct application to many HRI messages because it was developed on the basis of 

freeway driving. 

Driver workload management involves coordinating HRI messages with in-vehicle task 

demands, as well as with roadway and environment demands. Of course, some in-vehicle 

activities are unpredictable. Predictable demands include those that are related to other ITS 

functions and vehicle displays. This involves the general issue of system integration, treated in 

the recommendation below. 

Recommendation 4-27: Integrate ITS functions 

Integration allows displays, controls, and timing for various co-located ITS functions to work in 

a coordinated manner [Also see: Sections 6.2.3 and 6.2.5]. 

Rationale 

Integrating the various ITS functions provided to the driver is important for reducing confusions, 

assuring quick and accurate responding when needed, and managing driver workload. Most of 

the demonstration ITS systems of HRI services have been single purpose systems devoted to the 

HRI application. As ITS products and services proliferate, it will not be feasible to design each 

function as a stand-alone service. A range of ITS applications will have to share display and/or 

control features. This issue is greatest for in-vehicle systems, where many sorts of ITS services, 

as well as other sorts of in-vehicle communication or entertainment systems, may be present. 

However, it may also be an issue for roadway-based displays, if multiple systems exist or if a 

particular CMS is used for messages about things in addition to HRIs. ITS systems integration 

involves such considerations as prioritization of messages, the amount of information, 

compatibility of information displays and controls, user options, and so forth. Because the 

integration of ITS functions is primarily an in-vehicle issue, it is dealt with in Chapter 6. 

Recommendation 4-28: Avoid inappropriate road user expectancies about the 

roadway network, railway network, and traffic control system 

Design the ITS system to be compatible with road users’ expectations. If road users are likely to 

have an inaccurate expectancy, take additional measures to overcome the expectancy. Such 

measures may include more emphatic signing, explicit messages about the expectancy, changes 

in the appearance of the roadway or HRI, or public education efforts. 

Rationale 

Road users do not just respond to what they see but also to what they expect. The system of 

roadways, railways, and HRIs that road users encounter will help determine their behavior at any 

particular location. This is also related to the road user’s mental model of how the system works, 

discussed in Recommendation 4-7. Where road users have inaccurate expectancies about the 

system, responding may be slow or inaccurate, or messages may lack credibility. For example, if 

72
very few HRIs are in an area, and a roadway is relatively open and high speed with very few 

signals or roadside activity, the message of the road is that there are no impediments to free 

travel and no reason to slow down. Under these conditions, an ITS warning about an HRI ahead 

may lack credibility or may be responded to minimally until some visual verification occurs. 

Roadway users may have expectancies about the likelihood of HRI presence, about train speeds, 

about the expected times of trains, about the types of HRI control or ITS messages that might be 

used, about appropriate travel speeds, and so forth. The important consideration for the ITS 

developer is to recognize that road user response is related to expectancies and that expectancies 

should be brought in line with the actual conditions. Where a discrepancy exists, this may need 

to be directly addressed. For example, if train traffic in a corridor is normally low speed, but 

there is a single high-speed HRI, an ITS alert about an approaching train might be ignored at the 

high-speed crossing if the road user cannot see a train at the expected distance. In this case, 

additional information about train speed might be required. 

Recommendation 4-29: Integrate ITS HRI displays and controls with the roadway 

traffic control system 

Ensure that ITS messages about the HRI do not generate driver actions that are incompatible 

with other aspects of the traffic control system. 

Rationale 

This requirement is not unique to ITS displays; any HRI device should be integrated 

appropriately into the general traffic control environment. Messages should not be incompatible 

with traffic signals or other TCDs. While this is primarily an operational issue, human factors 

considerations exist as well. For example, an in-vehicle warning about an approaching train 

could cause a driver to slow on the approach to a green traffic signal (assuming the HRI is farther 

ahead), while following traffic without the in-vehicle system may not anticipate this slowing, 

resulting in traffic conflicts or crashes. Train pre-emption of traffic signals is another area where 

driver assumptions about signal sequences could lead to driver errors. Whether roadway-based 

or in-vehicle, the ITS message about the HRI should be considered in the context of the full 

traffic control environment. 

73

5. Roadside Displays 

5.1 Background 

On modern roadways, roadway users receive information from signs, lights, auditory signals, 

pavement markings, texture treatments (rumble strips), barriers, and roadway geometry. Visual 

information for drivers is much more common than auditory or tactile signals. As new ITS 

technologies are introduced, it is likely that most roadside displays will continue to be primarily 

visual. In-vehicle displays and displays for pedestrians, however, may have substantial auditory 

or tactile components. 

Although some ITS applications have included in-vehicle displays, their overall effectiveness 

will be limited until widespread penetration of the U.S. vehicle fleet occurs. Therefore, various 

types of roadside displays are likely to be the initial means of communicating ITS information 

for many applications. 

This chapter focuses on general issues for ITS roadside displays (including displays mounted 

above the roadway) that may be relevant to HRIs. Part IV will cover human factors issues and 

guidance that are particularly relevant for specific applications; the majority of the 

recommendations in this chapter concern roadside visual displays, with a particular emphasis on 

CMS (also called dynamic message signs in the National Transportation Systems [ITS] 

Architecture), and animated displays. A few recommendations on the use of in-pavement lights 

and roadside auditory and tactile signals are included that may have some application at the HRI. 

Although several of the recommendations given here would apply to many types of displays, 

they are intended for newer display technologies such as CMS in applications that provide road 

users with real-time information about the HRI. 

Detailed requirements for conventional TCDs, including roadside signs and other devices that 

are specified for use at HRIs, can be found in the MUTCD (Federal Highway Administration, 

2003). At a minimum, new roadway displays should be consistent with the principles and 

standards in that document. For information specifically on the use of CMSs, Dudek’s (2003) 

recent work on Developing Standards and Guidance for Changeable Message Signs in the 

Manual on Uniform Traffic Control Devices—Final Report is very thorough. Other useful 

information about the implementation of TCDs is given in the Traffic Control Devices Handbook 

(Pline, 2001), published by the Institute of Transportation Engineers (ITE). This chapter is not 

intended to duplicate the detailed and comprehensive guidance in these other sources. Rather, it 

draws on these resources to highlight human factors issues that are particularly relevant for 

innovative ITS displays for HRI applications. 

While conventional signs present a fixed message at a fixed location along the roadway, CMSs 

can convey real-time information, such as traffic and road conditions, alternative routing, and 

provide other dynamic guidance, including information about HRIs. Dudek (2003) has defined 

six types of CMSs that are currently in use. Any of the CMS Types 2 through 6 may be useful 

for ITS applications at the HRI. 

 Type 1: Manual CMS. Messages are changed manually without any electro-mechanical 

or electronic assistance). 

 Type 2: One-Message CMS. Displays a single fixed message when activated or is blank 

when not activated. 

75
 Type 3: Fixed Message CMS. Contains a small finite set of discrete messages. It may 

have several lines of text with each line changed independently of the others or a hybrid 

design where a word or symbol remains fixed for all messages and the other lines are 

changed among a finite set of messages. 

 Type 4: Speed Display CMS. A matrix sign with two characters that has the capability of 

displaying a variety of numbers. Hybrid designs may have a fixed word or graphic that is 

displayed in addition to the two variable characters. 

 Type 5: Variable CMS. A matrix sign with eight or more characters per line that is 

capable of displaying a very large variety of messages. Every pixel in a line is capable of 

independent activation. 

 Type 6: Dynamic CMS. Contains a full-matrix screen with small pixels and is capable of 

displaying a very large variety of messages that can be shown in full-color and fullmotion, including video images. 

Intelligent signing and advanced display capabilities have been used in a few implemented HRI 

applications, such as second train warnings, but several other display types may be envisioned 

for HRI applications as well. Some examples of cutting-edge highway signing used in other 

applications are described below: 

 Example 1. Figure 12 shows some prototype Graphic Route Information Panel (GRIP) 

signs that have been installed at the AVV Delft test center in The Netherlands (Roskam, 

Uneken, de Waard, Brookhuis, Breker, & Rothermel, 2002). In signs such as these, 

which show a road network, various segments are dynamically color coded to show 

advance information about traffic congestion, roadway conditions, or incidents. 

Figure 12. Prototype GRIP signs, AVV Test Centre 

 Example 2. The Road and Traffic Authority of New South Wales, Australia, has installed 

a CMS curve warning sign near the town of Kiama that uses color coding to indicate wet 

roadway conditions (Brisbane & Vasiliou, 2002). This illustrates how sign image, 

message, and color can be intelligently controlled based on the current situation. The 

sign display has three possible configurations, shown in Figure 13. The selection of the 

76
display is activated by a “moisture detection device, which is able to detect weather 

conditions and the amount of precipitation when raining as well as the pavement 

conditions in terms of dry/moist/wet.” Under normal, dry conditions, the background 

sign panel is green, there is a curve sign (similar to a W1-2 Curve warning sign), and an 

advisory speed plaque of 65 km/h (left panel of Figure 13). If weather is raining and the 

road surface is dry or moist, the background panel remains green, but the curve sign is 

replaced by a Slippery When Wet sign (similar to a W8-5 sign), and the advisory speed is 

55 km/h (center panel of Figure 13). If the road is wet, or if the weather is clear but the 

road is moist, the background color changes to red, and flashing lights attached to the 

sign are activated (right panel of Figure 13). 

Figure 13. Kiama, NSW, Australia curve warning sign 

 Example 3. An FHWA project (Hanscom, 2000) developed and evaluated an intersection 

collision warning system that included an animation component. It provides an example 

of intelligent signing using animation or through adding an active element to a standard 

highway sign. Active sign displays were used for the major road approaches and minor 

road approaches at a rural intersection test site in Arden, Virginia. The Collision 

Countermeasure System (CCS) used intelligent technology to provide motorists with 

information on potential conflicts. The minor road (Fleetwood Drive) is stop-controlled 

and described as having sight distance “extremely limited by buildings.” Vehicle icons 

indicated the presence of potentially conflicting traffic. Figure 14 shows the signs for the 

major road and minor road approaches. The sign on the major roadway (Arden Road) 

was an activated sign but used a flashing icon, not animation. If a vehicle was poised to 

enter the intersection, a vehicle icon appeared on the appropriate leg(s) of a W2-1 cross 

road warning sign, and the icon flashed. A message panel also read “TRAFFIC 

AHEAD.” The sign on the minor road showed animated movement of vehicles. When 

conflicting traffic was detected, an animated vehicle icon(s) moved across the display in 

the appropriate lane and in the appropriate direction. 

Each of the three signing system technologies described above could be used to convey 

information to roadway users about conditions at the HRI. The GRIP signs shown in Figure 12 

might be used to convey advance information about the HRI and provide alternative routing 

information. The CMS curve warning sign shown in Figure 13 might be adapted to provide 

dynamic advance information about the HRI, including warnings about train presence or weather 

related phenomena, such as a reduction in sight distance or slippery pavement conditions. The 

third example system, shown in Figure 14, has an obvious application at the HRI: to warn 

roadway users about approaching trains. 

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Figure 14. Collision warning signs for the major leg (left) 

and minor leg (right) of the intersection 

Although their messages can change, CMS and other advanced roadside display technologies 

occupy a fixed location relative to the roadway (and to the HRI), and, as a result, they share 

many of the same human factors limitations as conventional signs: 

 Roadside displays usually afford only brief viewing periods by drivers who are at large 

and rapidly changing distances and viewing angles. As a result, the length of a message 

that can be read by passing motorists is limited by their speed and by physical 

characteristics of the display which affect its legibility. Intervening objects, such as large 

vehicles or vegetation, can also limit viewing. 

 Drivers may not notice the display if it has unfavorable placement against a complex 

visual background, or if other conflicting demands on the driver’s attention occur during 

the critical viewing period. 

 Once drivers pass a roadside display, they can no longer see it. This places a memory 

demand on drivers who must remember the information long enough to act on it. 

 Ambient lighting on the display can vary dramatically throughout the day with changes in 

the relative position of the sun. Glare or extreme backlighting may reduce the legibility 

of the display. 

 The reliability of roadside displays is constantly challenged by physical deterioration 

from exposure to weather, pollution, encroachments by nature, and extreme changes in 

temperature. Electronic displays in particular are vulnerable to lightning strikes and 

power surges. Roadside displays which fail too often will instill a lack of trust in ITS 

systems. 

 As a result of their fixed, public locations, roadside displays may be read by all 

approaching roadway users, even those for whom the information is irrelevant. The 

number of roadside messages must be strictly limited to reduce the information 

processing demands on drivers and possible distraction by irrelevant messages. With this 

limitation, however, the information needs of individual drivers may not be fully 

satisfied. 

 Modern technologies allow for complex displays with large amounts of text, multiple 

panels, variable color, dynamic elements (flashing, scrolling, animation), and even video. 

Little guidance exists regarding the use or misuse of dynamic and color aspects of CMS, 

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and this raises concerns about the potential to confuse or overload drivers as they 

approach and pass the display. 

5.2 Key Human Factors Issues and Need for Guidance 

5.2.1 Issue: Placement of Roadway Signs 

For many types of standard signs and markings, including those related to HRIs in Part 8 of the 

MUTCD (Federal Highway Administration, 2003), the appropriate location of particular devices 

is well specified. This is not necessarily the case for roadway-based displays for ITS 

applications. Many different HRI ITS messages may use a fixed sign location, and the 

appropriate location will depend on message characteristics. For example, considerations for 

locating a message about a potential train collision at the HRI will be different than those 

associated with an active barrier device and very different from those associated with advance 

route recommendations related to a projected delay at an HRI. Because no specific guidance for 

innovative devices exists, decisions about ITS sign placement must rely on general principles 

regarding the location of TCDs. Signs should be located with respect to the hazard and driver 

decision points, other TCDs, driving task demands, driver expectancy, legibility concerns, and 

driver line of sight. A complicating factor for CMS displays is that a single sign may display a 

variety of messages, yet the ideal site for each individual message might not be the same. 

5.2.2 Issue: Conspicuity versus Distraction 

Roadway users must detect roadside displays if they are to receive useful information about the 

HRI. Display elements that draw attention serve the purpose of the display; however, displays 

must be conspicuous in the context of the entire driver-roadway system. Displays that draw the 

driver’s attention away from other roadway elements and critical vehicle control tasks at critical 

times or hold the driver’s attention too long are not safe. 

Drivers must detect roadside displays against complex visual backgrounds, under a variety of 

lighting conditions, and with limited visual capabilities. Many factors affect the probability that 

a display will be detected. The following lists some of these: 

Conspicuity Factors (from Ogden, 1990, cited in Hanscom & Dewar, 2001) 

 Size (large signs are more conspicuous) 

 Brightness (bright signs are more conspicuous) 

 Boldness (large letters are more conspicuous) 

 Edge sharpness (a border around the edge of the sign makes it more conspicuous) 

 Contrast (high contrast, especially in brightness, between the device and its background 

aids conspicuity) 

 Visual simplicity (a device is more easily detected against a simple background) 

 Eccentricity (a device is more difficult to detect if it is more than 6 to 7 degrees from the 

line of sight) 

Two other features of visual displays that are very powerful for attracting attention are motion 

and blinking (flashing). Although these features are commonly used on advertising signs, they 

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are used only sparingly for TCDs because of concerns over driver distraction. The MUTCD 

(Federal Highway Administration, 2003) explicitly discourages elaborate advertising-type CMS 

display formats with animation or flashing to be used for displaying informational messages: 

Standard: When a changeable message sign is used to display a safety or 

transportation-related message, the display format shall not be of a type that could 

be considered similar to advertising displays. The display format shall not 

include animation, rapid flashing, or other dynamic elements that are 

characteristic of sports scoreboards or advertising displays. 

Overly conspicuous displays may be distracting and annoying, particularly if the 

information is not relevant to the driver’s immediate needs. Recommendation 4-16 also 

addresses this general issue. 

5.2.3 Issue: Legibility 

Once drivers detect a roadside display, they must read and interpret the message. The legibility 

distance for a roadside display (maximum distance at which the driver can read the contents of 

the display) must be sufficient so that drivers have adequate time to read it before it is passed. 

Legibility distance, together with display location, must be adequate to give drivers enough time 

to read and act on information about hazards or alternative routes located at or downstream of the 

display. Legibility distance for roadside displays depends on many display-related factors (font 

type, font size, contrast between legend and background, use of symbols or graphics versus 

words), environmental factors (lighting, weather), and factors related to the roadway user (acuity, 

age). Hanscom and Dewar (2001) have summarized these factors. Legibility of symbols, icons, 

and other graphical elements has received much less attention from researchers, and a need for 

guidance in this area exists. The ability to dynamically vary color and action within a CMS 

poses additional questions about defining sign legibility. 

5.2.4 Issue: Message Comprehension 

Drivers may not understand messages even if the messages are successfully read within the time 

and distance available to view them. Isolated words and short phrases are particularly 

susceptible to misinterpretation, and the meaning of abbreviations, symbols, and graphical codes 

(e.g., color) may not be clear. 

The physical size of displays and the reading time available to drivers limit message lengths. 

This results in messages that are often just a few words or symbols. For the meaning of such a 

message to be correctly understood, the message must tap drivers’ previous experience and 

match their expectations. Not all drivers, however, have the same level of experience or the 

same expectations. Drivers who are familiar with a particular section of roadway will have 

different expectations than those who are in the area for the first time. Older and younger drivers 

may have a tendency to interpret phrases differently because of cognitive changes that occur with 

aging or different levels of driving experience. Even recent experience may affect expectations. 

Drivers who take different routes before reaching the same roadside display may have different 

sets of expectations and may interpret the same message differently. 

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5.2.5 Issue: Driver Information Overload 

Driver information overload is a concept developed to explain why driving performance 

deteriorates when drivers are faced with more information than they can process (Lerner et al., 

2003). In environments that are too information-rich, drivers may react by decelerating severely, 

driving too slowly, making erratic lane maneuvers, or failing to consider other traffic. Reducing 

the driver’s information load might reduce the frequency of these behaviors, which are obviously 

dangerous for the driver and for other roadway users. Information load depends on a complex 

interaction between the driver’s expectations and decision requirements, and the complexity of 

the entire roadway environment, including nearby signage and traffic conditions. The placement 

of new roadside displays should be considered carefully, with consideration of the information 

load imposed on the driver in the vicinity of the display. 

5.3 Recommendations 

Table 5 groups recommendations for roadside displays under six topics. For each topic, the 

individual recommendation statements are given. 

Table 5. Recommendations for roadside displays 

Location of roadside signs 

1. Locate roadside displays relative to the hazard or decision point. 

2. Locate ITS roadside displays to avoid driver information overload. 

Conspicuity and legibility of roadside displays 

3. Make displays conspicuous but not overly distracting. 

4. Use positive contrast orientation (legend lighter than background) for self-luminous roadside displays. 

5. Keep luminance contrast of CMS between 8 and 12. 

6. Adapt visual displays to ambient lighting. 

7. Design displays for the visual acuity of licensed drivers. 

8. Sequential (multiphase) messages may be used on CMS for non-crash avoidance messages, with 

certain constraints. 

9. Limit message length for CMS displays. 

Animation in roadside displays 

10. Use animation selectively. 

Ensuring that messages are understood 

11. Follow a systematic message design process. 

12. Use standardized words and symbols. 

13. Use icons where appropriate. 

14. Use color-coding selectively to enhance understanding. 

In-pavement lights 

15. Ensure that in-pavement warning lights, if used at the HRI, are installed and operated so that they are 

(1) effective, (2) consistent with other TCDs at the HRI, and (3) consistent with other traffic control 

applications of in-pavement lights. 

Nonvisual roadside displays 

16. Use acoustic signals to supplement HRI roadway visual displays. 

17. Consider using tactile signals at the HRI. 

5.3.1 Location of Roadside Signs 

Recommendation 5-1: Locate roadside displays relative to the hazard or decision 

point 

Locate roadway displays so that drivers have sufficient time to respond appropriately but not so 

far in advance that the information is not salient. For warning messages that have specific 

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maneuvers or driver actions associated with them, design sight distance requirements are the 

usual means of defining a minimum distance from the hazard point. For informational displays 

associated with route choice (e.g., crossing status, predicted delay, route alternatives), sign 

locations are defined by the potential diversion points where the driver may change routes. Sight 

distance requirements are determined by driver perception-reaction time (PRT), maneuver time, 

and vehicle speed. A variety of site, hazard, and driver issues also influence these factors. 

General guidance on sight distance requirements and sign placement may be found in the 

MUTCD (Federal Highway Administration, 2003), the American Association of State Highway 

and Transportation Officials (AASHTO) (2001) Policy on Geometric Design of Highways and 

Streets, the ITE Traffic Engineering Handbook (Pline, 1999), and the Traffic Control Devices 

Handbook (Pline, 2001). Dewar and Olson (2001) provide a good discussion on the human 

factors considerations that influence PRT and other sight distance considerations [Also see: 

Recommendations 4-11, 4-25, 9-12]. 

Rationale 

The required information presentation distance (calculated from driving speed, reading time, 

decision time, and maneuver time) and the legibility distance of the display (Hanscom & Dewar, 

2001) determine the appropriate location of roadside signs in advance of hazards. Simple 

behavioral models and an assumed PRT value and vehicle speed are the bases for sight distance 

design equations. A PRT of 2.5 seconds is typically used for simple decisions about emergency 

braking (stopping sight distance), and the assumed vehicle speed is based on roadway design 

speed or the 85th percentile operating speed (whichever is higher). For more complex decisions, 

other assumptions are made (e.g., use of decision sight distance instead of stopping sight 

distance). However, for innovative ITS devices and applications, these simple models should be 

applied cautiously, taking into account factors (e.g., unfamiliarity, message complexity, driver 

decision issues) that might lead to increased PRT or maneuver times. Drivers want to receive 

information about their route, such as traffic conditions or status of an HRI, at locations where 

they can decide among alternate routes (Lerner & Llaneras, 2000; Lerner & Steinberg, 2000). 

The probability that a driver will divert to an alternative route based on information about the 

present route depends on the point in time that the driver receives such information (Allen et al., 

1991; Khattak et al., 1991). Therefore, signs should communicate information sufficiently in 

advance of route decision points where opportunities to divert still exist. 

Recommendation 5-2: Locate ITS roadway displays to avoid driver information 

overload 

If HRI ITS displays are placed at points where other information sources and task requirements 

already put a high demand on the driver’s information processing abilities, delayed or inaccurate 

responding, inappropriate slowing, erratic maneuvers, or tunnel vision can occur. Information 

load will be affected by other signs in the area, off-roadway distractions and visual complexity, 

roadway features (e.g., curves, lane drops), traffic interactions (e.g., lane changing, merging), 

and the proximity to maneuver points [Also see: Recommendations 4-11, 4-26, 8-2]. 

Rationale 

The information load experienced by a driver over a section of roadway containing a visual 

display depends not only on the load imposed by that individual display (e.g., too much message 

content on a single sign), it depends on all of the TCDs (e.g., close spacing between signs) and 

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roadway features in the local area, as well as several driver dependent factors, such as experience 

and expectations (Lerner et al., 2003). A roadside display with high information content or 

complexity may be acceptable in a location where the driver’s information load from all other 

roadway features is low, but it may not be acceptable in an area where drivers already experience 

high information load from existing signs or decision demands. Consistent with this principle, 

Dudek (2003) has recommended that variable CMSs should not be located (1) within an 

interchange, (2) at locations where driver information load is already high due to guide signs and 

other types of information, and (3) in areas where high numbers of lane changing are anticipated 

by drivers in response to static guide sign information, merging, or weaving. The Positive 

Guidance Technique (Alexander & Lunenfeld, 1998; Lunenfeld & Alexander, 1990) provides 

some methods for properly distributing sign information. Lerner et al. (2003) provide a model 

for computing driver information load, but it is limited to freeway applications. 

5.3.2 Conspicuity and Legibility of Roadside Displays 

Recommendation 5-3: Make displays conspicuous but not overly distracting 

Roadside displays should be made conspicuous through visual features, such as size, brightness, 

edge sharpness, contrast with the background, and proximity to the driver’s line of sight, but 

display formats which promote lengthy or an excessive number of glances should be avoided. 

Roadside displays seen by drivers should not be overly conspicuous or require such long reading 

times that they encourage long glances (greater than two seconds) or an excessive number of 

glances (at-track displays intended to be viewed and read while drivers are stopped at the tracks 

are an exception to this general rule) [Also see: Recommendations 4-1, 8-10, 8-22]. 

Rationale 

Sensitivity of the visual system increases and decreases in response to the spatial, temporal, 

luminance, and chromatic visual features in the environment. Such changes in visual adaptation 

provide for good visual function over a wide range of luminance levels, and these changes 

support the detection of changes or differences from prevailing background conditions. Drivers 

are likely to detect targets that differ from their surroundings with respect to luminance, color, 

motion, size, and so forth. Visual contrast between roadside displays and their visual 

environments can enhance their conspicuity. Long duration glances at roadside displays are not 

consistent with safe driving behavior. Although typical glance durations are on the order of 1.0– 

1.5 seconds (see Green, 2001 for review), glances away from the road that exceed 0.75 seconds 

are often considered long, particularly in traffic (Beijer, 2004). The lack of attention to control 

and guidance aspects of the driving task for more than 2 seconds is likely to lead to situations 

where the driver is forced to react immediately upon returning attention to the roadway. Lane 

deviations, emergency braking, and possible rear-end collisions are all likely to occur if drivers 

make long-duration glances. Driver eye glance studies of roadside signs have found that 

complex dynamic signs can result in a substantial number of long glances (Beijer, 2004). 

Animated displays may be particularly problematic when the animation sequence cycle is long. 

Full-motion video images are not recommended for use in TCDs unless drivers see them only 

when stopped. 

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Recommendation 5-4: Use positive contrast orientation (legend lighter than 

background) for self-luminous roadside displays 

Rationale 

Luminous backgrounds can cause spreading of light across the display that reduces legibility and 

at night, which increases the likelihood that the display will be an annoying source of glare for 

roadway users. Evidence exists that positive contrast messages may be read from greater 

distances than negative contrast messages. In laboratory studies, Garvey and Mace (1996; as 

cited by Dudek, 2003) found a 29 percent improvement in nighttime legibility distance with 

positive as opposed to negative contrast. 

Recommendation 5-5: Keep luminance contrast of CMS between 8 and 12 

The luminance contrast of roadside CMS should be between 8 and 12 under all daylight 

conditions. 

Rationale 

Luminance contrast is a ratio defined as C = (Lon – Loff) / Loff and is determined empirically 

under daylight conditions by measuring the luminance of the entire character matrix illuminated 

(Lon) and the luminance of the display when all display elements are off (Loff). At night, where 

the luminance of the display in the OFF state tends toward zero, the luminance of the display 

elements in the ON state, rather than luminance contrast, should be used to determine legibility. 

Dudek (2003) recommended the values given above because higher contrast levels lead to 

irradiation, a condition where the lighter surface elements tend to bleed onto the darker surface 

elements, causing the message to appear blurred. Lower contrast levels are more difficult to read 

and result in a shorter legibility distance. 

Recommendation 5-6: Adapt visual displays to ambient lighting 

The luminance of the display elements should be at least 1000 candelas per square meter (cd/m

2

) 

during the day and much lower (approximately 30–50 cd/m

2

) at night. Consider developing 

displays that adapt to changes in the position of the sun, perhaps with movable shades or by 

slight changes in the physical orientation of the display with respect to the roadway. 

Rationale 

Dudek (2003) recommended the luminance values above based on legibility studies on simulated 

CMS and literature reviewed by Garvey and Mace (1996). During the day, the amount of 

skylight and direct sunlight falling on the roadside display changes over the course of the day. 

Ambient light reflected from the face of the display toward the roadway user can reduce the local 

luminance contrast between legend and background elements on a roadside display making the 

display characters look washed out and difficult to read. This reflected light may be partially 

reduced by slight changes in the orientation of the display with respect to approaching roadway 

users. More practically, the ON display elements should have higher luminance levels during the 

daytime to compensate for the ambient illumination, increasing the local contrast between the 

display legend and background. At night, the ON display elements should have lower luminance 

levels to avoid dazzling glare from the display and to improve legibility. 

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Recommendation 5-7: Design displays for the visual acuity of licensed drivers 

Provide an adequate legibility distance for drivers with visual acuity of 20/40. 

Rationale 

Most jurisdictions require high luminance visual acuity of at least 20/40 (6/12) while wearing 

corrective lenses, if necessary, to obtain and maintain a driver’s license. Legibility requirements, 

therefore, should be based on a design driver with 20/40 (6/12) acuity. For persons with this 

level of visual acuity, Hanscom and Dewar (2001) recommend a legibility index of 30 feet/inch 

for sign letter height. Legibility distances tend to be greatly reduced for many older drivers, 

particularly at night (Dewar, Kline, Schieber, & Swanson, 1994, cited by Hanscom & Dewar, 

2001). 

Recommendation 5-8: Sequential (multiphase) messages may be used on CMS 

for non-crash avoidance messages, with certain constraints 

For displays that are read by drivers who are moving, non-crash avoidance messages may be 

presented across more than one temporal phase (page), subject to the following limitations: 

 A maximum of two phases may be used, with each phase limited to three lines of text. 

 The entire message should be readable at least twice by drivers traveling at the speed 

limit or 85th percentile operating speed. 

 The message should be divided so that each phase contains a complete thought. 

 If more than one CMS is visible to roadway users, then only one such sign shall display a 

sequential message at any given time. 

 No visual transition effects, such as fading, dissolving, scrolling, or motion, should be 

used. 

Urgent crash avoidance messages should be simple and should be presented in a single phase to 

convey the warning as quickly as possible. For displays that are to be read by drivers and other 

roadway users who are stopped at the HRI, the CMS may be used to present messages with more 

than two phases depending on the nature of the message. Messages that contain an urgent timesensitive warning (such as a second train warning) must be presented quickly to inhibit the 

movement of the road user. 

Rationale 

The most important consideration for splitting a CMS message into phases is to enhance message 

comprehension. A two-phase display can enhance comprehension of complex messages because 

more words (information) can be presented in the limited display space over two temporal phases 

rather than in a single phase. In other cases, complex messages that can fit entirely within the 

space limits of a single phase of the CMS display may be split into two shorter information 

chunks to enhance readability and comprehension. 

Most guidance developed for CMS message phasing has focused on the use of CMS on limited 

access highways and expressways rather than on conventional roadways and low volume roads 

where at-grade HRIs are more likely to be found. Nevertheless, the specific limitations given 

above have been selected for presentation here because they are the best available guidance at 

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this time. In the future, as more trials are done with CMS technology on arterial and secondary 

roads, these limits may be changed. 

The MUTCD (Federal Highway Administration, 2003) has the following statement (Section 

2E.21), concerning the use of CMS on freeways and expressways: 

Standard: Messages shall be centered within each line of legend. If more than 

one changeable message sign is visible to road users, then only one such sign 

shall display a sequential message at any given time. A three-line changeable 

message sign shall be limited to not more than two messages. Techniques of 

message display such as fading, exploding, dissolving, or moving messages shall 

not be used. 

Thus, this standard covers the specific Limitations 1, 4, and 5 given above. Limitation 2 is taken 

from Jones’ (2001) chapter in Traffic Control Devices Handbook (Pline, 2001), and Limitation 3 

is based on Dudek’s (2003) guidance. The exact phase duration used should be based on factors 

such as legibility distance and reading time required. Studies by Dudek and Huchingson (1998; 

cited by Dudek, 2002) and Dudek, Trout, Booth, and Ullman (2000; cited by Dudek, 2002) 

found no significant differences in driver recall (or preference) for two-phase messages presented 

at 2 seconds per phase or 4 seconds per phase. The shorter time per phase may be preferable for 

roadways with higher traffic speeds to ensure that drivers will be able to read the entire message 

twice while they are within legibility distance of the display. Because the display may first 

become legible or noticed while it is in either phase, each phase of the message should make 

sense by itself and provide a complete thought. Pedestrians and other road users who are 

stopped at the HRI may allocate more visual attention to roadside displays than drivers who are 

engaged in controlling their vehicles. Therefore, visual displays for these road users may be 

somewhat more elaborate than those to be read by approaching drivers. 

Recommendation 5-9: Limit message length for CMS displays 

Message length should be limited by legibility distance, traffic speed, and display type. For 

typical 18-inch high characters, under the most favorable daylight lighting conditions, and with 

traffic speeds below 35 mph, a CMS can display five units of information. No more than four 

units of information should be displayed when operating speeds are 51 km/h (35 mph) or more. 

The maximum amount of information presented should be reduced for higher traffic speeds or 

less favorable lighting conditions. 

Rationale 

Road users take more time to process complex messages than simple messages. The concept of 

an information unit has been described in the literature to help quantify the amount of 

information contained within message displays. While no universally accepted definition exists 

for what constitutes a unit of information, the general principle is that the longer the message, the 

more processing time will be required. Detailed guidelines on the amount of information to be 

presented in variable CMSs have been worked out by Dudek (2003) based on a review of the 

literature. Dudek (2003) developed detailed guidelines on the amount of CMS information load. 

A unit of information is the answer to a question that a roadway user might ask (for example, 

what? where? when?) or the unit of data that a driver might use to make a decision. For CMSs, a 

unit of information is usually one to three words (occasionally four words). The maximum 

number of units of information to be presented depends on the type of display technology, 

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lighting conditions, and traffic speed. Other more general guidelines presented by Campbell et 

al. (1998) define an information unit in terms of the number of key nouns and adjectives 

contained within a message. For example, the phrase, “HIGH SPEED TRAIN 

APPROACHING” would constitute a message with four units of information. To help drivers 

keep their attention focused on the roadway, information messages should not present more than 

three to four units of information. 

5.3.3 Animation in Roadside Displays 

Recommendation 5-10: Use animation selectively 

Animated displays may be used for pedestrian applications or for displays located at the HRI 

(such as second train warnings) that are seen only by the stopped vehicles in the cue waiting to 

cross the HRI. Animated displays that are to be seen by drivers in moving traffic should be 

applied selectively for situations where a clear need to capture the driver’s attention exists and 

where animation provides an efficient way to communicate the message (perhaps as an 

alternative to multiphase messages, or to communicate with non-English-literate roadway users). 

If seen by drivers of moving vehicles, animated sequences should have a short duration so that 

they do not encourage long glances. 

Rationale 

The apparent motion effects produced by animation are highly conspicuous and may be effective 

for use as warning messages, especially for displays that must be located outside of road users’ 

central visual fields. To date, however, there has been very little research to support the use of 

animation in traffic control devices (Lerner et al., 2004). 

An animated eyes display (an animated pair of eyes that alternately look to the left and right) was 

tested at a stop sign controlled HRI in Polk County, Georgia (van Houten, 2001). The display 

which activated for 10 seconds when a vehicle was detected on the roadway was intended to 

encourage drivers to slow down and search for approaching trains. The authors reported that the 

percentage of drivers who crossed the tracks at greater than 24 km/h (15 mph) decreased from 

5.5 percent to 2.8 percent, and the percentage of vehicles exceeding 48 km/hr (30 mph) dropped 

from 2.1 percent to 0.6 percent from the baseline period to the sign-activated period. Although 

the observed reduction in speed may be partially attributable to the distracting effects of the 

novel display itself, rather than to its message, the speed data suggest that further trials are 

warranted for animated eyes displays at the HRI. 

Because of the potentially distracting effects of apparent motion for drivers who must attend to 

many other motion cues to safely guide their vehicles through traffic, animation should be used 

sparingly for HRI applications. 

5.3.4 Ensuring that Messages are Understood 

Recommendation 5-11: Follow a systematic message design process 

A systematic, rigorous design process should be followed when developing messages for new 

roadside displays. Candidate words, abbreviations, and icons used to denote HRI and train 

events on roadway displays should be tested with roadway users to ensure understanding and 

appropriate reaction before being implemented [Also see: Recommendations 4-6, 7-5]. 

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Rationale 

The usability of informational displays is much improved by following an iterative, usercentered design process (Koyani et al., 2003). Campbell, Richman, Carney, and Lee (2002) have 

outlined an example of such a process for icon development. 

Recommendation 5-12: Use standardized words and symbols 

A standardized set of words, abbreviations, and icons related to HRI information should be 

developed for roadside displays. These should be based on familiar, commonly understood 

terms and symbols so that conventional roadside signs, CMSs, and in-vehicle displays are 

consistent. TRAIN should not be abbreviated, and the abbreviation, HRI, should not be used on 

roadside displays at this time. Standards on acceptable and unacceptable abbreviations, as given 

in the MUTCD (Federal Highway Administration, 2003), should be applied to roadside displays 

[Also see: Recommendations 4-5, 4-24, 6-7, 8-6, 9-8, 9-9]. 

Rationale 

By using a consistent set of terms, symbols, and icons for HRI information, roadway users will 

quickly learn the meaning of messages and will react appropriately. Certain abbreviations are 

already standardized for use on traffic control devices. The MUTCD (Federal Highway 

Administration, 2003) lists many acceptable and unacceptable abbreviations. Some of these, 

which may be particularly relevant to messages about the HRI, are given here: 

Acceptable Abbreviations 

 LFT = left 

 HAZMAT = hazardous material 

 N-BND, S-BND, E-BND, W-BND = (North bound, South bound, etc.) 

 MIN = minute(s) 

 MI = mile(s) 

 MPH = miles per hour 

 RHT = right 

 RXR = railroad crossing 

 SPD = speed 

 WARN = warning 

Acceptable Abbreviations only when [preceded by] or (followed by) a prompt word 

 AHD = ahead (fog) 

 BLKD = blocked [lane] 

 CHEM = chemical (spill) 

 PREP = prepare (to stop) 

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Unacceptable Abbreviations 

 Xing = crossing (may be used only for crossings other than HRIs) 

 CLRS = clears 

 DLY = delay 

“TRAIN” should not be abbreviated because of its importance and short length. In addition, the 

abbreviation “HRI” should not be used on roadside displays because this term is not in common 

usage, and most roadway users would be unlikely to recognize it. New abbreviations should be 

tested with roadway users to ensure an adequate level of comprehension, such as correct 

interpretation by 85 percent or more of the people tested (e.g., Durkop & Dudek, 2001). 

Recommendation 5-13: Use icons where appropriate 

Icons may be considered for use on roadside displays based on the following indications: 

(1) quick and accurate recognition of a message is necessary (warnings); (2) visual or spatial 

concepts need to be conveyed; (3) the driver will be performing a visual search of alternatives; 

(4) the amount of information on the display is limited, and presenting textual information will 

take up too much space; and (5) an icon already exists and has a generally accepted meaning 

[Also see: Recommendation 6-7]. 

Rationale 

These considerations for the use of icons were adapted from those given by Campbell, Richman, 

Carney, and Lee (2002), based on a review of expert judgment and experimental data concerning 

the use of icons for in-vehicle displays. The general principles given here apply equally well to 

the use of icons on roadside displays for drivers and pedestrians. 

Recommendation 5-14: Use color coding selectively to enhance understanding 

If large areas of color are used as background or primary legend on roadside displays, they 

should conform to the standard color meanings and usages specified in the MUTCD (Federal 

Highway Administration, 2003). Color alone should not be used to convey information, but 

limited amounts of color can enhance understanding as an element of a graphical display. 

Rationale 

The use of color for roadside signs has been standardized so that it is used consistently for TCDs, 

and roadway users have come to expect certain colors to have specific meanings within the 

context of roadway systems. Color coding has been used in some nonstandard roadside displays 

to indicate travel time, congestion, road condition, route options, and facility status, little 

research has occurred on the benefits, problems, or optimal usage of color coding for these 

applications (Lerner et al., 2004). Color, by itself, is not a signal that can be interpreted correctly 

by all drivers. Approximately 8 percent of men and 0.5 percent of women have a reduced ability 

to discriminate colors (congenital color blindness). Others have acquired color vision 

deficiencies due to disease or exposure to toxins or drugs. Additionally, for targets viewed in the 

periphery of the visual field, all drivers have reduced color discrimination ability between 

2540 degrees from the fovea and nearly complete color blindness beyond 40 degrees (Judd & 

Wyszecki, 1975). 

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5.3.5 Pavement Lights 

Recommendation 5-15: Ensure that in-pavement warning lights, if used at the 

HRI, are installed and operated so that they are (1) effective, (2) consistent with 

other TCDs at the HRI, and (3) consistent with other traffic control applications of 

in-pavement lights 

Care must be taken when selecting and installing in-pavement lights to ensure that they will be 

visible to approaching motorists. Installing in-pavement lights across travel lanes at the HRI and 

activated by approaching trains is consistent with their use at pedestrian crossings, where inpavement lights activated by a pedestrian signal motorists to yield the right-of-way. The 

installation of in-pavement lights across the travel lanes at the position of the advance warning 

sign (W10-1), however, is not recommended. 

Rationale 

Pavement lights, like all TCDs, must be effective if they are to be used. According to the 

MUTCD (Federal Highway Administration, 2003), to be effective any TCD must do the 

following: 

 Fulfill a need 

 Command attention 

 Convey a clear, simple meaning 

 Command respect of road users 

 Give adequate time for proper response 

In addition, concerning the placement and operation of traffic control devices, the MUTCD 

states that 

Placement of a traffic control device should be within the road user’s view so that 

adequate visibility is provided. To aid in conveying the proper meaning, the 

traffic control device should be appropriately positioned with respect to the 

location, object, or situation to which it applies. The location and legibility of the 

traffic control device should be such that a road user has adequate time to make 

the proper response in both day and night conditions. 

In-pavement lights installed at the HRI, and activated by an approaching train, may increase the 

conspicuity of the crossing, especially at night. Installation of in-pavement lights across the 

travel lanes at the location of the advanced warning sign, however, is not recommended because 

the meaning of the lights and proper driver response may not be clear. Drivers who suddenly 

brake or stop at these lights may violate the expectations of following drivers, increasing the risk 

of rear-end collisions. Placement of in-pavement lights across the roadway in advance of the 

HRI is inconsistent with their use at pedestrian crosswalks, and the train tracks where the 

position of the in-pavement lights indicates the hazard position. 

Adequate visibility of in-pavement lights is also a concern. Lights must be sufficiently bright to 

be seen in daylight, and lenses must be kept clean and free of debris that reduces the intensity of 

the light seen from the approaching driver’s position. Because of the potential for damage, lights 

must be mounted flush with the roadway where snowplows are used. This can create problems 

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for aiming the lights optimally where the roadway approaching the HRI slopes at a different 

angle than the area where the lights are mounted. 

5.3.6 Nonvisual Roadside Displays 

Recommendation 5-16: Use acoustic signals to supplement HRI roadway visual 

displays 

Roadway-based acoustic signals may be used to supplement HRI roadway visual displays but not 

as the primary message mode. Speech-based roadside signals are not appropriate for messages 

intended for motor vehicle operators. Acoustic supplement signals should not be confusable 

with train horns or wayside horns. Acoustic signals should be audible under actual road user 

listening conditions [Also see: Recommendations 8-24, 11-9]. 

Rationale 

Audible signals are not normally used for roadway-based TCDs. Bells or other audible warnings 

that may be used in conjunction with flashing lights and gates at HRIs are one exception. 

Another is the use of audible tones to aid visually impaired pedestrians at pedestrian crossings. 

Train-based horns are another audible warning signal, and roadside horns are an infrastructurebased alternative for some situations (train horns, whether train-mounted or wayside, are not 

seen as ITS applications and not treated here). In these cases, audible signals supplement visual 

displays, which are the primary mode of communication. Visual displays are appropriate as 

primary roadside-based message modes because some road users may be hearing impaired, 

listening environments may be unfavorable, and road users expect visual messages. Acoustic 

signals may also be intrusive on the surrounding community. Nonetheless, acoustic signals may 

be useful supplements for some HRI applications. They can be used as conspicuity 

enhancements where visual displays are located in positions where they may not be highly 

noticeable. When used in this way, the sound source should be co-located with the visual display 

so that the road user’s attention is oriented toward the visual message. Audible cues may also be 

useful in conjunction with intelligent sensing of usual conditions at or near the HRI (e.g., 

arriving train, reduced visibility conditions, cued traffic, and slippery roads). If intended to be 

heard by vehicle operators, the signal should be detectable within the vehicle under typical 

listening conditions, which may include closed windows, climate control system noise, engine 

noise, entertainment system audio, and environmental noise. Because of the critical nature of 

train horn warnings, supplemental auditory signals should not be confusable with train horns. 

Guidance for the use of audible tones for pedestrian use may be found in Section 4E.06 of the 

MUTCD (Federal Highway Administration, 2003). Auditory alerts may be useful not only for 

visually impaired pedestrians but also for general pedestrian traffic when attention to visual 

displays may be questionable (e.g., second train situations). Intelligent technologies may allow 

for speech-based messages with specific information. Speech messages are not appropriate for 

messages intended for motor vehicle operators, where listening conditions will degrade 

intelligibility. A review of literature and applications revealed no examples of speech-based 

messages for pedestrians. Pending any research that demonstrates some advantage, speechbased messages are discouraged because nonspeakers of the message language(s) would not 

understand them. 

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Recommendation 5-17: Consider using tactile signals at the HRI 

The development of any dynamic tactile displays for roadway users (such as train activated popup rumble strips) should be guided by consideration of the needs of bicyclists and motorcyclists, 

as well as the full range of vehicle types, and should be tested extensively to assess driver 

reactions. Active tactile displays for pedestrian crossings may be especially useful for those who 

have visual or auditory disabilities. 

Rationale 

Although dynamic tactile signals have not been demonstrated at HRIs, train status information 

could be used to control roadway surface features Tactile displays, such as rumble strips and 

speed bumps, are used effectively as traffic calming devices; however, many drivers find them 

annoying and circumvent them. A tactile warning device upstream of the HRI, which is only 

active during train events, may have the potential to reduce train-struck-by-vehicle accidents and 

vehicle-to-vehicle rear-end crashes for drivers stopped at the HRI, without annoying drivers 

during periods with no train activity. Any such device, however, must be safe for use by 

motorcycles and bicycles under various weather conditions. Road users’ responses to such a 

device should also be evaluated. Startle responses are possible for those who do not expect the 

device to be deployed, and risky behaviors, such as driving around the device (into an opposing 

traffic lane), may occur. For pedestrians, pole-mounted touch panels or in-ground, vibro-tactile 

displays activated by an approaching train may be designed to mimic, amplify, and anticipate the 

natural ground vibrations that occur when the train moves through the HRI. Although all 

pedestrians may benefit from the redundant warning cue presented by tactile displays, this form 

of display may be particularly useful for pedestrians who are blind or deaf and may not notice 

visual or auditory signals. 

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6. In-Vehicle Displays 

6.1 Background 

Designers of in-vehicle systems that incorporate HRI information should seek to understand and 

accommodate the needs of all drivers who are likely to use such systems. For example, 

developers and manufacturers should serve the needs of older drivers who tend to require longer 

glances to read information and who tend to experience retention problems for complex 

messages. Older drivers may be particularly at risk when using in-vehicle devices if design 

decisions about size, complexity, information content, and location of displays and controls are 

made on the basis of the perceptual, cognitive, and psychomotor skills of either the average 

driver or the 85th percentile driver. 

Many other human factors issues are relevant to the provision of HRI information through invehicle devices. Concerns relate to the physical and operational properties of the devices 

(location of the display, size, brightness, clarity and detail of the image, amount and quality of 

information supplied by the system, etc.), as well as to drivers’ behaviors and perceptions related 

to their use (e.g., impacts on drivers’ mirror sampling, frequency of use, duration of glances to 

the device time-sharing, and ability to maintain situational awareness). 

This chapter addresses how to provide in-vehicle ITS information. The guidance is generally not 

specific to messages about the HRI but applies more broadly to vehicle-based ITS 

communications and interactions. A variety of sources provide guidance and recommendations 

for in-vehicle displays. In this document, which is specifically concerned with HRI applications, 

it is not appropriate to address all of the general human factors issues of in-vehicle displays, 

controls, and communications. At the same time, however, the appropriate design of in-vehicle 

systems may be critical for the success of various HRI applications. Therefore, this chapter 

introduces and discusses many of the important human factors issues and provides guidance 

(drawn from more general sources). Additional guidance, standards, and recommendations may 

be found in various sources, including those listed here: 

 Preliminary Human Factors Design Guidelines for Driver Information Systems (Green 

et al., 1995) 

 Preliminary Human Factors Guidelines for Crash Avoidance Warning Devices (Lerner 

et al., 1996) 

 Human Factors Design Guidelines for Advanced Traveler Information Systems (ATIS) 

and Commercial Vehicle Operations (CVO) (Campbell, Carney, & Kantowitz, 1998) 

 In-Vehicle Display Elements Task F: Final In-Vehicle Symbol Guidelines (Campbell, 

Richman, Carney, & Lee, 2002) 

 Statement of Principles, Criteria and Verification Procedures on Driver Interactions with 

Advanced In-Vehicle Information and Communication Systems—Draft Version 3.0 

(Driver Focus-Telematics Working Group, 2003) 

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6.2 Key Human Factors Issues and Need for Guidance 

6.2.1 Issue: Choice of Display Mode 

How information is presented can influence driver performance, and a need for guidance exists 

regarding the most appropriate display mode (auditory, visual, haptic) to use in vehicles. 

Information about HRI may be presented through different display modes, depending on the 

urgency and complexity of the information, but should be integrated with other driver 

information systems. Previous research on visual and auditory in-vehicle information systems is 

applicable to the design of systems to present HRI information. For example, for navigation 

systems, voice guidance is generally associated with better route navigation performance 

compared to electronic maps (Srinivasan & Jovanis, 1997). Complex audio messages, however, 

can lead to large numbers of navigation errors (Walker, Alicandri, Sedney, & Roberts, 1990). 

Simple, short messages (four elements or less) can be presented safely while driving (Graham & 

Mitchell, 1997; Llaneras, Lerner, Dingus, & Moyer, 2000). Increasing the time or duration that 

messages are displayed or providing a repeat function to alleviate some of the workload and 

pacing issues may aid drivers, particularly older drivers. 

The use of visual displays in the automotive environment raises issues, such as the location of 

the display, appropriate number of lines of text, need to capture driver attention, and the ability 

of drivers to process messages while maintaining safe driving performance. Popp and Farber 

(1991) found that a display positioned directly in front of the driver results in better driving 

performance (lane tracking and obstacle detection) than a peripherally mounted display. HeadUp Displays (HUDs) provide an alternative for presenting information to drivers, but these types 

of displays may not be the best option for dynamic text presentation because they may be 

distracting. The number of lines of text presented on a display appears to impact driving 

performance. Tijerina, Kiger, Rockwell, and Tornow (1995) examined workload impacts of text 

message displays in the context of an on-road study with 16 professional truck drivers ranging in 

age from 32 to 60 years. Message displays consisting of one, two, or four lines of text were 

presented on a 7-inch cathode ray tube or CRT display mounted above the instrument panel. 

Results of this on-road study found that two- and four-line text messages had substantial 

detrimental effects on visual allocation and lane keeping performance. These more demanding 

text displays were associated with more glances to the display, more steering reversals, fewer 

accelerator inputs, and more lane position variance and lane keeping errors. 

Llaneras, Lerner, Dingus, and Moyer (2000) examined how attention demand changes as a 

function of visual and auditory display characteristics and task type. Results indicated that 

auditory format and speech rate significantly affect vehicle steering (steering variability), speed 

(average, minimum, and variance), and headway (average and variance). Displays using 

embedded prose, for example, yielded more variance in steering wheel, vehicle speed, and 

headway driving measures. Results also suggested that accelerated speech displays (225 words 

per minute) can be used without sacrificing driver comprehension or driving performance. 

Furthermore, in contrast to visual displays, auditory displays had relatively low workload, 

enabling drivers to maintain a driving profile similar to that adopted during baseline driving; 

older drivers appeared to benefit most from auditory displays. 

Previous work, including that mentioned above, provides useful background information for the 

design of auditory displays, as well as visual text displays. These studies and others form a basis 

for guidance about how HRI information should be presented in the vehicle. 

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6.2.2 Issue: Driver Distraction 

Time spent away from processing the road scene while scanning in-vehicle displays, or attending 

to other nondriving-related secondary tasks, can significantly impair a driver’s ability to control 

the vehicle and detect and react to external events. A major consideration in the design of invehicle displays, therefore, is the glance frequency and duration to a display while driving. 

Zwahlen, Adams, and Debald (1988) suggested that the number of glances to displays be limited 

to three, with glance durations under 2 seconds. The challenge for telematics system designers is 

how to efficiently (and safely) present electronic text, particularly dynamically displayed text, to 

drivers when display space is limited. Driver distraction is believed to be a factor in a substantial 

proportion of collisions. Because distraction is hard to measure and can be defined in many 

different ways, it is difficult to put a precise estimate on its contribution to collisions. However, 

based on existing reports (e.g., Treat, 1980; Hendricks, Freedman, & Zador, 1999; Wierwille & 

Tijerina, 1994), a rough order-of-magnitude estimate would be that about 20–25 percent of 

collisions may be related to distraction. Vehicle-based personal computers, ITS, 

communications devices, entertainment centers, and other emerging technologies have the 

potential to further compound the problem. A recent inventory of in-vehicle telematics devices 

sponsored by NHTSA (Llaneras & Singer, 2002) found systems with a number of potentially 

distracting design elements, including displays that present large amounts of information and 

incorporate dynamic elements; unrestricted access to complex, multistep, and demanding tasks 

while driving; and systems that provide for multiple functions and expanded capabilities. Truck 

driver distraction due to in-vehicle technologies may differ from the automobile driver problem 

for a number of reasons. These include differences in the types and functions of in-vehicle 

devices, differences in device placement or design, the truck cab environment, trucking-related 

tasks, and vehicle control demands, among other aspects. 

6.2.3 Issue: Information Overload and Integration of Advisories and Warnings 

As the number of independent warning (and information) systems proliferates, it may be 

common for a single vehicle to be equipped with multiple systems. That is, the same vehicle 

may have several in-vehicle warning systems, including train approach warning, forward and 

side collision warning, lane departure warning, and drowsy driver warning systems that were all 

independently developed and installed. The concern is that the various collision warning 

systems (CWS) designed to alert drivers to potential and imminent collisions may themselves 

become hazards or may loose their effectiveness when more than one is present in the same 

vehicle. Developers must fully understand how issuance of multiple independent alerts can 

negatively affect driver performance and the ability to respond to threats. 

6.2.4 Issue: Behavioral Adaptation 

Also of interest is whether drivers change their driving behavior as a result of their perceived 

changes in the risk of driving that these technologies provide. This type of change in behavior 

has been called behavioral adaptation and refers to the response of drivers to the introduction of 

new technologies in vehicles. The changes in behavior can be positive, negative, or neutral in 

terms of their effect on safety. For example, if drivers perceive that the new technology makes 

the driving task easier, they may drive more miles or drive faster. Another possibility is that 

drivers are able to benefit from the feedback provided by some systems or by the reduced 

workload and maintain their performance for a longer period of time. Different adaptations can 

95
occur in the short and long term. In the short term, drivers may respond to the novelty of the 

device but in the long term may find it annoying and thus ignore it or turn it off. All of these 

behaviors play a role in the real world effectiveness of newly introduced technologies. 

6.2.5 Issue: Message Prioritization 

With the advent of new systems that convey in-vehicle messages to drivers, such as roadside 

information, including road-condition warnings and travel advice, and vehicle-status messages, 

including collision warnings and vehicle operating conditions, concern exists that these systems 

may distract or overburden drivers with information. Such messages may also compete for 

attention with other systems within the vehicle and may cause a lack of focus on operating the 

vehicle safely. Message prioritization is intended to provide the basis for selecting which set of 

messages that are competing for the same display time and space should be presented to the 

driver. Several standards development organizations are developing guidelines and industryrecommended practices to insure the clear and concise presentation of multiple ITS messages to 

drivers. SAE, for example, has outlined a procedure for determining the orderly presentation of 

information to drivers while taking into account time sensitivity, travel distance, and display 

space limitations. It describes a method for prioritizing in-vehicle messages and/or displayed 

information based on a defined set of criteria. Each criterion has a fixed number of levels that 

are used to rate or rank a given message or information item to determine its prioritization value. 

The prioritization value is then used to determine the priority in which simultaneous, or 

overlapping, in-vehicle messages are presented to the driver. This recommended practice is 

intended to lead to the development of consensus standards for the prioritization of in-vehicle 

messages that are displayed by ITS. 

6.3 Recommendations 

Table 6 groups recommendations for in-vehicle displays under seven topics. For each topic, the 

individual recommendation statements are given. 

Table 6. List of recommendations for in-vehicle displays 

Choice of mode 

1. Use visual displays to present spatially-based information and for long or complex messages 

(provided the vehicle is not in motion). 

2. Use audible presentation modes for delivering high priority information requiring immediate action. 

3. Use speech-based messages when high degree of detail is required and the meaning of other sounds 

may be ambiguous or forgotten under stress. 

4. Consider using visual icons rather than text-based messages. 

5. Consider using auditory icons in place of tones or beeps. 

Visual display attributes 

6. Locate visual displays for warning systems within the driver’s field of view, without obstructing the 

driver’s view of the dash controls, gauges, or mirrors. 

7. Use standardized icons and graphics for in-vehicle warnings. 

8. Ensure that visual display elements (characters, text, graphics, etc.) are sufficiently large to be read in 

moving vehicles and that the information can be assimilated with a few brief glances. 

9. Use some means to attract driver attention to the display (e.g., flashing lights) if the system relies 

exclusively on a visual display to communicate information (no audible warnings/messages). 

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Auditory (nonspeech) display attributes 

10. Audible warnings should be sufficiently loud so they can be detected and understood by the driver in 

the presence of background noise. 

11. Limit the number of different warning tones to three or four easily discriminable sounds. 

12. Auditory alerts should be used to notify drivers of high-priority messages and changes in status, as 

well as augment signage information. 

13. Tonal signals (nonverbal auditory signals) should use a frequency range between 500 and 3000 Hz 

and burst durations of about 100 ms. 

Speech display attributes 

14. Avoid the use of synthetic speech displays. 

15. Messages that require an immediate response should consist of a single word or short phrase and 

should be understood immediately. 

16. Provide a means for repeating speech messages. 

17. Ensure that messages are easily differentiated from other speech in vehicles. 

User control and adjustment 

18. Complex information and control interactions should not be designed for use in a moving vehicle. 

19. If multiple input or adjustment controls are present, design the controls so drivers can easily 

differentiate among the controls and their functions. 

Location of controls 

20. Locate system controls within the driver’s reach, with the most frequently used or accessed controls 

closer to the driver’s line of sight and reach. 

21. Match the type of control used to the types and levels of functions to be controlled. 

Operational issues related to in-vehicle systems 

22. At actively controlled crossings with gates, in-vehicle warnings should be timed (coordinated) with 

the activation of the crossing gates or other active warning devices. 

23. Provide system compatibility and integration. 

24. Indicate system status. 

25. Tailor information presented within the vehicle to match the driver’s specific situation and needs (e.g., 

approaching an HRI, waiting at an HRI, EMS personnel). 

26. Evaluate the potential effects of behavioral adaptation for new in-vehicle systems. 

6.3.1 Choice of Mode 

Recommendation 6-1: Use visual displays to present spatially-based information 

and for long or complex messages (provided the vehicle is not in motion) 

Displays that present lengthy or complex information should be accessible only when the vehicle 

is not in motion. Urgent or high priority messages that require immediate attention generally 

should not be presented visually; if the visual channel is used to communicate messages 

requiring immediate action, it should be used as a secondary communication means and should 

be prominently displayed and be accompanied by an alerting tone [Also see: Recommendation 

4-15]. 

Rationale 

The most appropriate mode to present in-vehicle information to drivers depends upon the nature 

of the information and the urgency with which driver response is required. In general, warnings 

used to alert drivers to a hazard (e.g., approaching train) should convey the level of the hazard 

(caution, warning, danger), recommended action to avoid the threat, and consequences of 

inaction. Information that is purely informative should generally be presented visually; auditory 

presentations may needlessly distract and annoy drivers. Avoid presenting complex visual 

displays for in-vehicle systems while the vehicle is moving because the visual demand required 

to access and read the displayed information may significantly interfere with drivers’ ability to 

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control and steer the vehicle. Drivers should be able to assimilate visual information within a 

few brief glances. Glance duration should be brief enough not to adversely affect driving (single 

glances should generally be under 2 seconds). Several methodological procedures are available 

to ensure that in-vehicle visual-based displays are suitable for presentation while the vehicle is in 

motion (Society of Automotive Engineers, 2004). 

Recommendation 6-2: Use audible presentation modes for delivering high 

priority information requiring immediate action 

Drivers perceive auditory information quickly and reliably which makes the auditory channel 

well-suited for the presentation of warning information to drivers. Some applications may 

benefit from a redundant visual display in situations where additional detail may be required to 

interpret the audible signal [Also see: Recommendation 4-15]. 

Rationale 

Auditory displays can quickly capture drivers’ attention. For this reason, auditory displays are 

ideal for short and important warnings and messages (typically using nonspeech forms). 

Nonspeech auditory displays in combination with visual displays are powerful; they have the 

advantage of drawing attention while being able to specify the nature of the problem. These 

types of multimodal displays decrease reaction time when compared with visual signals alone. 

Thus, different modalities can be used in combination to enhance the overall message. Because 

audible displays can annoy, they should be used sparingly and designed to avoid overloading or 

annoying drivers. 

Recommendation 6-3: Use speech-based messages when high degree of detail is 

required and the meaning of other sounds may be ambiguous or forgotten under 

stress 

Speech messages should not be used for time critical tasks because they can be inefficient and 

subject to masking [Also see: Recommendation 4-15]. 

Rationale 

Voice messages can transmit much more information than simple tones, but they are also subject 

to interference from ambient noise. Speech-based messages should be used sparingly since voice 

output can interfere with human speech communication. Speech should only be used if drivers 

have enough time to listen to the full message and to choose the correct action. More time is 

required to deliver a speech message than to alert the driver through other modes. For this 

reason, speech displays are not recommended for presenting specific information of a dynamic 

nature (Lerner et al., 1996). Older drivers, in particular, can have difficulty understanding voice 

messages in the presence of background noise. Speech-based systems should allow for 

adjustments in volume and the capability to repeat messages. Speech messages should be simple 

with the most important information presented at the beginning of the message (and repeated at 

end, optionally). If no alerting tone can be provided, supplement visual information with 

redundant speech information. 

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Recommendation 6-4: Consider using visual icons rather than text-based 

messages 

Visual icons may be used instead of text-based messages under the following conditions: (1) 

when the amount of display space is limited, (2) when icons currently exist and are well known 

and accepted by the population, and (3) when quick and accurate recognition of the message is 

required [Also see: Recommendation 4-15]. 

Rationale 

Icons are graphical symbols intended to transmit specific information and have the advantage 

that they are not language dependent (they can be universally recognized and understood across a 

diverse range of populations). Moreover, well designed symbols and icons are recognized more 

accurately and faster than text. Nevertheless, unless icons are already commonly associated with 

an idea or object, many icons must be learned. Good symbols and icons are detectable, 

discriminable, and meaningful to drivers. It is important to test and evaluate comprehension 

levels for icons before implementing them; ISO recommends comprehension levels of at least 66 

percent. In some cases, auditory information should supplement icon messages to make the 

message clearer or more salient. For example, symbols used for a warning, should be 

accompanied by textual or spoken speech (this captures attention and allows for instructions if 

feasible). Combine icons with auditory information when presenting high priority alerts and 

warnings and when static visual displays change to announce the presentation of the visual 

information. 

Recommendation 6-5: Consider using auditory icons in place of tones or beeps 

Auditory icons may be used to aid in the interpretation of the signal and speed driver response 

[Also see: Recommendation 4-15]. 

Rationale 

Auditory icons are representational sounds that have specific stereotyped meanings (e.g., train 

horn,6

 tire skidding). Because auditory icons represent familiar environmental sounds that 

intuitively convey information about objects or actions, they are generally better recognized than 

conventional tones or beeps whose meaning must be learned. To be effective, auditory icons 

must be identifiable as having relevance or conveying inherent meaning and should be used as a 

means of augmenting visual presentation of in-vehicle messages (not meant as a sole means of 

presenting messages). Meaningful sounds in the HRI context include a train horn or bells; these 

will likely capture driver attention because they are associated with danger or hazard at the HRI. 

No more than six auditory icons should be used to minimize memory demands (Campbell, 

Richman, Carney, & Lee, 2002). 

6 One reviewer, while agreeing with the general recommendation, took exception to the use of the train horn as a 

potential auditory icon, stating that a train horn “has its own specific meaning and should not be used by anything 

other than the actual train.” The reviewer believes other applications of the horn sound may undermine the actual 

train horn’s effectiveness, especially since other applications may require conservative triggering criteria and hence 

inappropriate warnings. Although the authors of these guidelines agree with this caveat, they feel that if a horn icon 

had demonstrated strong benefits for certain applications, it should not be ruled out with consideration of the tradeoffs. 

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6.3.2 Visual Display Attributes 

Recommendation 6-6: Locate visual displays for warning systems within the 

driver’s field of view, without obstructing the driver’s view of the dash controls, 

gauges, or mirrors 

Displays should be positioned (or designed) to minimize glare or reflections that make it more 

difficult to extract information. Visual displays should also be positioned in relation to their 

importance and frequency of use. 

Rationale 

Visual displays that carry information relevant to the driving task and visually intense 

information should be positioned as close as possible to the driver’s forward line of sight to 

reduce total eyes-off-road time. Driver’s forward line of sight refers to the direction of the 

driver’s gaze out the windshield and onto the road ahead. A display that is too low in the vehicle 

may divert the driver’s attention from the roadway. When installed, the system should not 

obstruct or interfere with the driver’s field of view of the roadway, existing vehicle controls, or 

displays required for driving (Stevens, Quimby, Board, Kersloot, & Burns, 2002). Displays 

located within the driver’s field of view will also take advantage of a drivers’ peripheral vision to 

detect movement ahead of the vehicle. Popp and Farber (1991) recommend display screens be 

mounted 15 degrees below horizontal and that they do not exceed 30 degrees. More specific 

equations concerning the maximum downward viewing angle are approximately in agreement 

with this value (Driver Focus-Telematics Working Group, 2003). Desirable display locations are 

high on the instrument panel near the area directly in front of the driver. Important visual 

information should be positioned near the forward line of sight (dashboard). If a Head-Up 

Display (HUD) is used, however, it should not cover the driver’s central field of view because it 

may obscure external objects. The information presented on the HUD should be limited to a few 

elements that can be quickly extracted from a virtual image that is 2.5-4 meters from the driver’s 

eyes (Stevens et al., 2002). 

Recommendation 6-7: Use standardized icons and graphics for in-vehicle 

warnings 

Consensus-based standard icons should be used for ITS displays to indicate an HRI and an 

approaching train. No such standards currently exist for in-vehicle displays. Icons incorporating 

the W-10 advance warning sign or R15-1 Crossbuck may be helpful but are not sufficient by 

themselves. If icons (or graphic formats) are used to communicate in-vehicle warning messages, 

they should have a direct and obvious meaning; drivers must be able to quickly recognize and 

interpret their meaning. Use symbols that the driver already associates with the object or idea 

[Also see: Recommendations 4-5, 4-24, 5-12, 8-6, 9-8, 9-9]. 

Rationale 

Drivers are familiar with the standardized W-10 advance and R-15 Crossbuck signs, and they are 

present at all HRIs. Because they are also present in the external environment, they provide 

redundant cues to drivers in a familiar form. Nevertheless, because a significant proportion of 

drivers may not understand the underlying meaning of these signs, it may be necessary to 

supplement these with prescriptive information (supplemental text, audio, or training) to clarify 

their meaning and direct behavior. Very few studies have examined use of warning formats 

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(such as graphics) to communicate presence of a train at an HRI. Work by Hoekstra, Williams, 

and Green (1993) suggests that the following alternate formats for an in-vehicle warning may be 

effectively used to communicate train presence: a text-only message “TRAIN AT CROSSING” 

or the W-10 sign graphic with supplemental lights above the standard RXR sign. The In-Vehicle 

Signing System for School Buses at Highway Grade Crossings used by Minnesota Department 

of Transportation used a W-10 graphic; however, this graphic was intended to communicate the 

presence of an HRI rather than a train at the crossing. Other applications have used animated 

train icons to indicate the presence of a train (Maryland Mass Transit Administration and Sabra, 

Wang, & Associates, Inc., 2001; PB Farradyne, 2002). The diversity of icons used in these 

examples illustrates the need to have a standardized, unambiguous message or sign graphic. 

Symbols must have a clear meaning; otherwise the message will not be understood and will be 

open to misinterpretation. FHWA has developed a set of human factors design guidelines for invehicle display icons, addressing key design issues such as icon recognition, interpretation, and 

legibility (Campbell et al., 2002). 

Recommendation 6-8: Ensure that visual display elements (characters, text, 

graphics, etc.) are sufficiently large to be read in moving vehicles and that the 

information can be assimilated with a few brief glances 

Maximize legibility of visual displays assuming glances of 1–1.5 seconds in duration. 

Rationale 

Information presented on visual displays should enable drivers to read and acquire the 

information easily and quickly without overburdening or distracting drivers. Limit the amount of 

text information displayed. Present brief messages that minimize what the driver must read. 

Design displays so that drivers are able to quickly extract information. Often displays can be 

designed so that the information remains displayed until the driver acknowledges it, rather than 

having the pace of information flow controlled by the system. Type size, contrast, and typeface 

will influence legibility and how quickly information can be read. Green et al. (1994) 

recommend using plain typefaces (e.g., Geneva, Helvetica) to maximize legibility and using 

mixed case instead of all capital letters for messages in excess of two or three words. Display 

brightness, image size, and resolution also contribute to legibility. A contrast ratio of at least 3:1 

is recommended. Characters to be read in moving vehicles should subtend a visual angle of at 

least 24 minutes of arc (Stevens et al., 2002). 

Recommendation 6-9: Use some means to attract driver attention (e.g., flashing 

lights) if the system relies exclusively on a visual display to communicate 

information (no audible warnings/messages) 

For in-vehicle systems, the use of an audible warning tone or message in association with a 

visual display is strongly recommended. Text displays for use in vehicles should be preceded by 

a tone and should be limited to a few words [Also see: Recommendations 4-1, 5-3, 8-10, 8-22]. 

Rationale 

Drivers may not detect warnings and alerts presented via visual displays because they require 

drivers to glance at the display. Audible cues, warnings, and alerts do not have this limitation. 

As a result, safety and advisory warnings should precede an auditory alert (alerting tone) to draw 

attention quickly. For in-vehicle systems, a short alert tone (100–150 ms in duration) may be 

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used to capture driver attention and draw them to the visual display message. If no audible 

display means is possible, flashing of any visual image can be used to attract attention. Blinking 

the display “on” and “off” (with a frequency between 2–10 Hz and a duty cycle of 50 percent) 

can also serve as an effective (fast and conspicuous) means of capturing attention (increases 

conspicuity). Objects placed in the periphery (away from main line of sight) can also be more 

readily detected when blinking. Blinking elements on displays can be annoying, so their use 

should be limited. Because driver overload and distraction away from the task of driving can be 

an issue for in-vehicle systems, avoid use of unnecessary attention-grabbing techniques. 

6.3.3 Auditory (Nonspeech) Display Attributes 

Recommendation 6-10: Audible warnings should be sufficiently loud so they can 

be detected and understood by the driver in the presence of background noise 

Audible message output should be 15–35 dB above the ambient noise level. This can be 

achieved by automatically adjusting audible warning output or muting onboard radios/stereos. 

Rationale 

Auditory output should be audible under a range of driving conditions. The volume should be 

adjustable over a reasonable range (between 50 dB and 90 dB). Avoid using sounds louder than 

90 dB(A). The signal should not exceed ambient noise by more than 25 dB because this may 

elicit a startle response. A tone that is not sufficiently intense relative to background noise 

impairs intelligibility; too intense produces startle (Benekohal et al., 2000). For urgent warnings 

requiring immediate action, use signal strength of 70–90 dB(A) and signal-to-noise ratio of 10– 

15 dB(A). It is desirable to have the signal level automatically adjust to the background noise. 

The system may also allow drivers to adjust volume within a range of +/-10dB(A). 

Recommendation 6-11: Limit the number of different warning tones to three or 

four easily discriminable sounds 

Create distinguishable sounds by varying two or more of the following: (1) spectral content, 

(2) pulse duration, (3) pulse shape, and (4) temporal pattern. Vary at least two acoustic 

parameters to ensure discriminability. The duration of a signal burst should be between 100 and 

150 ms. 

Rationale 

Warning tones should be distinguishable and readily recognizable. Drivers’ ability to remember 

the meanings of sounds is limited and decreases under high workload situations. Certain 

attributes for tonal warnings are important. These include conspicuity, discriminability, 

meaning, urgency, and response compatibility. The signal parameters cited in the 

recommendation are primary characteristics that relate to these attributes. Short signals are less 

likely to interfere with other signals, and they allow for more flexibility in coding. Warning 

tones should have some sort of time-varying or intermittent character because the perceptual 

system is geared toward change. Drivers may be most sensitive to temporal aspects of tonal 

signals. Consider using rates of 1–8 beeps per second or warbling sounds that rise and fall in 

pitch. 

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Recommendation 6-12: Auditory alerts should be used to notify drivers of highpriority messages, to communicate changes in status, and to augment signage 

information 

Alerts are intended to address information presented to drivers before the presentation of a 

message; they capture the driver’s attention. 

Rationale 

An alerting tone should precede high priority visual information because they have been shown 

to increase accuracy and speed response to message. High-priority alerting signals should be 

used for time-critical events requiring an immediate response. 

Recommendation 6-13: Tonal signals (nonverbal auditory signals) should use a 

frequency range between 500 and 3000 Hz and burst durations of about 100 ms 

The optimal range varies with age. Frequencies less than 2000 Hz are recommended for older 

drivers. Avoid continuous tones because they are easy to habituate. Signal burst duration should 

be approximately 100 ms to ensure detection and should be 10–15 dB over ambient noise levels. 

Rationale 

Alarm dimensions, such as speed, repetition rate, and pitch, can affect the perceived urgency of 

the alarm. The time characteristics appear to be the most efficient parameters to vary (so as to 

vary perceived urgency). Imminent crash warnings, for example, should convey more urgency 

than cautionary warnings. Changes in perceived urgency can be accomplished by varying signal 

intensity, oscillations in pattern, repetition rate, and fundamental frequency. Drivers must learn 

tones or beeps (require association between signal and message). If corresponding visual 

information exists, both should be presented simultaneously. 

6.3.4 Speech Display Attributes 

Recommendation 6-14: Avoid the use of synthetic speech displays 

Rationale 

Intelligibility is one of the key parameters for a successful speech display, addressing 

understandability of the speech and comprehension of the information. Spoken information 

should be highly intelligible and reliable so it can be synthesized or digitized from real human 

speech. Synthetic speech is generally less intelligible or preferred than recorded human speech 

and can potentially increase driver workload. Vocabulary must be familiar and based on known 

population stereotypes. 

Recommendation 6-15: Messages that require an immediate response should 

consist of a single word or short phrase, and they should be understood 

immediately 

Nonurgent messages should contain a maximum of seven units of information (approximately 

seven words). The most important information should be presented at the beginning and/or end 

of the message because it is easiest to recall [Also see: Recommendation 4-14]. 

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Rationale 

Speech warnings should be brief and concise, generally between one and three words. Longer 

messages are preferred if time is not a critical factor. Under time sensitive situations, drivers 

should be able to understand the message immediately. Longer messages require more 

processing time than shorter messages and are subject to forgetting. Presenting information in 

order of importance allows drivers to quickly focus and extract critical information. 

Recommendation 6-16: Provide a means for repeating speech messages 

For urgent speech messages (warnings), automatically repeat the message up to three times. If 

time permits, precede speech outputs with a short auditory nonspeech signal (e.g., chime) to 

attract attention. Drivers should have a control that allows them to easily repeat nonurgent 

speech messages. 

Rationale 

Unlike visually displayed information, spoken messages cannot be referenced once the 

information has been provided. Unless some mechanism allows drivers to easily repeat spoken 

messages, (at their discretion), the information can be quickly forgotten. Although repeating 

messages can help alleviate this problem, repeating nonurgent speech messages numerous times 

may annoy or irritate drivers. Providing an audible cue in advance of the message prepares 

drivers to attend to the message. A given speech warning or messages should be presented no 

more than three times. Repetitions should occur in immediate succession. If the duration of the 

condition is less than the time required for all three presentations, the speech message should be 

terminated once the threat is no longer present. 

Recommendation 6-17: Ensure that messages are easily differentiated from other 

speech in vehicles 

Rationale 

When more than one auditory signal exists to alert drivers to different types of conditions 

(existence of HRI, presence of train), discriminate among the auditory signals by varying their 

intensity, pitch, or harmonics. The number of distinct signals should not exceed four. 

6.3.5 User Control and Adjustment 

Recommendation 6-18: Complex information and control interactions should not 

be designed for use in a moving vehicle 

Systems should limit or restrict manual inputs by the driver when the vehicle is moving [Also 

see: Recommendation 4-16]. 

Rationale 

Lengthy task operations or complex control interactions will divert the driver’s attention away 

from the roadway and should not occur when the vehicle is in motion. One way to accomplish 

this is to lock out access to complex task interactions if the vehicle is moving. If a task is 

interrupted before it is completed (driver initiates a task when the vehicle is not moving but 

subsequently starts driving), the system should enable the driver to resume the task at the point 

where he/she was interrupted once conditions allow. This guideline does not necessarily apply 

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to speech-based interactions, only in situations where the driver is required to provide manual 

control inputs with high levels of visual demand. In general, drivers should not be allowed to 

conduct a task in a moving vehicle if the time required to execute the task in a static environment 

exceeds 15 seconds (SAE, 2004). 

Recommendation 6-19: If multiple input or adjustment controls are present, 

design the controls so drivers can easily differentiate among the controls and 

their functions 

Rationale 

Drivers can locate desired controls more quickly if they are coded in terms of their shape, size, 

color, or location. Searching and reaching for controls can be distraction hazards, particularly in 

a moving vehicle. Coding controls will enable drivers to minimize eyes-off-road time when 

accessing and making control adjustments. 

6.3.6 Location of Controls 

Recommendation 6-20: Locate system controls within the driver’s reach, with the 

most frequently used or accessed controls closer to the driver’s line of sight and 

reach 

Rationale 

Minimizing the time it takes for drivers to access and manipulate controls will help to reduce the 

time required to make control adjustments and minimize driver eyes-off-road time. Interested 

readers should consult SAE J287 (Society of Automotive Engineers, 1993) for specifications 

relating to driver reach envelopes. 

Recommendation 6-21: Match the type of control used to the types and levels of 

functions to be controlled 

Controls should be designed to be operated with one hand, and system feedback to control inputs 

should be immediate (within 250 ms) and perceptible. 

Rationale 

Abundant literature exists for detailing specifications for control designs. Interested readers may 

consult sources, such as Sanders and McCormick (1993) or Department of Defense (DoD) 

Military Standards—1472D (U.S. Department of Defense, 1989) for additional details. Drivers 

must be able to dedicate one hand to steering the vehicle, and systems should enable drivers to 

interact with the control in a manner that is consistent with this requirement. Controls should 

provide clear and immediate feedback (tactile, force, tones, etc.); delays can cause ambiguity and 

may result in repeated inputs. If a delay in responding exists due to system processing time, then 

a message or indication should be provided to the driver indicating that the input has been 

received and that the system is processing the request. 

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6.3.7 Operational Issues Related to In-Vehicle Systems 

Recommendation 6-22: At actively controlled crossings with gates, in-vehicle 

warnings should be timed (coordinated) with the activation of the crossing gates 

or other active warning devices 

The system should activate and begin issuing warnings when the external crossing treatments 

activate (e.g., gates start to lower) and subsequently end when the active crossing elements start 

to cycle off (e.g., gates start to rise). In practice, systems should have a maximum of 2 seconds 

release time. Greater delays may run the risk of reducing perceived system reliance [Also see: 

Recommendation 4-25]. 

Rationale 

Recommendation 4-25 addresses the timing relationship of in-vehicle and external displays, and 

it indicates that simultaneous presentation is not optimal for all situations. However, where there 

is a simple, unambiguous warning, or regulatory display to which drivers must respond, such as 

gate activation, timing consistency with the identical in-vehicle message is desirable. Warnings 

should be consistent with driver expectations and highway signing and controls, and minimize 

behavioral differences in equipped versus nonequipped vehicles when approaching an HRI. 

Most vehicles equipped with an in-vehicle warning system may stop (or slow) in response to a 

warning message (e.g., train approaching); however, these types of actions may not be expected 

or understood by surrounding drivers who did not receive the message. This also applies to 

passive crossings. In-vehicle warnings should be designed to supplement existing HRI warning 

systems available in the external environment (both passive and active treatments). The 

information provided by the display should agree with available TCDs that drivers are likely to 

encounter. 

Recommendation 6-23: Provide system compatibility and integration 

Avoid use of unique, stand-alone systems to deliver train arrival or presence information at 

HRIs. Use integrated systems where feasible. When an in-vehicle system includes multiple 

integrated functions, the system should have one common and consistent interface design (e.g., 

menus, formats, colors). All in-vehicle display messages (including auditory messages) must be 

coordinated. If the display is to be shared between different systems, a prioritization scheme 

must be implemented. (Time critical information should be presented first.) Information on HRI 

status should be communicated to drivers in a consistent and standardized manner, regardless of 

manufacturer or geographic location within the United States. 

Rationale 

This recommendation addresses two basic issues: (1) compatibility across systems and 

(2) integration of systems. Systems developed by different manufacturers should be functionally 

similar and operate a manner that is consistent with drivers’ expectations. Drivers traveling 

across the country (or within a State or region) should have the same general experience when 

they encounter an HRI, and drivers may come to expect consistent information at all HRIs. To 

the extent possible, the HRI function should be integrated within available ITS and in-vehicle 

systems; this limits the number of displays and systems (particularly in the vehicle), creates 

consistency, provides value added to existing systems, and presents the appearance of a seamless 

system to the user. Integrated systems may also allow for prioritization of messages in situations 

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where multiple warnings or system messages are competing for driver attention. HRI messages 

should be prioritized within the context of the complete driver information system, and messages 

should be presented serially. 

SAE’s Safety and Human Factors Committee is a key source for emerging guidance on ITS 

integration issues. It has issued recent documents for in-vehicle message priority 

(J2395_200202), navigation and route guidance function accessibility while driving 

(J2364_200408), a means for calculation of the time to complete various in-vehicle navigation 

and route guidance tasks (J2365_200205), and is currently developing guidance for integration 

of ITS in-vehicle user interfaces and ITS display legibility. The committee has also issued 

guidance for forward collision warning systems (J2400_200308) and adaptive cruise control 

(J2399_200312) and is developing guidance for lane change collision avoidance systems. While 

these warning systems are not directly relevant to HRI applications, they are useful for two 

reasons. First, they provide good illustrations of the kinds of considerations that should go into 

in-vehicle warnings. Second, these types of warnings, together with the navigation and route 

guidance tasks, indicate the types of other ITS functions with which the HRI service must be 

integrated. Further information is available on the SAE Web site (www.sae.org). 

Recommendation 6-24: Indicate system status 

Provide an indication that the in-vehicle system is operating and functioning normally. If the 

system functions at limited sites (or under specific conditions), include some means for 

communicating this information to drivers. Drivers must be able to know when their system is 

functioning and when the system is not active. 

Rationale 

Some means to communicate warning system status is needed; drivers should not think they are 

getting a warning when they are not. Section 3.1.5 describes an example with the school bus invehicle signing system (SRF Consulting Group, 1998). This system used a blue LED to indicate 

normal operation (system status). The blue LED also flashed when the vehicle was in the 

presence of a transmitter signal (not all HRIs were equipped). 

Recommendation 6-25: Tailor information presented within the vehicle to match 

the driver’s specific situation and needs (e.g., approaching an HRI, waiting at an 

HRI, EMS personnel) 

Rationale 

Motorists may have different information needs based on their familiarity with the HRI, distance 

from the HRI, and type of vehicle. Drivers waiting at the HRI for the tracks to clear may benefit 

from knowledge about estimated train crossing time and how long the train has been moving 

through the HRI. Approaching drivers, upstream of the HRI, may desire information about 

alternate routes. Differences may also exist in the amount and type of advance warning and level 

of accuracy needed by users (e.g., EMS, police, truck drivers, bus drivers). Systems should 

provide only relevant information in suitable forms to support driver decisionmaking. 

Information that is tailored for each vehicle type or for each driver may be much more specific 

and more useful than generic information. Additionally, presenting tailored information has the 

potential to reduce the number of annoying or distracting irrelevant messages that each driver 

receives. 

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Recommendation 6-26: Evaluate the potential effects of behavioral adaptation for 

new in-vehicle systems 

Before widespread implementation, new ITS systems should be tested extensively. The test plan 

should include an evaluation of changes in driving behavior that may occur as a result of using 

the new technology. Four particularly important periods for behavioral testing should be 

considered: (1) before being exposed to the system, (2) while learning to use the system, 

(3) shortly after learning to use the system, and (4) after long-term use of the system. 

Rationale 

Motorists may adapt to new technologies in ways not envisioned by system designers. These 

changes can be positive, negative, or neutral with respect to their effect on safety; therefore, it is 

important to evaluate these behavior changes before widespread deployment of any system. To 

assess behavioral changes in driving behavior, it is desirable to have baseline measurements of 

driving behavior before the technology has been introduced. Different behavioral adaptations 

can occur after short- and long-term experience with the technology. Measurements taken 

during the learning phase may reveal adaptations in driving behavior due to new physical or 

cognitive demands imposed by the technology, while later adaptations may reveal that the 

technology is no longer used due to factors such as annoyance. In the long term, driving 

behavior may even change to become so overly dependent on the technology that any initial 

safety benefits are neutralized. 

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7. Displays for Pedestrians 

7.1 Background 

This chapter provides guidance on infrastructure-based displays for pedestrians at the HRI. 

Although some ITS envisioned for pedestrians, particularly those who have a visual or auditory 

impairment, may include a small personal display device that is carried, the research team has 

restricted the guidance here to infrastructure-based solutions because these are more likely to be 

widely implemented in the immediate future. As in Chapters 5 and 6, the recommendations 

given here are general and may apply to several different ITS applications. Chapter 8 (Warnings 

about Train Arrival) and Chapter 11 (Light Rail Transit) give other recommendations concerning 

systems for pedestrians that are related to specific applications. 

Some HRIs, particularly those involving light rail, accommodate a large volume of pedestrians, 

making crosswalk safety of particular concern at these locations. For pedestrians, HRIs differ 

from highway-highway intersections in terms of the right-of-way sharing behavior required. 

Unlike crosswalks where cross traffic (motor vehicles) may be required to yield, pedestrian wayrail intersections never require that trains yield to pedestrians. Pedestrians are generally 

successful at avoiding being struck by trains, but when they are struck the result is often fatal. 

During a 3-year period (2000–2002), a total of 243 incidents (including 150 fatalities) occurred 

in which trains struck pedestrians at HRIs. This represents 3 percent of the total 7,694 highwayrail crossing incidents that involved a train striking a roadway user during this period (FRA, 

2002, 2003, 2004). These statistics do not include incidents in which a roadway user struck a 

train, trespassing incidents which occurred away from the HRI, or evident suicides. 

The characteristics and needs of pedestrians differ from those of motorists. Pedestrians travel 

more slowly and may require more time than motor vehicles to clear the HRI when there are 

multiple tracks. Pedestrians are less restricted, and more variable in their movements than motor 

vehicles. They may approach the HRI from several different angles, or they may choose to cross 

at undesignated locations when an opportunity exists to shorten the distance to their destination. 

Pedestrians may also find it easier than motorists to circumvent active controls, such as gate arms 

and swing gates. On the other hand, pedestrians may be able to react later than motorists to an 

approaching train and still avoid being struck. Because the inertia of a pedestrian is low 

compared with that of a motor vehicle, pedestrians are able to stop more quickly and initiate 

movement more quickly. If they are aware of the hazard, pedestrians are usually able to step out 

of the dynamic envelope of an approaching train in time. When approaching the HRI, the 

pedestrian’s go or no-go decision point may be quite close to the tracks, where sight distances in 

each direction are often better than those available to approaching motorists at their decision 

point some distance upstream from the HRI. 

Although an approaching train with its visual and auditory properties is a more powerful 

stimulus for pedestrians than for motorists who are somewhat insulated inside their vehicles, this 

stimulus is so powerful that sometimes it may mask a second train approaching the HRI in close 

proximity to the first. MTWs targeted to pedestrians may improve safety at HRIs that have 

frequent multiple train events (see Chapter 8). In an urban environment, the sounds of traffic and 

other noises may mask the sounds of an approaching train. This concern is especially relevant 

for light rail vehicles (LRVs) that tend to be much quieter than conventional trains. Pedestrians 

who have a visual, auditory, motor, or cognitive disability may be particularly at risk. 

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According to Siques (2001), there are 

...four key factors that enable pedestrians to walk through a grade crossing safely: 

(1) pedestrian awareness of the crossing, which can be enhanced by passive signs 

and tactile warnings; (2) the pedestrian path across the tracks, which is subject to 

pedestrian channelization and positive control devices; (3) pedestrian awareness 

of and ability to see an approaching light rail vehicle (LRV), which depends on 

pedestrian sight distance at the crossing and can be improved through active 

warning devices; and (4) pedestrian understanding of the potential hazards at 

grade crossing, which requires public outreach and education. 

ITS-based systems may contribute especially to Factors 1, 3, and 4 by providing specific 

warnings to pedestrians about characteristics of the crossing and about train arrival. By 

automatically detecting pedestrians approaching the HRI, pedestrians who are trespassing on the 

rail system right-of-way near the HRI, and pedestrians crossing the HRI in violation of active 

warning devices, it is possible to deliver specific warnings tailored to these groups. However, 

conventional technologies, such as channelization devices and other positive control devices, can 

also play an important role in pedestrian safety at the HRI, and these should be considered along 

with more technologically sophisticated devices. 

7.2 Key Human Factors Issues and Need for Guidance 

7.2.1 Issue: Locating Pedestrian Displays for Effectiveness 

Many general issues related to locating roadside displays (see Chapter 5) apply to pedestrian 

displays as well. Other issues are specific to locating pedestrian displays. Depending on the 

environment around the HRI, the pedestrian channelization treatments (if any) that are present, 

and the direction of pedestrian destinations downstream of the HRI, pedestrians may be oriented 

in several different directions as they approach the HRI. Pedestrians who approach within a 

crowd may be engaged in conversation or may be preoccupied with monitoring the movements 

of other pedestrians around them and may not scan for visual displays before stepping into the 

HRI. Shorter pedestrians and wheelchair users may have reduced sight distances due to people 

around them and often may emerge from a crowd at the HRI, without having been able to see 

any displays as they approached. Advertising signs, traffic signs, and other visual clutter near or 

beyond the HRI may reduce the conspicuity of visual displays for all pedestrians. In these 

situations, alternate mounting locations or conspicuity enhancements may be possible. Displays 

for pedestrians, however, should not be conspicuous to motorists who may be distracted by them 

as they approach and cross the HRI. 

7.2.2 Issue: Serving Pedestrians Who Have Sensory, Cognitive, or Motor 

Impairments 

Human factors guidance is needed to understand how ITS technologies may benefit pedestrians 

who have disabilities. For example, persons who are blind have several basic informational 

needs related to crossing the HRI that are similar to the problems encountered when crossing a 

roadway (Barlow, Bentzen, & Tabor, 2003). Some of these include identifying the HRI, 

detecting the edge of the HRI and the crosswalk, understanding the geometry of the HRI 

(including the number of tracks, angle of tracks relative to the crosswalk, and direction of 

destination), knowing when it is safe to cross, knowing if they are maintaining a straight path 

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across the tracks, understanding when a train is approaching (perhaps a relatively quiet LRV), 

knowing when more than one train is approaching, and knowing where it is safe to stand while 

trains pass by. Persons who have auditory or cognitive impairments will have similar 

informational needs related to safely crossing the HRI. All of these needs may be considered as 

opportunities for new technologies. Determining the best ways to meet these needs will require 

further research. 

7.2.3 Issue: Benefits of Enhanced Information about Train Arrival 

Intelligent systems may be able to provide pedestrians with specific temporal information, such 

as the time until train arrival or the amount of safe time remaining for crossing. It is not known 

whether such information would have safety benefits or be detrimental. For pedestrian crossings 

at signalized roadway intersections, countdown pedestrian signals are now an option in the 

MUTCD (Section 4E.07). These displays supplement the standard pedestrian signal display with 

a countdown timer that shows the number of seconds remaining in the pedestrian change interval 

(before the steady DON’T WALK phase, a few seconds before the release of conflicting traffic). 

Several research studies on countdown pedestrian signals (e.g., Huang & Zegeer, 2000; DKS 

Associates, 2001; Botha et al., 2002) have indicated that when pedestrians receive this temporal 

information, a higher rate of successful crossings occurs. Pedestrians are less likely to be present 

in a crossing when the pedestrian change interval ends and so are less exposed to conflicting 

traffic. At the same time, however, an increase in noncompliance also occurs, meaning that 

more people begin crossing after the clearance interval (flashing hand icon) appears. 

Nonetheless, the explicit temporal information apparently allows these pedestrians to better time 

their crossings, and the outcomes are better. The potential benefits or risks of temporal 

information for pedestrians at HRIs are not known. The guidance of this chapter does not 

provide a recommendation for the use of countdowns given the absence of knowledge about this. 

Based on the experience at signalized roadway intersections, however, improved pedestrian 

behavior may occur with more specific information, and this bears investigation. 

7.2.4 Issue: Intelligent Recognition of Pedestrians and Prediction of Their 

Behavior 

Warning and regulatory messages for pedestrians are typically based on the status of the HRI and 

the proximity of trains. The message is not related to the pedestrian’s behavior. If a pedestrian 

is in a particularly dangerous situation, however, it may be desirable to provide a more urgent 

warning. Emerging technologies for pedestrian detection provide the opportunity for intelligent 

recognition and communications. ITS approaches based on pedestrian detection are currently 

being explored for roadway applications. In these roadway situations, when a potentially 

hazardous situation is detected, the warning message may be presented to the pedestrian or to the 

vehicle driver, or there may be a direct change in assigned right-of-way (e.g., extend the red 

signal phase of conflicting traffic). These latter options are generally not feasible for the HRI. If 

pedestrians are detected to be in some dangerous situation, a warning must be directed toward 

the errant pedestrians themselves. Potential sensing technologies include infrared and 

microwave sensing, pressure sensitive surfaces, and real-time video image processing. 

Potentially, various sensing technologies could recognize such factors as pedestrian presence, 

pedestrian location relative to crossing features (e.g., rails), pedestrian speed and direction of 

travel, anticipated speed and direction of travel, and special user features (e.g., wheel chairs, 

children). Human factors questions include the determination of those situations for which 

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pedestrian sensing and warning may have meaningful potential safety benefits, the behavioral 

criteria for defining risky situations, and the types of messages and displays that will quickly 

generate the desired pedestrian response. 

7.3 Recommendations 

Table 7 groups recommendations about displays for pedestrians under four topics. For each 

topic, the individual recommendation statements are given. 

Table 7. Recommendations for pedestrian displays 

Positioning the display 

1. Install visual displays in locations that are consistent with pedestrians’ expectations, close to the 

intended crosswalk, and within a 20-degree cone of the forward line of sight. 

2. Ensure that warning displays are configured so that they are conspicuous for pedestrians who are in 

the process of crossing the tracks when a train warning is issued, as well as for pedestrians who are 

approaching the HRI. 

3. Separate messages for motorist from messages for pedestrians. 

Accessibility of the warning 

4. Consider multiple modes of display when providing warnings or other information to pedestrians at 

the HRI. 

5. Include pedestrians who have disabilities in the design and testing process for new display features. 

Directed warnings 

6. Consider providing a targeted “last chance” warning system for pedestrians who are in immediate 

danger. 

Use of conventional pedestrian control devices 

7. ITS displays for pedestrians should be used in conjunction with positive control devices, such as gates 

and barriers. 

7.3.1 Positioning the Display 

Recommendation 7-1: Install visual displays in locations that are consistent with 

pedestrians’ expectations, close to the intended crosswalk, and within a 20­

degree cone of the forward line of sight 

Design and locate displays for pedestrians who approach the HRI from various directions and for 

those whose attention may be oriented to different destinations downstream of the HRI. For 

displays mounted on the near side of the HRI, ensure that pedestrian displays are conspicuous 

and legible (or audible) to pedestrians with various eye (and ear) heights (from children and 

wheel-chair users to tall adults). 

Rationale 

Korve (1999) and Siques (2001) have recommended placing passive signs low, below 6.5 feet so 

as to be within pedestrians’ cone of vision while walking, but outside the intended pathway so 

that pedestrians do not accidentally bump into them. This recommendation also applies to active 

ITS-based displays at the HRI that are intended for pedestrians. According to the MUTCD 

(Federal Highway Administration, 2003), standard pedestrian signal heads (which are normally 

viewed from across an intersection) should be mounted somewhat higher, with the bottom of the 

signal housing at a minimum of 7 feet. Other considerations include the potential for injury from 

the low mounted displays and the potential for vandalism. 

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Differences in pedestrians’ eye heights may significantly affect the viewing angle for displays 

located close to pedestrians on the near side of the HRI. Pedestrians with unusually high or low 

eye heights may fail to notice visual displays mounted close to them if the viewing angle is too 

large. Pedestrians with lower eye (ear) heights may also have more difficulty seeing or hearing 

displays due to the screening effects of crowds. 

Recommendation 7-2: Ensure that warning displays are configured so that they 

are conspicuous for pedestrians who are in the process of crossing the tracks 

when a train warning is issued, as well as for pedestrians who are approaching 

the HRI 

[Also see: Recommendations 4-1, 8-10, 8-22] 

Rationale 

Displays located on the near side of the HRI and oriented for pedestrians approaching the HRI 

may not be visible (or audible) once the pedestrian is in the middle of the HRI. Displays should 

be effective at all positions in the crosswalk. 

Recommendation 7-3: Separate messages for motorists from messages for 

pedestrians 

Messages should be targeted exclusively to the intended audience. For example, an auditory 

speech warning directed to pedestrians should be configured so that the warning is clearly 

audible to pedestrians but does not confuse or distract motorists. Warnings for pedestrians and 

motorists should be coordinated so that they do not interfere with one another (e.g., warning bells 

masking a pedestrian speech warning). Visual displays for pedestrians should be positioned so 

that they do not distract motorists. 

Rationale 

Roadway users require meaningful and consistent information. The intended audience of train 

arrival messages must be clear to roadway users. This is especially important if different timing 

is used or if different message content is delivered to each audience [Also see: 

Recommendations 4-9, 4-20, 6-25]. 

7.3.2 Accessibility of the Warning 

Recommendation 7-4: Consider multiple modes of display when providing 

warnings or other information to pedestrians at the HRI 

These could include visual, auditory, and tactile displays. Information should be redundant and 

complementary across modes so that each one adequately expresses its message independently of 

the others to better serve a wide variety of pedestrians who may have visual, auditory, cognitive, 

or motor impairments. (This includes needs for displays with a lower visual angle or large size 

features.) Consider placing the display closer, to be read by pedestrians on the same side of the 

tracks. Also consider using auditory and tactile displays [Also see: Recommendations 4-21, 4­

22, 4-23, 11-9]. 

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Rationale 

Single-modality displays may not adequately communicate the warning message to pedestrians 

who have sensory disabilities. Using combined auditory and visual cues reduces this risk. The 

use of multiple modalities will also make the warning more conspicuous to pedestrians who do 

not have any disability, including those who may be distracted by secondary tasks (such as 

talking on a cell phone) or other environmental stimuli, such as roadway traffic, advertising 

displays, and other people. In compliance with ADA requirements, the U.S. Access Board 

develops accessibility guidelines for designers of government facilities and places of public 

accommodation. Designers of pedestrian access routes should consult the Draft Guidelines for 

Public Rights of Way (U.S. Access Board, 2002). Although this document contains only a few 

guidelines which directly address the HRI (Surface Gaps at Rail Crossings—1103.7 and 

Detectable Warnings—1103.7.1), the general principles described in other sections may also be 

helpful to designers of pedestrian access routes which cross the HRI. 

Recommendation 7-5: Include pedestrians who have disabilities in the design 

and testing process for new display features 

[Also see: Recommendations 4-21 through 4-23] 

Rationale 

To clearly understand pedestrians’ needs at the HRI, it is necessary to engage them in the design 

process. Initially, this may be done through observational study, focus groups, individual 

interviews, or other behavioral research techniques. From these data, a set of evidence-based 

user requirements can be written to represent pedestrians’ real needs. Persons who have 

particular disabilities may have somewhat different strategies and behaviors for navigating 

through the HRI than other pedestrians; therefore it is important to include them in user research 

so that their unique needs will be considered in user requirements documents. As development 

of the ITS system proceeds, concepts and prototypes may be tested with pedestrians as part of an 

iterative design process. Pedestrians who have disabilities should also be included at these 

stages of development because they may uncover safety or usability issues that would be missed 

by other users of the system. 

7.3.3 Directed Warnings 

Recommendation 7-6: Consider providing a targeted “last chance” warning 

system for pedestrians who are in immediate danger 

Consider providing an additional warning to pedestrians who remain between the tracks or 

within the train dynamic envelope after standard active warning devices have been activated. 

Train arrival warnings should be provided to pedestrians who have already begun crossing the 

tracks. The warning should indicate that a train is approaching and the appropriate action to 

take. An automated detection system can be used to determine whether a pedestrian is in the 

path of an oncoming train. Some visual detection systems can even detect speed and direction of 

movement, which may allow the system to determine whether the pedestrian is moving to clear 

the dynamic envelope. If it is determined that a pedestrian is in danger of being struck, a 

targeted warning may be the last chance to motivate the pedestrian to clear the HRI [Also see: 

Recommendations 4-13, 11-4]. 

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Rationale 

Pedestrians move more slowly than vehicles and therefore may take longer to clear the HRI. 

This is especially relevant at wide HRIs with multiple tracks. Automated detection systems have 

been used at HRIs for automated enforcement and to detect blocked HRIs (but have yet to be 

used to detect pedestrians who are too close to the tracks). Although automated enforcement of 

pedestrian crossings is not feasible, the existence of targeted warnings may serve to deter unsafe 

crossings or may alert pedestrians who, although not standing inside the tracks, may be inside the 

train’s dynamic envelope and unaware of the hazard. Some visual detection systems can even 

detect speed and direction of movement, which may allow the system to determine whether the 

pedestrian is moving to clear the dynamic envelope. The system should be designed in such a 

way as to prevent or discourage intentional system activation. 

7.3.4 Use of Conventional Pedestrian Control Treatments 

Recommendation 7-7: ITS displays for pedestrians should be used in 

conjunction with positive control devices, such as gates and barriers 

[Also see: Recommendation 11-1] 

Rationale 

Channelization of pedestrian traffic by fences, barriers, gates, and other non-ITS measures is 

effective to control pedestrians’ orientation with respect to the HRI, approaching trains, and 

warning displays (Siques, 2001, 2002). These devices reduce the variability among pedestrians’ 

lines of sight, focusing attention in the direction of the hazard and active warning devices. 

Automatic closing gates provide a cue that the train is approaching and a physical barrier to deter 

pedestrians from entering the HRI. Gates should open automatically when the tracks are clear, 

and they should open away from the tracks, providing an obvious, easy means of escape for 

pedestrians who get trapped inside the HRI. 

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Part IV: Human Factors Considerations for Specific Applications 

117

8. Warnings about Train Arrival 

8.1 Background 

This chapter provides human factors guidance concerning the use of ITS technology to warn 

roadway users about train arrival at HRIs, including the special case of warnings about multiple 

trains approaching. The specific issues discussed and the guidance given are restricted to 

warnings about train arrival, even though ITS applications that deliver such warnings may 

provide road users with additional information as well. Chapter 9 discusses alerts about the 

presence and status of HRIs and messages about alternate routing. Chapter 10 gives guidance 

concerning enforcement and control, and Chapter 11 presents guidance that is especially relevant 

for LRT applications. 

Typical active warning devices (lights and gates) present only a single, general message to 

roadway users about train arrival at the HRI: a train is somewhere in proximity to the HRI. 

However, with emerging ITS technology it is feasible to monitor train movements and predict 

train arrival times, making it possible to inform roadway users with more specific messages 

about the number of trains approaching, speed, position, heading, and time required for trains to 

clear the HRI. With the availability of this new information comes several human factors 

questions about the best ways to provide such information and how such information will affect 

driver and pedestrian behavior. For example, real-time, accurate train status information 

provided to motorists and pedestrians waiting at the track might reduce anxiety about long waits 

and might lower the risk of drivers violating active controls (driving around gates), thereby 

reducing the frequency and severity of vehicle-train crashes. On the other hand, if such 

information is unreliable or presented in the wrong way, it could encourage risky behaviors, 

thereby reducing or even eliminating net safety benefits.

7 

8.2 Key Human Factors Issues and Need for Guidance 

8.2.1 Issue: Information to Communicate about Train Arrival 

Train arrival warnings should support driver information needs and decisionmaking. Motorists 

approaching an HRI need to be able to orient to approaching trains or trains in the HRI, so that 

they can plan and execute appropriate behaviors. Various types of information may be 

communicated, including data addressing train dynamics, train characteristics, and predictive and 

historical information, as well as information detailing HRI site characteristics. Specific 

information elements may include number of trains near HRI; current train position, location, 

and presence (train approaching or occupying the HRI), estimated time of arrival at the HRI: 

7 Several reviewers expressed concerns about the reliability of train arrival estimates. One noted that “the arrival 

time accuracy is considerably degraded with distance from the crossing, particularly with light rail or commuter 

trains that can quickly accelerate or decelerate. This time information needs to be considered in providing rerouting 

information to drivers.” Another noted the some collisions are related to “non-standard movement” around a 

crossing (e.g., “stopping without being on the crossing or moving back and forth to pick up freight cars”). Another 

emphasized the need for better communications between the train and the crossing, stating that “while constant time 

warnings have improved these communications at crossings with active warning systems, they are not sensitive to 

variations in train movements. Too much attention, in some cases, is being given to automating all of the systems, 

and too little to the combination of manual and automated systems” (e.g., where switching movements take place 

near a crossing). 

119
train speed; train direction; train length; train type (e.g., freight, passenger, high-speed); 

estimated train crossing time (duration of the train event/blockage); how long the train has been 

moving through the HRI; and alternate route (closest grade separation) among others. Human 

factors concerns and issues relating to information about train arrival address the extent to which 

motorists are provided with relevant, consistent, and meaningful information to support their 

decisionmaking. The type of information, amount of information, and relevance and 

meaningfulness of the information should be consistent with driver needs and tasks. Providing 

too much information, or irrelevant information, may overwhelm drivers, slow information 

processing, and/or contribute to distraction. The relative importance of information may also 

vary as a function of the driver’s location relative to the HRI; motorists at the HRI may desire 

different information than those approaching the HRI. Those waiting at the HRI for a train to 

pass may also have more time and opportunity to process lengthy and detailed messages 

compared with those in transit. System designers should construct consistent standardized 

messages that support the needs of drivers approaching or waiting at an HRI, in a manner that 

allows drivers to quickly extract and understand important information about train arrival. 

8.2.2 Issue: Signal Characteristics (How to Communicate) 

The means through which train arrival information is communicated to drivers can play a 

significant role in how drivers interpreted, understood, and used that information. ITS 

applications at HRIs have employed a number of methods to transmit information to drivers, 

including in-vehicle and external roadside systems. A review of operational tests (Chapter 3) 

found a range of different designs and interfaces to provide train arrival information, including 

CMSs, HAR, fixed signing with dynamic elements, and stand-alone in-vehicle audio-visual 

displays, as well as information kiosks, integration with in-vehicle navigation systems, personal 

digital assistants (PDAs), cell phones, and Internet. Because driving is a complex task requiring 

significant mental and physical demands, the physical properties of the alerts, warnings, and 

messages about train arrival must be consistent with the environment and must stand out among 

other signals (and noise) to capture driver attention without being annoying. 

8.2.3 Issue: Coordination with External Controls and Traffic Management 

Centers 

New train arrival warnings must be compatible and consistent with existing traffic control 

systems and should take into consideration that not all drivers may have access to advance train 

information (particularly if it is provided in the vehicle). If ITS-equipped drivers, for example, 

receive advance knowledge of an approaching train (via an in-vehicle display), their behavior 

may not be predictable to surrounding traffic. Equipped drivers may stop their vehicle at the 

HRI before activation of any available active controls (gates), and this may result in increased 

vehicle-to-vehicle collisions. Another important feature of ITS applications, such as train arrival 

warnings, is the ability to coordinate and share information with Traffic Management Centers. 

These centers in turn can control signal phasing, disseminate train movement information, and 

coordinate with emergency services. 

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8.2.4 Issue: Signal Conspicuity 

The ability to capture the roadway user’s attention is a critical requirement for all types of train 

arrival warnings, including MTWs. This issue is important for in-vehicle displays and roadside 

displays. 

Drivers may not notice train arrival warnings presented through in-vehicle visual displays if the 

warnings are not positioned close to the cone of vision around the driver’s line of sight. For invehicle displays mounted on the dashboard, supplemental auditory signals or dynamic visual 

components (e.g., flashing light) may be needed to direct the driver’s attention. Auditory signals 

in vehicles may not be conspicuous if they do not adapt to changes in the ambient noise level. 

Train arrival warnings presented on roadside displays share many of the same conspicuity issues 

as other signage. For example, unfavorable lighting or weather-related conditions may reduce 

visibility. Conspicuity of roadway displays depends on many features of the display, such as 

size and location relative to the driver’s line of sight, and on contextual factors, such as the 

number of other signs present and the visual complexity of the background. 

Current MTWs use visual displays external to the vehicle (roadway signs). For roadway 

displays, the requirements related to the conspicuity of the MTW may be somewhat unique. For 

displays intended for vehicle traffic, the display must be visible to, and capture the attention of, 

the motorist in the vehicle immediately in front of the lowered gate. This is unlike the case of 

crossing lights and gates, which must be visible on the approach to the HRI; they must be within 

the cone of vision around the driver line of sight at some distance from the tracks. This is also 

unlike the case of intersection traffic signals, even though the driver may be stopped at the 

intersection. At a roadway-roadway intersection, the driver must monitor the traffic signal to 

know when to proceed. The driver stopped at a lowered railroad crossing gate will not be 

monitoring any overhead or roadside signals. Rather, his or her attention is likely to be fixed on 

the gate and the passing train, with the intent to proceed as soon as the track is perceived to be 

clear. The MTW must counter this intent even though the driver does not have attention directed 

at the display. For a driver stopped at the tracks, the viewing angle for displays mounted on mast 

arms over the track or at the roadside may be oblique and outside of the cone of vision around 

the likely line of sight. Therefore, it is essential that some action be taken to enhance the ability 

of the display to attract driver attention, through enhanced target value or placement or acoustic 

signals or other means. Current standards and guidelines do not address this problem. 

Similar problems may arise for pedestrian applications. In the absence of a pedestrian gate, the 

likelihood of proceeding across the tracks without noticing a train arrival warning or MTW may 

be even greater for pedestrians than for vehicles. In addition, ambient noise levels may be high 

or highly variable for pedestrians near the track due to motor vehicle traffic or nearby trains; 

therefore, auditory warnings must be designed carefully to retain their conspicuity under all noise 

conditions likely to be encountered. 

8.2.5 Issue: Message Timing 

Timing of train arrival messages is a concern for both triggering the onset of ITS alerts and 

warnings, and for their deactivation relevant to external systems. Although this issue is 

particularly relevant for active crossings, it also applies to the timing of information 

communicated by ITS at passive crossings. 

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Information on train arrival must be presented far enough ahead of the hazard so that the driver 

has time to process the information, make a decision, and take the appropriate action. The 

purpose of the alert or warning will determine how far in advance of the HRI the message should 

be communicated. Information about train arrival that is meant to guide drivers to alternative 

routes would likely be presented further upstream from the HRI than information meant to warn 

drivers to yield to an approaching train. At various time points during the driver’s approach to 

the HRI, as the driver’s information handling capability changes, it may be appropriate to present 

messages with different content and format. 

Other message timing concerns exist for MTWs. Current MTWs use dynamic displays with 

sequential phases. It may take a significant period of time (e.g., 9 seconds for the Maryland 

MTA implementation) to cycle through the entire message. The driver at risk for a second train 

collision is the impatient driver who proceeds without adequate search and who may circumvent 

gates. Therefore, the multiple train message must have impact on behavior quickly. The display 

needs to be activated with minimal or no delay after the first train passes. The initial phase of the 

display must inhibit the driver’s actions. The driver should not be expected to patiently wait for 

the entire sequence in order to get the meaning. Existing displays do not appear to have been 

evaluated from this perspective. 

8.2.6 Issue: Message Comprehension 

Train arrival warnings (and MTWs) should convey the specific idea that a train may be coming 

(or another train coming), that may not be visible yet, and a collision threat exists if the driver 

proceeds. No existing standard or common practice for this type of display is currently in place. 

It may be difficult to convey this idea quickly, reliably, and legibly. If the sign only conveys the 

idea of caution, some benefit may exist, but the promotion of desired behaviors will not be 

optimal. The display therefore needs to be specifically, reliably, and quickly understood by the 

full range of users. If combinations of graphic and/or text message elements are required to 

convey this message, visual complexity and clutter may compromise comprehension. 

8.3 Recommendations for Train Arrival Warnings 

Table 8 groups recommendations for train arrival warnings under four topics. Each topic 

includes individual recommendation statements. 

8.3.1 Information Provision (What to Communicate) 

Recommendation 8-1: Display train-related information only if it fulfills a need 

Define the specific driver information need(s) the train arrival display is intended to meet. Limit 

information to that which fulfills the need. Avoid providing related information in multiple 

forms; use a single type of metric in a simple form (e.g., time, distance). Generally, simple 

statements regarding the appropriate behavior are preferable to descriptive information about 

train arrival, especially quantitative information [Also see: Recommendations 4-9, 8-4]. 

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Table 8. Recommendations for warnings about train arrival 

Information provision (what to communicate) 

1. Display train-related information only if it fulfills a need. 

2. Limit the amount of information presented. 

3. Issue alerts about the presence of HRIs and warnings about the presence of trains. 

4. Present integrated, directly usable information. 

5. Design messages based upon information handling zones. 

6. Provide standardized message content on CMS at the HRI. 

7. Provide cues as to the direction of approaching trains. 

8. Provide a release indication. 

Signal characteristics (how to communicate) 

9. Use CMS as a primary means to communicate HRI status. 

10. Consider conspicuity enhancements for visual displays. 

11. Avoid temporal countdown displays for motorists. 

12. Provide accurate and reliable information. 

13. Minimize nuisance warnings for drivers not in potential conflict. 

Timing of signals for train arrival warnings 

14. Issue warnings throughout the entire duration of the train event, but provide a way to reduce the 

nuisance potential of the warning. 

15. Inform roadway users at HRIs where extended advance warning times are used. 

Coordination with external controls 

16. Coordinate ITS warnings and non-ITS traffic control devices. 

Rationale 

ITS capabilities may make it possible to provide a wide range of detailed information regarding 

train arrival. For example, there may be access to data on train speed, distance, time to arrival, 

time to gate activation, train length, time to clear, train direction, multiple trains, unusual signal 

timing (e.g., longer than 20 seconds constant warning time (CWT)), and so forth. This may 

make it tempting to provide road users with more information or more precise information. 

More, however, is not necessarily better. The driver should not receive too much information, 

irrelevant information, or information that promotes inappropriate driver actions. The 

information displayed should be based on driver information needs. Even if road users have a 

desire for certain types of information, presentation should be limited to needed information in 

its most effective form. Section 1A.02 of the MUTCD (Federal Highway Administration, 2003) 

specifies requirements for effective TCDs. Among these are fulfilling a need, conveying a clear 

simple meaning, and giving adequate time for proper response. Therefore, the display should 

select among potential information based on the specific scenario, road user information 

requirements, and the most appropriate information given the time and place of the message 

presentation. Generally, road users will not have a good sense of quantitative aspects. Is a 70­

mph train faster than normal? Is a 20-second train arrival time a comfortable margin for clearing 

an HRI? Therefore, qualitative statements (high-speed train) or specification of driver response 

(stop, do not enter) are generally preferable. Some messages (e.g., time for train to clear) may 

exists where there may be benefits to quantitative information, but careful consideration should 

occur whether drivers will actually use such information. 

Recommendation 8-2: Limit the amount of information presented 

Systems should provide drivers with the necessary information to make an informed, safe 

decision (e.g., cross the tracks, wait, re-route) while staying within the limits of the amount of 

information that the driver can process [Also see: Recommendations 4-11, 4-26, 5-2]. 

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Rationale 

Providing large amounts of information (or irrelevant information) may increase the time 

required to process system messages and may confuse or distract drivers. Distraction from 

reading or glancing at visual displays while driving is a particular concern. Lengthy text 

messages or visual displays may overload drivers or require them to take their eyes off the road 

for a significant length of time. Research on in-vehicle ATIS indicates that drivers generally 

only use a limited amount of information (two to three items) to support their decisionmaking 

(Lerner & Steinberg, 2000; Llaneras, Lerner, Huey, & Bensur, 2000). Prioritize the information 

and present only important items; primary items of interest will likely vary depending on the 

context and drivers’ specific situation. Consider limiting the amount and type of information 

provided to drivers to a few key items. The specific type and amount of information presented 

also depends on the form of the message (e.g., visual display, auditory display), as well as the 

context (e.g., in-vehicle, Internet, kiosk). Properly constructed auditory messages can be less 

demanding to process than complex visual displays. 

Recommendation 8-3: Issue alerts about the presence of HRIs and warnings 

about the presence of trains 

Drivers approaching an HRI should be provided with two general types of information, provided 

that the information is reliable: (1) an alert indicating the presence of an HRI and (2) a warning 

indicating that a train is present or approaching the HRI. Advanced ITS systems should support 

both types of advisories and warnings. The two should be clearly discernable and should reflect 

the urgency of the situation. While systems that only present advisories are particularly 

beneficial at passive crossings where drivers are responsible for detecting the presence of trains, 

they may have limited utility for familiar drivers. 

Rationale 

A two-stage warning that provides different levels of information (HRI ahead and train 

approaching) may facilitate driver performance by building expectation. Warnings should reflect 

the urgency of the situation; drivers should perceive a train approaching warning to be urgent 

and necessitating a fast response. Unfamiliar drivers will benefit from an advisory alerting them 

to the presence of an HRI. All drivers benefit from knowledge of an approaching train or train 

occupying the HRI. Field tests and implementations of in-vehicle signing systems have provided 

drivers with both types of information; however, if the information is not reliable, drivers may 

lose confidence in the system. 

Recommendation 8-4: Present integrated, directly usable information 

Providing integrated information that is meaningful to drivers supports their decisionmaking and 

does not require them to perform complex mental operations. Information communicated to 

drivers should be conveyed in a directly usable form. 

Rationale 

Although train speed, location, and direction information can be communicated to drivers and 

used to predict train arrival time at an HRI, it does not provide directly usable information (will 

the train be at the HRI when I get there?). Requiring drivers to integrate information elements 

can place an unnecessary demand on their attention. It is preferable to communicate estimated 

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train arrival time or a directly usable, individualized message about whether (and how long) they 

will have to wait for the train to pass if they continue on their present route toward the HRI. 

Recommendation 8-5: Design messages based upon information handling zones 

Information about train arrival should be appropriate for its location with respect to information 

handling zones upstream of the HRI. The content, format, and complexity of the message should 

be suitable for the information handling zone in which it is presented. Table 9 shows desirable 

characteristics for messages in various information handling zones. 

Table 9. Message characteristics for information handling zones 

Zone Defining Point 

Message 

Content Message Format 

Message 

Complexity 

Advance Before decision 

sight distance 

Planning, 

guidance 

information, HRI 

status 

Unrestricted; can 

include text, 

phased messages, 

dynamic elements 

Can be relatively 

complex if other 

roadway 

characteristics 

allow; information 

load as key 

criterion 

Approach Decision sight 

distance 

Safety-related 

information 

Warning format Simple graded or 

temporal 

information OK; 

should not require 

long total glance 

time; eye-off-road 

time as key 

criterion 

Non ­

recovery 

Stopping sight 

distance 

Crash avoidance 

specify single 

driver response 

Urgent safety 

warning format, 

high conspicuity 

Simple, immediate 

message; response 

time as key 

criterion 

Stop Point Gate, stop line, or 

other marking 

Safety or 

informational 

Warning or 

informational 

Can be relatively 

complex; message 

duty cycle must be 

consistent with 

driver behavior 

Rationale 

Information should be located so that the driver receives it with enough time to respond properly 

and without conflicting with other task demands, but not so far in advance that it is inappropriate, 

ignored, or forgotten. ITS messages about train arrival should be based on an analysis of where 

and when the information is needed. This is true for roadside and in-vehicle displays. One 

convenient simplifying scheme for characterizing message locations is to view the approach to 

an HRI as a sequence of information handling zones. This concept was developed within the 

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126

Positive Guidance Model of Driver Behavior (e.g., Alexander & Lunenfeld, 1975; Lunenfeld & 

Alexander, 1990), which described five zones in relation to some highway hazard: the advance 

zone, approach zone, nonrecovery zone, hazard zone, and downstream zone. The concept is 

applied to HRI applications in the Railroad-Highway Grade Crossing Handbook (Tustin, 

Richards, McGee, & Patterson, 1986), focusing on the approach, nonrecovery, and hazard zones. 

For ITS considerations, the hazard zone is probably of less relevance, but the advance zone is of 

more relevance. The highway design concepts of stopping sight distance and decision sight 

distance define the zones. Where an ITS system has sufficient intelligence regarding a specific 

vehicle (e.g., speed, location), these zones can be defined for each driver; otherwise, they are 

based on assumptions about vehicle speed. Figure 15 (from Lerner et al., 2002) illustrates the 

information handling zones. However, the hazard zone refers to the area where there is a 

potential collision; for HRI applications, this usually, though not necessarily, will be the dynamic 

envelope around the track. For example, an analysis could focus on an active barrier that is 

located in advance of the track.

Figure 15. Information handling zones (from Lerner et al., 2002)

Brief rationale statements for the recommendations in Table 9 follow:

 Advance zone. The advance zone is the area sufficiently in advance of the HRI that the 

driver does not need to be dealing with immediate decisions and actions about speed, 

path, visual search, or other actions at the HRI. Therefore, few restrictions are on the 

type of ITS information or manner of displaying it, other than good signing or display 

practices that would be appropriate to any roadway application. If the message is 

complex, consideration should be given to driver information load requirements, 

including the presentation of the message with respect to other signs, ITS messages, and 

driving demands.

 Approach zone. The approach zone begins at the decision sight distance, the theoretical 

distance required for a driver to plan and execute safe and efficient maneuvers to 

unexpected or difficult-to-perceive information or events. The approach zone is where 

the driver formulates and begins to execute the actions needed to avoid hazards (e.g., 

visual search) and operate the vehicle in a controlled manner (e.g., speed adjustments, 

HAZARD 

ZONE

15 ft either side 

of nearest rail

NONRECOVERY 

ZONE

Starts at stopping sight 

distance point

APPROACH 

ZONE

Starts at decision sight 

distance point

ADVANCE

APPROACH 

ZONE
smooth stopping). Because the driver must be planning safety-relevant actions here, ITS 

information in this area should be limited to safety information and be in a format that 

makes it clearly obvious that this is a safety message. Message content can be graded 

(e.g., levels of warning) or temporal (e.g., train arrival time). Because drivers must be 

planning and initiating a maneuver, however, the display should not require the drivers to 

take their attention away from the roadway, HRI, or traffic for extended periods. 

 Nonrecovery zone. The nonrecovery zone begins at the stopping sight distance, the 

theoretical last moment that the driver could respond to a message and stop the vehicle 

before entering the hazard zone. Because drivers reaching this zone must quickly react to 

any potential hazard, only high-priority safety messages requiring an immediate response 

should be presented here. Messages must be conspicuous, simple, quickly 

comprehended, and indicate a clear sense of the required maneuver. 

 Stop point. The term stop point (not a zone in the Positive Guidance model) is used here 

to indicate the situation where information about trains is provided to drivers who are 

already stopped at the HRI. Because the vehicle is stationary, concerns about driver 

distraction and eye-off-road time are minimal. Therefore, displays can be more complex 

and have longer duty cycles, if required. The message may be informational or safetyrelated. Safety-relevant messages at this point would be meant to discourage the 

initiation of unsafe behaviors (e.g., unsafe to proceed, second train warning). 

Informational messages should not encourage unsafe behaviors (e.g., indicate a long 

delay before the train’s arrival in the HRI). 

Recommendation 8-6: Provide standardized message content on CMS at the HRI 

CMSs located at the HRI should provide a limited set of messages that are based on established 

consensus standards.

8 In the absence of such standards, messages should be designed to initially 

notify drivers of an approaching train and subsequently cycle through a set of messages 

providing minimum required information to ensure safety (e.g., warning of train approach, time 

to HRI, time to clear the tracks). For new applications where standards do not yet exist, 

messages should be tested with roadway users to ensure comprehension [Also see: 

Recommendations 4-5, 4-24, 5-12, 6-7, 9-8, 9-9]. 

Rationale 

Zaworski, Bell, Hunter-Zaworski, and Sacmaci (1996) have recommended using CMS messages 

for stopped motorists at the HRI to reduce driver uncertainty and increase the likelihood that 

drivers will comply with TCDs. Although no standardized set of messages has been developed, 

several suggested CMS message sequences have been proposed. Table 10 outlines two 

alternatives. Bell, Hunter-Zaworski, and Zaworski (1997), for example, suggest that CMSs 

should initially advise drivers to stay clear of the tracks when a train is approaching and then 

cycle through a set of messages, providing four basic information elements when a train has been 

detected. The National Plan for ITS Highway-Rail Intersection User Service #30 proposes more 

specific CMS wording. Both proposals include a provision for a default All Clear indication 

8 One reviewer commented that in addition to standardized message content, the user should consider a standard 

format now recommended by the “traffic industry.” This format is Line 1 (or frame 1): state the condition; Line 2 

(or frame 2): state the location; and Line 3 (or frame 3): state the desired action. 

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when no train is present or approaching the HRI. Use of such an All Clear indication 

encompasses a different alerting strategy than current practice at active crossings (where the lack 

of a signal indicates no trains are approaching or present). The message sequence in the HRI 

User Service provides some additional information, including estimated time to clear the HRI 

and a release indication to notify drivers when it is safe to proceed. While the recommended 

messages below are helpful, the wording may not be optimal, and these examples do not take 

advantage of CMS graphics capabilities. In the absence of validated consensus standards, 

messages such as these should be evaluated for user comprehension. 

Table 10. Proposed message content for CMS displays at the HRI 

National Plan for ITS Highway-Rail Bell et al. (1997) Intersection User Service #30 (1996) 

(1) Default display indicating no train is 

present or arriving at the HRI. 

(2) A message warning drivers to stay clear 

from track when a train is approaching. 

(3) Indicate when the train will arrive. 

(4) “TRAIN CANNOT STOP BEFORE 

CROSSING!” 

(5) Indicate the direction to the nearest gradeseparated crossing. 

(1) “PROCEED” (HRI clear) 

(2) “TRAIN(S) ARRIVING, CLEAR THE 

INTERSECTION” (30–60 seconds before 

train arrival) 

(3) “STOP – DO NOT ENTER – WAIT FOR 

TRAIN(S) TO CLEAR CROSSING” 

(20–30 seconds before arrival) 

(4) “TRAIN(S) WILL CLEAR CROSSING IN 

## SECONDS and/or WATCH FOR 

OTHER TRAIN” 

(5) “CAUTION” (after the train(s) clear the 

HRI) 

(6) “WAIT FOR PROCEED SIGNAL” 

(7) “PROCEED” 

Recommendation 8-7: Provide cues as to the direction of approaching trains 

This can be accomplished by spatially coding train location information using available invehicle speaker systems or trackside equipment to communicate train direction. 

Rationale 

Humans detect, localize, and automatically orient toward sounds and novel visual stimuli. 

Spatially coded signals (either in-vehicle or in the outside environment) allow drivers to locate 

the direction of the hazard (e.g., approaching trains). The location from which the signal 

emanates can be used to convey the direction of the train. Drivers may react to warning signals 

by first visually confirming the presence of the hazard. If the driver’s attention is guided more 

quickly to the approaching train by spatially coded signals, then appropriate evasive actions can 

occur more quickly. 

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Recommendation 8-8: Provide a release indication 

Systems, particularly in-vehicle, must provide an indication to the driver when the conditions are 

safe to cross the tracks once the train has cleared the intersection (release indication). The 

system should allow for the need to re-issue a warning based on a second train event. 

Rationale 

This recommendation is targeted to passive crossings where no external release indications are 

present and drivers are required to assess whether it is safe to cross. Some concern does exist 

that drivers may assume it is safe to cross after the initial train has passed, but a second train may 

be approaching. An All Clear or Proceed message provides a redundant safeguard and a positive 

confirmation that the HRI is clear. Use of a release indication is a separate and distinct issue 

than that of issuing a default proceed or all clear message when no train is present or 

approaching the HRI. The release indication should be triggered in association with a warning 

message. 

8.3.2 Signal Characteristics (How to Communicate) 

Recommendation 8-9: Use CMS as a primary means to communicate HRI status 

CMSs should be used to communicate HRI status information to motorists until in-vehicle 

systems become widespread [Also see: Recommendations 8-7, 8-8]. 

Rationale 

Current fleet penetration for in-vehicle systems is too low for this to serve as a primary means of 

motorist communication, however helpful it may be to those who have such devices. HAR is 

inadequate because it requires an active response from the driver. Passive signs with active 

elements (e.g., flashers) have been used for some applications. CMS is preferred, however, 

because it permits the full set of helpful messages and can be viewed by all drivers. 

Recommendation 8-10: Consider conspicuity enhancements for visual displays 

If the train arrival warning system relies primarily on a visual display, then some conspicuity 

enhancements should be used to attract the driver’s attention to the display (e.g., flashing lights, 

strobes, dynamic features, or color on CMS). Supplemental audible alerts and warnings may 

also be used to enhance the conspicuity of visual displays. The use of an audible warning tone or 

message in association with a visual display in vehicles is strongly recommended, and 

supplemental audio cues may also be used at pedestrian crossings to enhance the conspicuity of 

the train arrival warning. Conspicuity enhancements that involve visual features are also 

recommended for MTWs [Also see: Recommendations 4-1, 5-3, 6-9, 8-22]. 

Rationale 

Road users approaching the HRI are likely to be engaged in both transportation-related and non 

transportation-related tasks besides looking for trains. Those whose visual attention is not 

captured by the train itself (hazard) may be alerted to the danger by a visual display. However, 

the same demands on visual attention that may prevent the road user from noticing the train may 

interfere with them noticing the train warning display, especially if the display is not positioned 

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directly in the road user’s line of sight. Drivers must notice train arrival warnings if they are to 

be effective, and various conspicuity enhancements may help to draw attention to the display. 

Recommendation 8-11: Avoid temporal countdown displays for motorists 

Information on train arrival should be expressed in a manner that does not induce risky or 

undesirable behavior. Avoid use of countdown type warnings that provide a sequential timebased, countdown to train time to arrival. These types of formats may encourage risky driver 

behavior (drivers may race to attempt to beat the clock/train). Also avoid time estimates that 

imply greater precision than is available with the system or useful to roadway users [Also see: 

Recommendation 4-19]. 

Rationale 

Although drivers may need to know estimated train arrival time to support their decisions, 

systems that continuously display a time-based countdown may encourage reckless behavior. 

Little or no research exists on behavioral impacts of these types of countdown displays, and this 

area should be studied further. Nevertheless, precise estimates may not be necessary and could 

erode driver confidence in the system if inaccurate. It may be more desirable to provide drivers 

with estimated time to clear the HRI rather than time to arrival. Furthermore, drivers may be 

able to base decisions on generalized time-to-arrival information without resorting to countdown 

type displays. Bell et al. (1997) proposed a possible configuration for a series of repeating CMS 

messages to alert motorists to the presence of an approaching train. The signs would rotate 

through a series of set messages: “High Speed Train Approaching,” “Extreme Danger Train 

Speed 110 mph,” “Train Will Arrive at Crossing in 1 min. 20 sec,” “Train Cannot Stop Before 

Crossing.” These messages repeat, and the time is updated. This configuration provides 

estimated train arrival time without necessarily providing a clock-like countdown. 

Recommendation 8-12: Provide accurate and reliable information 

Drivers must perceive train warning information to be accurate and reliable. Predictions of train 

arrival time should be as accurate as possible. Drivers will tolerate some inaccuracy (e.g., errors 

in time estimates, false alarms), without significant loss in trust. Strive for reliability rates that 

are more than 80 percent.

9

 Systems should also be reliable under a variety of operational 

conditions, particularly low visibility situations. Systems must reliably detect trains when they 

are present [Also see: Recommendation 4-8]. 

Rationale 

Unreliability leads to mistrust and uncertainty, possibly negatively impacting driver behavior and 

response to the system. Drivers may ignore system warnings or delay in responding to the 

warnings if the system is perceived to be unreliable. Research suggests drivers are likely to 

search for confirmatory evidence and delay braking as a consequence of false alarms; issuing a 

warning when no threat exists can erode driver confidence in the system and have measurable 

impacts in driver behavior (Chugh & Caird, 1999). Research suggests greater loss in trust at 

9 The 80-percent reliability recommendation is based on empirical research on maintaining user trust. Higher levels 

may be required for other reasons, and, in particular, missed detections are much more safety critical than false 

positives. 

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50-percent reliability than 83-percent reliability. If drivers come to rely on the system 

exclusively and do not seek out confirmation, system failures could lead to catastrophic 

consequences. Systems should operate in degraded visual conditions, acting as a redundant precue to approaching trains under low-visibility conditions (e.g., fog, rain, snow, or nighttime) 

where drivers may fail to detect approaching trains. 

Recommendation 8-13: Minimize nuisance warnings to drivers not in potential 

conflict 

Train arrival warning systems should be designed so that alerts and warnings are issued to 

approaching traffic and not to drivers who have crossed over the HRI (or traveling in the 

opposite direction, away from the HRI). The system should not activate unless the vehicle 

direction of travel will take it through the HRI [Also see: Recommendations 4-9, 4-18, 9-6]. 

Rationale 

This is an annoyance issue (nuisance warnings). Systems should be designed to avoid or 

minimize nuisance alarms when the vehicle is in the vicinity of an HRI but not intending to cross 

the tracks. The warning zone around the HRI should be tuned according to the geometry and 

environment to prevent nuisance alarms. 

8.3.3 Timing of Signals for Train Arrival Warnings 

Recommendation 8-14: Issue warnings throughout the entire duration of the train 

event, but provide a way to reduce the nuisance potential of the warning 

Once a driver has been alerted to the presence of a train (i.e., received the warning message), an 

in-vehicle system should provide a means to reduce the nuisance potential of the warning. 

Nevertheless, warning signals should continue to be issued throughout the entire duration of the 

train event to alert approaching traffic [Also see: Recommendation 4-18]. 

Rationale 

Repeating alert and warning messages (or repeatedly cycling through the same warning) to 

drivers with in-vehicle systems can become a nuisance. This is particularly true for audible or 

voice warning messages. In-vehicle warning devices should provide a means to reduce the 

nuisance potential of an alert once it has been issued. This can be accomplished by muting or 

reducing the volume of any audible warnings after it has cycled through several times, limiting 

the number of times or cycles the warning is issued, including a driver confirmation button and 

changing the mode of the warning (change from audible to visual warnings) (Benekohal et al., 

2000). The Minnesota Department of Transportation Field Operational Test of an in-vehicle 

signing system for school buses varied the number of repetitions based on the warning type: two 

repetitions of their audible warning for the HRI alert and eight repetitions of the tone upon initial 

detection for the train approaching warning. Tones should be repeated (re-activated) for each 

additional train warning signal (e.g., second train). 

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Recommendation 8-15: Inform roadway users at HRIs where extended advance 

warning times are used 

The recommended warning time for activating a TCD is generally 20 seconds before train 

arrival. For ITS applications, such as blocked track warnings issued to train operators, vehicles 

must be cleared from the HRI more than 20 seconds before train arrival, so that if a vehicle or 

other object remains on the tracks after the gates descend, the train operator can be notified with 

enough time to initiate emergency braking procedures. If warning times (gate closings) at 

certain HRIs equipped with ITS technology are significantly longer than the warning times 

provided at conventional active crossings, roadway users should be informed about the estimated 

time until the train arrives or at least given an indication that the particular HRI has a longer than 

normal advance warning time [Also see: Recommendation 4-7]. 

Rationale 

Warning times at active crossings should be consistent with roadway users’ expectations. If 

flashing lights and gates are activated more than 20 seconds before train arrival, roadway users 

may become impatient waiting for the train to arrive at the HRI and assume that the gates are 

malfunctioning. This may lead to risky behaviors, such as driving around the gates. 

8.3.4 Coordination with External Controls 

Recommendation 8-16: Coordinate ITS warnings and non-ITS traffic control 

devices 

In general, similar messages should occur at similar times for all information sources. Some ITS 

applications, however, may allow for situation-specific timing that is more precise and 

appropriate than non-ITS applications. For example, warning time algorithms could incorporate 

vehicle speed, vehicle type, road surface condition, traffic, or train speed. These advantages 

should not necessarily be sacrificed to maintain identical timing of all information sources. 

However, the effects of variable timing, particularly if only some vehicles receive the 

information, should be considered in system design. The possible disadvantages of variable 

timing of messages across roadway users should be considered along with the advantages of 

providing more advance warning to drivers who have in-vehicle systems [Also see: 

Recommendation 4-29]. 

Rationale 

Warnings should be consistent with driver expectations and highway signing and controls, and 

they should not encourage drastic behavioral differences in equipped versus nonequipped 

vehicles when approaching an HRI. Vehicles equipped with in-vehicle warning systems may 

stop (or slow) in response to a warning message (e.g., train approaching); however, these types 

of actions may not be expected or understood by surrounding traffic whose drivers may not have 

benefit of this information. In-vehicle warnings should be designed to supplement existing HRI 

warning systems available in the external environment (both passive and active treatments). The 

information provided by the in-vehicle display should agree with TCDs that drivers encounter; 

otherwise drivers may lose confidence in the system. 

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8.4 Specific Recommendations for MTWs 

Table 11 groups recommendations for MTWs

10

 under three topics. Each topic includes 

individual recommendation statements. 

Table 11. Recommendations for message content and message comprehension for MTWs 

Message content and message comprehension for MTWs 

17. Use an active caution message. 

18. Convey all important elements of the warning message either explicitly or implicitly. 

19. Ensure complete message comprehension. 

20. Present consistent behavioral cues during multiple train events. 

Signal conspicuity for MTWs 

21. Attract the attention of at-risk road users. 

22. Enhance conspicuity with visual features. 

23. Ensure that both text and graphic display elements are legible. 

24. Supplement MTW displays with acoustic signals. 

Message timing and phasing for MTWs 

25. Initiate MTW before first train passes. 

26. Limit the length of message phase times. 

MTWs for drivers 

27. Use the following components of MTW displays for motor vehicle traffic. 

28. Install a roadway-based MTW display in a location appropriate for motor vehicle traffic. 

MTWs for pedestrians 

29. Provide an MTW to pedestrians at HRIs where more than one train often passes through the HRI in 

close proximity. 

30. Use the following components of MTW displays for pedestrians. 

31. Install an MTW display in a location appropriate for pedestrian traffic. 

8.4.1 Message Content and Message Comprehension for MTWs 

Recommendation 8-17: Use an active caution message 

The MTW display should contain distinct elements to convey the message that there is a hazard 

present that requires caution. This should include an active display component. 

Rationale 

The general message that a hazard is present and caution is required may be conveyed by a 

signal word (e.g., “WARNING” or “CAUTION”), sign shape and color (e.g., yellow, diamond in 

the MUTCD), icon (e.g., ISO “!”), or supplementary signal (e.g., amber flasher). Some portion 

of this message should be active (i.e., present only when the second train threat is present); 

passive elements, such as sign background shape or color, are not sufficient because they do not 

indicate to the road user a change in status from the time they were initially encountered. 

Components of the message that describe the event (second train) should not in themselves be 

assumed to evoke an immediate and consistent sense of danger. A need to convey an immediate 

10 Although MTW systems are currently in use, one reviewer expressed reservation, arguing that it is not possible to 

detect multiple trains and provide accurate warnings “except in the simplest of situations and then not to a degree 

that is reliable enough to make a railroad’s law department recommend use.” Another reviewer expressed a related 

concern, arguing that because MTW collisions are “99.999 percent likely to be litigated,” the cost-benefit of 

developing an adequately accurate system may not be favorable. 

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and unambiguous sense of threat exists to prevent an impulsive roadway user from proceeding 

before processing the complete message. 

Recommendation 8-18: Convey all important elements of the warning message 

either explicitly or implicitly 

The MTW should include an unambiguous indication that a subsequent train is about to reach the 

HRI after the first train. This message should be appropriate for all viewers, including the nonEnglish literate. The viewer should understand (1) the nature of the event, (2) the consequence 

of the hazard, and (3) how it should be avoided. It is not necessary that each of these elements 

be explicitly and separately stated or illustrated, but each must be conveyed. In particular, the 

consequence may be assumed to be conveyed if the hazard event of the approaching train is 

understood. 

Rationale 

The nature of the threat and how to avoid it are elements of effective warning devices. No 

formal indication is in the literature that existing MTW implementations meets this requirement. 

Recommendation 8-19: Ensure complete message comprehension 

The display should reliably convey both the general message that a danger is present and the 

specific message that another train is approaching. Comprehension by the intended user 

population should be confirmed by appropriate testing [Also see: Recommendations 4-6, 4-21, 

7-5]. 

Rationale 

Good warning practice requires that a communication device clearly convey (1) that this is a 

warning message and (2) the type of hazard, its consequence, and how to avoid it. The warning 

aspect helps to direct attention to the message and induce caution, while the specific hazard 

information is necessary for good compliance. Although a particular display successfully 

conveys one of these aspects, the viewer may not understand the other aspect. Displays used for 

MTWs generally do not appear to have been formally evaluated for road user comprehension, 

with the exception of the Los Angeles MTW application. They reported that a survey of 

pedestrians at the Vernon Avenue site found a very high proportion understood that caution was 

necessary, but very few (4 percent) understood the specific second train situation. This indicates 

the need for warnings based on testing with appropriate user populations. 

Recommendation 8-20: Present consistent behavioral cues during multiple train 

events 

Systems intended to detect and communicate multiple train events should provide drivers with a 

consistent set of behavioral cues and expectations. This includes keeping active warning system 

components, if present (e.g., gates, bells, lights) engaged in-between train events. Ensure that 

roadway users do not get conflicting signals from gates, warning lights, and MTW displays. In 

particular, gates should not start to move into their upright position during multiple train events 

[Also see: Recommendations 4-7, 4-28]. 

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Rationale 

The sight of a first train clearing the crossing is a cue to roadway users that it is safe to cross the 

HRI. MTWs, when activated, must act to overcome this cue by presenting a clear message that it 

is not yet safe to cross. Active controls (gates, lights, bells) also represent an important primary 

cue to drivers signaling when the HRI is safe to cross. Therefore, it is important that the 

information that they provide is coordinated and completely consistent with information 

provided by the MTW, including any supplemental MTW displays. Gates in particular serve as 

a strong visual cue and are likely to attract the driver’s attention if they begin to retract to their 

upright positions (this event will likely cue drivers to prepare and/or start to move). An 

ascending gate that stops after only a few seconds and then immediately descends again as it is 

activated by a second train may be perceived to be malfunctioning and ignored. This problem 

would be especially serious at locations where false gate activations are known to occur. 

Moving gates may also attract attention away from critical visual displays used to inform drivers 

about multiple train events. Conflicting signals, such as gate movement when it is not safe for 

drivers to cross the HRI, erode confidence in the system and may lead to dangerous behaviors, 

such as driving under or around gates. For these reasons, gate movement should be retarded 

during multiple train events. The Transit Cooperative Research Program (1999) describes some 

specific strategies to prevent the gate behavior described above (known as gate pumping). 

8.4.2 Signal Conspicuity for MTWs 

Recommendation 8-21: Attract the attention of at-risk road users 

Visual displays for MTWs, once activated, should quickly and reliably attract the attention of atrisk road users as defined by their location or actions. Dynamic visual or acoustic display 

features (e.g., strobes) may be considered [Also see: Recommendations 4-1, 4-13, 7-6, 8-22, 8­

24, 11-3, 11-4]. 

Rationale 

Roadway users are unlikely to monitor an inactive MTW display. Their attention will probably 

be directed toward the passing train, gates, up-road, up-track, or elsewhere. Furthermore, the 

road user may not expect to encounter a sign at the HRI, particularly not at the MTW signal’s 

location. When a sign location is inconsistent with driver expectancy, sign detection is slower 

and less reliable. If the visual display does not draw attention at the time a hazard is detected, 

the roadway user may proceed without an opportunity to receive the warning. Conspicuity will 

be a function of the location of the display(s), the number of displays, and the features of 

displays. Conspicuity when activated is a necessary consideration for both infrastructure-based 

and on-board systems. The at-risk users may include motor vehicle operators, pedestrians, and 

bicyclists, depending on the application. Those at-risk are defined by their location relative to 

the tracks and trains and the time for track clearance. 

Recommendation 8-22: Enhance conspicuity with visual features 

Where the display cannot be located near the target road user’s probable line of sight, the 

conspicuity of the display should be enhanced. Static attributes of visual displays, such as size, 

brightness, color, and contrast, all influence whether the display will be noticed. However, 

dynamic changes will be more effective because (1) they are strong contributors to conspicuity 

and (2) they draw attention at the time the display is relevant, not at irrelevant times. Therefore, 

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flashing beacons or strobes are recommended for roadway-based displays, even if other static 

enhancements are made. Dynamic elements should not interfere with display legibility [Also 

see: Recommendations 4-1, 5-3, 6-9, 7-4, 8-10]. 

Rationale 

Road users must be aware of the MTW sign only when it is activated. Static improvements to 

conspicuity are not sufficient because once viewers detect the inactive display, they may not 

direct further attention to it. The message display alone on an activated roadway sign may not be 

sufficient to ensure it is noticed. Even if animation is used, the likely positioning of the sign 

means that roadway users may not notice it unless an effective stimulus for peripheral vision 

exists. Adjacent flashing amber beacons, or bright strobes, are typical treatments for enhancing 

roadway sign and signal conspicuity. These enhancements must not create glare, especially if 

used at night. 

Recommendation 8-23: Ensure that both text and graphic display elements are 

legible 

Text and graphic elements must be legible from all likely viewer positions. Specific wording 

and/or icons should be tested to verify roadway users understand them. A mix of text and 

graphics may be used, but this should not result in clutter, small images, or long sequences of 

displays. Text should not scroll. Iconic elements should ideally include recognizable images of 

the tracks, trains, and road user (vehicle or pedestrian). It may be desirable to have the display 

reflect the actual spatial and temporal sequence of events (e.g., direction of train movement), but 

any degree of benefit is unknown [Also see: Recommendation 4-3]. 

Rationale 

The MTW must meet good display criteria as would any sign. No specific wording and pictorial 

content are recommended because alternatives should be tested for comprehension. Since the 

nature of the hazard event is defined by the relationship of the trains, tracks, and road user, 

however, it would seem that the image should include all three elements. No specific 

recommendation is made with respect to the perspective view that should be shown (e.g., 

overhead, profile, or linear perspective). It may be desirable to have the display reflect the actual 

sequence of events; for example, if the first train is on the near track approaching from the left 

and the second train is on the far track approaching from the right, the display accurately reflects 

this relationship. It is conceivable that, if some location or direction of approach is shown that 

does not match the actual situation, there could be some confusion for the road user, and visual 

search might be misdirected. This could be of most concern where more than two tracks exist 

and the potential exists for a subsequent train arriving on any track and from either direction. 

However, because it is not known whether showing a specific relationship is likely to have 

ultimate safety consequence, it does not seem warranted at this point to require a display to be 

sensitive to the actual location and direction of the first and subsequent trains. 

Recommendation 8-24: Supplement MTW displays with acoustic signals 

An acoustic signal may supplement the visual display. The signal should originate from the 

direction of the visual display. The appropriateness of a supplementary acoustic signal must be 

considered in the context of other acoustic signals (e.g., bells) and noise (e.g., passing train) 

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present in the environment. For the intended road user, it must be detectable, localizable, and 

easily discriminated from other sources. 

Rationale 

Acoustic signals may enhance conspicuity and perceived urgency, and they may serve as useful 

supplements to visual MTW displays. For onboard warning systems, the requirements for 

acoustic warnings probably are not unique from other types of warnings. For infrastructurebased applications, applications issues differ somewhat for pedestrian and motor vehicle 

applications. Under ideal conditions, an acoustic cue associated with the visual display could 

enhance the ability of the display to draw attention. This can only be achieved if the signal itself 

orients attention, and that attention is directed toward the location of the visual display. This 

may be difficult to achieve for road users inside vehicles but may be more practical for 

pedestrian applications. In either case, because the MTW occurs during the pass-by of the initial 

train, any acoustic signal will need to occur in the context of train noise, bells, or other audible 

warning devices associated with the normal operation of the gates and flashing light signals. An 

acoustic MTW signal should only be used if it can practically meet the needs of detection, 

discrimination, and localization while being environmentally appropriate. 

8.4.3 Message Timing and Phasing for MTWs 

Recommendation 8-25: Initiate MTW before first train passes 

The MTW display for stopped traffic or pedestrians should activate as soon as the multiple train 

event is detected. The message must initiate sufficiently before the initial train passes so that the 

entire warning message can be displayed and understood. The range of the warning activation 

envelope should be extended for a subsequent train once the initial train has activated the gate. 

Rationale 

Impatience and impulsiveness are likely factors in crashes with a second train. A message, 

therefore, must have its impact quickly. If the onset of the warning is late or if the display takes 

a long time to cycle, the impatient road user may react before processing the entire message. 

The road user may initiate action in response to the passing of the end of the train or the 

initiation of the gate rising. Once the road user begins to move forward, it may become very 

difficult to read a roadside warning display because the viewing angles become extreme. Invehicle displays may also be less likely to be noticed because attention will be directed outside at 

the tracks and roadway ahead. The MTW display should to immediately inhibit inappropriate 

road user actions. The entire MTW message (possibly consisting of multiple phases) should be 

displayed before the end of the first train passes because impatient roadway users may try to 

cross the tracks at this time. A scenario of particular concern is where the initial train passes, the 

crossing signal display is terminated, and gates begin to rise before the entry of the second train 

into the warning activation zone. Vehicles could become trapped, or road users may think that 

the signals and gates are malfunctioning. To prevent such problems, the advance warning time 

for the second train could be lengthened to preclude premature termination of the initial warning. 

By this logic the warning time for the second train should be extended by at least the amount of 

time remaining until the gate reaches its upright position. 

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Recommendation 8-26: Limit the length of message phase times 

If a dynamic display consists of a sequence of phases, the initial phase should inhibit the 

initiation of movement by the road user. This phase should be of sufficient duration so that the 

viewer has the opportunity to orient toward the display and interpret the text or image. 

Subsequent phases should allow enough time for the viewer to process the information, but the 

total duty cycle for the display should not be so long that road users are discouraged from 

attending to the full cycle. Phase times will generally be in the 1.53.5 second range, depending 

on complexity [Also see: Recommendation 4-14]. 

Rationale 

Some MTWs have employed a sequence of phases. This may have the advantage of simplifying 

the image and message for any given phase and the disadvantage of requiring the viewer to 

attend to multiple displays to get the full message. The MTW must quickly inhibit driver action. 

For this reason, the initial phase should include an easily perceived message or image (e.g., 

“stop,” “warning,” “danger,” lights, or sounds). The duration of the phase should include time to 

orient toward the sign and time to process the image. Processing times may be taken as a 

minimum of about 1 second; allowing for orientation, this suggests a minimum phase of 1.5 

seconds for simple messages or images. Complex images may require substantially longer times 

(some formulas for roadway signs suggest estimating 1 second per symbol and 0.5 second per 

word or number). An upper bound on the order of 3.5 seconds is suggested based on the 

assumption that if a phase takes longer than this, the image may be too complex to warrant being 

part of a phased sequence. The total duty cycle for the display is the sum of the durations of all 

the phases. An impatient road user needs to get the message in a reasonable time, but little 

empirical basis exists for defining an acceptable maximum for this application. 

8.4.6 MTWs for Drivers 

Recommendation 8-27: Use the following components of MTW displays for motor 

vehicle traffic 

MTW displays intended for motor vehicle traffic, whether roadway based or on-board, should be 

composed of the following elements: 

 An indication that a hazard exists and this is a warning message. 

 An iconic indication that a subsequent train is about to arrive at the HRI after the current 

train. 

 A text (or in-vehicle voice) indication of a subsequent train, unless the iconic display is 

demonstrated to have high comprehension for the range of anticipated viewers. 

 For roadway-based displays, a flashing amber beacon mounted adjacent to the display 

panel that is activated throughout the display cycle. 

 An acoustic cue at the onset of an on-board display. An acoustic signal is optional for a 

roadway display. Acoustic signals for roadway-based MTWs should continue throughout 

the warning display cycle and should be localized from the position of the visual display. 

Drivers must be able to easily discriminate MTW acoustic cues from other acoustic 

signals used at the HRI (bell, horns). 

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Rationale 

The recommendation given here is based on several recommendations listed above. No basis 

exists for recommending specific icons or wording for the display, so candidate messages should 

be evaluated by testing with drivers. 

Recommendation 8-28: Install a roadway-based MTW display in a location 

appropriate for motor vehicle traffic 

For MTWs that are infrastructure-based (on the roadway), the visual display(s) should be located 

at a position appropriate for motorists, in all travel lanes, stopped at the track. If possible, the 

display should be located within a 20-degree cone of vision around the driver’s forward line of 

sight, or as close to this as possible, for motorists stopped at the track. Mounting height should 

be at a minimum 15 feet and at a maximum 25.6 feet. The display should be oriented so that the 

images and text are legible, despite oblique viewing angles, for motorists in all lanes. The MTW 

should not be located where it will be obscured by passing trains. Viewer eye position may be 

assumed to be 6 feet from the lowered gate position, with an eye height of 3.5 feet. 

Rationale 

The motorists of most concern for this display are those at the front of a queue at the HRI. While 

other vehicles behind the lead vehicle may pass waiting traffic to circumvent signals or gates, the 

problem of viewing angle is not as severe. For a vehicle stopped near the track, the angle of the 

display, relative to the driver forward line-of-sight, may be large in the vertical dimension for 

cantilever displays mounted above the roadway or in the horizontal dimension for displays 

mounted at the roadside. The greater this visual displacement, the less likely drivers will notice 

the signal. Furthermore, whether vertically or horizontally displaced from the driver, the face of 

the display may need to be angled toward the viewer to prevent illegible displays at the most 

oblique viewing angles. The criterion in the guideline for the 20-degree viewing angle comes 

from MUTCD guidance (Section 4D.15) on the placement of traffic signals (Federal Highway 

Administration, 2003). Because the MTW display must function as a stop indication, criteria for 

traffic signals are a useful guide; Section 4D.15 contains further detail on signal placement for 

roadway intersection signal control applications. The cone of vision around the driver line of 

sight typically is considered good within 10 degrees and adequate within 20 degrees (McKinley, 

2001). Mounting height requirements also come from Section 4D.15. The mount must be low 

enough so that the vehicle roof line does not obscure the display from the driver position. The 

assumed viewer position of 6 feet from the lowered gate is a worst-case estimate. Vehicles with 

relatively short bumper-to-driver seat positions place the viewer’s eyes about 6 feet from the 

bumper. Assuming a lead vehicle pulls up immediately in front of the gate, the viewer would be 

about 6 feet from the gate. The driver eye height assumption of 3.5 feet comes from the use of 

this value for highway sight distance design purposes. Using these values and assuming an 18­

foot cantilevered mounting height for the display, the MTW sign would need to be at least 40 

feet downstream from the gate position to remain within 20 degrees. Lateral viewing angles 

depend on the roadway geometry. Although 20 degrees is specified as a target viewing angle, 

even this may be problematic, given the possible driver focus of attention on the gate 

immediately in front of the vehicle and the fact that no expectancy may exist for a sign in this 

location. 

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8.4.5 MTWs for Pedestrians 

Recommendation 8-29: Provide an MTW to pedestrians at HRIs where more than 

one train often pass through the HRI in close proximity 

Rationale 

Pedestrians are often more susceptible than motorists to collisions with trains during multiple 

train events. This is because pedestrian behavior is more difficult to control, especially without 

the presence of restrictive devices, such as gate arms or pedestrian swing gates. MTWs can aid 

pedestrians’ decisionmaking by confronting the incorrect assumption that it is safe to cross after 

the first train has passed and alert them to a specific hazard. Second Train Approaching signs 

have been recommended for use at locations where two or more LRT tracks are present and LRV 

typically have short headways due to many trains running or due to scheduled meet points in the 

operating plan (Transit Cooperative Research Program, 1999). 

Recommendation 8-30: Use the following components of MTW displays for 

pedestrians 

MTW displays intended for pedestrians should include the following elements: 

 An indication that is a hazard exists and this is a warning message. 

 An iconic indication that a subsequent train is about to arrive at the HRI after the current 

train. 

 A text or voice indication of a subsequent train, unless the iconic display is demonstrated 

to have high comprehension for the range of anticipated viewers. 

 An acoustic signal is optional. Acoustic signals should continue throughout the warning 

display cycle and should be localized from the position of the visual display and easily 

discriminated from other acoustic signals used at the HRI (bell, horns). 

 A flashing amber beacon may be required if display location criteria of Recommendation 

8-21 are not met. 

Rationale 

The recommendation given here is based on several recommendations listed above. No basis 

exists for recommending specific icons or wording for the display, so any candidate messages 

should be evaluated by testing with pedestrians of various ages including those who have 

sensory, cognitive, or motor disabilities. 

Recommendation 8-31: Install an MTW display in a location appropriate for 

pedestrian traffic 

An MTW visual display(s) intended for pedestrians should be located at a position appropriate 

for pedestrians stopped 6 feet from the nearest track. The display location should be within a 20­

degree cone of the forward line-of-sight or as near to it as possible. The display should be 

oriented so that the display is legible, despite oblique viewing angles, for pedestrians at any 

lateral point across the pedestrian right-of-way. If the display is displayed beyond 20 degrees for 

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some viewing positions, consider enhancements such as greater size, dynamic elements, or 

acoustic signals. 

Rationale 

The need for the display to draw viewer attention is the same for pedestrians as that for 

motorists. A display intended for pedestrians may be the same display intended for motorists or 

may be an independent display. In either case, the location must be appropriate for pedestrians. 

The constraints on placement relative to viewer position may not be as severe for pedestrianoriented displays as they are for roadway-based motor vehicle displays. Pedestrian displays can 

generally be mounted lower, lateral displacement does not need to be great, and vehicle 

components (roof, pillars) are not present to obscure peripheral detection. Nonetheless, 

pedestrians may still be standing near the tracks so that oblique viewing angles can be large. 

Therefore, a reasonable minimum distance to assume might be the edge of the train dynamic 

envelope, which is generally 6 feet from the track according to the MUTCD, Section 8B (Federal 

Highway Administration, 2003). 

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9. Advance Information about the HRI and Dynamic Route Guidance 

9.1 Background 

While the previous chapter focused specifically on ITS applications for warning roadway users 

about train arrival at the HRI, this chapter focuses on applications that may improve safety and 

travel efficiency by giving roadway users other types of information in advance of the HRI. The 

two application areas covered are (1) providing advance information about safety-relevant 

features of the HRI and (2) presenting route guidance information about HRIs before route 

decision points. The emphasis is on providing information to motorists because this group is the 

most likely to receive benefits from the implementation of HRI advance warnings and route 

guidance information. This chapter considers what information to present and how to present it, 

as well as the likely behavioral impacts of such information. Advance information about the 

HRI can affect driving behavior in positive ways. For example, motorists may react to the 

information appropriately by reducing speed, increasing searching for trains, or making sound 

navigational decisions about alternate routes and timely maneuvers necessary to carry out these 

choices. However, there may be other, unintended consequences of providing this information, 

such as driver annoyance, information overload, or increases in unsafe driving behaviors [Also 

see: Recommendations 4-16 through 4-19]. 

ITS technology introduces the possibility that fixed roadside warning signs may be supplemented 

or replaced by intelligent systems. Such systems may be capable of presenting a richer and more 

distinct set of cues to promote proper behavior and facilitate decisionmaking. In current practice, 

the standard Crossbuck (R15-1) and Advance Warning (W10-1) signs are sometimes 

supplemented by other roadside signs that warn of unusual or hazardous conditions related to the 

HRI, including unusual grade crossing geometry and types of rail traffic. Roadway users may 

benefit from knowing in advance about potentially hazardous geometric features of the HRI, 

including limited sight distance, high-profile (humped) crossings, multiple tracks, skewed 

crossing angles, and roadway intersections and signals near the HRI, as well as the type of traffic 

controls present (active or passive). Other information about rail traffic, such as the presence of 

high-speed trains, mixed-rail operations, and the potential for multiple train events, may also be 

useful to motorists and could be communicated through ITS displays. Additionally, ITS-based 

HRI warnings may prove to be a viable, relatively inexpensive alternative to installing active 

controls (gate arms, bells, and lights) at passive crossings.

11 

Although conventional supplemental grade crossing signs are limited to warnings regarding 

fixed characteristics of the HRI, ITS applications are capable of presenting dynamic warnings 

regarding transient states, such as road surface conditions, obstacles on or near the track, and 

queued traffic. To avoid fixed or transient conditions, such as lengthy delays, drivers who have 

been alerted to these conditions may choose to take an alternative route, especially if alternative 

route guidance is provided. 

Route guidance information may be presented as an integrated part of in-vehicle displays or on 

roadside CMS systems. ITS systems may be able to draw on information from many sources to 

predict the time until an HRI will be clear and expected travel times on alternate routes. 

11 One reviewer cautioned that it is an “urban myth” that “ITS crossings will be less expensive than conventional 

systems.” 

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Information such as anticipated train arrivals, projected delays, travel times, and route 

restrictions (for carriers or vehicles with low-ground clearance) should be incorporated into route 

guidance systems. 

Dynamic advance warnings and the sophisticated route guidance capabilities mentioned here will 

require sensor and information processing technology to change messages to motorists as 

conditions near the HRI change and as conditions on alternative routes change. Existing 

technologies, such as video detection, loop sensors, and Global Positioning System (GPS), 

among others, can play a role. 

9.2 Key Human Factors Issues and Need for Guidance 

9.2.1 Issue: Information Timing 

To achieve maximal effectiveness of HRI warnings or actionable route guidance, information 

must be presented to motorists in a timely manner. Adequate (minimum) timing is a function of 

fairly well understood variables, such as the time required for motorists to perceive and process 

the information, and time required to perform any necessary actions (e.g., decelerate, choose 

alternate route, look for trains), and some simple constraints exist. For example, information that 

may inform the driver’s choice of route must be presented (and acted upon) in advance of route 

decision points. On the other hand, it is not clear how much advance time is optimal for different 

kinds of information.

12 Research is needed to specify a maximum amount of advance time for 

alerts, warnings, or route guidance information. Presenting information too far in advance of 

when it is needed may cause annoyance and will create an unnecessary burden on the driver’s 

memory. 

9.2.2 Issue: Information Amount 

The amount of information to present to motorist is a major human factors consideration. 

Although this issue applies to virtually any application of driver information, some issues are 

specific to HRI information. For example, to reroute a vehicle to another HRI location, the 

motorist could be given additional instructions, such as directions for an alternate route. 

Although the potential benefits are obvious, such information may increase driver information 

load and divert attention from the driving task. Similar concerns arise with any attempt to 

present multiple messages. 

9.2.3 Issue: User-Specific Information 

User-specific information should be directed to all targeted motorists. Additionally, targeted 

information should not be presented to any motorists for whom the message is irrelevant. This 

may be relatively simple for in-vehicle systems but more difficult for presentations external to 

the vehicle. The ITS system must recognize the vehicle or its characteristics. For example, ITS 

messages related to HAZMAT restrictions or humped crossings are nuisances for most drivers, 

and ideally the system should discriminate those vehicles for which the message is relevant. If a 

message is presented externally and targeted to one vehicle, it is likely that many other motorists 

12 One reviewer reported that in his/her experience, the characteristics of the traffic are a factor in when to present 

information. Commuters require “far less time to respond and are more likely to do so” than travelers from “outside 

the area like tourists.” 

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will notice it and perhaps be distracted by it. Another concern is that for in-vehicle messages and 

external messages, a targeted motorist may notice a relevant message but decide that the message 

is irrelevant. The message duration, activation and deactivation method, and wording may all 

affect the likelihood that the relevance of user-specific information will be misinterpreted. 

9.2.4 Issue: Message Medium and Format 

Current non-ITS HRI warnings commonly use textual and/or iconic messages. When 

implementing or upgrading advance HRI warning devices using ITS technology, it is important 

to present warnings in a way that is consistent with the mental models of message recipients. 

The use of CMS is fairly consistent with current warning signage in both location and 

appearance. The MUTCD (Federal Highway Administration, 2003) supports the use of CMS for 

warning applications, and the roadside location of such warnings is similar to typical non-ITS 

signage. 

Another way to present HRI warnings to drivers is to transmit information wirelessly to the invehicle environment. An advantage of this message format relative to standard sign plaques and 

CMS is that a greater amount of information can be given to the motorist, and this information 

can be tailored to individual needs. Unlike CMS, however, in-vehicle presentation of HRI 

information is novel and inconsistent with current signage. Furthermore, the presence of invehicle visual displays may require drivers to take their eyes off the road, potentially leading to 

driver distraction. An additional difficulty of in-vehicle displays is that the display must be 

installed in a variety of vehicles, each of which has a unique configuration that may prevent 

uniform installation. Because of the novelty of this approach, the risk of distraction, and the cost 

of vehicle fleet instrumentation, this application may be most likely to succeed if targeted only to 

vehicles deemed to be at high risk for certain hazards (e.g., heavy trucks, buses, vehicles with 

low ground clearance, and vehicles containing hazardous materials). 

9.3 Recommendations 

Table 12 groups recommendations for providing advance information about HRI and route 

guidance under three topics. Each topic provides the individual recommendation statements. 

9.3.1 Advance Information about the HRI 

Recommendation 9-1: Provide advance information about HRI status and 

characteristics subsequent to a general warning about the presence of the HRI, 

except where this conflicts with other criteria for message placement or timing 

For roadway-based displays, this means the message about HRI status should be located between 

the Advance Crossing (W10-1) sign and the crossing. The display, however, must meet the 

location criteria in described in Section 5.3. For in-vehicle displays, the message about HRI 

status should follow the general warning about the presence of the crossing or may be integrated 

with that message. 

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Table 12. Recommendations for advanced information about the HRI 

Advance information about the HRI 

1. Provide advance information about HRI status and characteristics subsequent to a general warning 

about the presence of the HRI, except where this conflicts with other criteria for message placement 

or timing. 

2. For in-vehicle systems, include advance information about fixed features and hazards at the HRI that 

is typically conveyed by conventional roadside signs. 

3. Provide motorists with additional advance information about transient conditions at the HRI that is 

not typically conveyed by conventional roadside signs. 

4. For advance information to motorists about potential hazards at the HRI, identify the hazard and 

advise the driver how to respond. 

5. Provide advance information about the HRI only to roadway users for whom the information is 

relevant. 

6. Distinguish between active and passive crossings when providing advance information about HRI 

location. 

Route guidance 

7. Develop consensus standards for providing dynamic route guidance through or around HRIs. 

8. Standardize CMS messages for dynamic route guidance so that they have a consistent format with 

other CMS messages to motorists. 

9. Route guidance concerning the HRI should be based the most current and complete information 

available. 

10. Provide motorists with dynamic route guidance information that incorporates predicated as well as 

current conditions at the HRI. 

11. Support the driver’s navigational decisions by providing all relevant information about the HRI in 

advance of route diversion points. 

12. Provide a driver-oriented reason when an alternative route is recommended to divert around the HRI. 

13. If an alternate route is recommended over the primary route across the HRI (driver’s typical route or 

normal best choice route), provide an estimate of travel time on the alternative route. 

14. Emphasize quantitative information over qualitative information when expressing delays associated 

with the HRI. 

15. Recommend alternative routes when opportunities for significantly reduced travel times exist as 

defined by the driver’s personal preferences or when emergency situations arise at the HRI. 

User control 

16. Give the user control over the types of advance information about the HRI that will be presented in 

the vehicle and the conditions that will trigger recommendations for selecting alternative routes. 

Rationale 

The recommendation for roadway-based sign placement is consistent with recommendations for 

fixed signs in National Cooperative Highway Research Program (NCHRP) Report 470 (Lerner et 

al., 2002). If the message about HRI status follows the message about the presence of the 

crossing, the meaning may be clearer and have more impact. The supplementary message is less 

likely to interfere with perception and processing of the standard highway sign. For some 

hazards, however, this placement might not meet the criteria of Recommendations 5-1 and 5-2 

and the message may have to be presented earlier. For example, if the problem is that a traffic 

queue has backed up from the crossing, the driver must be informed sufficiently in advance of 

the queue, not the crossing. If a steep grade and possible slippery conditions lead to the crossing, 

the driver must be informed sufficiently in advance of the hill. If the warning is specific to 

heavy trucks, placement criteria must be based on stopping distance criteria for such vehicles. 

For in-vehicle messages, it may be possible to incorporate the specific message about HRI status 

with the general warning about HRI presence (e.g., obstacle is blocking rail crossing ahead). In 

no case should a general warning follow a specific warning about HRI status. 

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Recommendation 9-2: For in-vehicle systems, include advance information about 

fixed features and hazards at the HRI that is typically conveyed by conventional 

roadside signs 

The roadside signs listed below, which are included in the MUTCD (Federal Highway 

Administration, 2003), provide advance information about the HRI to all motorists. An ITSbased in-vehicle navigation or warning system could be used to notify motorists about these 

same conditions when the message is relevant, but not when the message is irrelevant. 

Signs located at, or in advance of, the HRI that may be supplemented by in-vehicle displays 

 EXEMPT crossing (W10-1a, R15-3) 

 TRAINS MAY EXCEED 80 MPH (W10-8) 

 NO TRAIN HORN (W10-9) 

 NO SIGNAL (W10-10) 

 NO GATES OR LIGHTS (W10-13) 

 USE NEXT CROSSING (W10-14a) 

 ROUGH CROSSING (W10-15) 

 TRACKS OUT OF SERVICE (R8-9) 

 Railroad tracks close to (within 100 ft) parallel roadway (W10-2, W10-3, W10-4) 

 Low ground clearance (W10-5) 

 Limited storage space near crossing (W10-11, W10-11a, W10-11b) 

 Skewed crossing (W10-12) 

 Number of tracks (R15-2) 

 Emergency notification sign (I-13, I-13a) (could be displayed on demand) 

[Also see: Recommendation 4-24] 

Rationale 

Although standard advance warning signs are usually only readable by an approaching motorist 

for a short period of time, in-vehicle notification could be triggered when the motorist is further 

upstream of the HRI and could remain readable (or audible) for a longer period of time after the 

motorist passes the fixed advance warning sign. Alternatively, in-vehicle systems may provide 

the capability to replay an alert message that was missed. In-vehicle systems may also provide 

information that is tailored more closely to the motorist’s needs, perhaps playing only a subset of 

the possible alerts and warning messages that are relevant to the motorist at the time or based on 

personal criteria established by the motorist [Also see: Recommendation 9-16]. The level of 

redundancy between in-vehicle warnings and roadside signage may be increased when the 

visibility of roadside signs is reduced by adverse weather or lighting conditions. 

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Recommendation 9-3: Provide motorists with additional advance information 

about transient conditions at the HRI that is not typically conveyed by 

conventional roadside signs 

In addition to the HRI information typically provided to motorists on roadside signs (see 

Recommendation 9-2), ITS-based systems should provide advance warnings to motorists (either 

via in-vehicle displays or roadside displays) about transient characteristics of the HRI that may 

present a special hazard. Such characteristics include the following: 

 Limited visibility at the HRI due to atmospheric conditions, such as fog, smoke, heavy 

rain, or snow 

 Hazardous road surface conditions near the HRI (ice on roadway) 

 Obstacles on or near the track (stalled vehicle, railway maintenance equipment, train 

stopped in HRI) 

 Queued traffic upstream of the HRI (this may be especially important where the approach 

to the HRI follows a curve or where sight distance to the HRI is otherwise limited) 

 Limited storage space beyond track due to a downstream traffic queue (with a warning to 

not stop on tracks) 

 Malfunctioning gates and lights 

Because no standard messages or icons exist for these hazards, displays should be evaluated for 

comprehension and should use a standard warning format [Also see: Recommendations 4-3 

through 4-7]. 

ITS technologies make it possible to detect transient hazardous conditions and to convey this 

information to roadway users. Advance warning of these conditions allows drivers more time to 

prepare and respond to the hazard. 

Recommendation 9-4: For advance information to motorists about potential 

hazards at the HRI, identify the hazard and advise the driver how to respond 

For example, in advance of a passive crossing, most drivers should be warned about the presence 

of the HRI and told to slow down and search for trains. Other drivers, such as school bus 

drivers, may be reminded to stop at the HRI and search for trains [Also see: Recommendation 

8-4]. 

Rationale 

Depending on the nature of the hazard and urgency of the warning, drivers may not know how to 

react. By briefly stating a recommended course of action, drivers do not have to spend time 

evaluating their possible responses. For extremely urgent warnings such as collision avoidance, 

the recommended course of action (i.e., STOP) may be more important than the reason for the 

warning. 

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Recommendation 9-5: Provide advance information about the HRI only to 

roadway users for whom the information is relevant 

Use warning system intelligence to limit advance information to those drivers for whom the 

information is important or to preclude the display for those drivers for whom it is clearly not 

relevant. The ability to do this depends on what attributes the ITS application can recognize. 

For example, the system might recognize vehicle attributes (e.g., clearance), special requirements 

(HAZMAT, school buses), planned route (through the vehicle’s navigation system or via 

tracking), or even driver attributes (e.g., familiarity with the specific HRI). If presentation of a 

message cannot be restricted to certain vehicles, it may sometimes be appropriate to identify the 

intended user by a message heading (e.g., TRUCKS) so that other road users do not have to fully 

process the message. 

Rationale 

Limiting the message to drivers who require it will help reduce message proliferation and 

improve credibility. This should benefit user acceptance, reduce annoyance, and promote 

attention to and compliance with the warnings [Also see: Recommendations 4-9, 4-18, 8-13]. 

Recommendation 9-6: Distinguish between active and passive crossings when 

providing advance information about HRI location 

Rationale 

Providing information about the type of crossing is helpful for setting roadway users’ 

expectations about the HRI (e.g., active crossings are more conspicuous, have more train traffic). 

Approaching motorists who know what type of HRI to expect may see the HRI sooner and react 

more appropriately than those who make an incorrect assumption about the type of HRI that they 

are approaching. 

9.3.2 Route Guidance 

Recommendation 9-7: Develop consensus standards for providing dynamic 

route guidance through or around HRIs 

These standards should evolve as technology changes to maintain a balance between the needs of 

the individual roadway user with the needs for overall traffic network efficiency and safety. ITS 

systems should be designed so that motorists appreciate the capabilities and limitations of the 

system and the need for overall traffic management, while retaining a sense of control over their 

own vehicles and route choices [Also see: Recommendations 4-5, 4-24, 5-12, 6-7, 8-6, 9-8]. 

Rationale 

It is possible to design roadside CMS messages and in-vehicle messages in such a way as to 

influence the number of motorists who divert to an alternative route (e.g., Dudek, 2003). A 

critical factor for controlling the number of motorists who divert may be the amount and 

specificity of information presented about delays and travel times (Lerner, Huey, & Harpster, 

1999; Lerner & Llaneras, 2000; Llaneras, Lerner, Huey, & Bensur, 1999). A route guidance 

system that is designed primarily to minimize individual personal travel time may have the 

unintended consequence of increasing congestion on alternate routes, possibly increasing safety 

risks and reducing the overall efficiency of the transportation system. Traffic management 

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systems and vehicle guidance systems that operate under the same set of consensus standards 

could be coordinated to provide a balance between the needs of individual roadway users, 

including emergency vehicles and transit vehicles, with the need for overall network efficiency. 

As standards for coordination between in-vehicle systems and infrastructure-based systems are 

developed, opportunities for public education and public comment may be helpful for reducing 

driver frustration and misunderstandings about the new technologies. Greater levels of 

acceptance and satisfaction may be achieved by helping motorists adopt valid mental models 

about how such systems operate and by considering their concerns during the design process. 

Recommendation 9-8: Standardize CMS messages for dynamic route guidance 

so that they have a consistent format with other CMS messages to motorists 

The following informational elements (AND EXAMPLES) given below are common to many 

types of CMS messages and should be considered when designing messages to convey route 

guidance information in advance of an HRI. Because of limitations on the amount of 

information that drivers can read and process while approaching the CMS (see Chapter 5), 

usually only a subset of the elements can be displayed; however, depending on the HRI condition 

to be reported, not all elements may be needed. 

 Descriptor of HRI condition. (TRAIN; FOG AT RR CROSSING; GATE

MALFUNCTION, VEHICLE STALLED ON TRACKS, TRAIN ACCIDENT)

 Location. (1/2 MILE, PAST MAIN ST, AT CLOVER) 

 Effect on travel. (15 MINUTE DELAY; NO THROUGH TRAFFIC; MAJOR DELAY; 

LANES REOPEN IN 5 MINUTES) 

 Audience for action. (LOW TRUCKS, ORLANDO, DOWNTOWN TRAFFIC) 

 Action. (REDUCE SPEED; LOOK FOR TRAINS; PREPARE TO STOP; USE OTHER 

ROUTES; USE ROUTE 18 SOUTH; USE OVERPASS ON SOUTH ST) 

 Good reason for following the action. (SAVE 9 MIN; AVOID 15 MIN DELAY;

AVOID COLLISION)

Although not all elements may be used in each message, the order of the elements should be 

preserved to maintain consistency with other CMS messages [Also see: Recommendations 4-5, 

4-24, 5-12, 6-7, 8-6, 9-7]. 

Rationale 

The message elements and element presentation order given above have been adapted from those 

proposed by Dudek (2003) as elements of the base message for incident and work zone messages 

presented on CMS. A consistent set of message elements and consistent ordering of elements 

support driver expectancies that may result in better driver performance. 

Recommendation 9-9: Route guidance concerning the HRI should be based upon 

the most current and complete information available 

To avoid diverting motorists to routes that end up being less favorable than the present route, 

recommendations to use an alternative route should be based on the best information possible. 

As ITS capabilities develop, such information may include current traffic flow and road 

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conditions on the alternative route or, if that is not available, historical traffic volume data (for 

the current time of day and day of week), predictions about the number of vehicles expected to 

divert, predictions about the expected time until the original route is open (whether the HRI is 

blocked because a train is moving through the intersection, a train is performing a switching 

maneuver, or an incident has occurred that has closed the HRI, etc.). Information about the 

direction and speed of all trains in the vicinity should also be considered with respect to the 

alternative route guidance plan. For example, motorists should not be diverted from their present 

route to avoid a delay caused by a train traveling through the HRI if the diversion takes them to 

another HRI where a second train is approaching. Physical characteristics of the alternative 

route and the driver’s vehicle should also be considered. Large trucks should not be diverted 

through underpasses that are too low, over bridges with low-weight restrictions, or through 

narrow city streets that require sharp turns [Also see: Recommendations 4-8, 8-12]. 

Rationale 

Motorists who choose to follow an alternative route that actually turns out to be less efficient 

than their original route in terms of travel time may not be upset by small differences. In fact, 

research using realistically simulated trips found that drivers were confident that they had made 

the best route choice, even when they chose inefficient routes (Llaneras et al., 1999). On the 

other hand, drivers have an interest in knowing if they made the correct choice (Wenger et al., 

1990; Khattak et al., 1991); if it is obvious that the recommended alternative route is inferior in 

terms of travel time, or because of conflicts like those mentioned above, they may become 

frustrated and lose confidence in the system. Therefore, it is important for algorithms that 

provide alternative routing information near the HRI to incorporate many sources of information 

on both fixed and transient local roadway and rail conditions so that routing information and 

guidance is as accurate as possible. 

Recommendation 9-10: Provide motorists with dynamic route guidance 

information that incorporates predicted as well as current conditions at the HRI 

For real-time in-vehicle systems and for Web-based or other pre-trip route planning systems, 

predictions about the status of an HRI as far as 15–20 minutes in advance may be useful for 

approaching motorists, especially where train schedules are regular or where alternative routes 

across the railroad right-of-way are far from the intended route. Re-routing motorists across 

train tracks to avoid a predicted HRI-related delay upstream on the planned route may be 

considered, but in all cases safety of the motorist should take precedence over potential 

reductions in trip time. 

Rationale 

With ITS technologies such as GPS, it may be feasible to track train movements far in advance 

of the HRI. Drivers may be more willing to change routes if a projected status is available, 

particularly if there is some indication given of the confidence level of the prediction. Based on 

experimental findings (Lerner & Steinberg, 2000), projections of about 15–20 minutes ahead are 

compatible with typical commuter trips, and the combination of current status and projected 

status provides adequate decision support for most commuter trips (Khattak, Schofer, & 

Koppelman, 1993). Conditions at HRIs due to the presence of a train or other incidents may 

change quickly; therefore, it is essential that predictions are updated frequently. 

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Recommendation 9-11: Support the driver’s navigational decisions by providing 

all relevant information about the HRI in advance of route diversion points 

Other information about the HRI that is unlikely to affect routing decisions may be presented to 

the driver after he/she has passed the route diversion point. 

Rationale 

If a condition exists at the HRI that may give the driver a reason to divert to an alternative route, 

the driver must receive this information early enough to have time to process the information, 

make a decision to divert (or not), and safely maneuver to the alternative route before it has been 

passed. Lerner and Llaneras (2000) have summarized the general issue in this way: 

Drivers want to receive traffic information [. . .] at locations where decisions can 

be made with respect to alternative routes (Dudek et al., 1971; Lerner & 

Steinberg, 2000). Usually, if advice is not followed, most often it is because it is 

given too late (Bonsall & Joint, 1991). The point in time during the journey at 

which the driver receives information regarding the route and traffic conditions 

affects the probability that the driver will divert to an alternative route (Allen 

et al., 1991; Khattak et al., 1991). Therefore, information should be 

communicated while opportunities to divert still exist. 

[Also see: Recommendation 4-11] 

Recommendation 9-12: Provide a driver-oriented reason when an alternative 

route is recommended to divert around the HRI 

In many cases, the primary reason to divert to an alternative route will be to reduce travel time. 

Rationale 

Different drivers have different motivations and different preferences regarding reasons that they 

would elect to divert to an alternative route. As long as route choice remains the driver’s 

decision, any recommendation to divert to another route should be accompanied by some 

rationale that the driver may consider in making a route choice. For information presented on a 

CMS, Dudek (2003) has described this message element as the “good reason for following the 

action.” One important reason for diverting to another route is to reduce travel time. Lerner and 

Llaneras (2000) have noted that “numerous studies of driver decisionmaking as well as efforts to 

quantitatively model actual trip-making (Mahmassani & Liu, 1996; Aty & Jovanis, 1997) agree 

in finding that trip time is the dominant factor in route selection.” A secondary preference factor 

that may influence route recommendations is roadway function class, where, in general, drivers 

prefer higher class roadways; however, for urban commuters some bias may exist to avoid 

extended freeway trips (Aty & Jovanis, 1997). Lower path complexity, clearly designated routes 

(e.g., marked with route numbers), lower traffic density and level of traffic interaction, fewer 

traffic signals, fewer turns, and lower costs also tend to be preferred by drivers (Khattak et al., 

1991; Lerner & Llaneras, 2000). For some drivers, the secondary factors may be sufficient 

reasons to divert to an alternative route. 

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Recommendation 9-13: If an alternate route is recommended instead of the 

primary route across the HRI (driver’s typical route or normal best choice route), 

provide an estimate of travel time on the alternative route 

Rationale 

Lerner & Llaneras, 2000 previously made this recommendation. When drivers are given 

guidance to take an alternative route, the estimated trip time becomes a key piece of information 

that they wish to know (Lerner, Huey, & Harpster, 1999). Drivers will be more likely to comply 

with the route guidance if the estimated trip time is included and accurate; however, it may be 

preferable to design travel time estimation algorithms with a slight bias toward overestimating 

trip times so that underestimates occur less frequently than overestimates. This is because 

commuters are less tolerant of underestimates than overestimated times (Mahmassani & Liu, 

1996). 

Recommendation 9-14: Emphasize quantitative information over qualitative 

information when expressing delays associated with the HRI 

Rationale 

For delays associated with traffic incidents, people generally prefer quantitative indications (e.g., 

12-minute delay) more than qualitative statements (e.g., moderate delay) (Lerner, Huey, Zador, 

Duncan, & Harpster, 1998; Llaneras et al., 1999). Providing temporal information, such as delay 

time or travel time, is one of the most important factors influencing route choice (Lerner, Huey, 

Zador, Duncan, & Harpster, 1998). Quantitative information about traffic delays yields higher 

diversion rates than qualitative information alone (Khattak, Kanafani, & Colletter, 1994). 

Recommendation 9-15: Recommend alternative routes when opportunities for 

significantly reduced travel times exist, as defined by the driver’s personal 

preferences or when emergency situations arise at the HRI 

An alternative route recommendation should not be given unless that route is significantly better 

than the present route. At all other times, alternative route information should be available upon 

request, subject to applicable ATIS standards concerning system features that are appropriate for 

use in vehicles that are in motion. Lerner and Llaneras (2000) recommended certain threshold 

values for the amount of expected travel time savings necessary to suggest a diversion from a 

planned route. A general-use value for this threshold is 18 percent of the travel time remaining 

but not less than 1 minute. If user-specific preferences and conditions are known, the following 

threshold values are recommended: 

 Drivers with a low tolerance for late arrival: 5 percent (if current route jeopardizes ontime arrival) 

 Drivers who are unfamiliar with the area: 20 percent 

 Drivers who have specified route criteria other than time (e.g. scenic, costs):

20-25 percent

 Where the estimated time on the alternative route is highly variable: 20–25 percent 

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Rationale 

Following nonemergency advisories about adverse conditions at the HRI, alternative route 

information should be available to the driver upon request but should not be presented 

automatically, unless triggered by the motorist’s preset criteria. Presenting information to 

drivers automatically when they do not expect it may contribute to driver distraction and 

information overload. Many drivers are likely to be annoyed by the automatic presentation of 

alternative routing information and advance information about the HRI that they have not 

specifically requested. They may even try to disable the system, perhaps while they are driving. 

Under certain circumstances, however, alternative route information may be relevant even to 

drivers who usually do not change routes. When emergency situations arise that require a 

change of route, motorists should be informed about alternative routes, perhaps in a coordinated 

way that best supports public safety. 

Drivers who are already en route have a bias to stay on their current route, even when small 

travel time savings is possible on other routes. Only when the travel time savings becomes 

sufficiently large will drivers divert to an alternate route. While little empirical evidence exists 

to quantify the threshold values given above, these are best estimates from the existing data 

(Lerner & Llaneras, 2000). 

9.3.3 User Control 

Recommendation 9-16: Give the user control over the types of advance 

information about the HRI that will be presented in-vehicle and the conditions that 

will trigger recommendations for selecting alternative routes 

In-vehicle systems should allow users to tailor the operation of the system to their preferences. 

Although many types of advance information about the HRI may be available, consider 

providing user options to suppress information that is not desired. In addition, algorithms should 

trigger recommendations about alternative routes that incorporate individual driver preferences. 

Rationale 

Motorists will have different needs regarding advance information about HRIs and route 

guidance. If certain aspects of the system are annoying, distracting, or do not meet the user’s 

needs, the system may be completely disabled. By user configuration options, however, the 

motorist’s sense of control, and the information provided may be more useful, making it more 

likely that he or she will use the system. Drivers are likely to be more satisfied with (and follow 

the advice given by) an in-vehicle system in which route diversion recommendations reflect their 

own personal decision criteria. Lerner & Llaneras, 2000 gave a similar rationale for customized 

route diversion systems. In that study, personal characteristics related to the use of traffic 

information were age, gender, spatial ability, education level, and local familiarity with the 

roads. 

Several reasons exist as to why the information needed by one driver approaching the HRI may 

differ from that needed by another. Drivers who are in a familiar area where they frequently 

travel may not want to receive alerts about the mere presence of a downstream HRI, while 

drivers who are traveling in an unfamiliar area, perhaps at night, may want to be alerted to the 

presence of HRIs. Drivers who are very concerned about reducing their travel times may 

appreciate automatic alternative route recommendations that save them only a few minutes, 

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while other drivers may prefer to receive route guidance only upon request or, for example, when 

the expected travel time advantage of an alternative route exceeds a limit that they set, such as 

5 minutes. 

Table 13 lists several hypothetical drivers along with categories of HRI information that may be 

most useful to them. The categories given include the following types of information: 

 HRI ahead. Distance, name of road that intersects tracks 

 Train approaching. Estimated time until HRI is blocked, time until HRI is clear, train 

type, multiple trains approaching 

 Fixed features at HRI. Unusual crossing geometry, no gates, number of tracks 

 Transient conditions at HRI. Ice, gates malfunctioning, traffic backups, construction, or 

maintenance work in progress 

 Alternative routing recommendations. Automatic or on-demand routing guidance to 

avoid delays, hazardous conditions, or to match user route preferences 

These information categories are not specific recommendations for system design. Table 13 is 

meant only as an illustration of the potential differences in information needs of different 

roadway users. Real drivers may choose to receive different combinations of HRI information 

on in-vehicle displays than those shown. 

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Table 13. Information needed by drivers in advance of the HRI 

Types of Information Needed in Advance of HRI 

Train HRI Alternative 

HRI Approaching HRI Fixed Transient Routing 

Driver Ahead HRI Features Conditions Recommendations 

Urban 

Commuter 

Small Town 

Residents 

Delivery 

Truck 

Driver 

Tourist 

School Bus 

Driver 

No Yes No Yes Yes 

(Familiar (Familiar (May want to 

with all with all HRIs minimize travel 

HRIs in encountered. time and travel 

area) Conventional time variability) 

roadway 

signage is 

sufficient.) 

No Yes No Yes No 

(Familiar (Familiar (Knows alternative 

with all with all HRIs routes and little 

HRIs in encountered. benefit of rearea) Conventional routing exists) 

roadway 

signage is 

sufficient.) 

Yes Yes Yes Yes Yes 

(May be (May want to 

driving in minimize travel 

unfamiliar time, may be 

area) unfamiliar with 

area) 

Yes Yes Yes Yes Yes 

(May be (Unfamiliar with 

driving in area) 

unfamiliar 

area) 

Yes Yes Yes Yes No 

(Required (Driver is (Must follow a 

to stop at familiar with fixed route) 

all HRIs) route, but 

additional 

information 

may improve 

safety.) 

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10. Enforcement and Control of Vehicles 

Originally, these guidelines were to include a chapter to provide human factors guidance for ITS 

applications that deal with enforcement or direct vehicle control at the HRI. In reviewing the 

technologies and issues, however, it became apparent that neither direct intervention in vehicle 

control nor automated enforcement applications provide meaningful ITS human factors guidance 

needs at this point. 

10.1 Control of Vehicles 

If an errant vehicle is on a course to enter the HRI when a train is in hazardous proximity, it may 

be possible to intervene directly and prevent the vehicle from reaching the point of conflict. 

Such intervention could take two forms. One approach is to provide an infrastructure-based 

barrier between the vehicle and the train dynamic envelope. The other approach is to directly 

intervene in vehicle operation (braking or throttle) through telematic control. 

None of the physical barrier systems deployed or under serious consideration appear to involve 

intelligent control of barrier deployment. Rather, the barrier is always activated when a train is 

approaching, as an additional element of a normally gated system (see Chapter 3). Therefore, 

this is not an ITS application. No intelligent application of the barrier occurs. Although it is 

conceivable that an active barrier could be designed to deploy only when an errant vehicle is 

sensed, this does not appear to be evolving, and it is not clear what, if any, human factors issues 

might be involved in deployment other than informing road users about the presence of the 

device. Obviously a major challenge in developing an intelligently deployed barrier would be to 

reliably detect and define threat situations in a manner that allowed enough time and distance to 

stop vehicles of various sizes and to do so without causing frequent nuisance deployments and 

without causing injuries from nontrain collisions (collision with barrier, collision with another 

vehicle, run off road). Deployment of the VAB for minor crossing violations is likely to result in 

frequent capture of vehicles that were not in danger of colliding with trains. At the other 

extreme, if only very late, major infractions activate the barrier, drivers may perceive that minor 

infractions are acceptable, and the rate of minor violations may increase. 

Motorists’ reactions to VAB deployment would be an important area for study. VABs, if 

implemented at HRIs, would be novel systems, and vehicle capture events should be rare. 

Therefore, drivers who are captured (or about to be captured) are likely to be surprised and 

confused. Driver confusion may result in any of a variety of reactions before and during contact 

with the VAB, including attempting to accelerate, brake, turn, or not reacting at all. Once the 

vehicle is brought to a stop, drivers may be confused, embarrassed, frightened, or panicked. 

They may worry about injuries to themselves or passengers, damage to the vehicle, their distance 

from the approaching train, or the possibilities of blocking traffic or receiving a traffic citation. 

In their confusion, they may take unsafe actions, such as attempting to accelerate through the 

VAB or reversing hastily and risking a collision with queued traffic. 

Drivers who strike the VAB are not the only ones whose reaction must be considered. VAB 

deployment would also affect surrounding drivers. If a vehicle strikes a VAB, the path of 

following vehicles will be obstructed until it is retracted. Drivers may attempt to turn around or 

even attempt to cross the tracks using opposing lanes (if the deployed VAB does not span the 

entire roadway) or by leaving the roadway, which may be very hazardous. 

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If intelligent barrier systems are developed, it will be necessary to investigate the many potential 

effects on driver behavior and the overall implications for roadway safety. At this point, 

however, little indication exists for how such systems might operate. 

No serious consideration of direct intervention in vehicle emergency control at rail crossings 

appears to exist, and, in fact, opinions the project team have received in discussions with 

government, industry, and research experts has discouraged this concept. There appears to be 

little support in the United States for such intervention across the span of ITS applications, not 

just HRIs. There has been ITS research activity related to infrastructure-based control of vehicle 

speed and path on automated highway lanes (e.g., Bishop, 2001). This is a case, however, where 

the driver voluntarily cedes normal control to the intelligent system, not a case where the system 

intervenes automatically in a potential crash situation. Furthermore, the interest has primarily 

been in improving roadway capacity rather than vehicle safety. Visions of the automated 

highway system have been reduced in terms of scale, degree of intervention, and timetable 

(Bishop, 2001). Considerable work has occurred on vehicle-based crash avoidance warnings 

(e.g., National Highway Traffic Safety Administration, 2002), especially for various vehiclevehicle crash scenarios (e.g., forward collision warning), lane keeping, and road departure. In 

addition to not being directly relevant to vehicle-train crash scenarios, however, the development 

of this area has clearly focused on warnings, as opposed to autonomous braking or steering. 

Perhaps the most relevant parallel in the area of ITS development for roadway applications is the 

area of roadway intersection collision warnings. Here the infrastructure (independently or 

cooperatively with vehicle-based systems) must detect a threat from vehicles traveling on 

conflicting (roadway) paths and intervene in a timely way to help avoid a collision. In 

discussing this program area with FHWA staff, it is again clear that direct intervention in 

dynamic control of vehicles in traffic is not the current strategy. Thus, although it is technically 

conceivable that an ITS application could directly brake or steer an errant vehicle at an HRI, the 

clear consensus in both roadway and highway-rail communities at this time is that this is not the 

recommended approach. Overall, very significant safety and policy concerns regarding direct 

intervention in vehicle emergency control, and no mature or evident emerging systems exist. 

Such systems would also require cooperative technologies in the vehicle. Support for such 

systems does not appear to exist in the HRI area in the foreseeable future. A great many 

unknowns exist regarding the potential safety and human factors issues for such HRI systems. 

Therefore, the most reasonable guidance is that direct infrastructure control of braking or 

steering at the HRI is not recommended without a more substantial research base. 

Thus at this time it does not appear warranted to propose human factors guidance for either 

intelligent barriers or systems that intervene directly in vehicle control. Barrier systems 

investigated to date do not have intelligent deployment and are not ITS applications. 

10.2 Automated Enforcement 

Automated enforcement is a means of applying intelligent sensing of vehicle actions to detect 

violators and identify them (by recording license plates, and sometimes images of drivers) for 

traffic citation. Automated enforcement of traffic signal violations at roadway intersections is 

increasingly common in the United States, though it remains controversial and is not as 

widespread as in Europe and Australia. Because enforcement of violations at HRIs is difficult 

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and usually quite limited, automated enforcement would appear to be a promising approach.

13 

As indicated in Chapter 3, however, automated enforcement at HRIs has not been adopted for 

wide-scale deployment in any jurisdiction, although several field demonstrations do exist, 

suggesting that it may reduce illegal track crossings. 

Although automated enforcement is an ITS application, few requirements for human factors 

guidance exist. The major issues for greater deployment are technological (reliable detection and 

vehicle recognition), legislative, judicial, and societal (e.g., Blackburn & Gilbert, 1995). A 

recent set of operational guidelines for red light camera systems (Federal Highway 

Administration & National Highway Traffic Safety Administration, 2005) emphasizes the need 

for public education and warning signs to alert motorists that cameras are in use. Although some 

human factors issues related to automated enforcement may exist, it is not clear if any of these 

are unique to the HRI application. Furthermore, even for the roadway intersection application, 

little basis exists on which to provide such guidance. In a major review of red light camera 

enforcement, McGee and Eccles (2003) concluded that “to date, there have not been any research 

and effectiveness evaluations conducted to address or answer the question of what factors related 

to the intersection design or operations, the use of warning signs, the level of fines, or any public 

outreach, have on observed crash changes.” One human factors question of interest is in how to 

use signage to most effectively influence driver behavior. This question must be addressed on 

both a specific-crossing and systemwide basis. McGee and Eccles discuss the alternatives of 

posting warning signs at camera-equipped sites versus systemwide signing but no good basis 

exists for recommendations, even for the highway intersection case. Thus, at this point, human 

factors guidance does not exist regarding automated enforcement at the HRI. 

13 One reviewer expressed the view that automated enforcement will not be successful if the traffic and train control 

system does not “make sense” to the road user. If the crossing system is not meaningful or trains are likely to block 

crossings for extended periods, cameras will not change motorist behavior. This reviewer further argued that traffic 

control practices with poor credibility for the driver (e.g., certain speed limits or stop signs at grade crossings) “may 

be teaching the motorist that the devices are not of real value.” 

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11. Light Rail Transit 

11.1 Background 

The emphasis of this chapter is on issues that are unique to, or particularly relevant for, the 

highway-LRT intersection. Many of the human factors problems for highway-LRT intersections 

are similar as those for conventional HRIs; therefore, readers interested in LRT should also 

consult the relevant sections in the rest of this document. Chapter 3 and Chapter 9 discuss 

MTWs for LRT, and Chapter 9 gives general guidance about train arrival warnings. Chapter 7 

discusses displays for pedestrians. Other sources of information on safety at highway-LRT 

intersections also may be helpful (Korve et al., 1996; Coifman & Bertini, 1997; Transit 

Cooperative Research Program, 1999; Farran, 2000; Siques, 2001, 2002). 

LRT facilities are found in urban and suburban areas where highway-LRT intersections have a 

large volume of crossing traffic and a greater variety of roadway users than is found at a typical 

HRI on a conventional railroad. Various types of track alignments have been used to integrate 

LRT systems into cities, and these usually result in a close proximity between LRT tracks and 

roadways (Korve et al., 1996). In fact, light rail vehicles (LRVs) often operate on semiexclusive or shared LRV right-of-way with motor vehicles, creating the need for integration of 

rail traffic control systems and highway traffic control systems. As traffic volumes on roadway 

systems grow, increasingly sophisticated levels of cooperation between highway and rail signal 

systems may be implemented to alleviate congestion and prevent gridlock. One form of 

cooperation between systems allows LRVs to pass through signalized highway intersections 

without waiting, by preempting the traffic signals at these points. 

Traffic signal preemption refers to “the transfer of the normal operation of a traffic signal to a 

special control mode for the purpose of serving special vehicles or for other tasks that require 

termination of the normal traffic control” (Obenberger & Collura, 2001). When a signalized 

highway intersection is located near an HRI, the effects of control activities at one location can 

affect the other, with potential safety consequences. For example, downstream of the highwayLRT intersection signalized intersections may cause traffic queues to back up across the tracks. 

Additionally, roadway traffic waiting for an LRV to clear the HRI may queue up for a 

considerable distance, blocking roadway intersections upstream of the highway-LRT 

intersection. Traffic signal preemption is not in itself viewed as an ITS application unique to 

HRI, so the general issue of preemption is not included as a separate chapter in this report. ITS 

technologies, however, may provide opportunities to improve preemption implementations. 

Advance preemption algorithms will likely require LRV detection further in advance of the HRI 

and ITS technologies, such as GPS, which may play an important role in specifying and 

coordinating train movements. Although advance preemption strategies may be implemented at 

signalized intersections near conventional railroad crossings, the topic is included this chapter 

because preemption is used extensively at and near highway-LRT intersections. 

Highway-LRT intersections are usually found in visually complex metropolitan environments 

that contain many TCDs, advertising signs, buildings, complex roadway geometry, and high 

volumes of vehicular and pedestrian traffic. Large vehicles, such as buses and delivery trucks, 

may block the motorist’s view of the roadway ahead, behind, or to either side. All of this visual 

complexity makes it difficult to recognize highway-LRT intersections and to detect approaching 

LRVs. 

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Visibility of LRVs may also be a problem for bicyclists and pedestrians, especially at crossings 

adjacent to light rail stations. The cognitive demands due to motor vehicle traffic, advertising 

displays, and crowds make it more likely that pedestrians will not notice an approaching LRV. 

Other pedestrians who may be visiting the particular city for the first time may not be familiar 

with the operational characteristics of LRVs or the risks that they present (also see Chapter 7). 

Highway-LRT intersections are often located close to, or are part of, existing highway-highway 

intersections, and, in the environments where they exist, it may be difficult for approaching 

motorists to distinguish which intersections have LRT cross traffic. As a consequence, the 

motorist’s expectations of events at these intersections may be more appropriate for a standard 

highway-highway intersection, and these false expectations can lead to dangerous behaviors, 

such as turning in front of an approaching LRV. 

11.2 Key Human Factors Issues and Need for Guidance 

11.2.1 Issue: Conspicuity of Highway-LRT Intersections and LRVs in Highly 

Complex Urban Environments 

Highway-LRT intersections often appear to be standard highway-highway intersections to the 

roadway user, and LRVs tend to be less conspicuous than conventional trains. They are smaller 

and much quieter, and they travel in environments where they may be masked by noise and 

visual clutter. In addition, because LRT tracks often run along medians or on other right-ofways that are parallel to the roadway, LRVs and highway vehicles are often oriented in the same 

direction. This makes LRVs much less conspicuous to parallel traffic. The LRV profile is 

smaller when seen head-on, and the LRVs are especially difficult to detect when approaching a 

driver from behind. The lack of conspicuity presents a problem for motorists and nonmotorized 

roadway users. 

11.2.2 Issue: Conflicting Needs of Different Roadway Users at the Highway-LRT 

Intersection 

The typical urban environment for highway-LRT intersections is likely to have a wide variety of 

different roadway users and types of vehicles that are not commonly found at standard HRIs 

located outside of urban centers. Besides automobiles, roadway traffic at highway-LRT 

intersections is likely to include many taxi-cabs, buses, long limousines with low-ground 

clearance, and several types of straight trucks used for deliveries. All of these urban vehicles 

have a tendency to double-park, which can further obscure the visibility of LRVs. Other users of 

the highway-LRT intersection may include motorized scooters, bicycle couriers, street vendors 

with push carts, and possibly even horse-drawn vehicles (e.g., Hansom cabs). 

Large numbers of pedestrians, including those who have sensory, cognitive, or physical 

disabilities, may cross the highway-LRT intersection as well. All of these users share the need to 

detect LRVs and to know when it is safe for them to cross the intersection; however, in some 

cases, the needs of one group may conflict with the needs of another group. For example, 

wheelchair users require smooth ramps and continuous surfaces, while pedestrians who are 

visually impaired may prefer the unambiguous tactile boundaries provided by curbs. Similarly, 

auditory signals at the highway-LRT intersection may be essential for pedestrians with visual 

impairments, but ineffective for motor vehicle operators, and possibly annoying to local roadway 

users who have businesses or residences near the intersection. ITS technologies may enable 

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warnings to be tailored for different roadway users. For example, in-vehicle displays could 

present warnings to heavy truck operators about limited storage space downstream of the LRT 

tracks. 

11.2.3 Issue: Traffic Congestion Near the Highway-LRT Intersection and 

Preemption of Traffic Signals 

The primary objective of preemptive control is to clear conflicting traffic from the HRI before 

the train’s arrival. This may introduce conflicts for roadway users. For example, pedestrian 

crossing phases may be abruptly terminated, and pedestrians in the process of crossing the 

highway intersection may be in conflict with vehicles clearing the area. Other conflicts arise 

when multiple LRVs in close proximity preempt the traffic signals at a shared intersection. 

Multiple preemptions may cause some phases of the traffic signal cycle to be minimized or 

skipped entirely. This is particularly dangerous when the protected left turn phase is skipped. 

Impatient motorists, thinking that the signal is malfunctioning, may proceed against the signal 

and turn left into the path of an approaching LRV. 

The criteria for preemption and the determination of the most effective procedures at highwayLRT intersections and conventional HRIs are complex issues that preclude simple guidance. In 

developing its guidance on recommended practice for preemption of traffic signals near railroad 

grade crossings with active warning devices, the Institute of Transportation Engineers (1997) 

stated that 

Preemption of traffic signals for railroad operations is very complex and must be 

designed and operated for a specific location, often with unique conditions. With 

the extremely large number of variables involved, it is difficult [. . .] to simply 

quantify time or distance components. 

One of the difficulties in preemption is that it typically relies on the same circuitry as that used 

for train detection for control of the rail crossing signals and gates. This means that typically 

about 20 to 30 seconds of advance time exists in which to implement the preemption strategy and 

clear the conflicting traffic. Advance preemption (starting highway signal preemption sequences 

before activation of railroad warning devices) can be achieved by adding earlier train detection 

points. This can establish a clearance phase to reduce traffic cues downstream from the HRI. 

Sometimes very long track circuits are required to achieve the necessary amount of advance train 

detection time to implement complex advance preemption strategies. ITS technologies, 

however, offer greater opportunities to detect trains in advance, estimate arrival times, and 

implement more effective and less disruptive preemption methods. Venglar, Jacobson, and 

Engelbrecht (2000) discuss these techniques and their possibilities, and Korve et al. (2001) 

discuss many of the technical issues for implementing LRT preemption or advance preemption. 

11.2.4 Issue: Conflicts for Motorists Turning in Front of LRVs 

Vehicles turning in front of LRVs is one of the most common causes of collisions at signalized 

highway-LRT intersections. Farran (2000) has provided the following summary of conditions 

where these turning collisions occur: 

 Motorists make illegal left turns across the LRT right-of-way immediately after 

termination of their green left-turn signal. They know it will still take a few seconds for 

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the parallel traffic to enter the intersection from their stopped position; however, they are 

unaware that an LRV is rapidly approaching the intersection, typically from behind. 

 Motorists violate the left-turn signal when leading left-turn indications to proceed are 

preempted (eliminated) by an approaching LRV. Usually, this illegal movement is not a 

conscious choice on the part of the motorist, who has simply learned to expect the green 

turn indication before the through movement. 

 Motorists waiting to turn left across the LRT tracks become impatient as a result of red 

time extensions resulting from multiple LRV preemptions and illegally turn across the 

LRT right-of-way in the belief that the signal is malfunctioning. This type of accident is 

most likely to occur when the traffic signal does not recover to the left-turn movement 

after the LRV has cleared the intersection. 

 Motorists violate active No Left/Right Turn (R3-2/R3-1) signs at signalized intersections 

with permissive turns (i.e., without an exclusive turn signal indication). 

 Motorists violate a right-turn signal indication activated by an approaching LRV because 

they do not sufficiently know the vehicle code. Most motorists fail to recognize that it is 

not possible to turn right on red whenever a red right-turn signal indication (i.e., red turn 

arrow) is active. 

A number of non-ITS countermeasures have been proposed for these problems (Farran, 2000; 

Korve et al., 2001), but this is an area where ITS-based countermeasures could also be effective. 

11.2.5 Issue: Roadway Users’ Understanding of Potential Hazards at the HighwayLRT Intersection and Compliance with TCDs 

Roadway users may have misconceptions about the operation of LRVs and may not fully 

appreciate the risks involved in crossing the LRT tracks. For example, pedestrians may not 

understand that the LRV dynamic envelope extends beyond the boundary of the tracks, and they 

may stand too close, especially if other factors are at play, such as being unfamiliar with the area, 

being impaired by alcohol, or being at the front of a pressing crowd. Unlike motor vehicles such 

as buses, LRVs are generally not obligated to (and may not be able to) yield to pedestrians. This 

inconsistency may violate the expectations of some pedestrians who think that LRVs operate 

more like buses than trains. In addition, some pedestrians who tend to take the shortest possible 

path to reach their destination (even if this path involves trespassing along LRT right-of-ways or 

violates the geometry of established pedestrian pathways at the highway-LRT intersection) may 

not understand the level of risk associated with their actions. Other pedestrians, who do not have 

a driver’s license, or who may not understand signs printed in English, may violate the directions 

given by TCDs because they do not understand either the meaning of the message or the 

appropriate response. 

Motorists may also not fully appreciate the risks of violating TCDs, such as posted regulatory 

signs that prohibit driving on the LRT tracks, stopping on the tracks, making turns across the 

tracks, or passing a stopped train. ITS applications may be able to detect errant pedestrians and 

motorists and provide them with additional specific and more urgent warnings beyond the 

general regulatory and advisory signs designed to be seen by all roadway users. 

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11.3 Recommendations 

Table 14 groups recommendations for LRT under two topics. Each topic includes individual 

recommendation statements. 

Table 14. Recommendations for LRT 

Uses of ITS applications at highway-LRT intersections 

1. Use ITS applications for highway-LRT intersections when they fulfill a need or solve a problem that 

cannot be addressed as effectively by other technologies. 

2. Use automated enforcement of vehicles at the highway-LRT intersection to deter hazardous 

behaviors. 

3. Detect potential violators of left-turn prohibitions across LRT right-of way and warn them to stop. 

4. Detect pedestrians who are standing in a hazardous location and warn them. 

5. Supplement blank out signs that prohibit turns across the LRT right-of-way with an active indication 

that an LRV is approaching. 

6. Use ITS technologies to enhance conspicuity of highway-LRT intersections and LRVs approaching 

the intersection. 

7. Detect traffic queues and provide upstream active warnings against blocking the highway-LRT 

intersection. 

8. Provide an in-vehicle indication of nearby LRV. 

9. Provide an auditory warning at highway-LRT intersections for pedestrians. 

Preemption of traffic signals by LRVs 

10. Consider driver expectancies and behaviors when implementing ITS-based, advance preemption 

strategies at highway-LRT intersections. 

11.3.1 Uses of ITS Applications at Highway-LRT Intersections 

Recommendation 11-1: Use ITS applications for highway-LRT intersections when 

they fulfill a need or solve a problem that cannot be addressed as effectively by 

other technologies 

The use of ITS technologies to improve safety at highway-LRT intersections should be 

considered after first exploring conventional countermeasures. Simple, relatively low-cost and 

low-maintenance solutions, such as passive gates, pedestrian channeling treatments, barriers, 

passive gates, and conventional signs, may often be effective as or more effective than 

technology-intensive solutions. Non-ITS technologies should continue to be developed and 

implemented wherever they are most effective [Also see: Recommendation 7-8]. 

Rationale 

ITS-based systems that show promise when deployed sometimes prove to be less effective than 

conventional countermeasures. Additionally, a number of highly effective non-ITS strategies 

have been developed for improving the safety of pedestrians and motorists at highway-LRT 

intersections (Korve et al., 1996, 2001; Coifman & Bertini, 1997; Transit Cooperative Research 

Program, 1999; Farran, 2000; Siques, 2001). The implementation of ITS solutions should not be 

driven only by technical feasibility or by the false assumption that more sophisticated 

technologies will be more effective than conventional solutions. 

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Recommendation 11-2: Use automated enforcement of vehicles at the highwayLRT intersection to deter hazardous behaviors 

Photo enforcement or other automated enforcement strategies can deter illegal left turns across 

tracks, driving around lowered gates, and driving on the LRT right-of-way. Wherever 

implemented, conventional signs should be posted at or near the highway-LRT intersection to 

inform drivers that automated enforcement is being used. 

Rationale 

Criteria for using automated enforcement at HRIs is still not well established (see Chapter 10). 

Photo enforcement, however, has been an effective tool for reducing the number of violations at 

some highway-LRT intersections. For example, LACMTA introduced a photo enforcement 

program at highway-LRT intersections in the 1990s. In this system, inductive loop detectors 

detected vehicles driving around the tip of a horizontal gate arm. Citations were issued based on 

a series of two photographs taken of the violating vehicle. This program reduced the number of 

crossing-gate violations by 92 percent and reducing the number of LRT-motor vehicle collisions 

by 70 percent (Korve et al., 2001). Posting signs that inform drivers that automated enforcement 

is in use may inhibit risky behaviors. Violators who may have a low perceived risk of being 

struck by an LRV may be deterred from engaging in risky, illegal crossing behaviors if they 

perceive that it is highly likely that they will receive a citation based on evidence from automated 

enforcement equipment. Automated enforcement provides another reason (besides the obvious 

danger) not to drive under or around gates, or to violate other traffic controls. 

Recommendation 11-3: Detect potential violators of left-turn prohibitions across 

LRT right-of-way and warn them to stop 

ITS technologies can detect vehicles likely to cross the tracks in front of an approaching LRV. 

Left-turning vehicles that pull forward (some distance) beyond the stop line as if to make a left 

turn could be detected, and an auditory warning could be issued during periods when left turns 

are prohibited (LRV approaching). An in-vehicle system or an audible wayside signal could 

deliver such a warning. An activated blank-out sign, collocated with the sound source, could 

also be used to deliver a message to the potential violator [Also see: Recommendation 4-13]. 

Rationale 

One of the most common causes of LRT collisions is motorists making left turns across the 

tracks. Coifman & Bertini, (1997) recommended a warning for left-turning vehicles at highwayLRT intersections. Vehicles at highway-LRT intersections travel at relatively low speeds, 

particularly turning vehicles. Audible alarms are appropriate when the message calls for 

immediate action and when visual attention is otherwise engaged (McCormick & Sanders, 1982), 

as is the case for a driver making a left-turn maneuver. A wayside directional sound source(s) 

could be positioned close to the violating driver and would serve to stop the driver before 

entering the LRV dynamic envelope. If possible, the system should direct the violating driver’s 

attention toward the approaching LRV. In addition to alerting inattentive violating drivers about 

the hazard, a highly conspicuous auditory alarm may serve as a deterrent for drivers who 

knowingly violate the left-turn prohibition when the LRV is approaching. The auditory signal 

should be loud enough to be heard inside the violating vehicle and should make it obvious which 

vehicle triggered the alarm, calling attention to the violator. If local residents and business 

owners are annoyed by auditory signals, a highly conspicuous visual signal, such as a strobe, 

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could be considered. Whether auditory or visual, the alarm should be activated only by vehicles 

in danger rather than by each approaching LRV. 

Recommendation 11-4: Detect pedestrians who are standing in a hazardous 

location and warn them 

An ITS system may detect and warn pedestrians who violate automatic gates or who stand too 

close to the tracks when an LRV is approaching. The system may detect pedestrians standing 

within the dynamic envelope of an approaching LRV and issue an urgent audible or visual 

warning. If possible, this warning message should (1) be directed in such a way that it is clear 

which pedestrian is in violation, (2) convey that the pedestrian is currently in a dangerous 

position, and (3) clearly indicate what action should be taken to avoid the hazard [Also see: 

Recommendations 4-13, 7-6]. 

Rationale 

Despite the use of conventional pedestrian controls, such as gates, lights, signs, painted 

markings, and pavement treatments, various situations may arise where pedestrians violate these 

controls and end up within the hazard zone when an LRV is approaching. To handle these 

exceptional but dangerous situations, the passive or active crossing could have some controls that 

are reactive (Coifman & Bertini, 1997). Technology exists to detect the presence of pedestrians 

in specific locations, although the ITS applications under development on street crossings rather 

than rail crossings (e.g., Bechtel, Geyer, & Ragland, 2004). Activating a warning signal may be 

the last chance to capture the errant pedestrian’s attention with enough time to escape from being 

hit by the approaching LRV. The warning should be directed at the pedestrian (or pedestrians) 

who are in danger so that the violators do not assume that someone else triggered the warning, 

and the nature of the violation and danger should be clearly conveyed so that the pedestrian does 

not assume that merely standing off the tracks is a sufficiently safe. 

Recommendation 11-5: Supplement blank-out signs that prohibit turns across 

the LRT right-of-way with an active indication that an LRV is approaching 

The LRT approaching-Activated Blank-Out (W10-7) warning sign or a similar active indication 

should be used along with transient Turn Prohibition signs at highway-LRT intersections. Inpavement lights installed at the HRI and visible to turning vehicles may also be used as an active 

indication that an LRV is approaching. 

Rationale 

Turn prohibition signs are active only when an LRV is near, so drivers usually encounter the 

signs in the blanked-out state and are permitted to make turns across the tracks. An activated 

turn prohibition sign directly controls a driver’s behavior on only a small percentage of 

approaches to the intersection. (In fact, the sign only directly controls the first driver in the 

turning queue; the movement of other vehicles in the turn queue is restricted by vehicles 

blocking the way ahead of them.) This means that drivers have relatively little experience 

restricting their turn movements based on the turn prohibition signs. As a result, their normal 

visual scanning patterns, expectations, and habitual behaviors preceding the turning maneuver 

may lead them to proceed, unknowingly in violation of the turn prohibition. 

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Where transient turn prohibitions across LRT tracks are in effect, the supplemental LRT 

Approaching (W10-7) warning sign can provide motorists with rationale for the activated turn 

prohibitions and an indication of the hazard associated with violating the turn prohibition. 

Where the LRV preempts the traffic signal, the W10-7 sign notifies motorists that the left-turn 

phase is delayed because an LRV is approaching and not because the traffic detector circuit or 

some other part of the signal system has failed. If it is located near the Activated Blank-Out 

Turn Prohibition Sign (R3-1a, R3-2a), the LRV Approaching sign may enhance conspicuity and 

comprehension of the overall message. Alternatively, the LRT Approaching warning sign may 

be more effective if it is installed close to the turning driver’s line of sight, which may be 

relatively low for drivers who are scanning for gaps in traffic to make their turn. In-pavement 

lights may also be effective because they may be closer to the turning driver’s line of sight than 

the turn prohibition sign, which typically would be mounted above the roadway. 

Recommendation 11-6: Use ITS technologies to enhance conspicuity of highwayLRT intersections and LRVs approaching the intersection 

Conspicuity of LRVs is most important when they are approaching a highway-LRT intersection. 

The general recommendation is to use ITS technology to coordinate dynamic conspicuity 

enhancements between approaching LRVs and highway-LRT intersections. Strobe lights are one 

such enhancement that may be considered for use on the LRV and at the highway-LRT 

intersection. Auditory warnings are another [Also see: Recommendation 4-1]. 

Rationale 

A recognized need exists for enhancing the conspicuity of LRVs, especially with regard to 

maximizing the front-end visual impact of the LRV (Korve, 1996). Enhanced conspicuity is 

needed at all points where potential conflicts exist between roadway users and LRVs, but not 

necessarily at other locations where the LRV may be stopped or moving through a track section 

configured in an exclusive LRT alignment. Due to the already high level of visual clutter in the 

urban environment, it may not be sufficient (or aesthetically desirable) to introduce static 

conspicuity enhancements, such as more vivid paint colors, to LRVs. Roadway users may 

habituate to static conspicuity enhancements, but dynamic enhancements, such as a flashing 

light, may maintain their effects over long periods of time. However, because dynamic elements, 

such as flashing lights are one of the strongest forms of conspicuity enhancement available to 

traffic engineers, they should be used sparingly to retain effectiveness. Therefore, dynamic 

enhancements should activate to attract attention to the LRV only when the greatest potential for 

conflict exists, such as when the LRV is approaching a highway-LRT intersection. For example, 

the combination of two coordinated strobes at the intersection and on the LRV may promote 

perceptual grouping of the approaching LRV and the highway-LRT intersection, and, if a slight 

delay separates the coordinated flashes, an apparent motion effect may be created, providing an 

additional visual cue to enhance conspicuity. Laboratory studies have found that apparent 

motion effects significantly improve sensitivity and reduce reaction times for targets presented 

on simulated in-vehicle displays (Cohn, 1996). Coordinated auditory signals from LRV and HRI 

could help compensate for the fact that LRVs may approach relatively quietly. 

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Recommendation 11-7: Detect traffic queues and provide upstream active 

warnings against blocking the highway-LRT intersection 

Rationale 

One such system implemented in Edmonton, Canada, detects queues forming downstream of 

LRT tracks. Before a traffic queue actually builds back far enough to block the tracks, the 

system activates beacons mounted on a fixed Do Not Block Crossing sign located immediately 

upstream of the HRI (Korve et al., 2001). 

Recommendation 11-8: Provide an in-vehicle indication of nearby LRV 

If a visual in-vehicle display is used, consider the Light Rail Approaching—Activated Blank-Out 

(W10-7) warning sign given in the MUTCD (Federal Highway Administration, 2003). 

Supplement the visual indication with an in-vehicle auditory alert. 

Rationale 

Although measures designed to improve the conspicuity of the LRVs may help roadway users 

approaching the highway-LRT intersection from the crossing direction, roadway users who are 

traveling parallel to the LRT tracks often encounter LRT vehicles that approach them from 

behind. An in-vehicle alert may act as a countermeasure for the problem of drivers turning in 

front of an overtaking LRV. If an icon is used on an in-vehicle display to represent an 

approaching LRV, it should be consistent with the roadside display. Chapter 6 and Chapter 9 

give other guidance concerning in-vehicle displays and train arrival warnings. 

Recommendation 11-9: Provide an auditory warning at highway-LRT 

intersections for pedestrians 

Audio warning devices can help pedestrians who are visually impaired, especially at highwayLRT intersections where auditory warnings are not used because of noise concerns or at HRIs 

where vehicles are controlled by automatic gates, and auditory warnings are turned off once the 

gates descend to their horizontal position [Also see: Recommendations 7-4, 7-6]. 

Rationale 

LRVs are much quieter than conventional locomotives, and other noises in the urban 

environment can mask their approach. LRT pedestrian facilities should be accessible and usable 

by all pedestrians, including those who have impaired vision. ITS technologies can provide 

advance auditory warnings about approaching LRVs, as well as an all clear release indication 

when it is safe for pedestrians to cross the tracks. Various types of small audio warning devices 

for pedestrians have been implemented in Sacramento, California, and Portland, Oregon 

(Korve et al., 2001). These devices can be much quieter than wayside bells because they can be 

located and directed very close to pedestrians. 

169
11.3.2 Preemption of Traffic Signals by LRVs 

Recommendation 11-10: Consider driver expectancies and behaviors when 

implementing ITS-based, advance preemption strategies at highway-LRT 

intersections 

Many factors are considered when designing advance preemption strategies for highway-LRT 

intersections and nearby intersections; however, because of the large number of variables 

involved and the unique characteristics of each highway-LRT intersection, little universally 

applicable guidance or standards are available. Nevertheless, the following lists four guidance 

points concerning preemption that address human factors issues. The related human factors 

issues are explained in the rationale sections. Only some of these recommendations may be 

relevant for any particular highway-LRT intersection [Also see: Recommendations 4-7, 4-17]. 

Point 1 

Consider programming the traffic signals at intersections located adjacent to LRT crossings so 

that the protected left turns (across the tracks) from the parallel street follow the parallel street 

through movements (this sequence is called lagging left turns). Then, when exiting from LRT 

preemption, recover to the lagging left-turn phase first before serving cross-street traffic, if this 

can be done without dangerously long traffic queues building up on the cross street (Transit 

Cooperative Research Program, 1999). 

Rationale for Point 1 

The most prevalent type of LRV-motor vehicle accident involves motor vehicles turning across 

the LRT tracks (Farran, 2000). Point 1 is meant as a countermeasure to avoid some of the 

collisions involving vehicles turning left from a parallel roadway across LRT tracks located in 

the median. At intersections where a leading left-turn indication is used (protected left phase 

precedes the through movement), motorists expectations are violated when LRV preemption 

eliminates the green left-arrow phase. In this case, the normal sequence of traffic movements is 

altered, and the motorist may begin to make a left turn as soon as the cross traffic is stopped, 

anticipating that he/she will have a green left arrow without realizing that his/her left-turn 

maneuver is now prohibited due to the approaching LRV. By changing the signal phase 

sequence to have a lagging left indication (green left arrow follows the through movement and 

precedes the cross-street movement), left-turning motorists cannot anticipate the left turn signal 

based on the behavior of the cross traffic. Some LRT systems have adopted the lagging left-turn 

sequence with noted reductions in accidents at the locations where the change was made (Korve 

et al., 1996; Farran, 2000). 

The second part of Point 1, to recover from preemption sequence to the protected left-turn 

movement, addresses the problem that multiple LRV preemptions may violate the expectations 

of left-turning motorists. In these cases, the left-turn phase may not occur for multiple cycles, 

while some of the other traffic movements are allowed (e.g., through movement parallel to the 

tracks). This can lead impatient drivers to assume that the traffic signal is malfunctioning and to 

proceed across the tracks against the signal, without seeing that another LRV is approaching the 

intersection. When the preemption sequence is followed by the protected left-turn movement, 

impatient motorists can safely clear the intersection. Typically, if lagging left-turn sequence is 

used, the next movement to be served will be the through cross traffic, which may have a long 

queue. The ITE has supported this approach: “With frequent preemption (as with commuter rail 

170
or LRT operation), the traffic signal may be programmed to first service turn movements from 

the highway parallel to the track” (Institute of Transportation Engineers, 1997), as have several 

other authors (Korve et al., 1996; Farran, 2000; Korve et al., 2001). 

Point 2 

As an alternate preemption exit strategy, record the exact point in the signal cycle that was 

interrupted by preemption, and recover to that phase if only a small proportion of the phase time 

had been served before the preemption; or if most of the phase time had been served before 

preemption, recover to the next phase in the sequence (Transit Cooperative Research Program, 

1999). 

Rationale for Point 2 

An alternative to always recovering to the same traffic movement following the preemption 

sequence is to recover to the movement that was eliminated by the preemption sequence. This 

reduces the wait time for drivers whose signal phase was interrupted and who have been waiting 

at the intersection the longest. This may reduce their perception that the traffic signal system is 

malfunctioning, which can lead to drivers violating the traffic control signals. 

Point 3 

For low-speed LRT systems where it is possible to stop the LRV regularly at highway 

intersections, and where multiple LRVs may approach the same intersection in closely spaced 

intervals, consider denying LRV preemption requests in some circumstances and make the LRV 

wait for their turn to proceed. For example, consider canceling all LRV preemption requests that 

occur within a short period of time (1 or 2 minutes) following the activation of a preemption 

cycle. In addition, consider granting preemption requests only from LRVs traveling in one 

direction at certain times of the day, such as the peak load direction during peak commute hours 

(Farran, 2000). 

Rationale for Point 3 

This purpose of this recommendation is to reduce the incidence of multiple LRV preemptions 

occurring close together in time. Because of the long wait times, drivers experiencing multiple 

LRT preemptions may lose confidence in the traffic signal system and think that it is 

malfunctioning. By reducing successive LRV preemptions, the operation of the traffic signals 

will more closely match drivers’ expectations, and drivers may violate signals less frequently. 

Such restrictions on LRT preemption have been used in San Francisco and San Jose, California 

(Farran, 2000). In places where LRVs operate at speeds greater than 35 mph (55 km/h), it may 

be necessary to preempt traffic signals at certain highway-LRT intersections all the time. 

Point 4 

When using ITS technology to detect the approaching LRV far ahead of the intersection, account 

for changes in LRV speed by frequently updating the predicted arrival time at the HRI and 

making any necessary adjustments in the advance preemption traffic signal sequences or signal 

phase times, while preserving approximately constant warning times for active wayside controls. 

171
Rationale for Point 4 

To avoid conflicts between railroad active warnings and traffic signals, and to maintain roadways 

users’ confidence in the traffic control system, it is necessary to coordinate railroad warning 

devices and highway traffic controls beyond the initial train detection notification. LRT wayside 

warning devices often incorporate the constant warning time principle, so the train speed is 

monitored, and warning activation onset time adjusts accordingly to provide an approximately 

constant amount of time between activation of the wayside warning devices (lights, gates) and 

arrival of the LRV at the HRI. The interconnected traffic signal controller, however, typically 

operates on a single early detection input from the rail system and does not have any opportunity 

to adjust to delays in activation of wayside warnings caused by a decelerating LRV. A condition 

known as preempt trap may occur when the green track-clearance phase of the preemption 

sequence terminates before the railroad warning devices activate (Venglar, Jacobson, Sunkari, 

Engelbrecht, & Urbanik, 2000; Korve et al., 2001). This circumstance violates motorists’ 

expectations as they queue up across the tracks, unaware that an LRV is approaching, and they 

get trapped by the descending automatic gates. Some proposed solutions to preempt trap are to 

use longer track-clearance green times or to install a not-to-exceed timer that forces the 

activation of wayside warning devices (lights, gates) before the time that they would be activated 

by the railroad system for predicted train arrival at the HRI (Venglar et al., 2000). As ITS 

technologies produce longer advance preemption times (as may be needed for complex advance 

preemption strategies involving multiple traffic signals), systems may require more extensive 

communication between the rail system and traffic signal controllers, along with traffic 

controller algorithms that can intelligently adapt signal phase timings to better coordinate with 

the activation of wayside warning systems. Korve (1999) reached a similar conclusion: 

As more accurate train position information becomes available, traffic signal 

systems that are adjacent to highway-rail grade crossings could be equipped to 

accept more detailed data about train position, speed, and estimated time to 

crossing. With this data, the traffic signal controller would be able to 

accommodate train movements without the abrupt preemption process, improving 

highway-rail grade crossing safety and efficiency. 

Smoother transitions between normal traffic signal sequences and preemption sequences may 

result from incorporating ITS technologies. One example of Venglar, Jacobson and Engelbrecht 

(2000) proposed a smoother preemption transition algorithm, called the Transitional Preemption 

Strategy. Improvements to current preemption practices at highway-LRT intersections could be 

more consistent with roadway users’ expectations. Traffic signals may appear to operate more 

uniformly over time, providing a more consistent, predictable experience for roadway users at 

the highway-LRT intersection, whether an LRV is approaching or not. 

172
References 

Advanced Traffic Analysis Center. (2003). Moorhead area integrated train detection and 

traffic control system, Phase II-A Evaluation Report. Fargo, ND: Minnesota Department of 

Transportation. 

Alexander, G. J. (Ed.) (n.d.). Positive guidance in Maryland, guidelines and case studies. 

Hanover, MD: Maryland State Highway Administration. 

Alexander, G. J., & Lunenfeld, H. (1975). Positive guidance in traffic control. Washington, 

DC: Federal Highway Administration. 

Alexander, G. J., & Lunenfeld, H. (1998). In Ontario traffic manual Book 1, Appendix C: 

Positive guidance toolkit. Ontario, Canada: Ministry of Transport, Ontario. 

Allen, R. W., Stein, A. C., Rosenthal T. J., Zeidman, D., Torres, J. F., & Halati, A. (1991). 

Laboratory assessment of driver route diversion in response to in-vehicle navigation and 

motorist information systems. Transportation Research Record, 1306, 82-91. 

American Association of State Highway and Transportation Officials. (2001). A policy on 

geometric design of highways and streets (4th

 ed.). Washington, DC: American Association 

of State Highway and Transportation Officials. 

Askey, S., & Sheridan, T. (1996). Safety of high-speed ground transportation systems human 

factors phase II: Design and evaluation of decision aids for control of high-speed trains: 

Experiments and model. Washington, DC: Federal Railroad Administration. 

Aty, M. A., & Jovanis, P. P. (1997). Understanding driver route preferences, UC Davis 

experiment 2. (Unpublished draft report to Federal Highway Administration under Contract 

DTFH61-95-R-0017.) 

Aycin, M. F., & Benekohal, R. F. (2002). Performance evaluation of the pilot study of advisory 

on-board vehicle warning systems at railroad grade crossings. Urbana-Champaign, IL: 

Illinois Department of Transportation, ITS Program Office. 

Barfield, W., & Dingus, T. A. (1998). Human factors in intelligent transportation systems. 

Mawah, NJ: Lawrence Erlbaum Associates, Incorporated. 

Barlow, J., Bentzen, B., & Tabor, L. (2003). Accessible pedestrian signals: Synthesis and guide 

to best practice, final report. Research Results Digest 278 (Report no. NCHRP 3-62). 

Washington, DC: National Cooperative Highway Research Program, Transportation 

Research Board, National Research Council. 

Bechtel, A. K., Geyer, J., & Ragland, D. R. (2004). A review of ITS-based pedestrian injury 

countermeasures. In Proceedings of the Transportation Research Board’s 83rd Annual 

Meeting, Washington, DC. 

Beijer, D. (2004). Observed driver glance behavior at roadside advertising. Transportation 

Research Record, 1899, 96-103. 

Bell, C. A., Hunter-Zaworski, K. M., & Zaworski, D. D. (1997). Low volume highway-rail 

grade crossing treatments for the Oregon high speed rail corridor (Report no. FHWA-ORRD-97-08). Washington, DC: Federal Highway Administration. 

173
Bell, C. A., & Zaworski, D. D. (1997). Low volume highway-rail grade crossing treatments for 

the Oregon high speed rail corridor (Report no. FHWA-OR-RD-97-08). Washington, DC: 

Federal Highway Administration. 

Benekohal, R., Aycin, M., Sikaras, C., Johak, C., & Kennedy, T. (2000). Lessons learned and 

achievements in the development of an in-vehicle railroad warning system. Presented at the 

ITS America 10th Annual Meeting, Boston, MA. 

Bishop, R. (2001, August). Whatever happened to automated highway systems (AHS)? Traffic 

Technology International. Retrieved February 11, 2005, from the University of Washington 

Web site: http://faculty.washington.edu/jbs/itrans/bishopahs.htm 

Blackburn, R. R., & Gilbert, D. T. (1995). Photographic enforcement of traffic laws. NCHRP 

Synthesis of Highway Practice, 219. 

Bonsall, P. W., & Joint, M. (1991). Driver compliance with route guidance advice: The 

evidence and its implications. In Proceedings of the 2nd Vehicle Navigation & Information 

Systems Conference, 47-59. 

Botha, J. L., Zabyshny, A. A., Day, J. E., Northouse, R. L., Rodriguez, J. O., & Nix, T. L. 

(2002). Pedestrian countdown signals: An experimental evaluation–Volume 1. Retrieved 

April 12, 2005, from www.sanjoseca.gov/transportation/forms/report_pedcountdown.pdf 

Brisbane, G., & Vasiliou, A. (2002). Dynamic warning signs act as signs of rain. Vaisala News, 

159, 30-32. 

Campbell, C., Carney, C., & Kantowitz, B. H. (1998). Human factors design guidelines for 

advanced traveler information systems (ATIS) and commercial vehicle operations (CVO) 

(Report no. FHWA-RD-98-057). Seattle, WA: Battelle Human Factors Transportation 

Center Seattle. 

Campbell, J., Richman, J. B., Carney, C., & Lee, J. D. (2002). In-vehicle display icons and 

other information elements task F: Final in-vehicle symbol guidelines (Report no. FHWARD-99). Washington, DC: Federal Highway Administration. 

Carroll, A., Passera, A., & Tingos, I. (2001). Vehicle proximity alert system for highwayrailroad grade crossings prototype research (Report no. DOT/FRA/ORD-01/01). 

Washington, DC: Federal Railroad Administration. 

Carroll, A. A., & Warren, J. D. (2002). The use of photo enforcement at highway-rail grade 

crossings in the U.S. In Proceedings of the Transportation Research Board’s 81st Annual

Meeting, Washington, DC. 

Carter, M., Cluett, C., DeBlasio, A., Dion, F., Hicks, B., Lappin, J., Novak, D., Rakha, H., Riley, 

J., St-Onge, C., & Van Aerde, M. (2000). Metropolitan model deployment initiative San 

Antonio evaluation report (Report no. FHWA-OP-00-017). Washington, DC: U.S. 

Department of Transportation. 

Chappell, D., & Carroll, A. (2000). Comparative analysis of innovative high-priority ITS 

highway-rail grade crossing projects: Interim Report. Presented at the ITS America 10th 

Annual Meeting, Boston, MA. 

174
Chugh, J., & Caird, J. (1999). In-vehicle train warnings (ITW): The effect of reliability and 

failure type on driver perception response time and trust. In Proceedings of the Human 

Factors and Ergonomics Society 43rd Annual Meeting, 1012-1016. 

Cohn, T. (1996). Engineered visibility warning signals: Tests of time to react, detectability, 

identifiability and salience program, ITS-IDEA Program project final report. Washington, 

DC: Transportation Research Board. 

Coifman, B., & Bertini, R. (1997). Median light rail crossings: Accident causation and 

countermeasures (California PATH working paper UCB-ITS-PWP-97-13). Berkeley, CA: 

California PATH Program Institute of Transportation Studies. 

Coleman, F., & Venkataraman, K. (2001). Driver behavior at vehicle arresting barriers: 

Compliance and violations during the first year at the McLean site. Transportation Research 

Record, 1754, 68-76. 

Dewar, R. E. (2001). Railroad grade crossing accidents. In R.E. Dewar & P.L Olson (Eds.), 

Human factors in traffic safety (pp. 506-523). Tucson, AZ: Lawyers and Judges Publishing 

Company, Inc. 

Dewar, R. E., & Olson, P. L. (2001). Human factors in traffic safety. Tucson, AZ: Lawyers 

and Judges Publishing Company, Inc. 

DKS Associates. (2001). San Francisco pedestrian countdown signals: Preliminary evaluation 

summary. San Francisco, CA: San Francisco Department of Parking and Traffic. 

Driver Focus-Telematics Working Group. (2003). Statement of principles, criteria and 

verification procedures on driver interactions with advanced in-vehicle information and 

communication systems, version 3.0. Washington, DC: Alliance of Automobile 

Manufacturers. 

Dudek, C. L., (1991). Guidelines on the use of changeable message signs (Report no. FHWATS-90-043). Washington, DC: Federal Highway Administration. 

Dudek, C. L. (2002). Guidelines for changeable message sign messages: Final report (Report 

no: FHWA-RD-94-077). Washington, DC: Federal Highway Administration. 

Dudek, C. L. (2003). Developing standards and guidance for changeable message signs in the 

manual on uniform traffic control devices. Washington, DC: Federal Highway 

Administration. 

Dudek, C.L., & Huchingson, R.D. (1998). Results of human factors studies: Repetition of twoframe messages. VMS and HAR Project, Technical Memorandum 7296-5-10. Submitted to 

the New Jersey Department of Transportation. 

Dudek, C. L., Messer, C. J., & Jones, H. B. (1971). Study of design considerations for real-time 

freeway information systems. Highway Research Record, 363, 1-17. 

Dudek, C.L., Trout, N., Booth, S., & Ullman, G. (2000). Improved dynamic message sign 

messages and operations (Report no. FHWA/TX/-01/1882-2). Austin, TX: Texas 

Department of Transportation. 

Durkop, B. R., & Dudek, C. L. (2001). Texas driver understanding of abbreviations for 

changeable message signs. Transportation Research Record, 1748, 87-95. 

175
Edworthy, J., Loxley, S., & Dennis, I. (1991). Improving auditory warning design: 

Relationship between warning sound parameters and perceived urgency. Human Factors, 

33, 2, 205-231. 

Elvik, R. (2004). To what extent can theory account for the findings of road safety evaluation 

studies? Accident Analysis and Prevention, 36, 841-849. 

Endsley, M. R. (1995). Measurement of situation awareness in dynamic situations. Human 

Factors, 37, 1, 65-84. 

Endsley, M. R. (1996). Automation and situation awareness. In R. Parasuraman & M. Mouloua 

(Eds.), Automation and human performance: Theory and applications (pp.163-181). 

Hillsdale, NJ: Erlbaum. 

Evans, L. (1991). Traffic safety and the driver. New York: Van Nostrand Reinhold. 

Farran, J. I. (2000). No turns allowed–Controlling vehicles turning in front of LRVs. In 

Proceedings of the Transportation Research Board’s 79th Annual Meeting, Washington, DC. 

Federal Highway Administration. (2000). Advanced warning for railroad delays in San 

Antonio: Lessons learned from the metropolitan model deployment initiative (Report no. 

FHWA-OP-01-038). Retrieved April 13, 2005, from the Federal Highway Administration 

Web site: http://www.itsdocs.fhwa.dot.gov//JPODOCS/REPTS_TE//13284.html 

Federal Highway Administration. (2001). Intelligent transportation systems at highway-rail 

intersections, a cross-cutting study (Report no. FHWA-OP-01-149P). Washington, DC: 

Federal Highway Administration. 

Federal Highway Administration. (2003). Manual on uniform traffic control devices for streets 

and highways, 2003 edition. Washington, DC: Federal Highway Administration. 

Federal Highway Administration & National Highway Traffic Safety Administration. (2005). 

Red light camera systems: Operational guidelines. Publication no. FHWA-SA-05-002. 

Washington, DC: U.S. Department of Transportation. 

Federal Railroad Administration. (2002). Railroad safety statistics annual report 2000. 

Retrieved from the Federal Railroad Administration Web site: http://www.fra.dot.gov 

Federal Railroad Administration. (2003). Railroad safety statistics final report 2001. Retrieved 

from the Federal Railroad Administration Web site: http://www.fra.dot.gov 

Federal Railroad Administration. (2004). Railroad safety statistics final report 2002. Retrieved 

from the Federal Railroad Administration Web site: http://www.fra.dot.gov 

Fitzpatrick, K., Bartoskewitz, R., & Carlson, P. (1997). Demonstration of automated 

enforcement systems at selected highway-railroad grade crossings in Texas (Report no. 7­

927-2F). College Station, TX: Texas Transportation Institute. 

Fuller, R., & Santos, J. A. (2002). Human factors for highway engineers. New York: 

Pergamon. 

Garvey, P. M., & Mace, D. J. (1996). Changeable message sign visibility (Report no. FHWARD-94-077; Final Report). Washington, DC: Federal Highway Administration, U.S. 

Department of Transportation. 

176
Goolsby, M., Vickich, M., & Voigt, A. (2003). Railroad grade crossing monitoring system. 

Houston, TX: Texas Transportation Institute, and Austin, TX: Texas Department of 

Transportation. 

Grade crossing system tested at New Hyde Park. (2001). The New Hyde Park Illustrated News. 

Retrieved June 8, 2001, from the Anton Community Newspapers Web site: 

http://www.antonnews.com/illustratednews/2001/06/08/news/ 

Graham, R., & Mitchell, V. A. (1997). An evaluation of the ability of drivers to assimilate and 

retain in-vehicle traffic messages. In Y. I. Noy (Ed.), Ergonomics and safety of intelligent 

driver interfaces (pp. 185-201). Mahwah, NJ: Lawrence Erlbaum Associates. 

Green, P. (2001). Where do drivers look while driving (and for how long)? In R. E. Dewar and 

P. L. Olson (Eds.), Human factors in traffic safety (pp. 43-76). Tucson, AZ: Lawyers and 

Judges Publishing Company, Inc. 

Green, P., Levison, W., Paelke, G., & Serafin, C. (1995). Preliminary Human Factors Design 

Guidelines for Driver Information Systems (Report no. FHWA-RD-94-087). Washington, 

DC: Federal Highway Administration. 

Hanscom, F. R. (2000). Rural stop-sign controlled intersection accident countermeasure system 

device: Vehicle-behavioral evaluation. Presented at the ITS America 10th Annual Meeting, 

Boston, MA. 

Hanscom, F., & Dewar, R. (2001). Human factors. In J. L. Pline (Ed.), Traffic control devices 

handbook (pp. 19-47). Washington, DC: Institute of Transportation Engineers. 

Hendricks, D. L., Freedman, M., & Zador, P. L. (1999). Determine the conditions under which 

speeding and other problematic driving behaviors are hazardous. Draft final report volume 

I: Technical findings (Contract no. DTNH22-94-C-05020). Washington, DC: National 

Highway Traffic Safety Administration. 

Hoekstra, E., Williams, M., & Green, P. (1993). Development and driver understanding of 

hazard warning and location symbols for IVSAWS, Final report (Report no. UMTRI-93­

9311). Washington, DC: Federal Highway Administration. 

Huang, H. F., & Zegeer, C. V. (2000). The effects of pedestrian countdown signals in Lake 

Buena Vista. Retrieved April 12, 2005, from Florida Department of Transportation Web site: 

http://www.dot.state.fl.us/Safety/ped_bike/handbooks_and_research/research/CNTREPT.pdf 

Illinois Commerce Commission. (2002). Photo enforcement at highway-rail grade crossings: 

2001 status report to the general assembly (Transportation division working paper 2002-02). 

Chicago, IL: Illinois Commerce Commission. 

Institute of Transportation Engineers. (1997). Preemption of traffic signals at or near railroad 

grade crossings (Report no. RP-025A). Washington, DC: Institute of Transportation 

Engineers, Traffic Engineering Council. 

Insurance Institute for Highway Safety. (2005). Fatality facts 2004: Older people. Arlington, 

VA: Insurance Institute for Highway Safety. 

Jones, R. W. (2001). Guide and motorist information signs. In J. L Pline (Ed.), Traffic control 

devices handbook. Washington, DC: Institute of Transportation Engineers. 

177
Judd, D. B., & Wyszecki, G. (1975). Color in business, science and industry. New York: John 

Wiley and Sons. 

Kantowitz, B. H., Hanowski, R. J., & Kantowitz, S. C. (1996). Development of human factors 

guidelines for advanced traveler information systems and commercial vehicle operations: 

The effects of inaccurate traffic information on driver acceptance of in-vehicle information 

systems (Report no. FHWA-RD-96-145). Washington, DC: Federal Highway 

Administration. 

Khattak, A. J., Kanafani, A., & Le Coletter, E. (1994). Stated and reported route diversion 

behavior: Implications of benefits of advanced traveler information system. Transportation 

Research Record, 1464, 28-35. 

Khattak, A. J., Schofer, J. L., & Koppelman, F. S. (1991). Factors influencing commuters’ en 

route diversion behavior in response to delay. Transportation Research Record, 1318, 125­

136. 

Khattak, A. J., Schofer, J. L., & Koppelman, F. S. (1993). Commuters’ enroute diversion and 

return decisions: Analysis and implications for advanced traveler information systems. 

Transportation Research, 27A, 101-111. 

Khawani, V. (2001). “Second Train Coming” Warning sign demonstration project. 

Transportation Research Record, 1762, 32-36. 

Knoblauch, R., & Pietrucha, M. (1985). Motorists’ comprehension of regulatory, warning and

symbol signs, Volume II: Technical report (Contract no. DTFH61-83-C-00136). 

Washington, DC: Federal Highway Administration. 

Korve, H. W. (1999). Traffic signal operations near highway-rail grade crossings. NCHRP 

Synthesis of Highway Practice, 271. Washington, DC: Transportation Research Board. 

Korve, H. W., Farran, J. I., & Mansel, D. M. (1996). Integration of light rail transit into city 

streets (TCRP Report 17). Washington, DC: Transportation Research Board. 

Korve, H., Ogden, B., Siques, J., Mansel, D., Richards, H., Gilbert, S., Boni, E., Butchko, M., 

Stutts, J. C., & Hughes, R. G. (2001). Light rail service: Pedestrian and vehicular safety 

(TCRP Report 69). Washington, DC: Transportation Research Board. 

Koyani, S. J., Bailey, R. W., & Nall, J. R. (2003). Research-based web design & usability 

guidelines. Bethesda, MD: National Cancer Institute, National Institutes of Health. 

Lammert, J. K. (1999). Application of automated enforcement for highway-railroad grade 

crossings. In Compendium: Graduate Student Papers on Advanced Surface Transportation 

Systems 1999 (pp. 283-315). College Station, TX: Advanced Institute in Transportation 

Systems Operations and Management, Texas A&M University. 

Lee, J. D., Hoffman, J. D., & Hayes, E. (2004). Collision warning design to mitigate driver 

distraction. In Proceedings of the SIGCHI Conference on Human Factors in Computing 

Systems, 6, 65-72. 

Lerner, N. D., Benel, D. C. R., & Dekker, D. K. (1995). Understanding driver performance 

variability and perception of risk (Contract no. DTFH 61-92-R-00207). Washington, DC: 

Federal Highway Administration. 

178
Lerner, N. D., Dekker, D. K., Steinberg, G. V., & Huey, R. W. (1996). Inappropriate alarm 

rates and driver annoyance (Draft report under contract no. DTNH22-91-C-07004). 

Washington, DC: National Highway Traffic Safety Administration. 

Lerner, N. D., Huey, R., & Harpster, J. (1999). Driver opinion of message requirements for 

advanced traveler information systems. In Proceedings of the 43rd Annual Human Factors 

and Ergonomics Society Meeting, 962-967. 

Lerner, N. D., Huey, R., Zador, P., Duncan, G., & Harpster, J. (1998). Information selection 

experiment (Unpublished draft report to the Federal Highway Administration under contract 

no. DTFH61-95-R-00017). 

Lerner, N. D., Kotwal, B. M., Lyons, R. D., & Garner-Bonneau, D. J. (1996). Preliminary 

human factors guidelines for crash avoidance warning devices (Report no. DOT HS 808 

342). Washington, DC: National Highway Traffic Safety Administration. 

Lerner, N. D., & Llaneras, R. E. (2000). Driver information demand guidelines: Ensuring that 

traffic and routing information conforms to driver information needs (Contract no. DTFH61­

95-C-00017). Washington, DC: Federal Highway Administration. 

Lerner, N. D., Llaneras R. E., McGee, H., & Stephens, D. (2002). Traffic-control devices for 

passive railroad-highway grade crossings (NCHRP Report 470). Washington, DC: 

Transportation Research Board. 

Lerner, N. D., Llaneras, R. E., McGee, H., Taori, S. & Alexander, G. (2003). Additional 

investigations on driver information overload (NCHRP Report 488). Washington, DC: 

Transportation Research Board. 

Lerner, N. D., Ratte, D., & Walker, J. (1989). Driver behavior at rail-highway crossings 

(Project no. DTFH61-88-Z-00145). Washington, DC: Federal Highway Administration. 

Lerner, N. D., Singer, J., & Huey, R. (2004). Animation and color in changeable message signs 

used for traffic control device applications Task 1 report: Information search and summary 

(Interim report under contract no. DTFH61-01C-00049, Task 7). Washington, DC: Federal 

Highway Administration. 

Lerner, N. D., & Steinberg, G. (2000). Driver information requirements for decision making 

(Unpublished draft report to the Federal Highway Administration under contract no. 

DTFH61-95-R-00017). 

Llaneras, R. E., Lerner, N. D., Dingus, T. A., & Moyer, J. (2000). Attention demand of IVIS 

auditory displays: An on-road study under freeway environments. In Proceedings of the 44th 

annual meeting of the Human Factors and Ergonomics Society, 238-241. 

Llaneras, R. E., Lerner, N. D., Huey, R. W., & Bensur, A. (1999). ATIS simulator laboratory 

study: Influence of ATIS information and traffic density levels on driver en-route decision 

making (Draft report to Federal Highway Administration under contract no. DTFH61-95-R00017). Rockville, MD: Westat. 

Llaneras, R., & Singer, J. (2002). Inventory of in-vehicle technology human factors design 

characteristics, final report (Contract no. DTNH22-99-D-07005). Washington, DC: 

National Highway Traffic Safety Administration. 

179
Lunenfeld, H. & Alexander, G. J. (1990). User’s guide to positive guidance (3rd

 ed) (Report no. 

FHWASA-90/017). Washington, DC: Federal Highway Administration. 

Lyman, S., Ferguson, S. A., Williams, A. F., & Braver, E. R. (2001). Older driver involvements 

in police-reported crashes and fatal crashes: Trends and projections. Arlington, VA: 

Insurance Institute for Highway Safety. 

Mahmassani, H. S., & Liu, Y. (1996). Day-to-day dynamics of commuter route choice behavior 

under real-time information. Presented at Planning and Transport Research and 

Computation (International) Co. Meeting, Austin, TX. 

Mahmassani, H. S., & Liu, Y. (1996). Pre-trip and en-route path switching decisions of 

commuters under real-time information: Laboratory experiment results (Unpublished report 

to the Federal Highway Administration under contract no. DTFH61-95-R-00017). 

Marshall, D., Lee, J. D., & Austria, A. (2001). Annoyance and urgency of auditory alerts for invehicle information systems. In Proceedings of the 45th Annual Meeting of the Human 

Factors and Ergonomics Society, 1627-1631. 

Maryland Mass Transit Administration & Sabra, Wang, and Associates, Inc. (2001). Second 

train coming warning sign demonstration project. Final report, transit cooperative research 

program (Project A-5A). Baltimore, MD: Maryland Mass Transit Administration. 

Massie, D. L., & Campbell, K. L. (1993) Analysis of accident rates by age, gender, and time of 

day based on the 1990 nationwide personal transportation survey. Final report (Report no. 

UMTRI-93-7). Ann Arbor, MI: University of Michigan Transportation Research Institute. 

McCormick, E. J., & Sanders, M. J. (1983). Human factors in engineering and design. New 

York: McGraw-Hill Book Company. 

McGee, H. W., & Eccles, K. A. (2003). Impact of red light camera enforcement on crash 

experience. ITE Journal, 73, 3, 44-48, 54. 

McKinley, D. W. (2001). Traffic signals. In J. L. Pline (Ed.), Traffic control devices handbook 

(pp. 261-363). Washington, DC: Institute of Transportation Engineers. 

Miller, J. M., Lehto, M. R., & Frantz, J. P. (2001). Warnings and safety instructions: Annotated 

and indexed. Ann Arbor, MI: Fuller Technical Publications. 

Mortimer, R. G. (1988). Human factors in highway-railroad grade crossing accidents. In G. A. 

Peters & B. J Peters, (Eds.), Automotive engineering and litigation, volume 2 (pp.35-69). 

New York: Garland Law. 

Mortimer, R. G., Blomberg, R. D., Alexander, G. J., & Vingilis, E. (2004). Human factors in 

traffic crashes. In I. Noy & W. Karkowski (Eds.), Handbook of Human Factors in Litigation 

(Part III, pp. 1-65). Boca Raton, FL: Taylor and Francis. 

Multer, J., Rudich, R., & Yearwood, K. (1998). Human factors guidelines for locomotive cabs 

(Report no. DOT-VNTSC-FRA-98-8). Washington, DC: Federal Railroad Administration. 

National Highway Traffic Safety Administration. (2002). Automotive collision avoidance 

system field operation test: Warning cue implementation summary report (Report no. DOT 

HS 809 462). Washington, DC: National Highway Traffic Safety Administration. 

180
Nowakowski, C., Lenneman, J., Kojima, M., & Green, P. (1999). The development of trafficinformation Web-site design guidelines (Report no: UMTRI-99-30). Ann Arbor, MI: The 

University of Michigan Transportation Research Institute. 

Nowakowski, C., Green, P., & Kojima, M. (2000). How to design a traffic-information Web 

site: A human factors approach. ITS Quarterly, 8, 41-51. 

Noy, Y. I. (1997). Ergonomics and safety of intelligent driver interfaces. Mahway, NJ: 

Lawrence Erlbaum Associates, Incorporated. 

Obenberger, J., & Collura, J. (2001). Transition strategies to exit preemption control: State-ofthe-practice assessment. Transportation Research Record, 1748, 72-79. 

O’Hara, J. M., Higgins, J. C., Persensky, J. J., Lewis, P. M., & Bongarra, J. P. (2004). Human 

factors engineering program review model (NUREG-0711, rev. 2). Retrieved May 26, 2004, 

from the U.S. Nuclear Regulatory Commission Web site: http://www.nrc.gov/readingrm/doc-collections/nuregs/staff/sr0711 

Oriol, N., Sheridan, T., & Multer, J. (2004). Supporting railroad roadway worker 

communications with a wireless handheld computer: Volume I: Usability for the roadway 

worker (Report no. DOT-VNTSC-FRA-04-02). Washington, DC: Federal Railroad 

Administration. 

Parasuraman, R. (1997). Humans and automation: Use, misuse, disuse, abuse. Human Factors, 

39, 230-253. 

Parkes, A. M., & Franzen, S. (1993). Driving future vehicles. Bristol, PA: Taylor and Francis, 

Incorp. 

Farradyne, P. B. (2002). Final report for the second train warning sign demonstration project 

on the Los Angeles metro blue line (Report no. FTA-CA-26-7017-01). Washington, DC: 

Federal Transit Administration. 

Pline, J. L. (1999). Traffic engineering handbook (5th ed.). Washington, DC: Institute of 

Transportation Engineers. 

Pline, J. L. (2001). Traffic control devices handbook. Washington, DC: Institute of 

Transportation Engineers. 

Popp, M. M., & Farber, B. (1991). Advanced display technologies, route guidance systems and 

the position of displays in cars. In A. G. Gale (Ed.), Vision in vehicles–III (pp. 219-225). 

Amsterdam: Elsevier Science. 

Post, T. J., Alexander, G. J., & Lunenfeld, H. (1981). A user’s guide to positive guidance (2nd 

ed.) (Report no. FHWA-TO-81-1, Final Report). Washington, DC: Federal Highway 

Administration. 

Roskam, A., Uneken, E., de Waard, D., Brookhuis, K., Breker, S., & Rothermel, S. (2002). 

Evaluation of the comprehensibility of various designs of a full colour information panel. 

Groningen, Nethetherlands: Groningen Rijksuniversiteitand. 

Rumar, K., Berggrund, U., Jerberg, P., & Ytterbom, U. (1976). Driver reaction to technical 

safety measures–studded tires. Human Factors, 18, 5, 443-454. 

181
Sanders, M. S., & McCormick, E. J. (1993). Human factors in engineering and design (7th

 ed.). 

New York: McGraw-Hill, Inc. 

Singer, J. P., Balliro, G. M., & Lerner, N. D. (2003). Manufacturers guide to developing 

consumer product instructions (T.P. Smith, Ed.). Washington, DC: U.S. Consumer Product 

Safety Commission. 

Siques, J. T. (2001). Pedestrian warning and control devices, guidelines, and case studies. 

Transportation Research Record, 1762, 18-24. 

Siques, J. T. (2002). Effects of pedestrian treatments on risky pedestrian behavior. 

Transportation Research Record, 1793, 62-70. 

Smiley, A. (2000, Winter). Auto safety and human adaptation. Issues In Science and 

Technology Online. Retrieved October 23, 2003 from the National Academies Press Web 

site: http://www.nap.edu/issues/17.2/smiley.html 

Smiley, A. (2000). Behavioral adaptation, safety, and intelligent transportation systems. 

Transportation Research Record, 1724, 47-51. 

Sobhi, N., & Kelly, M. (1999). Human factors recommendations for TMC design. Retrieved 

April 12, 2005, from Federal Highway Administration, Public Roads Web site: 

http://www.tfhrc.gov/pubrds/mayjun99/hfactors.htm 

Society of Automotive Engineers. (1993). Driver hand control reach (Document no. J287). In 

1993 SAE Handbook. Warrendale, PA: Society of Automotive Engineers. 

Society of Automotive Engineers. (2004). SAE recommended practice: Navigation and route 

guidance function accessibility while driving; draft recommended practice (Document no. 

J2364). Warrendale, PA: Society of Automotive Engineers. 

SRF Consulting Group, Inc. (1998). In-vehicle signing for school buses at railroad-highway 

grade crossings. Evaluation report. Minneapolis, MN: Minnesota Department of 

Transportation. 

SRF Consulting Group, Inc. (2000). Moorhead area integrated train detection and traffic 

control system: Phase one project report. St. Paul, MN: Minnesota Department of 

Transportation. 

Srinivasan, R., & Jovanis, P. P. (1997). Effect of selected in-vehicle route guidance systems on 

driver reaction times. Human Factors, 39, 2, 200-215. 

Staplin, L., Lococo, K., Byington, S., & Harkey, D. (2001a). Guidelines and recommendations 

to accommodate older drivers and pedestrians (Report no. FHWA-RD-01-051). 

Washington, DC: Federal Highway Administration. 

Staplin, L., Lococo, K., Byington, S., & Harkey, D. (2001b). Highway design book for older 

drivers and pedestrians (Report no. FHWA-RD-01-103). Washington, DC: Federal 

Highway Administration. 

Stevens, A., Quimby, A., Board, A., Kersloot, T., & Burns, P. (2002). Design guidelines for 

safety of in-vehicle information systems (Report no. PA3721/01). Crowthorne, England: 

Department of Transport and Local Government. 

182
Stutts, J., Feaganes, J., Rodgman, E., Hamlett, C., Meadows, T., Reinfurt, D., Gish, 

Mercandante, M., & Staplin, L. (2003). Distractions in everyday driving. Washington, DC: 

AAA Foundation for Traffic Safety. 

Tan, A., & Lerner, N. D. (1995). Multiple attribute evaluation of auditory warning signals for 

in-vehicle crash avoidance warning systems (Report no. DOT HS 808 535). Washington, 

DC: National Highway Traffic Safety Administration. 

Texas Transportation Institute. (1999). When every second counts [Electronic version]. Texas 

Transportation Researcher, 35, 2. Retrieved February, 2004, from Texas A&M University 

Web site: http://tti.tamu.edu/researcher/v35n2/everysec.stm 

Texas Transportation Institute. (2001). Train notification system alerts drivers [Electronic 

version]. Texas Transportation Researcher, 37, 4. Retrieved February, 2004, from Texas 

A&M University Web site: http://tti.tamu.edu/researcher/v37n4/train_notification.stm 

Tijerina, L., Kiger, S., Rockwell, T. H., & Tornow, C. E. (1995). Final Report–Workload 

assessment of in-cab text message system and cellular phone use by heavy vehicle drivers on 

the road (Contract no. DTNH22-91-07003). Washington, DC: National Highway Traffic 

Safety Administration. 

Traffic Engineering Council. (1997). Preemption of traffic signals at or near railroad grade 

crossings with active warning devices. Washington, DC: Institute of Transportation 

Engineers. 

Transit Cooperative Research Program. (1999). Light rail service: Vehicular and pedestrian 

safety (TCRP, Project A-13). Research Results Digest, 34. 

Transit Cooperative Research Program. (2002). Second train coming warning sign 

demonstration projects (TCRP Project A-5A). Research Results Digest, 51. 

Trans-Link Train Monitoring Project. (2002). Retrieved January 1, 2002, from Texas A&M 

University Web site: http://railview.tamu.edu/Rail_Monitoring_xml.htm 

Transportation Research Board. (2002). Transit: Intermodal facilities, rail transit, commuter 

rail, light rail transit, maintenance, and ferry transportation. Transportation Research 

Record, 1793. 

Treat, J. R. (1980). A study of precrash factors involved in traffic accidents. University of 

Michigan Highway Safety Research Institute Research Review, 10, 6; 11, 1, 1-35. 

Turner, S., & Polk, A. (1998). Overview of automated enforcement in transportation. ITE 

Journal, 68, 6, 20-29. 

Tustin, B. H., Richards, H., McGee, H., & Patterson, R. (1986). Railroad-highway grade 

crossing handbook–Second edition (Report no. FHWA-TS-86-215). Washington, DC: 

Federal Highway Administration. 

U.S. Access Board. (2002). Draft guidelines for accessible public rights-of-way. Retrieved 

January 3, 2005, from the U.S. Access Board Web site: http://access-board.gov/rowdraft.htm 

U.S. Access Board. (2004). ADA and ABA Accessibility Guidelines for Buildings and Facilities. 

Retrieved January 3, 2005, from the U.S. Access Board Web site: http://www.accessboard.gov/ada-aba/final.pdf 

183
U.S. Department of Defense. (1989). DoD military standards–1472D human engineering 

design criteria for military systems equipment and facilities. Retrieved October 31, 2001, 

from the Joint Chiefs of Staff Web site: 

http://jcs.mil/htdocs/teinfo/directives/soft/humeng.html 

Van Houten, R. (2001). Animated LED “eyes” traffic signals (ITS-IDEA Project 73, Final 

Report). Washington, DC: Transportation Research Board. 

Venglar, S. P., Jacobson, M. S., & Engelbrecht, R. J. (2000). Enhanced algorithm for railroad 

preemption of traffic signals. In Proceedings of the Transportation Research Board’s 79th 

Annual Meeting, Washington, DC. 

Venglar, S. P., Jacobson, M. S., Sunkari, S., Engelbrecht, R. J., & Urbanik, T. (2000). Guide for 

traffic signal preemption near railroad grade crossing (Report no. FHWA/TX-01/1439-9). 

Austin, TX: Texas Department of Transportation. 

Vedantam, S. (2004). Human response to technology scrutinized: Emotional interactions draw 

interest of psychologists and marketers. The Washington Post Online Edition. Retrieved 

June 6, 2004, from the Washington Post Web site: http://www.washingtonpost.com/wpdyn/articles/A20688-2004Jun6.html 

Walker, J., Alicandri, E., Sedney, C., & Roberts, K. (1990). In-vehicle navigation devices: 

Effects on the safety of driver performance, final report (Report no. FHWA-RD-90-053). 

Washington, DC: Federal Highway Administration. 

Wenger, M. J., Spyridakis, J. H., Haselkorn, M. P., Barfield, W., & Conquest, L. (1990). 

Motorist behavior and the design of motorist information systems. Transportation Research 

Record, 1281, 159-167. 

Westat. (1999). Task 1: Evaluation of research (Interim report under project no. NCHRP 3­

57). Washington, DC: Transportation Research Board. 

Wierwille, W., & Tijerina, L. (1996). An analysis of driving accident narratives as a means of 

determining problems caused by in-vehicle visual allocation and visual workload. In A. G. 

Gale et al. (Eds.), Vision in vehicles–V (pp. 79-86). Amsterdam: Elsevier Science. 

Zaworski, D. D., Bell, C. A., Hunter-Zaworski, K. M., & Sacmaci, M. (1995). ITS applications 

to high speed rail grade crossing safety. Seattle, WA: Transportation Northwest. 

Zwahlen, H. T., Adams, C. C., & DeBald, D. P. (1988). Safety aspects of CRT touch panel 

controls in automobiles. In A. G. Gale et al. (Eds.), Vision in vehicles–II (pp. 335-344). 

Amsterdam: Elsevier Science. 

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Appendix.

List of Recommendations

CHAPTER 4: MESSAGE FACTORS 

Factors to ensure message is noticed 

1. Ensure adequate conspicuity of the message. 

2. Limit displays to needed messages. 

Factors to improve comprehension of message 

3. Ensure legibility and audibility under probable operating conditions. 

4. Make the desired road user action explicit and unambiguous. 

5. Use standard or common wording, abbreviations, images, and formats. 

6. Test for road user comprehension. 

7. Promote compatibility with the road user’s mental model of how the system works. 

Factors to improve credibility of message 

8. Assure that information is accurate and timely. 

9. Minimize the frequency of all categories of nonuseful alerts. 

10. Consider road user perceptions about the motivations and criteria of traffic-rail authorities. 

Factors to improve compliance with the message 

11. Provide adequate response time, consistent operation, and controlled workload. 

12. Avoid excessively conservative criteria. 

13. Provide road user feedback regarding noncompliance and unsafe behaviors. 

Distinguishing safety-critical messages 

14. Design safety-critical messages to be immediately recognizable as urgent safety alerts and 

discriminable from other messages. 

Choice of message display mode 

15. Consider the advantages and disadvantages of alternative display modes. 

Unintended consequences of the message 

16. Avoid driver distraction. 

17. Consider the potential effects of automation complacency and risk compensation (behavioral 

adaptation). 

18. Minimize annoyance. 

19. Anticipate road user misuse of information. 

Message appropriateness for specific road users 

20. Customize ITS messages for the current situation. 

21. Devise messages for effective communication with non-English-literate road users. 

22. Devise messages for effective communication with older road users. 

23. Devise messages for effective communication with road users having disabilities. 

System considerations 

24. Provide uniform messages and displays across information sources and sites. 

25. Provide compatible message timing among information sources. 

26. Manage information demand and driver workload. 

27. Integrate ITS functions. 

28. Avoid the development of inappropriate road user expectancies about the roadway and railway 

network. 

29. Integrate ITS HRI displays and controls with the roadway traffic control system. 

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CHAPTER 5: ROADSIDE DISPLAYS 

Location of roadside signs 

1. Locate roadside displays relative to the hazard or decision point. 

2. Locate ITS roadside displays to avoid driver information overload. 

Conspicuity and legibility of roadside displays 

3. Make displays conspicuous but not overly distracting. 

4. Use positive contrast orientation (legend lighter than background) for self-luminous roadside displays. 

5. Keep luminance contrast of CMS between 8 and 12. 

6. Adapt visual displays to ambient lighting. 

7. Design displays for the visual acuity of licensed drivers. 

8. Sequential (multiphase) messages may be used on CMS for non-crash avoidance messages, with 

certain constraints. 

9. Limit message length for CMS displays. 

Animation in roadside displays 

10. Use animation selectively. 

Ensuring that messages are understood 

11. Follow a systematic message design process. 

12. Use standardized words and symbols. 

13. Use icons where appropriate. 

14. Use color-coding selectively to enhance understanding. 

In-pavement lights 

15. Ensure that in-pavement warning lights, if used at the HRI, are installed and operated so that they are: 

(1) effective, (2) consistent with other TCDs at the HRI, and (3) consistent with other traffic control 

applications of in-pavement lights. 

Nonvisual roadside displays 

16. Use acoustic signals to supplement HRI roadway visual displays. 

17. Consider using tactile signals at the HRI. 

CHAPTER 6: IN-VEHICLE DISPLAYS 

Choice of mode 

1. Use visual displays to present spatially-based information and for long or complex messages 

(provided the vehicle is not in motion). 

2. Use audible presentation modes for delivering high-priority information requiring immediate action. 

3. Use speech-based messages when high degree of detail is required and the meaning of other sounds 

may be ambiguous or forgotten under stress. 

4. Consider using visual icons rather than text-based messages. 

5. Consider using auditory icons in place of tones or beeps. 

Visual display attributes 

6. Locate visual displays for warning systems within the driver’s field of view, without obstructing the 

driver’s view of the dash controls, gauges, or mirrors. 

7. Use standardized icons and graphics for in-vehicle warnings. 

8. Ensure that visual display elements (characters, text, graphics, etc.) are sufficiently large to be read in 

moving vehicles and that the information can be assimilated with a few brief glances. 

9. Use some means to attract driver attention to the display (e.g., flashing lights) if the system relies 

exclusively on a visual display to communicate information (no audible warnings/messages). 

Auditory (nonspeech) display attributes 

10. Audible warnings should be sufficiently loud so they can be detected and understood by the driver in 

the presence of background noise. 

11. Limit the number of different warning tones to three or four easily discriminable sounds. 

12. Auditory alerts should be used to notify drivers of high-priority messages, changes in status, and to 

augment signage information. 

13. Tonal signals (nonverbal auditory signals) should use a frequency range between 500 and 3000 Hz 

and burst durations of about 100 ms. 

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Speech display attributes 

14. Avoid the use of synthetic speech displays. 

15. Messages that require an immediate response should consist of a single word or short phrase, and they 

should be understood immediately. 

16. Provide a means for repeating speech messages. 

17. Ensure that messages are easily differentiated from other speech in vehicles. 

User control and adjustment 

18. Complex information and control interactions should not be designed for use in a moving vehicle. 

19. If multiple input or adjustment controls are present, design the controls so drivers can easily 

differentiate among the controls and their functions. 

Location of controls 

20. Locate system controls within the driver’s reach, with the most frequently used or accessed controls 

closer to the driver’s line of sight and reach. 

21. Match the type of control used to the types and levels of functions to be controlled. 

Operational issues related to in-vehicle systems 

22. At actively controlled crossings with gates, in-vehicle warnings should be timed (coordinated) with 

the activation of the crossing gates or other active warning devices. 

23. Provide system compatibility and integration. 

24. Indicate system status. 

25. Tailor information presented within the vehicle to match the driver’s specific situation and needs (e.g., 

approaching an HRI, waiting at an HRI, EMS, etc.) 

26. Evaluate the potential effects of behavioral adaptation for new in-vehicle systems. 

CHAPTER 7: DISPLAYS FOR PEDESTRIANS 

Positioning the display 

1. Install visual displays in locations that are consistent with pedestrians’ expectations, close to the 

intended crosswalk, and within a 20-degree cone of the forward line of sight. 

2. Ensure that warning displays are configured so that they are conspicuous for pedestrians who are in 

the process of crossing the tracks when a train warning is issued, as well as for pedestrians who are 

approaching the HRI. 

3. Separate messages for motorist from messages for pedestrians. 

Accessibility of the warning 

4. Consider multiple modes of display when providing warnings or other information to pedestrians at 

the HRI. 

5. Include pedestrians who have disabilities in the design and testing process for new display features. 

Directed warnings 

6. Consider providing a targeted last chance warning system for pedestrians who are in immediate 

danger. 

Use of conventional pedestrian control devices 

7. ITS displays for pedestrians should be used in conjunction with positive control devices, such as gates 

and barriers. 

CHAPTER 8: WARNINGS ABOUT TRAIN ARRIVAL 

Recommendations for Train Arrival Warnings 

Information provision (what to communicate) 

1. Display train-related information only if it fulfills a need. 

2. Limit the amount of information presented. 

3. Issue alerts about the presence of HRIs and warnings about the presence of trains. 

4. Present integrated, directly usable information. 

5. Design messages based upon information handling zones. 

6. Provide standardized message content on CMS at the HRI. 

7. Provide cues as to the direction of approaching trains. 

8. Provide a release indication. 

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Signal characteristics (how to communicate) 

9. Use CMS as a primary means to communicate HRI status. 

10. Consider conspicuity enhancements for visual displays. 

11. Avoid temporal countdown displays for motorists. 

12. Provide accurate and reliable information. 

13. Minimize nuisance warnings to drivers not in potential conflict. 

Timing of signals for train arrival warnings 

14. Issue warnings throughout the entire duration of the train event, but provide a way to reduce the 

nuisance potential of the warning. 

15. Inform roadway users at HRIs where extended advance warning times are used. 

Coordination with external controls 

16. Coordinate ITS warnings and non-ITS traffic control devices. 

Specific Recommendations for MTWs 

Message content and message comprehension for MTWs 

17. Use an active caution message. 

18. Convey all important elements of the warning message either explicitly or implicitly. 

19. Ensure complete message comprehension. 

20. Present consistent behavioral cues during multiple train events. 

Signal conspicuity for MTWs 

21. Attract the attention of at-risk road users. 

22. Enhance conspicuity with visual features. 

23. Ensure that both text and graphic display elements are legible. 

24. Supplement MTW displays with acoustic signals. 

Message timing and phasing for MTWs 

25. Initiate MTW before first train passes. 

26. Limit the length of message phase times. 

MTWs for drivers 

27. Use the following components of MTW displays for motor vehicle traffic. 

28. Install a roadway-based MTW display in a location appropriate for motor vehicle traffic. 

MTWs for pedestrians 

29. Provide an MTW to pedestrians at HRIs where more than one train often passes through the HRI in 

close proximity. 

30. Use the following components of MTW displays for pedestrians. 

31. Install an MTW display in a location appropriate for pedestrian traffic. 

CHAPTER 9: ADVANCE INFORMATION ABOUT THE HRI AND DYNAMIC ROUTE 

GUIDANCE 

Advance information about the HRI 

1. Provide advance information about HRI status and characteristics subsequent to a general warning 

about the presence of the HRI, except where this conflicts with other criteria for message placement 

or timing. 

2. For in-vehicle systems, include advance information about fixed features and hazards at the HRI that 

is typically conveyed by conventional roadside signs. 

3. Provide motorists with additional advance information about transient conditions at the HRI, which is 

not typically conveyed by conventional roadside signs. 

4. For advance information to motorists about potential hazards at the HRI, identify the hazard and 

advise the driver how to respond. 

5. Provide advance information about the HRI only to roadway users for whom the information is 

relevant. 

6. Distinguish between active and passive crossings when providing advance information about HRI 

location. 

Route guidance 

7. Develop consensus standards for providing dynamic route guidance through or around HRIs. 

8. Standardize CMS messages for dynamic route guidance so that they have a consistent format with 

other CMS messages to motorists. 

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9. Route guidance concerning the HRI should be based on the most current and complete information 

available. 

10. Provide motorists with dynamic route guidance information, which incorporates predicated, as well as 

current, conditions at the HRI. 

11. Support the driver’s navigational decisions by providing all relevant information about the HRI in 

advance of route diversion points. 

12. Provide a driver-oriented reason when an alternative route is recommended to divert around the HRI. 

13. If an alternate route is recommended over the primary route across the HRI (driver’s typical route or 

normal best choice route), provide an estimate of travel time on the alternative route. 

14. Emphasize quantitative information over qualitative information when expressing delays associated 

with the HRI. 

15. Recommend alternative routes when opportunities for significantly reduced travel times exist as 

defined by the driver’s personal preferences or when emergency situations arise at the HRI. 

User control 

16. Give the user control over the types of advance information about the HRI that will be presented in 

the vehicle, and the conditions that will trigger recommendations for selecting alternative routes. 

CHAPTER 10: ENFORCEMENT AND CONTROL OF VEHICLES 

Vehicle arresting barriers (VABs) 

Automated enforcement (AE) 

CHAPTER 11: LRT 

Uses of ITS applications at highway-LRT intersections 

1. Use ITS applications for highway-LRT intersections when they fulfill a need, or solve a problem that 

cannot be addressed as effectively by other technologies. 

2. Use automated enforcement of vehicles at the highway-LRT intersection to deter hazardous 

behaviors. 

3. Detect potential violators of left turn prohibitions across LRT right-of way and warn them to stop. 

4. Detect pedestrians who are standing in a hazardous location and warn them. 

5. Supplement blank out signs which prohibit turns across the LRT right-of-way with an active 

indication that an LRV is approaching. 

6. Use ITS technologies to enhance conspicuity of highway-LRT intersections and LRVs approaching 

the intersection. 

7. Detect traffic queues, and provide upstream active warnings against blocking the highway-LRT 

intersection. 

8. Provide an in-vehicle indication of nearby LRV. 

9. Provide an auditory warning at highway-LRT intersections for pedestrians. 

Preemption of traffic signals by LRVs 

10. Consider driver expectancies and behaviors when implementing ITS-based, advance preemption 

strategies at highway-LRT intersections. 

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Acronyms and Abbreviations 

AASHTO American Association of State Highway and Transportation Officials 

ADA Americans with Disabilities Act 

ATIS advanced traveler information system 

AWARD Advance Warning to Avoid Railroad Delays 

BNSF Burlington Northern Santa Fe Railroad 

CCS Collision Countermeasure System 

cd/m

2 

candelas per square meter 

CMS, CMSs changeable message sign(s) 

CWS collision warning system 

CWT constant warning time 

DB decibel 

DOT Department of Transportation 

EMS emergency medical services 

FHWA Federal Highway Administration 

FRA Federal Railroad Administration 

FTA Federal Transit Administration 

GPS Global Positioning System 

GRIP graphic route information panel 

HAR highway advisory radio 

HAZMAT hazardous materials 

HRI, HRIs highway-rail intersection(s) 

HUD, HUDs Head-Up Display(s) 

IGC intelligent grade crossing 

ISO International Organization for Standardization 

ITE Institute of Transportation Engineers 

ITS intelligent transportation systems 

km/h kilometers per hour 

LACMTA Los Angeles County Metropolitan Transportation Authority 

LED, LEDs light emitting diode(s) 

LRT light rail transit 

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LRV, LRVs light rail vehicle(s) 

min minute(s) 

mph miles per hour 

ms millisecond(s) 

MTA Mass Transit Administration 

MTW multiple train warning (second train warning) 

MUTCD Manual on Uniform Traffic Control Devices for Streets and Highways 

NCHRP National Cooperative Highway Research Program 

PDA, PDAs personal digital assistant(s) 

PRT perception-reaction time 

SAE Society of Automotive Engineers 

SAIC Science Applications International Corporation 

sec second(s) 

TCD, TCDs traffic control device(s) 

VAB vehicle arresting barrier 

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