http://safety.fhwa.dot.gov 

Advancing Innovating Intersection 

Safety Treatments for Two-Lane 

Rural Highways 

FHWA Safety Program 
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This document is disseminated under the sponsorship of the U.S. Department of 

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1. Report No. 

FHWA-SA-16-003

2. Government Accession No. 3. Recipient's Catalog No. 

4. Title and Subtitle 

Advancing Innovative Intersection Safety Treatments for

Two-Lane Rural Highways

5. Report Date 

December 2015

7. Author(s) 

D.J. Torbic, D.J. Cook, J.M. Hutton, K.M. Bauer, and

J.M. Sitzmann

8. Performing Organization Report No. 

110818.01.004 

9. Performing Organization Name and Address 

MRIGlobal 

425 Volker Boulevard 

Kansas City, MO 64110-2241 

10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

DTFH61-12-C-00023

12. Sponsoring Agency Name and Address 

Federal Highway Administration

Office of Safety

1200 New Jersey Avenue SE

Washington, DC 20590

13. Type of Report and Period Covered 

Final Report

September 2012 - December 2015

14. Sponsoring Agency Code 

15. Supplementary Notes 

Project Manager: Jeffrey Shaw

16. Abstract 

Intersection safety is a national, state, and local priority. Approximately 26 percent of the fatal crashes

that occur in the United States are intersection or intersection-related crashes. The objective of this

guide is to advance efforts to improve safety at unsignalized intersections with minor-road stop control

along rural two-lane roads, by focusing on strategies that are not yet widespread. The safety

effectiveness of three low-cost safety treatments was evaluated to estimate their expected

effectiveness in reducing crashes. The low-cost safety treatments included: (1) single luminaire

intersection lighting, (2) transverse rumble strips in advance of stop-controlled approaches, and (3)

supplementary pavement markings on intersection approaches.

The effectiveness of each treatment in reducing crashes was estimated using the Empirical Bayes (EB)

observational before-after safety evaluation analysis approach. Analyses were performed to estimate

the effectiveness of each treatment in reducing crashes for different severity levels and crash types. An

economic analysis of the treatments was also performed. Each of the treatments is effective in

reducing crashes of different types and severity levels, and is economically justifiable for most traffic

volumes.

The information in this report can be combined with information on other strategies to reduce

intersection or intersection-related crashes at unsignalized intersections with minor-road stop control

along rural two-lane roads. With such information, agencies can make informed decisions about

planning and programming safety improvements at intersections under their jurisdiction.

17. Key Words 

Highway safety

Intersection safety

Lighting

Rumble strips 

Pavement markings

Countermeasure evaluation 

Crash modification factor 

Empirical Bayes before-after analysis 

18. Distribution Statement 

No restrictions. This document is 

available to the public through the 

National Technical Information Service, 

Springfield, Virginia 22161 

19. Security Classif. (of this 

report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified

21. No. of Pages 

90

22. Price 

Form DOT F 1700.7 (8-72)Reproduction of completed page authorized 

MRIGlobal-ISR\110818-01-005_R i 
https://www.fhwa.dot.gov/publications/convtabl.cfm

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CONTENTS 

CHAPTER 1. INTRODUCTION ..................................................................................................1 

Background ............................................................................................................1 

Objective ................................................................................................................1 

How to Use This Guide ..........................................................................................2 

CHAPTER 2. RESEARCH APPROACH .....................................................................................3 

Selection of Treatments for Evaluation..................................................................3 

Selection of Treatment and Nontreatment Sites.....................................................6 

Data Collection.......................................................................................................7 

Analysis Approach .................................................................................................9 

CHAPTER 3. Single Luminaire ..................................................................................................15 

Treatment Description..........................................................................................15 

Safety Evaluation .................................................................................................16 

Economic Analysis...............................................................................................22 

Implementation.....................................................................................................24 

CHAPTER 4. Transverse Rumble Strips.....................................................................................27 

Treatment Description..........................................................................................28 

Safety Evaluation .................................................................................................28 

Economic Analysis...............................................................................................40 

Implementation.....................................................................................................42 

CHAPTER 5. Supplementary Pavement Markings .....................................................................49 

Treatment Description..........................................................................................50 

Safety Evaluation .................................................................................................52 

Economic Analysis...............................................................................................66 

Implementation.....................................................................................................69 

CHAPTER 6. Conclusions...........................................................................................................73 

CHAPTER 7. References.............................................................................................................75 

APPENDIX A. PENNSYLVANIA DESIGN GUIDELINES FOR INSTALLATION OF 

PAVEMENT MARKINGS..................................................................................77 

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FIGURES 

Figure 1. Equation. CMF for lighting............................................................................................4 

Figure 2. Equation. Benefit-cost ratio for 3-leg intersections .....................................................13 

Figure 3. Equation. Benefit-cost ratio for 4-leg intersections .....................................................13 

Figure 4. Photo. Examples of single luminaire intersection lighting (Image credit: Google 

EarthTM Mapping Service). ..........................................................................................16 

Figure 5. Equation. Base model for predicted crashes per year. .................................................19 

Figure 6. Equation. Model for predicted crashes per year for specific crash types and severity 

levels, and accounting for local conditions. .................................................................19 

Figure 7. Equation. CMF for total crashes. .................................................................................22 

Figure 8. Photo. Examples of transverse rumble strips placement (Image credit: Google 

EarthTM Mapping Service). ..........................................................................................29 

Figure 9. Equation. Base model for predicted crashes per year. .................................................33 

Figure 10. Equation. Model for predicted crashes per year for specific crash types and severity 

levels, and accounting for local conditions. .................................................................34 

Figure 11. Diagram. MoDOT’s design guidance for placement of transverse rumble strips. ......44 

Figure 12. Diagram. MoDOT’s design detail for transverse rumble strips. ..................................45 

Figure 13. Diagram. North Dakota DOT’s transverse rumble strip design detail.........................46 

Figure 14. Diagram. KDOT transverse rumble strip installation and design detail......................47 

Figure 15. Photo. Aerial view and street view of supplementary pavement markings on stopcontrolled approach (Image credit: Google EarthTM Mapping Service)......................51 

Figure 16. Photo. Supplementary pavement markings on uncontrolled approach. (Image credit: 

Pennsylvania DOT)......................................................................................................52 

Figure 17. Equation. Base model for predicted crashes per year. .................................................57 

Figure 18. Equation. Model for predicted crashes per year for specific crash types and severity 

levels, and accounting for local conditions. .................................................................58 

Figure 19. Diagram. Minnesota guidance for placement of STOP AHEAD pavement marking 

relative to W3-1a sign..................................................................................................71 

Figure 20. Diagram. Minnesota guidance for placement of W3-1a sign relative to stop bar. ......72 

Figure 21. Diagram. Placement guidance for supplementary pavement markings on uncontrolled 

approach.......................................................................................................................72 

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TABLES 

Table 1. Crash reduction estimates for lighting from The Handbook of Road Safety 

Measures........................................................................................................................4 

Table 6. Single luminaire: summary of nighttime crash statistics for the before and after 

Table 7. Single luminaire: summary of nighttime crash statistics for the entire study period for 

Table 8. Single luminaire: SPF coefficients, target crash proportions, and calibration factors by 

Table 9. Single luminaire: safety effectiveness on nighttime crashes for 3- and 4-leg 

Table 10. Single luminaire: benefit-cost ratios for treatment at 3-leg rural stop-controlled 

Table 11. Single luminaire: benefit-cost ratios for treatment at 4-leg rural stop-controlled 

Table 12. Prioritization of lighting at rural intersections by traffic volume and 

Table 13. Transverse rumble strips: number of sites by State, number of intersection legs, and 

Table 14. Transverse rumble strips: summary crash statistics for the before and after treatment 

Table 15. Transverse rumble strips: summary crash statistics for the entire study period for 

Table 16. Transverse rumble strips: SPF coefficients, target crash proportions, and calibration 

Table 17. Transverse rumble strips: safety effectiveness on target crashes by number of 

Table 18. Transverse rumble strips: benefit-cost ratios for treatment on two minor-road 

approaches at 4-leg rural stop-controlled intersection for $10,000 installation cost and 

Table 19. Transverse rumble strips: benefit-cost ratios for treatment on two minor-road 

approaches at 4-leg rural stop-controlled intersection for $2,000 installation cost and 

Table 20. Supplementary pavement markings: number of sites by State, number of intersection 

Table 21. Supplementary pavement markings installed on stop-controlled approaches: summary 

crash statistics for the before and after treatment periods for treatment intersections by 

Table 22. Supplementary pavement markings installed on stop-controlled approaches: summary 

crash statistics for the entire study period for nontreatment intersections by State and 

Table 2. States included in the safety evaluation of each treatment type. ...................................7 

Table 3. Crash costs by severity level assumed for economic analysis.....................................12 

Table 4. Major- and minor-road AADT ranges assumed for economic analysis. .....................12 

Table 5. Single luminaire: number of sites by number of intersection legs...............................17 

treatment periods for treatment intersections by number of intersection legs.............17 

nontreatment intersections by number of intersection legs..........................................18 

number of intersection legs for EB analysis. ...............................................................20 

intersections combined.................................................................................................21 

intersection...................................................................................................................23 

intersection...................................................................................................................24 

functional class.............................................................................................................25 

number of treated approaches. .....................................................................................30 

periods for treatment intersections by State and number of intersection legs. ............31 

nontreatment intersections by State and number of intersection legs..........................32 

factors by State and number of intersection legs. ........................................................35 

intersection legs. ..........................................................................................................39 

20-yr service life. .........................................................................................................41 

5-yr service life. ...........................................................................................................42 

legs, and number of treated approaches.......................................................................53 

State and number of intersection legs. .........................................................................55 

number of intersection legs..........................................................................................56 

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Table 23. Supplementary pavement markings installed on uncontrolled approaches: summary 

crash statistics for the before and after treatment periods for treatment intersections by 

State and number of intersection legs. .........................................................................57 

Table 24. Supplementary pavement markings installed on uncontrolled approaches: summary 

crash statistics for the entire study period for nontreatment intersections by State and 

number of intersection legs..........................................................................................57 

Table 25. Supplementary pavement markings installed on stop-controlled approaches: SPF 

coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs. ..........................................................................................................59 

Table 26. Supplementary pavement markings installed on uncontrolled approaches: SPF 

coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs. ..........................................................................................................63 

Table 27. Supplementary pavement markings installed on stop-controlled approaches: safety 

effectiveness on target crashes by number of intersection legs. ..................................65 

Table 28. Supplementary pavement markings installed on uncontrolled approaches: safety 

effectiveness on target crashes.....................................................................................66 

Table 29. Benefit-cost ratios for installing STOP AHEAD pavement marking on the stopcontrolled approach of a 3-leg intersection for $750 installation cost and 1-yr service 

life. ...............................................................................................................................67 

Table 30. Benefit-cost ratios for installing STOP AHEAD pavement markings on the stopcontrolled approaches of a 4-leg intersection for $1,500 installation cost and 1-yr 

service life....................................................................................................................67 

Table 31. Benefit-cost ratios for installing STOP AHEAD pavement marking on the stopcontrolled approach of a 3-leg intersection for $500 installation cost and 2-yr service 

life. ...............................................................................................................................68 

Table 32. Benefit-cost ratios for installing STOP AHEAD pavement markings on the stopcontrolled approaches of a 4-leg intersection for $1,000 installation cost and 2-yr 

service Life...................................................................................................................68 

Table 33. Benefit-cost ratios for installing supplementary pavement markings on uncontrolled 

approaches at 4-leg stop-controlled intersections. .......................................................69 

Table 34. Placement of supplementary pavement markings relative to intersection by posted 

speed. ...........................................................................................................................72 

Table 35. Summary of treatment effectiveness by treatment and intersection type and crash type 

and crash severity level................................................................................................73 

MRIGlobal-ISR\110818-01-005_R vi 
CHAPTER 1. INTRODUCTION 

 

 

 

 

 

 

 

 

 

 

 

 

 

BACKGROUND 

Intersection safety is a national, state, and local priority. Approximately 26 percent of the fatal 

crashes that occur in the United States are intersection or intersection-related crashes.

(1,2) In the 

period between 2009 and 2013, the average number of intersection-related fatal crashes was 

approximately 7,960 per year.(1) 

Crashes in rural areas are often more severe than in urban areas because of higher vehicle speeds, 

and the outcome of crashes may be more severe, in part, due to longer emergency response 

times. In rural areas, more fatal and severe injury crashes occur at stop-controlled intersections 

than at signalized intersections.(3) At stop-controlled intersections, most crashes are caused by a 

failure to stop at a stop-controlled approach or an acceptance of an insufficient gap when 

entering the intersection.

(4)

OBJECTIVE 

The objective of this guide is to advance efforts to improve safety at unsignalized intersections 

with minor-road stop control along rural two-lane roads, by focusing on strategies that are not yet 

widespread. The safety effectiveness of three low-cost safety treatments was evaluated to 

estimate their expected effectiveness in reducing crashes. The low-cost safety treatments 

included: 

• Single luminaire intersection lighting

• Transverse rumble strips in advance of stop-controlled approaches

• Supplementary pavement markings (such as STOP AHEAD) on intersection approaches

The information in this guide can be combined with information on other strategies to reduce 

intersection or intersection-related crashes at unsignalized intersections with minor-road stop 

control along rural two-lane roads. For example, the National Cooperative Highway Research 

Program (NCHRP) Report 500 Guidance for Implementation of the AASHTO Strategic Highway 

Safety Plan, Volume 5: A Guide for Addressing Unsignalized Intersection Collisions provides 

proven, tried, and experimental strategies for reducing crashes at unsignalized intersections.(5) 

The American Association of State Highway and Transportation Officials (AASHTO) Highway 

Safety Manual (HSM) provides crash prediction methods for estimating the predicted and/or 

expected crash frequency at unsignalized intersections on rural two-lane roads and related crash 

modification factors (CMFs).(6) Similarly, the online CMF Clearinghouse, sponsored by the 

Federal Highway Administration (FHWA), houses a web-based database of CMFs along with 

supporting documentation to help transportation engineers identify appropriate countermeasures 

for their safety needs.(7) With such information, agencies can make more informed decisions 

when planning and programming safety improvements at intersections under their jurisdiction. 

The overall goal of this guide is to increase the deployment of treatments that reduce motor 

vehicle fatalities and injuries at unsignalized intersections with minor-road stop control along 

rural two-lane roads by providing practitioners with knowledge about their installation and 

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expected safety benefits. Throughout this guide, the term “intersections” refers to unsignalized 

intersections with minor-road stop control along rural two-lane roads unless otherwise stated. 

HOW TO USE THIS GUIDE 

This guide serves as both a technical report of the treatments evaluated in the research, and as a 

practical guide for practitioners who may be interested in implementing the treatments evaluated. 

Guidance includes, where appropriate, the conditions under which the treatment is expected to be 

effective and design and installation considerations. 

Chapter 2 of this guide includes general information about how the research was conducted, 

including identification of intersections for inclusion in the research, the data that were collected, 

and the analysis approach. 

Chapters 3 through 5 each discuss one of the three treatments evaluated as part of this research in 

depth: single luminaire intersection lighting, transverse rumble strips, and supplementary 

pavement markings. Each chapter begins with a summary table of key information about the 

treatment, its use, and its expected effectiveness. The chapter then includes a detailed discussion 

under the following subheadings: 

• Description of treatment 

• Safety evaluation 

• Economic analysis 

• Implementation 

Conclusions are presented in Chapter 6. 

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CHAPTER 2. RESEARCH APPROACH 

 

 

 

 

 

 

 

 

 

This Chapter describes the general approach to the research, including identification of 

treatments to be evaluated, selection of treatment and nontreatment sites (i.e., intersections) for 

inclusion in the safety evaluations, a description of the data elements collected for the safety 

evaluations, and descriptions of the methodological approaches used to evaluate the safety 

effectiveness and economic benefits of the treatments. 

SELECTION OF TREATMENTS FOR EVALUATION 

At the beginning of the project, the research team identified 32 low-cost safety treatments 

applicable to unsignalized intersections on rural two-lane roads for which limited knowledge 

about their safety effectiveness was available. The list of treatments was developed by gathering 

information through a combination of a literature review, a virtual/desktop scan of national and 

international experiences, and telephone discussions and email exchanges with highway agency 

staff and consultants. Examples of treatment types considered for evaluation as part of this 

research included, but were not limited to, the following: 

• Geometric modifications

• Enhanced and/or dynamic forms of existing traffic control devices

• Roadside design features

• Lighting

• Pavement treatments

For each potential treatment considered for evaluation, the following information was gathered: 

• Description of the treatment and the specific safety problems the treatment addresses

• The expected safety effectiveness of the treatment based upon limited previous research

or anecdotal evidence

• If the treatment is included in NCHRP Report 500 (Vol. 5), status of the treatment as

either “tried” or “experimental”

• If the treatment is included in the CMF Clearinghouse, the star rating of the treatment

• Potential treatment locations for data collection

• The likely performance measure(s) that would be used to evaluate the treatment

• Technical uncertainties that would be anticipated if the treatment was analyzed (e.g., Will

it be difficult to identify sites where the treatment was installed? Is there a wide range of

designs that may impact the effectiveness of the treatment?)

• Whether the treatment was currently being evaluated in another ongoing research project

• International experience with the treatment’s safety effectiveness

• The likelihood of developing reliable safety effectiveness estimates for the treatment

given the availability of potential study sites and other data needed for analysis

After several iterations of prioritizing potential treatments, three were selected for evaluation: 

• Single luminaire intersection lighting

• Transverse rumble strips in advance of stop-controlled approaches

• Supplementary pavement markings (such as STOP AHEAD) on intersection approaches

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Estimating the safety effectiveness of installing a single luminaire at a stop-controlled 

intersection on a rural two-lane highway was identified as a high priority because safety 

effectiveness information for this treatment available in the HSM is general in nature and was 

adapted from studies that were not specific to rural intersections. HSM Chapter 10, Predictive 

Method for Rural, Two-Lane, Two-Way Roads, includes the following CMF for intersection 

lighting at stop-controlled intersections:(6) 

CMFLighting = 1 - 0.38 × pni 

Figure 1. Equation. CMF for lighting. 

where pni is the proportion of total crashes for unlighted intersections that occur at night. 

The CMF is applicable to total crashes, and the base condition is the absence of intersection 

lighting. This CMF indicates that intersection lighting is expected to reduce nighttime crashes at 

intersections on rural two-lane roads by 38 percent. Chapter 10 of the HSM states that the CMF 

is adapted from crash reduction estimates presented in The Handbook of Road Safety Measures 

by Elvik and Vaa.(8) The Handbook provides the following crash reduction estimates for roadway 

lighting for crashes that occur in darkness based on a meta-analysis of 25 studies from several 

countries conducted between 1948 and 1993 (Table 1). 

Table 1. Crash reduction estimates for lighting from The Handbook of Road Safety Measures.

(8) 

Crash severity Percent reduction in crashes 

occurring in darkness 

Fatal 64 

Injury 28 

Property-damage-only 17 

No information specific to intersections or rural roads is presented. 

HSM Chapter 14, Intersections, which provides information about intersection treatments that 

goes beyond what is provided in the predictive methods chapters, includes a CMF for 

intersection lighting. The Chapter 14 CMF for intersection lighting on nighttime crashes is 0.62 

(38 percent reduction, as shown in Chapter 10), but is specified for injury crashes only. In 

addition, a CMF for pedestrian nighttime injury crashes of 0.58 is provided. Chapter 14 of the 

HSM cites four sources (8,9,10,11) for these intersection lighting CMFs rather than the single 

reference (8) provided in HSM Chapter 10. However, in only one of the sources (11) is the safety 

effectiveness estimate for roadway lighting based solely on data from unsignalized intersections 

along rural two-lane roads. The study by Preston and Schoenecker (11) is also cited in NCHRP 

Report 500 (Vol. 5), A Guide for Addressing Unsignalized Intersection Collisions,

(5) which lists 

“Improve Visibility of the Intersection by Providing Lighting” as a “proven” safety treatment, 

yet the results of the Preston and Schoenecker study are not incorporated into the HSM Chapter 

10 predictive methodology for intersections on rural two-lane roads. 

By conducting a detailed safety evaluation for the installation of a single luminaire at stopcontrolled intersections on rural two-lane roads, the intention is to develop a more reliable 

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estimate for intersection lighting specific to the condition of interest (i.e., unsignalized 

intersection with minor-road stop control on rural two-lane roads) than what is currently 

provided in the HSM. In addition, this study includes in the analysis only intersections where a 

single luminaire was installed, making the results specific to this type of lighting 

implementation, which is currently not specified in the HSM or other available literature. 

Estimating the safety effectiveness of transverse rumble strips installed on minor-road 

intersection approaches was identified as a high priority because it is a relatively common 

treatment, but reliable safety estimates specific to stop-controlled intersections on rural two-lane 

roads are not available. HSM Chapter 14 provides a discussion of rumble strips installed on 

intersection approaches, and suggests that they are frequently used to inform drivers of an 

upcoming change in the roadway or as traffic calming devices. The discussion notes that in-lane 

rumble strips appear to reduce all crash types of all severities on urban roads, but that the 

magnitude of the effect is not known. No information is provided regarding rural intersections. In 

a recent before-after study using crash data from 3- and 4-leg stop-controlled intersections in 

rural areas, Srinivasan et al. reported that transverse rumble strips reduce KAB (fatal and injury) 

crashes by 21 percent and KA (fatal and severe injury) crashes by 39 percent.

(12) The results of 

this study are included in the CMF Clearinghouse, with star ratings ranging from 3 to 4 stars. 

However, it is unknown whether the analysis results from this study are based on intersections 

located exclusively along rural two-lane roads or a combination of sites located along rural twolane roads and rural multilane divided highways, and due to sample size issues, no definitive 

conclusions were provided regarding the impacts on specific crash types. Therefore, it is 

desirable to develop a crash reduction estimate for transverse rumble strips specifically for 

unsignalized intersections with minor-road stop control on rural two-lane roads and to estimate 

the safety effects of this treatment on specific target crashes (e.g., angle and rear-end). 

As with transverse rumble strips, supplementary pavement markings (such as STOP AHEAD) 

were identified as a high priority treatment for evaluation because they are relatively common 

treatment, but little reliable information is available regarding their impact on crashes. CMFs for 

STOP AHEAD pavement markings on various intersections types and for various crash types 

and severities are included in Chapter 14 of the HSM, but they are not incorporated into the 

HSM predictive chapters. Only one of the CMFs—for all crash types and severities at stopcontrolled rural intersections—has a standard error low enough for it to be considered reliable. It 

indicates a 31 percent crash reduction when STOP AHEAD pavement markings are used. All the 

STOP AHEAD pavement marking CMFs in Chapter 14 of the HSM are based on a study by 

Gross et al.,

(13) which used the Empirical Bayes before-after analysis approach. No CMF is 

provided specifically for unsignalized intersections with minor-road stop control on rural twolane roads. The CMF Clearinghouse includes CMFs with ratings of 3 or 4 stars for this treatment 

based upon the study by Gross et al.(13) Therefore, it was desirable to develop a more reliable 

crash reduction estimate specifically for supplementary pavement markings (such as STOP 

AHEAD) for unsignalized intersections with minor-road stop control on rural two-lane roads for 

possible inclusion in HSM Chapter 10. It was also desirable to estimate the safety effects of this 

treatment on specific target crashes (e.g., angle and rear-end) for the conditions of interest. 

In seeking potential study sites for this treatment, the research team did not limit the 

supplementary pavement marking message to STOP AHEAD only. While a majority of sites did 

have this message (installed on the minor approaches), several sites were identified at which a 

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supplementary pavement marking treatment was installed on the major (uncontrolled) 

approaches to the intersection. Since no reliable safety effectiveness estimates were available for 

this specific application, a separate analysis of the safety effectiveness of this treatment was 

conducted as well. 

SELECTION OF TREATMENT AND NONTREATMENT SITES 

After selecting the three treatment types to be evaluated, the research team contacted state and 

county highway agencies to request location information (e.g., major-road name, minor-road 

name, county) for intersections at which a treatment of interest had been installed. The research 

team then gathered additional data for each site, including intersection geometrics and site 

charateristics data, traffic volumes, installation dates, and construction history to determine if 

each site was suitable for inclusion in the analysis. The following criteria were used to narrow 

the list of potential treatment sites to those included in the analysis: 

• Installation year: Ideally, the treatment was installed between 2005 and 2008, allowing

the research team to gather four to five years of crash data before and after the

installation. Some sites were included in the safety evaluation with earlier or later

installation years; these exceptions are discussed in later sections.

• Availability of crash and traffic volume data by year: In some cases, when traffic

volume data were not available for all years of the study period, it was interpolated from

years with known traffic volumes. Traffic volume data had to be available for both

major- and minor-roads for the intersection to be included in the analysis.

• Construction history: Treatment sites were limited to those at which no substantial

construction had taken place, other than installation of the treatment, during the study

period.

Additional details about the data collection process are provided in the discussion on data 

collection later in this chapter. 

Table 2 shows the states in which treatment sites included in the analysis were located. 

Once the list of treatment sites for inclusion in the analysis was finalized, the research team 

identified nontreatment sites in each state where treatment sites were located. Nontreatment sites 

are used in the before-after analysis to account for crash trends over time. Potential nontreatment 

sites were identified by searching aerial and street-view images of rural roads in the vicinity of 

treatment intersections, and then expanding that search to similar, nearby routes. Nontreatment 

sites were selected from the potential sites using the following criteria: 

• No treatment installed at site over study period (this includes the three treatments

evaluated in this research)

• Crash and traffic volume data available by year

• Traffic volumes for major- and minor-roads that fall within the range of those at the

treatment sites in that state

• Proportion of 3-leg and 4-leg nontreatment sites similar to that proportion for treatment

sites in the same state

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Table 2. States included in the safety evaluation of each treatment type. 

States 

Single 

luminaire 

intersection 

lighting 

Transverse 

rumble 

strips 

Supplementary 

pavement 

markings 

Arkansas Yes Yes 

Kansas Yes 

Minnesota Yes Yes 

Missouri Yes 

Nebraska Yes 

North Dakota Yes 

Oregon Yes 

Pennsylvania Yes 

Vermont Yes 

Approximately 30 nontreatment sites were identified in each state for inclusion in the analysis. 

All nontreatment sites in each state were used in the analysis of all treatments in that state. 

The discussion of the statistical analysis in Chapters 3, 4, and 5 includes descriptive statistics for 

the treatment and nontreatment sites included in the analysis. 

DATA COLLECTION 

The following data are critical for performing a safety evaluation of a treatment: 

• Treatment installation date

• Crash data for treatment (before and after treatment installation) and nontreatment sites

(matching periods)

• Traffic volume data for treatment (before and after treatment installation) and

nontreatment sites (matching periods)

• Intersection characteristics data for treatment and nontreatment sites

Final selection of intersections for inclusion in the analyses was determined, in part, by the 

availability of such data. 

Treatment Installation Date 

For each potential treatment site, the research team obtained the treatment installation year from 

state highway agencies. This information was critical for defining the appropriate analysis period 

for evaluation of the treatment at the respective intersection. The goal was to include sites at 

which treatments were installed between 2005 and 2008 so that four to five years of crash data 

would be available after installation of the treatment, and before-period data would be from 

within the last 15 years. In cases where only a limited number of treatment sites met this 

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criterion, exceptions were made to allow sites with fewer years of before or after data in the 

analysis or include “before” period crash data prior to 2000 in the analysis. In cases where the 

installation date of an intersection treatment was unknown, that intersection could not be 

included in the Empirical Bayes (EB) before-after evaluation. The EB before-after analysis 

methodology is discussed below, under “Analysis Approach.” . 

The research team also requested information from state highway agencies as to whether 

substantial improvements or changes other than the installation of the treatment being evaluated 

were made during the study period at any of the intersections considered for inclusion in the 

evaluation. Intersections where other substantial improvements or changes were made were 

either excluded from the evaluation or the study period was adjusted to only include the years 

prior to or after the changes were made. Where possible, the research team used Google Earth to 

review images over a number of years to assess the history of changes to intersections. These 

images were used to gather construction history data when the highway agency was not able to 

provide it or to validate construction history information when it was provided. The history of 

changes to nontreatment intersections was assessed in the same manner. 

Crash Data 

The research team obtained crash data from state highway agencies for treatment and 

nontreatment sites in electronic form. As indicated above, the goal was to obtain crash data for 

four to five years before and four to five years after installation of the treatment at the treatment 

sites. Data were requested up to the most recent year of available data, even if this resulted in 

more than five years of after-period data. For a given treatment and state, crash data for 

nontreatment sites were requested for years covering the full range of before and after periods of 

the treatment sites included in the analysis. For Minnesota, some crash data were obtained from 

the Highway Safety Information System (HSIS) for the analysis. 

Data for individual crashes were obtained at the crash and vehicle levels. The primary crash data 

elements of interest for the safety evaluations included: 

• Crash location

• Crash date

• Time of day

• Severity level

• Number of vehicles involved

• Crash type and manner of collision

• Lighting condition

• Sequence of events (including first harmful event and most harmful event)

• Relationship to intersections/junctions

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Traffic Volume Data 

The research team obtained traffic volumes [annual average daily traffic (AADT)] for the majorand minor-road approaches of each treatment and nontreatment intersection. AADTs were 

obtained for as many years as available for the study period. If the AADTs differed for both 

major-road approaches to an intersection, the greater of the two AADT values was used in the 

analysis; AADTs for the minor-road approaches were treated in a similar fashion. If an AADT 

for a particular year was missing, and AADTs for years before and after that year were known, 

then the AADT for the missing year was estimated through interpolation. If an AADT was 

missing at the beginning or end of a study period, then the closest AADT was simply used for 

that year. If AADTs were missing for most or all study years, the intersection was excluded from 

the analysis. 

Intersection Characteristics Data 

Treatment and nontreatment site characteristics were obtained using Google Earth and Google 

Street View. Data for the following intersection characteristics were collected: 

• Type of traffic control

• Area type

• Number of intersection legs

• Number of major-road approaches with left-turn lanes

• Number of major-road approaches with right-turn lanes

• Intersection skew angle

• Presence of lighting

• Number of light poles in the vicinity of the intersection

• Presence of transverse rumble strips

• Presence of supplementary pavement markings

• Distance of transverse rumble strips/supplementary pavement markings to intersection

• Number of treated approaches

These data were used to 1) choose the appropriate safety performance function (SPF) and CMFs 

to predict the expected number of crashes at the intersection, and 2) to better define the specific 

implementation of the treatment. 

ANALYSIS APPROACH 

The effectiveness of each treatment in reducing crashes was estimated using the Empirical Bayes 

(EB) observational before-after safety evaluation analysis approach. An economic analysis of the 

treatments was also performed using the safety effectiveness information developed in this 

research. The general approach to these analysis methodologies is described below, while 

specific details of how each approach was applied for the individual treatments is provided in the 

respective chapters. 

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EB Before-After Safety Evaluation Method 

The collected data lent themselves to an Empirical Bayes (EB) observational before-after safety 

evaluation with reference sites. The EB method is now a standard approach to safety 

evaluations.(14,15) The EB method has been applied by members of the research team in a number 

of recent projects (16,17) and by others (13,18). 

The EB approach overcomes the difficulties associated with conventional before-after 

comparisons by: 

• Properly accounting for regression-to-the-mean

• Overcoming the difficulties of using crash rates in normalizing for volume differences

between the before and after periods

• Reducing the level of uncertainty in the estimates of the safety effects

The specific EB approach used for this evaluation follows the steps presented in Appendix 9A in 

Chapter 9 of the HSM.

(6) The analysis approach is comprised of four basic steps. 

STEP 1: Calibrate the appropriate HSM SPFs within each state using the reference site 

data within that State. The research team also included the “before” period data 

for the treatment sites within that State in this step. 

STEP 2: Estimate the expected number of crashes in the before period by taking a 

weighted average of the observed crash count and the predicted crash frequency 

calculated from the calibrated HSM SPF to estimate the EB-adjusted expected 

crash frequency in the before period. 

STEP 3: Estimate the expected number of crashes in the “after” period had the treatment 

not been installed. This estimate is obtained by adjusting the EB-adjusted 

expected crash frequency from the before period (as calculated in Step 2) for the 

difference between before and after AADTs and between before and after number 

of years. 

STEP 4: Estimate the effectiveness of the treatment by comparing the observed number of 

crashes in the after period to the expected number of crashes in the after period, 

had the treatment not been installed (as calculated in Step 3). 

The effectiveness of each treatment in reducing crashes was estimated separately for the 

following crash severity levels and crash types: 

Severity level: 

• Total crashes (all severity levels combined)

• Fatal and severe (FS) crashes

• Fatal and all injury (FI) crashes

• Property-damage-only (PDO) crashes

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Crash type: 

• All crashes combined (excluding single luminaire)

• Nighttime crashes (single luminaire only)

• Angle crashes (excluding single luminaire)

• Rear-end crashes (excluding single luminaire)

The injury scale used in this analysis can be translated to the KABCO crash severity scale as 

follows: 

• Total crashes = K, A, B, C and O crashes

• FS crashes = K and A crashes

• FI crashes = K, A, B and C crashes

• PDO crashes = O crashes

where: 

K = fatal crash 

A = disabling injury crash 

B = evident injury crash 

C = possible injury crash 

Economic Analysis 

An economic analysis was performed for each of the three intersection treatment types to 

estimate the benefit-cost ratio of each treatment. The benefit-cost ratio is the ratio of the present 

benefit of a treatment, measured in monetary terms of the number of crashes reduced due to 

installation of the treatment, to its construction costs. For a countermeasure to be economically 

justified, its benefit-cost ratio should be greater than 1.0. The most desirable countermeasures are 

those with the highest benefit-cost ratios. The safety effectiveness results of the three treatments 

were incorporated in the economic evaluations. 

Implementation Cost and Service Life 

The implementation costs and service lives of the safety treatments were determined based on 

input from State highway agencies. Costs and service lives can vary by geographic regions. For 

example, a cold-weather State may want to assume a shorter service life than a warm-weather 

State for pavement markings due to snowplows damaging the treatment. Care should be taken to 

select a service life appropriate to the region in which the treatment is being installed. 

Crash Reduction Benefit 

The annual benefits for the safety treatments were estimated as follows: 

1. Estimate crash frequency by crash severity level for the existing 3-leg and 4-leg stopcontrolled intersections on rural two-lane roads prior to installation of the treatment,

based on the HSM Part C predictive methods.

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2. Estimate the reduction in crash frequency by severity due to the treatment

implementation, based on CMFs derived from this research.

3. Calculate annual crash cost savings.

Table 3 presents the crash costs used in the analysis, which are the values provided in HSM 

Chapter 7. Transportation agencies may use different values for crash costs that may be more 

current or specific to a location than the values shown in Table 3. A 2015 NHTSA report (19)

estimates the economic and societal impact of a motor vehicle crash fatality to be $9,146,000, 

while a June 2015 memo from the Office of the Secretary of Transportation (20) provides 

guidance for transportation analyses to use $9.4 million as the economic value of a statistical life. 

Substituting higher values, such as these, for the values shown in Table 3 will only increase the 

calculated benefit of a given treatment. The crash cost values presented in Table 3 were used in 

the economic analyses for consistency with the HSM. 

Table 3. Crash costs by severity level assumed for economic analysis.

(6) 

Crash Severity Level 

Comprehensive Societal 

Crash Costs 

Fatal (K) $4,008,900 

Disabling injury (A) $216,000 

Evident injury (B) $79,000 

Possible injury (C) $44,900 

Property damage only (O) $7,400 

The SPFs in the HSM Part C predictive methods require major- and minor-road AADTs to 

compute predicted crash frequencies. The intersections used to produce CMFs in this research 

consisted of a wide range of traffic volumes on both the major- and minor-road approaches. 

Annual crash reduction benefits were calculated for each treatment type by varying the majorroad AADT in 1,000-veh/day increments. The minor-road AADT was varied as a percentage of 

the major-road AADT from 5 to 95 percent, in increments of 5 percent. Table 4 presents the 

major-road and minor-road AADT ranges used in the economic analysis. 

Table 4. Major- and minor-road AADT ranges assumed for economic analysis. 

Treatment Type Intersection Type 

Major-Road AADT 

Range (veh/day) 

Minor-Road AADT 

Range (veh/day) 

Single luminaire 3 legs 220 to 5,900 30 to 2,000 

4 legs 315 to 2,100 210 to 1,750 

Transverse rumble strips 4 legs 200 to 5,000 90 to 3,185 

Supplementary pavement 3 legs 115 to 5,200 40 to 2,940 

markings installed on stopcontrolled approach (i.e., 

STOP AHEAD) 

4 legs 155 to 3,650 40 to 1,500 

Supplementary pavement 

markings installed on 

uncontrolled approaches 

4 legs 2,310 to 14,000 330 to 2,730 

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Benefit-Cost Ratio 

To estimate the benefit-cost ratio of a treatment, it is necessary to convert the annual benefit of a 

treatment to a net present value. To do so, a discount rate or minimum attractive rate of return of 

7 percent was assumed, in accordance with current Federal guidelines. The benefit-cost ratio is 

computed by dividing the net present value of the crash reduction benefit by the implementation 

cost. Results of the economic analysis for each treatment are provided in Chapters 3 through 5. 

The benefit-cost ratio for a given treatment installed at 3-leg stop-controlled intersections on 

rural two-lane roads is calculated using the following equation: 

Figure 2. Equation. Benefit-cost ratio for 3-leg intersections 

The benefit-cost ratio for a given treatment installed at 4-leg stop-controlled intersections on 

rural two-lane roads is calculated using the following equation: 

Figure 3. Equation. Benefit-cost ratio for 4-leg intersections 

where: 

B/C = benefit-cost ratio 

CMF = crash modification factor for total intersection crashes for a given treatment or 

combination of treatments 

Cr = calibration factor for SPF 

AADTmaj = major-road AADT 

AADTmin = minor-road AADT 

i = discount rate (assumed 7 percent) 

n = service life 

CImp = installation cost ($) 

CAnn = annual operational cost of treatment ($) 

CK = fatal crash cost ($ per fatal crash) 

PK = proportion of total intersection crashes that are fatal crashes 

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CA = disabling injury crash cost ($ per disabling injury crash) 

PA = proportion of total intersection crashes that are disabling injury crashes 

CB = evident injury crash cost ($ per evident injury crash) 

PB = proportion of total intersection crashes that are evident injury crashes 

CC = possible injury crash cost ($ per possible injury crash) 

PC = proportion of total intersection crashes that are possible injury crashes 

CO = property damage only crash cost ($ per property damage only crash) 

PO = proportion of total intersection crashes that are property damage only crashes 

MRIGlobal-ISR\110818-01-005_R 14 
CHAPTER 3. SINGLE LUMINAIRE 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Treatment Name Single Luminaire 

Description A single luminaire is installed at an intersection to make drivers aware of the 

presence of the intersection at night. 

States Data from one state—Minnesota--were included in the safety evaluation of this 

treatment. 

Safety 

Effectiveness 

Reduction by severity level: 

The EB analysis showed a 71-percent reduction in nighttime crashes (SE = 29 

percent) for all severity levels combined. 

Cost and Economic 

Benefits 

Benefit-cost ratios ranged from 0.5 to 35.0, assuming an $8,000 installation cost 

and $300 annual energy cost over a 20-year life. These costs assume light 

fixtures that used traditional wired power and the availability of a nearby power 

source. However, street lighting that uses solid-state LED bulbs and solar power 

generally have no need for a wired power source near the intersection and have 

no annual energy cost. 

Where to 

Implement 

This treatment should be considered at intersections with a high proportion of 

crashes occurring during hours of darkness, or simply at intersections with a 

moderate to high frequency of nighttime crashes. Intersections with patterns of 

nighttime crashes that suggest drivers are unaware of the presence of the 

intersections (such as near horizontal curves or locations with skewed 

approaches) may particularly benefit from this treatment. 

Additional Factors 

for Consideration 

If there is vegetation near the intersection, foliage should be trimmed and 

maintained on a regular basis so it does not cause shadows or reduce the 

visibility generated from the luminaire. Luminaire poles should have a breakaway 

design and should be located so as to minimize the risk of being struck by a 

vehicle. 

TREATMENT DESCRIPTION 

A single luminaire is a safety treatment used to reduce nighttime crashes by making drivers 

aware of the presence of an intersection that may otherwise be difficult to see at night. For 

drivers on a stop-controlled approach, the lighting may provide additional time for the 

approaching driver to perceive the need to stop by increasing the visibility of features located at 

the site such as pavement markings and signs. For drivers on the uncontrolled approach, the 

lighting may provide an indication that drivers may be entering the roadway at that location and 

can improve the visibility of vehicles, bicyclists, and pedestrians located near the intersection. 

The luminaire may be pole-mounted near one corner of the intersection, or may be wire-mounted 

over the intersection. Example installations of the single luminaire treatment at rural 

intersections are shown in Figure 4. 

MRIGlobal-ISR\110818-01-005_R 15 
 

 

Figure 4. Photo. Examples of single luminaire intersection lighting (Image credit: Google 

EarthTM Mapping Service).(21)

SAFETY EVALUATION 

The safety effectiveness of installing a single luminaire at an intersection with minor-road stop 

control on a rural two-lane road was estimated using the EB before-after analysis approach as 

discussed in Chapter 2 (Analysis Approach). The illuminance or luminance level generated from 

MRIGlobal-ISR\110818-01-005_R 16 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

the single luminaire was not considered in the safety evaluation as neither measure was recorded 

in the field at the 

treatment sites. The descriptive statistics, research methodology, and analysis results of the 

safety evaluation are presented below. 

Descriptive Statistics 

A total of 27 treatment and 61 nontreatment sites in Minnesota were available for analysis of the 

safety effectiveness of a single luminaire installation. Their breakdown by number of intersection 

legs is shown in Table 5. 

Table 5. Single luminaire: number of sites by number of intersection legs. 

State 

Number of 

Intersection 

Legs 

Number of Sites 

Treatment Nontreatment 

MN 

3 21 21 

4 6 40 

All legs 27 61 

Crash and traffic volume data were available for varying periods before and after treatment 

installation, depending on treatment installation date at the individual sites. Only nighttime 

crashes, at four crash severity levels—total, fatal and severe injury (FS), fatal and all injury (FI), 

and property damage only (PDO)—were considered in the analysis of this treatment. Table 6 

(treatment intersections) and Table 7 (nontreatment intersections) summarize the crash data used 

in the analysis. They present nighttime crash data summed across all intersections of a given 

configuration. 

Table 6. Single luminaire: summary of nighttime crash statistics for the before and after 

treatment periods for treatment intersections by number of intersection legs. 

Before Period After Period 

Years Number 

Nighttime Crash Counts Range 

of Years Number 

Nighttime Crash Counts 

Number of Data Number of of Data Number of 

State of Legs in State of Sites Site-Years Total FS FI PDO in State of Sites Site-Years Total FS FI PDO 

MN 3 5 21 105 18 0 7 11 1 to 3 21 34 1 1 1 0 

4 5 6 30 2 0 0 2 1 to 2 6 9 0 0 0 0 

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Table 7. Single luminaire: summary of nighttime crash statistics for the entire study period for 

nontreatment intersections by number of intersection legs. 

State 

Number 

of 

Legs 

Entire Study Period 

Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Nighttime Crash Counts 

Total FS FI PDO 

MN 3 9 21 189 16 0 6 10 

4 8 40 320 11 0 3 8 

Methodology 

The safety effectiveness of installing a single luminaire was evaluated using an EB before-after 

method. To implement this method, the following steps were taken: 

1. Select appropriate SPF: The SPFs for intersections on rural two-lane roads from

Chapter 10 of the HSM were selected. These are given for total crashes only. The

coefficients of these SPFs vary by number of intersection legs. Use of the intersection

SPFs from Chapter 10 of the HSM provides an estimate of the intersection-related

predicted crash frequency for sites included in the analysis in the absence of the

treatment.

2. Obtain the proportions of target crashes (PR1) relevant to the evaluation: The proportion

of nighttime crashes to all crashes for each severity level (total, FS, FI, and PDO) were

calculated using all crashes from nontreatment sites and from the before-period years of

treatment sites in Minnesota. These proportions were calculated separately for 3- and 4-

leg intersections. These proportions scale the total crash predictions (i.e., all crash types)

to predictions for the target crashes (i.e., nighttime crashes).

3. Obtain the proportions of FS, FI, and PDO crashes (PR2): These proportions were

calculated as the ratio of all (daytime plus nighttime) FS, FI, or PDO crashes over total

crashes using all crashes from the nontreatment sites and from the before-period years of

treatment sites in Minnesota. These proportions were calculated separately for 3- and 4-

leg intersections. These proportions scale the total crash predictions (i.e., all severity

levels combined) to predicted crashes for specific severity level crashes (i.e., FS, FI, and

PDO).

4. Calibrate the SPFs to the local jurisdiction: Calibration was performed using all crashes

(total daytime plus nighttime crashes), separately for each intersection configuration,

again using all nontreatment intersections and before-period years from treatment

intersections combined. Total crash counts rather than target crashes were used due to

the scarcity of nighttime crashes, especially FS and FI crashes. The calibration factor

adjusts the HSM SPFs for varying conditions in the local jurisdiction such as crash

reporting thresholds, environmental factors, etc.

The SPFs presented in the HSM for intersections on rural two-lane roads for total severity level 

(i.e., all severity levels combined) have the general form: 

MRIGlobal-ISR\110818-01-005_R 18 
 

 

 

 

 

 

Predicted crashes/yr = exp[a + b(lnAADTmaj) + c(lnAADTmin)] 

Figure 5. Equation. Base model for predicted crashes per year. 

where a, b, and c are the regression coefficients shown in Table 8. These coefficients apply to 

base conditions and vary by number of intersection legs. For the intersection SPFs in Chapter 10 

of the HSM, the base conditions are: 

• Intersection skew angle: 0 degrees 

• Number of intersection left-turn lanes: None on approaches without stop control

• Number of intersection right-turn lanes: None on approaches without stop control

• Presence of lighting: None 

Crash modification factors (CMFs), calibration factor (Cr), proportions of nighttime crashes 

(PR1), and proportions of FS, FI, and PDO crashes (PR2) were then used to adjust for local 

conditions as follows: 

Predicted crashes/yr = {exp[a + b(lnAADTmaj) + c(lnAADTmin)]} × PR1 × PR2 × CMFCombined × Cr 

Figure 6. Equation. Model for predicted crashes per year for specific crash types and severity 

levels, and accounting for local conditions. 

The CMFCombined is the product of the CMFs from Chapter 10 of the HSM for skew angle 

(CMF1i), number of major-road left-turn lanes (CMF2i), and number of major-road right-turn 

lanes (CMF3i), for a particular intersection configuration (note that the CMF for intersection 

lighting, CMF4i , equals 1 in all cases for this treatment evaluation). 

SPF coefficients (a, b, and c and overdispersion parameter), nighttime crash proportions (PR1), 

proportions of FS, FI, and PDO crashes (PR2), and calibration factors (Cr) are shown for each 

intersection configuration in Table 8. The table also shows the default proportions of PR1 and 

PR2 presented in Chapter 10 of the HSM (see HSM Tables 10-15 and 10-5, respectively). Note 

that PR2 is always equal to 1 for total crashes. The decision of which proportions to use—those 

calculated from the data or those provided by the HSM—was based on whether calculated 

proportions of nighttime crashes (PR1) were nonzero for all severity levels. If PR1 was equal to 

zero for any severity level, then the default HSM proportions (both PR1 and PR2) were used in 

the EB before-after analysis. The proportions used in the analysis are indicated with an asterisk 

in Table 8 (HSM proportions in all cases in this analysis). 

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Table 8. Single luminaire: SPF coefficients, target crash proportions, and calibration factors by number of intersection legs for 

EB analysis. 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Number of 

Crashes, 

Nighttime

Only 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of 

Nighttime

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

3 315 

Total 69 34 

-9.86 0.79 0.49 0.54 

0.49 0.26* 1.00 1.00* 

0.60 

FS 1 0 0.00 0.26* 0.01 0.06* 

FI 24 13 0.54 0.26* 0.35 0.42* 

PDO 45 21 0.47 0.26* 0.65 0.59* 

4 390 

Total 63 13 

-8.56 0.60 0.61 0.24 

0.21 0.24* 1.00 1.00* 

0.23 

FS 3 0 0.00 0.24* 0.05 0.06* 

FI 28 3 0.11 0.24* 0.44 0.43* 

PDO 35 10 0.29 0.24* 0.56 0.57* 

NOTE 1: Asterisked proportions were those used in the analyses. 

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Safety Effectiveness 

The EB analysis was based on before and after traffic volumes and crash data from 27 treatment 

and 61 nontreatment intersections in Minnesota, and HSM SPFs for 3- and 4-leg intersections on 

rural two-lane roads. Traffic volumes at the treatment sites ranged from 200 to 7,300 veh/day (3­

leg intersections) and from 315 to 2,100 (4-leg intersections) on the major-road approaches and 

from 30 to 2,000 veh/day (3-leg intersections) and from 210 to 1,750 (4-leg intersections) on the 

minor-road approaches. The EB method was first applied separately to 3-leg and 4-leg 

intersections. However, only six 4-leg intersections were available, and none experienced any 

crashes in the after period. It was, therefore, decided to pool 3- and 4-leg intersections to 

estimate the safety effectiveness of installing a single luminaire across both 3- and 4-leg 

intersections combined. The EB before-after analysis results are shown in Table 9 for the 

following crash types and severity levels: 

• Total nighttime crashes

• FI nighttime crashes

• PDO nighttime crashes

Although the analyses for FS injury crashes were performed, the analysis results were not 

considered reliable and are therefore not shown. The occurrence of FS crashes was too rare 

across all intersections in the study (both treatment and nontreatment sites). 

The statistics shown in Table 9 for each crash severity are: 

• Number of treatment intersections

• Percent change in nighttime crash frequency due to the treatment: estimate and standard

error

• An indication of whether the treatment had a statistically significant effect on crash

frequency for the crash severity level of interest at the 95- or 90-percent confidence level

A negative percent safety effectiveness indicates that crash frequencies decreased due to the 

treatment. 

Table 9. Single luminaire: safety effectiveness on nighttime crashes for 3- and 4-leg intersections 

combined. 

Crash 

Severity 

Number of 

Treatment 

Sites 

Safety 

Effectiveness 

(%) 

SE of 

Treatment 

Effect (%) Significance 

3- and 4-Leg Intersections Combined

Total 

27 

-71 29 Significant at 95% CL 

FI -21 79 Not significant at 90% CL 

PDO -100a NC NC 

a Crashes recorded in before period; none in after period. 

NC=Not Calculated; standard error and significance could not be estimated. 

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The following general observations can be made based on Table 6, Table 8, and Table 9: 

• Only one nighttime crash occurred in the after period across all 27 treatment sites.

• PDO crashes decreased from 13 (before) to 0 (after), yielding a 100-percent reduction in

crash counts; in such cases, the standard error of the effectiveness estimate cannot be

calculated.

• The calibration factors for the SPFs are 0.23 (4-leg intersections) and 0.60 (3-leg

intersections).

The EB analysis results from Minnesota sites indicate that installing a single luminaire reduced 

total nighttime crashes by 71 percent; this safety effect is statistically significant at the 95-

percent confidence level. Although the analysis shows a 21-percent reduction in FI nighttime 

crashes, the result is not significant at the 90-percent confidence level due to the large standard 

error of the estimate. 

The EB analysis made use of AADT data for the entire day. Traffic volume information for 

nighttime hours was not incorporated into the analyses, so interpretation of the analysis results 

should be taken with this analysis approach in mind. 

ECONOMIC ANALYSIS 

An economic analysis was conducted to calculate benefit-cost ratios to estimate the economic 

benefits of installing a single luminaire at 3-leg and 4-leg stop-controlled intersections on rural 

two-lane roads. The Economic Analysis discussion in Chapter 2 describes the procedure used to 

calculate the benefit-cost ratios. 

The estimated crash reduction benefit is calculated using the CMF for total nighttime crashes 

produced in this study for installing a single luminaire at an intersection, which is 0.29 for 3- and 

4-leg stop-controlled intersections combined. The following equation uses the proportion of total

nighttime crashes at 3-leg and 4-leg rural stop-controlled intersections to translate the single

luminaire CMF, that applies to nighttime crashes, to a CMF that applies to total crashes during

the entire 24-hour day:

CMFTotal = (CMFLighting – 1) × PR1 + 1 

Figure 7. Equation. CMF for total crashes. 

where PR1 is the proportion of total crashes that occur at night. The HSM provides default values 

for PR1 (shown as pni). The value used in this economic evaluation is the HSM default provided 

in Table 10-15 in Chapter 10, which is 0.26 for 3-leg stop-controlled intersections and 0.24 for 4-

leg stop-controlled intersections. 

To calculate the treatment cost for the economic analysis, both installation and maintenance costs 

were included. The calculations assume an $8,000 installation cost for a single luminaire, an 

annual energy cost of $300, and a service life of 20 years. These estimates were obtained from 

the state DOTs that provided data for the safety analysis. 

MRIGlobal-ISR\110818-01-005_R 22 
 

 

 

 

Table 10 displays the benefit-cost ratios for installing a single luminaire at a 3-leg stopcontrolled intersection on rural two-lane roads. The AADTs in the table cover the range of 

AADTs of the study sites used for the estimation of the CMF. At very low intersection volumes, 

the treatment does not always produce a benefit-cost ratio above 1.0. However, single luminaire 

installation is economically justified at intersections with a major-road AADT at or above 1,000 

veh/day, regardless of the minor-road AADT. 

Table 11 presents the benefit-cost ratios for installing a single luminaire at a 4-leg stopcontrolled intersection on rural two-lane roads. The AADTs in the table cover the range of 

AADTs of the study sites used for the estimation of the CMF. The single luminaire is 

economically justified at all AADT levels represented in the study, with all the benefit-cost ratios 

exceeding 3.0. 

Table 10. Single luminaire: benefit-cost ratios for treatment at 3-leg rural stop-controlled 

intersection. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 60% 70% 80% 90% 

300 N/A 0.5 0.5 0.6 0.7 0.8 0.8 0.9 0.9 1.0 1.1 1.2 1.2 1.3 

1,000 1.5 2.1 2.6 3.0 3.3 3.6 3.9 4.1 4.4 4.6 5.1 5.5 5.8 6.2 

2,000 3.6 5.1 6.2 7.2 8.0 8.8 9.4 10.1 10.7 11.2 12.3 13.3 14.2 15.0 

3,000 6.1 8.6 10.5 12.1 13.4 14.7 15.9 16.9 17.9 18.9 20.7 N/A N/A N/A 

4,000 8.8 12.4 15.1 17.4 19.4 21.3 22.9 24.5 25.9 27.3 N/A N/A N/A N/A 

5,000 11.8 16.5 20.1 23.2 25.9 28.3 30.5 32.6 N/A N/A N/A N/A N/A N/A 

5,900 14.5 20.4 24.9 28.7 32.0 35.0 N/A N/A N/A N/A N/A N/A N/A N/A 

CMF = 0.82 (total crashes, entire day), CMFLighting = 0.29 (total night crashes), PR1 = 0.26 (proportion of 

nighttime crashes to total crashes) 

Installation cost = $8,000 

Annual energy cost = $300 

Service life = 20 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study. 

MRIGlobal-ISR\110818-01-005_R 23 
 

 

 

 

 

 

 

 

 

 

Table 11. Single luminaire: benefit-cost ratios for treatment at 4-leg rural stop-controlled 

intersection. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

10% 15% 20% 25% 30% 40% 50% 55% 60% 70% 80% 85% 90% 95% 

400 N/A N/A N/A N/A N/A N/A N/A 3.3 3.4 3.8 4.1 4.3 4.4 4.6 

1,000 N/A N/A N/A 6.1 6.8 8.1 9.3 9.9 10.4 11.4 12.4 12.9 13.3 13.8 

2,000 N/A 10.3 12.3 14.1 15.8 18.8 21.6 22.9 24.1 26.5 28.7 29.8 N/A N/A 

2,100 8.6 11.0 13.1 15.0 16.8 20.0 22.9 24.2 25.6 28.1 30.5 N/A N/A N/A 

CMF = 0.83 (total crashes, entire day), CMFLighting = 0.29 (total night crashes), PR1 = 0.24 (proportion of 

nighttime crashes to total crashes) 

Installation cost = $8,000 

Annual energy cost = $300 

Service life = 20 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study. 

IMPLEMENTATION 

As indicated in Volume 5 of the NCHRP Report 500 Series, A Guide for Addressing 

Unsignalized Intersection Collisions (5), the primary purposes of providing lighting at an 

intersection to reduce nighttime crashes are to: 

• Increase drivers’ awareness of the intersection

• Reduce their perception-reaction times

• Increase available sight distance

• Improve the visibility of pedestrians and bicyclists

Agencies should consider installation of a single luminaire at intersections with minor-road stop 

control on rural two-lane roads where the proportion of nighttime crashes to total crashes is 

above the statewide average for this intersection type, or simply at intersections of this type that 

have a moderate to high frequency of nighttime crashes. Except at intersections with very low 

major-road AADTs (e.g., 3-leg intersections with minor-road AADTs less than 300 veh/day), 

this treatment is economically justifiable. In particular, agencies may want to consider 

installation of a single luminaire at intersection locations where view of the intersection may be 

obstructed by horizontal curves or significant skew angles. (This assumes that the skew angle for 

an intersection is defined as the absolute value of the deviation from an intersection angle of 90 

degrees.) At these locations, a single luminaire may increase driver awareness of the intersection 

and available sight distance. 

For agencies considering installation of a single luminaire at intersections with minor-road stop 

control on rural two-lane roads, the FHWA Lighting Handbook may be a useful reference.

(22)

The handbook provides guidance to designers and state, city, and town officials concerning the 

application of roadway lighting. In particular, it includes several examples of warrants others 

have developed to prioritize the need for intersection lighting. For example, Table 12 illustrates a 

simple approach developed by Preston and Schoenecker for establishing priorities for installing 

lighting at rural intersections based on traffic volumes and major-road functional 

classification.(11)

MRIGlobal-ISR\110818-01-005_R 24 
 

 

 

Table 12. Prioritization of lighting at rural intersections by traffic volume and functional class.

(11)

Priority 

Major-Road Functional Classification 

Principal 

Arterial Minor Arterial Collector Local 

Major-Road Volumes in veh/day 

(% of Major-Street Volume that is Recommended on the Minor-Street) 

Low 0-2,000

(10%)

0-1,000

(10%)

0-5,000

(10%)

0-250

(10%)

Moderate 2,000-5,000 

(15%) 

1,000-2,000 

(15%) 

500-1,000

(15%)

250-500

(15%)

High >5,000

(20%)

>2,000

(20%)

>1,000

(20%)

>500

(20%)

Additionally, the AASHTO Roadway Lighting Design Guide may serve as a useful reference.

(23)

While it does not provide specific information regarding the need for and design of intersection 

lighting, it reflects current practices in roadway lighting. 

MRIGlobal-ISR\110818-01-005_R 25 
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MRIGlobal-ISR\110818-01-005_R 26 
CHAPTER 4. TRANSVERSE RUMBLE STRIPS 

 

 

 

 

 

 

 

 

 

Treatment Name Transverse Rumble Strips 

Description Grooves or elevated strips placed in the travel lane perpendicular to the direction of travel, 

generally used in sets in advance of a stop sign to bring drivers’ attention to the stop ahead 

condition. 

States Data from the following states were included in the safety evaluation of this treatment: 

Arkansas, Kansas, Missouri, North Dakota, and Oregon. 

Safety Effectiveness Reduction by severity level: 

The estimated safety effects of this 

treatment in reducing total crashes (all 

crash types combined) at 3-leg and 4-leg 

intersections are as follows: 

3-Leg Intersections:

• 37% reduction in FI crashes

(SE = 20%)

4-Leg Intersections:

• 13% reduction in total crashes

(SE = 7%)

• 29% reduction in FI crashes

(SE = 8%)

Reduction by crash type: 

The estimated safety effects of this 

treatment in reducing angle and rear-end 

crashes at 3-leg and 4-leg intersections are 

as follows: 

3-Leg Intersections:

Angle crashes 

• 61% reduction in PDO crashes

(SE = 28%)

Rear-end crashes 

• 60% reduction in FI crashes

(SE = 29%)

4-Leg Intersections:

Angle crashes 

• 25% reduction in FI crashes

(SE = 10%)

Rear-end crashes 

• 56% reduction in total crashes

(SE = 8%)

• 78% reduction in FI crashes

(SE = 8%)

• 54% reduction in PDO crashes

(SE = 10%)

Cost and Economic 

Benefits 

Benefit-cost ratios calculated for 4-leg intersections ranged from 1.1 to 241.1 when 

assuming installation costs between $1,000 and $5,000 per intersection approach. 

Where to Implement The treatment should be considered for stop-controlled approaches to intersections where 

crash patterns indicate that drivers fail to recognize the stop condition (e.g., angle crashes 

related to stop sign violations). Rumble strips may be particularly effective on the stopcontrolled approach to an intersection that is hidden from view due to horizontal or vertical 

curvature. Intersections following a long tangent section may also benefit from this 

treatment. 

The economic analysis indicates this treatment is economically justifiable, even at 

intersections with low traffic volumes. 

The proximity of the intersection to nearby residents or businesses should be considered 

prior to selecting this treatment for implementation, as noise generated from the rumble 

strips may result in complaints from nearby residents. 

Additional Factors for Typically, transverse rumble strips are considered for implementation after less intrusive 

Consideration measures have been tried and failed to improve the crash experience at an intersection. 

Several unintended consequences of this treatment may occur, and should be considered 

prior to any decision to implement this treatment, including: (a) potential loss-of-control 

problems for motorcyclists and bicyclists, (b) difficulties associated with snowplow 

operations, and (c) inappropriate driver responses such as using the opposing travel lanes 

to drive around the rumble strips (5). 

MRIGlobal-ISR\110818-01-005_R 27 
 

 

 

 

 

 

 

 

 

 

 

 

TREATMENT DESCRIPTION 

Transverse rumble strips are grooves in the roadway surface or elevated strips placed in the 

travel lane perpendicular to the direction of travel. They are designed to generate noise and 

vibration in the vehicle as the driver crosses over them to alert the driver to a condition that may 

require attention or action. The specific application of transverse rumble strips evaluated in this 

research is their placement on the stop-controlled approach to intersections on rural two-lane 

roads. The rumble strips are placed at a distance in advance of the stop sign sufficient to allow 

the driver time to perceive the need to stop, react to that need, and brake appropriately. 

Transverse rumble strips are generally placed in sets of several closely-placed strips to form a 

set, and sometimes more than one set is used on a given approach. The strips may be located 

only in the wheel path or across the full lane width. They are often used in conjunction with stop 

ahead signing. 

Transverse rumble strips may be rolled or grooved into asphalt, formed into fresh concrete, or 

created as epoxy strips on the surface of the pavement. Figure 8 shows pictures of rumble strips 

milled into asphalt. 

SAFETY EVALUATION 

The safety effectiveness of transverse rumble strips installed on the stop-controlled approaches 

of intersections on rural two-lane roads was estimated using the EB before-after analysis 

approach as discussed in Chapter 2 (Analysis Approach). The descriptive statistics, research 

methodology, and analysis results are presented below. 

Descriptive Statistics 

A total of 72 treatment and 126 nontreatment sites in five states—Arkansas, Kansas, Missouri, 

North Dakota, and Oregon—were available for analysis of the safety effectiveness of transverse 

rumble strips installed on stop-controlled approaches of intersections on rural two-lane roads. 

Their breakdown by state, number of intersection legs, and number of treated approaches (1 or 2; 

always 1 for 3-leg intersections) is shown in Table 13. Traffic volumes at the treatment sites 

ranged from 245 to 11,700 veh/day (3-leg intersections) and from 165 to 6,700 veh/day (4-leg 

intersections) on the major-road approaches and from 110 to 7,000 veh/day (3-leg intersections) 

and from 65 to 4,120 veh/day (4-leg intersections) on the minor-road approaches. 

Crash and traffic volume data were obtained for varying before- and after-treatment installation 

periods, depending on treatment installation date at the individual sites. Three crash types were 

considered in this analysis: all collision types combined, angle crashes, and rear-end crashes. 

Table 14 (treatment intersections) and Table 15 (nontreatment intersections) summarize the crash 

data used in the analysis. They present total, angle, and rear-end crash data summed across all 

intersections of a given configuration (3-leg or 4-leg) within each state. 

MRIGlobal-ISR\110818-01-005_R 28 
Figure 8. Photo. Examples of transverse rumble strips placement (Image credit: Google EarthTM

Mapping Service).

(21)

MRIGlobal-ISR\110818-01-005_R 29 
 

 

 

 

 

 

 

 

 

 

 

Table 13. Transverse rumble strips: number of sites by State, number of intersection legs, and 

number of treated approaches. 

State 

Number of 

Intersection 

Legs 

Number of 

Treated 

Approaches 

Number of Sites 

Treatment Nontreatment 

AR 4 

1 1 

19 

2 1 

KS 4 1 2 18 

MO 

3 1 5 6 

4 

1 5 

31 

2 10 

NDa 

3 1 17 13 

4 

1 20 

17 

2 6 

OR 

3 1 3 8 

4 

1 1 

14 

2 1 

All sites 72 126 

a No control intersections were available in North Dakota; 

nontreatment sites from Nebraska were used in the analysis. 

MRIGlobal-ISR\110818-01-005_R 30 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 14. Transverse rumble strips: summary crash statistics for the before and after treatment 

periods for treatment intersections by State and number of intersection legs. 

Number 

of Legs State 

Before Period After Period 

Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts 

Total FS FI PDO Total FS FI PDO 

ALL CRASHES 

3 

MO 4 to 5 5 23 12 0 7 5 3 to 9 5 35 19 2 7 12 

ND 5 17 85 9 0 2 7 2 to 3 17 41 4 0 2 2 

OR 5 3 15 9 0 3 6 3 to 8 3 16 8 0 2 6 

4 

AR 5 2 10 14 6 10 4 9 to 10 2 19 14 2 7 7 

KS 5 2 10 4 2 2 2 1 to 2 2 3 0 0 0 0 

MO 3 to 5 15 67 75 12 42 33 4 to 10 15 111 174 28 77 97 

ND 5 26 130 14 0 7 7 2 to 3 26 62 11 0 2 9 

OR 5 2 10 14 0 7 7 8 to 9 2 17 28 3 19 9 

ANGLE CRASHES 

3 

MO 4 to 5 5 23 3 0 3 0 3 to 9 5 35 5 0 3 2 

ND 5 17 85 0 0 0 0 2 to 3 17 41 0 0 0 0 

OR 5 3 15 0 0 0 0 3 to 8 3 16 0 0 0 0 

4 

AR 5 2 10 9 3 6 3 9 to 10 2 19 7 2 4 3 

KS 5 2 10 3 2 2 1 1 to 2 2 3 0 0 0 0 

MO 3 to 5 15 67 53 11 36 17 4 to 10 15 111 115 23 56 59 

ND 5 26 130 2 0 1 1 2 to 3 26 62 4 0 1 3 

OR 5 2 10 6 0 2 4 8 to 9 2 17 9 2 9 0 

REAR-END CRASHES 

3 

MO 4 to 5 5 23 3 0 2 1 3 to 9 5 35 6 1 1 5 

ND 5 17 85 0 0 0 0 2 to 3 17 41 1 0 1 0 

OR 5 3 15 1 0 0 1 3 to 8 3 16 2 0 0 2 

4 

AR 5 2 10 2 2 2 0 9 to 10 2 19 5 0 2 3 

KS 5 2 10 0 0 0 0 1 to 2 2 3 0 0 0 0 

MO 3 to 5 15 67 9 1 3 6 4 to 10 15 111 17 0 3 14 

ND 5 26 130 5 0 2 3 2 to 3 26 62 3 0 0 3 

OR 5 2 10 0 0 0 0 8 to 9 2 17 5 0 3 2 

MRIGlobal-ISR\110818-01-005_R 31 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 15. Transverse rumble strips: summary crash statistics for the entire study period for 

nontreatment intersections by State and number of intersection legs. 

Number of 

Intersection 

Legs State 

Entire Study Period 

Range of 

Years of 

Data in 

State 

Number 

of Sites 

Number 

of 

SiteYears 

Crash Counts 

Total FS FI PDO 

ALL CRASHES 

3 

MO 14 6 84 8 0 2 6 

ND 9 13 117 24 3 7 17 

OR 14 8 112 71 1 42 29 

4 

AR 16 19 304 160 35 96 64 

KS 8 18 144 25 1 11 14 

MO 14 31 434 189 30 100 89 

NDa 9 17 153 41 8 26 15 

OR 15 14 210 88 0 52 36 

ANGLE CRASHES 

3 

MO 14 6 84 2 0 0 2 

ND 9 13 117 4 2 3 1 

OR 14 8 112 0 0 0 0 

4 

AR 16 19 304 98 24 63 35 

KS 8 18 144 10 1 7 3 

MO 14 31 434 102 24 65 37 

NDa 9 17 153 21 6 16 5 

OR 15 14 210 29 0 20 9 

REAR-END CRASHES 

3 

MO 14 6 84 1 0 0 1 

ND 9 13 117 2 0 0 2 

OR 14 8 112 18 0 9 9 

4 

AR 16 19 304 15 3 8 7 

KS 8 18 144 3 0 1 2 

MO 14 31 434 24 1 8 16 

NDa 9 17 153 5 2 3 2 

OR 15 14 210 15 0 8 7 

a No control intersections were available in North Dakota; nontreatment sites from 

Nebraska were used in the analysis. 

MRIGlobal-ISR\110818-01-005_R 32 
 

 

 

 

 

 

 

Predicted crashes/yr = exp[a + b(lnAADTmaj) + c(lnAADTmin)] 

 

Methodology 

The safety effectiveness of installing transverse rumble strips was evaluated using an EB method 

similar to that discussed in Chapter 3 for the EB evaluation of a single luminaire installation. 

Prior to implementing the EB method, the following points were addressed: 

1. Select appropriate SPF: The SPFs for intersections on rural two-lane roads from

Chapter 10 of the HSM were selected. These are given for total crashes only. The

coefficients of these SPFs vary by number of intersection legs. Use of the intersection

SPFs from Chapter 10 of the HSM provide an estimate of the intersection-related

predicted crash frequency for sites included in the analysis in the absence of the

treatment.

2. Obtain the proportion of target crashes for total, FS, FI, and PDO crashes (PR1): The

proportions of target crashes (angle and rear end) to all crashes for each severity level

(total, FS, FI, and PDO) were calculated using all crashes from nontreatment sites and

from the before-period years of treatment sites. These proportions were calculated

separately for 3- and 4-leg intersections. These proportions scale the total crash

predictions (i.e., all crash types) to predictions for the target crashes (i.e., angle and rearend crashes).

3. Obtain the proportions of FS, FI, and PDO crashes (PR2): These proportions were

calculated as the ratio of all FS, FI, or PDO crashes over total crashes using all crashes

from the nontreatment sites and from the before-period years of treatment sites. These

proportions were calculated separately for 3- and 4-leg intersections. These proportions

scale the total crash predictions (i.e., all severity levels combined) to predicted crashes

for specific severity level crashes (i.e., FS, FI, and PDO).

4. Calibrate the SPFs to the local jurisdiction: Calibration was performed using all crashes

(all collision types combined), separately for each intersection configuration within a

given state, again using all nontreatment intersections and before treatment intersections

combined. Total crash counts were used rather than target crashes due to the scarcity of

target crashes, especially FS and FI angle and rear-end crashes. The calibration factor

adjusts the HSM SPFs for varying conditions in the local jurisdiction such as crash

reporting thresholds, environmental, etc.

The SPFs presented in the HSM for intersections on rural two-lane roads for total severity level 

(i.e., all severity levels combined) have the general form: 

Figure 9. Equation. Base model for predicted crashes per year. 

where a, b, and c are the regression coefficients shown in Table 16. These coefficients apply to 

base conditions and vary by number of intersection legs. For the intersection SPFs in Chapter 10 

of the HSM, the base conditions are: 

MRIGlobal-ISR\110818-01-005_R 33 
Predicted crashes/yr = {exp[a + b(lnAADTmaj) + c(lnAADTmin)]} × PR1 × PR2 × CMFCombined × Cr 

 

 

 

 

• Intersection skew angle: 0 degrees 

• Number of intersection left-turn lanes: None on approaches without stop control

• Number of intersection right-turn lanes: None on approaches without stop control

• Presence of lighting: None 

Crash modification factors (CMFs), calibration factors (Cr), proportions of angle and rear-end 

crashes (PR1), and proportions of FS, FI, and PDO crashes (PR2) were then used to adjust for 

local conditions as follows: 

Figure 10. Equation. Model for predicted crashes per year for specific crash types and severity 

levels, and accounting for local conditions. 

The CMFCombined is the product of the CMFs from Chapter 10 of the HSM for skew angle 

(CMF1i), number of major-road left-turn lanes (CMF2i), and number of major-road right-turn 

lanes (CMF3i), for a particular intersection configuration. 

SPF coefficients (a, b, and c and overdispersion parameter), target crash proportions (PR1), 

proportions of FS, FI, and PDO out of total crashes (PR2), and calibration factors (Cr) are shown 

for each intersection configuration in Table 16. Number of site-years, total crash counts (all 

severity levels), and target crash counts are also displayed. The table also shows the default 

proportions of PR1 and PR2 presented in Chapter 10 of the HSM (see Tables 10-6 and 10-5, 

respectively). Note that PR2 is always equal to 1 for total crashes. The decision of which 

proportions to use—those calculated from the data or those provided by the HSM—was based on 

whether calculated proportions of target crashes (PR1) were nonzero for all severity levels. If 

they were not, then the HSM proportions (both PR1 and PR2) were used in the EB before-after 

analysis. The selection of which proportions were used is indicated in Table 16 by an asterisk. 

The calibration factors for the SPFs shown in Table 16 ranged from 0.53 to 6.98, meaning that 

several of the sites used in this analysis had substantially different crash experience than the sites 

used to develop the SPFs. For example, 4-leg intersections in Arkansas had a calibration factor 

of 6.98, indicating that those intersections experienced approximately 7 times more crashes than 

the 4-leg intersections used to develop the SPFs in the HSM. 

Safety Effectiveness 

The EB before-after method was applied to estimate the safety effectiveness of installing 

transverse rumble strips on stop-controlled approaches to intersections on rural two-lane roads. 

The analysis included treatment and nontreatment sites in Arkansas, Kansas, Missouri, Nebraska 

(nontreatment sites only), North Dakota (treatment sites only), and Oregon, and used HSM SPFs 

for 3- and 4-leg intersections on rural two-lane roads. 

MRIGlobal-ISR\110818-01-005_R 34 
 

 

 

 

 

 

 

 

 

 

 

 

Table 16. Transverse rumble strips: SPF coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs. 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

AR 4 314 Total 174 Angle 107 

-8.56 0.60 0.61 0.24 

0.62* 0.43 1.00* 1.00 

6.98 

Rear End 17 0.10* 0.24 1.00* 1.00 

FS 41 Angle 27 0.66* 0.53 0.24* 0.06 

Rear End 5 0.12* 0.21 0.24* 0.06 

FI 106 Angle 69 0.65* 0.53 0.61* 0.43 

Rear End 10 0.09* 0.21 0.61* 0.43 

PDO 68 Angle 38 0.56* 0.35 0.39* 0.57 

Rear End 7 0.10* 0.27 0.39* 0.57 

KS 4 154 Total 29 Angle 13 

-8.56 0.60 0.61 0.24 

0.45 0.43* 1.00 1.00* 

1.86 

Rear End 3 0.10 0.24* 1.00 1.00* 

FS 3 Angle 3 1.00 0.53* 0.10 0.06* 

Rear End 0 0.00 0.21* 0.10 0.06* 

FI 13 Angle 9 0.69 0.53* 0.45 0.43* 

Rear End 1 0.08 0.21* 0.45 0.43* 

PDO 16 Angle 4 0.25 0.35* 0.55 0.57* 

Rear End 2 0.13 0.27* 0.55 0.57* 

MRIGlobal-ISR\110818-01-005_R 35 
 

 

 

 

 

 

 

 

 

 

 

Table 16. Transverse rumble strips: SPF coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

MO 3 107 Total 20 Angle 5 

-9.86 0.79 0.49 0.54 

0.25 0.24* 1.00 1.00* 

0.53 

Rear End 4 0.20 0.28* 1.00 1.00* 

FS 0 Angle 0 0.00 0.28* 0.00 0.06* 

Rear End 0 0.00 0.26* 0.00 0.06* 

FI 9 Angle 3 0.33 0.28* 0.45 0.42* 

Rear End 2 0.22 0.26* 0.45 0.42* 

PDO 11 Angle 2 0.18 0.21* 0.55 0.59* 

Rear End 2 0.18 0.29* 0.55 0.59* 

4 501 Total 264 Angle 155 

-8.56 0.60 0.61 0.24 

0.59* 0.43 1.00* 1.00 

1.01 

Rear End 33 0.13* 0.24 1.00* 1.00 

FS 42 Angle 35 0.83* 0.53 0.16* 0.06 

Rear End 2 0.05* 0.21 0.16* 0.06 

FI 142 Angle 101 0.71* 0.53 0.54* 0.43 

Rear End 11 0.08* 0.21 0.54* 0.43 

PDO 122 Angle 54 0.44* 0.35 0.46* 0.57 

Rear End 22 0.18* 0.27 0.46* 0.57 

MRIGlobal-ISR\110818-01-005_R 36 
 

 

 

 

 

 

 

 

 

 

 

Table 16. Transverse rumble strips: SPF coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

ND 3 202 Total 33 Angle 4 

-9.86 0.79 0.49 0.54 

0.12 0.24* 1.00 1.00* 

0.97 

Rear End 2 0.06 0.28* 1.00 1.00* 

FS 3 Angle 2 0.67 0.28* 0.09 0.06* 

Rear End 0 0.00 0.26* 0.09 0.06* 

FI 9 Angle 3 0.33 0.28* 0.27 0.42* 

Rear End 0 0.00 0.26* 0.27 0.42* 

PDO 24 Angle 1 0.04 0.21* 0.73 0.59* 

Rear End 2 0.08 0.29* 0.73 0.59* 

4 283 Total 55 Angle 23 

-8.56 0.60 0.61 0.24 

0.42* 0.43 1.00 1.00 

0.55 

Rear End 10 0.18* 0.24 1.00 1.00 

FS 8 Angle 6 0.75* 0.53 0.15 0.06 

Rear End 2 0.25* 0.21 0.15 0.06 

FI 33 Angle 17 0.52* 0.53 0.60 0.43 

Rear End 5 0.15* 0.21 0.60 0.43 

PDO 22 Angle 6 0.27* 0.35 0.40 0.57 

Rear End 5 0.23* 0.27 0.40 0.57 

MRIGlobal-ISR\110818-01-005_R 37 
 

 

 

 

 

 

 

 

 

 

 

 

Table 16. Transverse rumble strips: SPF coefficients, target crash proportions, and calibration factors by State and number of 

intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

OR 3 127 Total 80 Angle 0 

-9.86 0.79 0.49 0.54 

0.00 0.24* 1.00 1.00* 

1.17 

Rear End 19 0.24 0.28* 1.00 1.00* 

FS 1 Angle 0 0.00 0.28* 0.01 0.06* 

Rear End 0 0.00 0.26* 0.01 0.06* 

FI 45 Angle 0 0.00 0.28* 0.56 0.42* 

Rear End 9 0.20 0.26* 0.56 0.42* 

PDO 35 Angle 0 0.00 0.21* 0.44 0.59* 

Rear End 10 0.29 0.29* 0.44 0.59* 

4 220 Total 102 Angle 35 

-8.56 0.60 0.61 0.24 

0.34 0.43* 1.00 1.00* 

1.79 

Rear End 15 0.15 0.24* 1.00 1.00* 

FS 0 Angle 0 0.00 0.53* 0.00 0.06* 

Rear End 0 0.00 0.21* 0.00 0.06* 

FI 59 Angle 22 0.37 0.53* 0.58 0.43* 

Rear End 8 0.14 0.21* 0.58 0.43* 

PDO 43 Angle 13 0.30 0.35* 0.42 0.57* 

Rear End 7 0.16 0.27* 0.42 0.57* 

NOTE: Asterisked proportions were those used in the analyses. 

MRIGlobal-ISR\110818-01-005_R 38 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

The EB before-after analysis results are shown in Table 17 for the following crash types and 

severity levels: 

• Total crashes (all collision

types combined)

o Total crashes

o FI crashes

o PDO crashes

• Angle crashes

o Total crashes

o FI crashes

o PDO crashes

• Rear-end crashes

o Total crashes

o FI crashes

o PDO crashes

Table 17. Transverse rumble strips: safety effectiveness on target crashes by number of 

intersection legs. 

Number of 

Treatment 

Sites 

Safety

Effectiveness 

(%) 

SE of 

Treatment 

Effect (%) Significance 

ALL S

Crash 

Severity 

TATES COMBINED; 3-LEG INTERSECTIONS 

ALL CRASHES 

Total 

25 

-18 16 Not significant at 90% CL 

FI -37 20 Significant at 90% CL 

PDO -13 21 Not significant at 90% CL 

ANGLE CRASHES 

Total 

25 

-43 26 Not significant at 90% CL 

FI -44 33 Not significant at 90% CL 

PDO -61 28 Significant at 95% CL 

REAR-END CRASHES 

Total 

25 

-16 29 Not significant at 90% CL 

FI -60 29 Significant at 95% CL 

PDO -6 37 Not significant at 90% CL 

ALL STATES COMBINED; 4-LEG INTERSECTIONS 

All Crashes 

Total 

47 

-13 7 Significant at 90% CL 

FI -29 8 Significant at 95% CL 

PDO -14 9 Not significant at 90% CL 

ANGLE CRASHES 

Total 

47 

-13 8 Not significant at 90% CL 

FI -25 10 Significant at 95% CL 

PDO -13 12 Not significant at 90% CL 

REAR-END CRASHES 

Total 

47 

-56 8 Significant at 95% CL 

FI -78 8 Significant at 95% CL 

PDO -54 10 Significant at 95% CL 

MRIGlobal-ISR\110818-01-005_R 39 
 

 

 

 

 

 

 

 

Although the analyses for FS injury crashes were performed, the analysis results were not 

considered reliable and are therefore not shown. The occurrence of FS crashes was too rare 

across all intersections in the study (both treatment and nontreatment sites). 

The EB method was applied to all states combined based on the following reasoning: (1) only a 

small number of treatment sites were available in some states—individually, they could not have 

been used for evaluation; and (2) all EB intermediate calculations (up to the final effectiveness 

calculations) are performed on a state/site basis, thus using SPFs, proportions (PR1 and PR2), 

combined CMFs, and calibration factors (Cr) specific to that state. This approach, to some extent, 

takes differences among states into account, while increasing site and crash sample sizes. 

The EB method was applied separately to 3-leg and 4-leg intersections, but at 4-leg intersections, 

sites with treatment installation on a single approach and on both approaches were pooled to 

ensure a sufficient sample size for evaluation. 

The statistics shown in Table 17 for each crash severity are: 

• Number of treatment intersections

• Percent change in crash frequency due to the treatment: estimate and standard error

• An indication of whether the treatment had a statistically significant effect on the crash

types and severity level of interest at the 95- or 90-percent confidence level

A negative percent safety effectiveness indicates that crash frequencies decreased due to the 

treatment. 

The following general observations can be made when looking at Table 14, Table 16, and Table 

17 together: 

• At 3-leg intersections, the analysis results indicate that, for all crash types combined,

transverse rumble strips reduce FI crashes by 37 percent. When considering target crash

types, FI rear-end crashes and PDO angle crashes were each reduced by approximately

60 percent.

• At 4-leg intersections, the analysis results indicate that, for all crash types combined,

transverse rumble strips reduced total crashes by 13 percent and FI crashes by 29 percent.

When evaluating target crash types, FI angle crashes were reduced by 25 percent, while

total, FI, and PDO rear-end crashes were reduced by 56, 78, and 54 percent respectively.

These results suggest that transverse rumble strips are more effective at reducing rear-end

crashes than angle crashes.

ECONOMIC ANALYSIS 

An economic analysis was conducted to estimate the economic benefits of installing transverse 

rumble strips at stop-controlled intersections on rural two-lane roads. The economic analysis was 

based on calculations assuming installation of transverse rumble strips on both stop-controlled 

approaches of 4-leg intersections. The Economic Analysis discussion in Chapter 2 describes the 

MRIGlobal-ISR\110818-01-005_R 40 
 

 

 

 

 

 

 

 

 

 

 

 

 

procedure used for estimating the benefit-cost ratios of the treatment. The economic benefits of 

this treatment were estimated using the safety effectiveness estimates developed in this research. 

The estimated crash reduction benefit of the treatment was calculated using the CMF for total 

crashes (all severity levels and crash types combined) for 4-leg intersections (CMF = 0.87), 

which was statistically significant at the 90-percent level. The CMF for total crashes for 3-leg 

intersections was not significant at the 90-percent level. 

Cost and service life of transverse rumble strips may vary by geographic region and installation 

type. Two scenarios were used to calculate the installation costs of transverse rumble strips in 

this evaluation. In the first scenario, a $5,000 installation cost per approach and a 20-year life 

cycle were assumed. These figures were reported by the Oregon Department of Transportation. 

Table 18 presents the benefit-cost ratios as a function of major- and minor-road AADTs for a 4-

leg stop-controlled intersection on a rural two-lane highway where transverse rumble strips are 

installed on both stop-controlled approaches. The AADTs in the table cover the range of AADTs 

of the study sites used for the estimation of the CMF. All the benefit-cost ratios shown are equal 

to or greater than 1.0, meaning that the installation of transverse rumble strips is economically 

justified at all AADT ranges included in this study. 

Table 18. Transverse rumble strips: benefit-cost ratios for treatment on two minor-road 

approaches at 4-leg rural stop-controlled intersection for $10,000 installation cost and 20-yr 

service life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 20% 30% 40% 45% 50% 60% 65% 70% 75% 80% 90% 95% 

200 N/A N/A N/A N/A N/A 1.1 1.1 1.3 1.3 1.4 1.5 1.5 1.6 1.7 

1,000 N/A 3.0 4.5 5.8 6.9 7.5 8.0 8.9 9.3 9.8 10.2 10.6 11.4 11.8 

2,000 4.5 6.9 10.5 13.5 16.1 17.2 18.4 20.6 21.6 22.6 23.6 24.5 26.3 27.2 

3,000 7.4 11.3 17.2 22.0 26.2 28.2 30.0 33.6 35.3 36.9 38.5 40.0 43.0 44.4 

4,000 10.4 15.9 24.3 31.2 37.1 39.9 42.6 47.6 49.9 52.2 54.5 N/A N/A N/A 

5,000 13.7 20.9 31.9 40.8 48.6 52.3 55.7 62.3 N/A N/A N/A N/A N/A N/A 

CMF = 0.87 (total crashes) 

Installation cost = $10,000 (i.e., $5,000 per approach) 

Service life = 20 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study 

In the second scenario, a $1,000 installation cost per approach and a 5-yr service life were 

assumed. This installation cost was reported by the Kansas Department of Transportation for 

milled transverse rumble strips. Kansas did not report a service life for this treatment; however, 

for the sake of the analysis, a shorter service life was assumed. Assuming that a longer service 

life will only increase the benefit of the treatment, selecting a short service life represents a 

conservative approach for a benefit-cost analysis. 

Table 19 displays the benefit-cost ratios as a function of major- and minor-road AADTs for a 4-

leg stop-controlled intersection on a rural two-lane highway where transverse rumble strips are 

installed on both stop-controlled approaches. The AADTs in the table cover the range of AADTs 

MRIGlobal-ISR\110818-01-005_R 41 
 

 

 

 

 

 

of the study sites used for the estimation of the CMF. The installation of transverse rumble strips 

again are economically justified at all AADT levels, all benefit-cost ratios are greater than 4.0. 

Table 19. Transverse rumble strips: benefit-cost ratios for treatment on two minor-road 

approaches at 4-leg rural stop-controlled intersection for $2,000 installation cost

 and 5-yr service life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 20% 30% 40% 45% 50% 60% 65% 70% 75% 80% 

200 N/A N/A N/A N/A N/A 4.1 4.4 4.9 5.2 5.4 5.6 5.8 

1,000 N/A 11.5 17.6 22.5 26.9 28.9 30.8 34.4 36.1 37.8 39.4 41.0 

2,000 17.5 26.7 40.7 52.1 62.1 66.8 71.2 79.6 83.5 87.4 91.2 94.8 

3,000 28.5 43.6 66.5 85.1 101.5 109.0 116.3 130.0 136.5 142.8 148.9 154.9 

4,000 40.4 61.7 94.2 120.6 143.7 154.4 164.7 184.1 193.3 202.2 210.9 N/A 

5,000 53.0 80.8 123.4 158.0 188.3 202.3 215.7 241.1 N/A N/A N/A N/A 

CMF = 0.87 (total crashes) 

Installation cost = $2,000 (i.e., $1,000 per approach) 

Service life = 5 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study 

IMPLEMENTATION 

The primary purpose of installing transverse rumble strips on stop-controlled approaches to 

intersections on rural two-lane roads is to alert drivers to a condition that requires attention and 

action. In this case, the treatment is intended to increase drivers’ awareness of the intersection 

and to the traffic control, as drivers are required to stop along the controlled approach before 

proceeding into the intersection. Transverse rumble strips should be considered for installation 

on stop-controlled approaches to intersections where a pattern of crashes is present related to a 

lack of driver recognition of the presence of a stop sign (e.g., angle crashes related to stop sign 

violations).(5) In particular, transverse rumble strips should be considered along the stopcontrolled approach to an intersection that is hidden from view due to horizontal or vertical 

curvature.(24) In addition, transverse rumble strips should be considered along the stop-controlled 

approach to an intersection following a long tangent section as drivers may become less attentive 

to their environment or may underestimate their approach speed to the intersection having driven 

for a long time at a significantly higher speed. Typically, transverse rumble strips are considered 

for implementation after less intrusive measures have been tried and failed to improve the crash 

experience at an intersection. The economic analysis provided above shows that this treatment is 

economically justifiable, even along roads with low traffic volumes. 

Noise generated from transverse rumble strips may disturb nearby residents or businesses. The 

proximity of the intersection to nearby residents or businesses should be considered prior to 

selecting this treatment for implementation. 

There is not a single recommended design for installing transverse rumble strips on stopcontrolled approaches to intersections on rural two-lane roads. Design details are provided below 

from three states to serve as examples of current implementation practice. Agencies may choose 

MRIGlobal-ISR\110818-01-005_R 42 
 

 

 

 

 

 

 

 

 

to adopt or modify one of these example designs when developing their own rumble strip policy. 

The examples illustrate that while the dimensions of the actual rumble strips themselves are 

fairly consistent, there is a great deal of variation in the placement of the strips and how many 

individual sets of rumble strips are used in advance of a stop condition. 

Figure 11 illustrates the transverse rumble strip placement guidance used by Missouri 

Department of Transportation (MoDOT). Design details of the rumble strips themselves are 

shown in Figure 12. 

Figure 13 illustrates North Dakota Department of Transportation’s design details for transverse 

rumble strips, which includes six sets of rumble strips encountered by a driver approaching a 

stop condition. The dimensions of the milled rumble strips are as follows: 

• Length: Varies with the width of the travel lane 

• Width: 4 in 

• Depth: 0.5 in to 0.625 in 

• Spacing: 12 in (on-center) 

Figure 14 illustrates design guidance for transverse rumble strips provided by the Kansas 

Department of Transportation (KDOT). KDOT’s policy is to include three sets of 25 lateral 

grooves provided in advance of the warning area. KDOT’s policy recommends application of 

transverse rumble strips at intersections where three or more right-angle collisions have occurred 

in a 12-month period that involve stop sign violations, where the crash rate is higher than 15 

crashes per 10 million entering vehicles, and where the previous intersection on that road 

requiring a stop or vehicle maneuver is more than 15.5 miles prior to the intersection. 

MRIGlobal-ISR\110818-01-005_R 43 
Figure 11. Diagram. MoDOT’s design guidance for placement of transverse rumble strips.(24)

MRIGlobal-ISR\110818-01-005_R 44 
Figure 12. Diagram. MoDOT’s design detail for transverse rumble strips.(24)

MRIGlobal-ISR\110818-01-005_R 45 
Figure 13. Diagram. North Dakota DOT’s transverse rumble strip design detail.(25)

MRIGlobal-ISR\110818-01-005_R 46 
 

 

Figure 14. Diagram. KDOT transverse rumble strip installation and design detail.(26)

MRIGlobal-ISR\110818-01-005_R 47 
 

 

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MRIGlobal-ISR\110818-01-005_R 48 
CHAPTER 5. SUPPLEMENTARY PAVEMENT MARKINGS 

 

 

 

 

 

 

 

 

 

 

Treatment Name Supplementary Pavement Markings 

Description This evaluation considered two applications of supplementary pavement markings. In the first 

application, STOP AHEAD pavement markings were installed on the stop-controlled 

approach to an intersection. These markings are used to alert drivers of the presence of the 

intersection and the need to stop before proceeding into the intersection. These markings are 

intended to reduce crashes related to a failure to stop at the intersection. 

In the second application, supplementary pavement markings were installed on uncontrolled 

approaches to an intersection. These pavement markings include a graphical depiction of the 

intersection with one of the following symbols: ┼, ├, or ┤, and are used to alert drivers of the 

presence of the intersection and of the potential for vehicles turning onto or off the roadway at 

that location. 

States Data from the following states were included in the safety evaluation of this treatment: 

Arkansas, Minnesota, Nebraska, Pennsylvania, and Vermont. 

Safety Reduction by severity level: Reduction by crash type: 

Effectiveness The estimated safety effects of this treatment 

in reducing total crashes (all crash types 

combined) at 3-leg and 4-leg intersections 

are as follows: 

Markings on stop-controlled approaches 

3-Leg Intersections:

• 67% reduction of total crashes

(SE = 7%)

• 76% reduction in FI crashes

(SE = 7%)

• 72% reduction in PDO crashes

(SE = 7%)

4-Leg Intersections:

• 66% reduction in total crashes

(SE = 4%)

• 69% reduction in FI crashes

(SE = 5%)

The estimated safety effects of this 

treatment in reducing angle and rear-end 

crashes at 3-leg and 4-leg intersections are 

as follows: 

Markings on stop-controlled approaches 

3-Leg Intersections:

Angle Crashes

• 92% reduction in total crashes

(SE = 5%)

• 88% reduction in FI crashes

(SE = 7%)

Rear-End Crashes 

• 95% reduction in total crashes

(SE = 4%)

• 96% reduction in FI crashes

(SE = 5%)

97% reduction in PDO crashes

(SE = 3%) • 77% reduction in PDO crashes

(SE = 4%) 4-Leg Intersections:

Angle Crashes

• 74% reduction in total crashes

(SE = 4%)

• 71% reduction in FI crashes

(SE = 5%)

• 88% reduction in PDO crashes

(SE = 3%)

Rear-End Crashes 

• 89% reduction in total crashes

(SE = 3%)

• 86% reduction in FI crashes

(SE = 5%)

• 95% reduction in PDO crashes

(SE = 2%)

MRIGlobal-ISR\110818-01-005_R 49 
 

 

 

 

 

 

 

 

 

 

 

Treatment Name Supplementary Pavement Markings 

Safety 

Effectiveness 

Reduction by severity level: 

Markings on uncontrolled approaches 

3-Leg and 4-Leg Intersections Combined

• 46% reduction in total crashes

(SE = 5%)

• 49% reduction in FI crashes

(SE = 7%)

• 50% reduction in PDO crashes

(SE = 6%)

Reduction by crash type: 

Markings on uncontrolled approaches 

3-Leg and 4-Leg Intersections Combined

Angle Crashes

• 38% reduction in total crashes

(SE = 7%)

• 42% reduction in FI crashes

(SE = 8%)

• 35% reduction in PDO crashes

(SE = 10%)

Rear-End Crashes 

• 69% reduction in total crashes

(SE = 7%)

• 76% reduction in FI crashes

(SE = 9%)

• 75% reduction in PDO crashes

(SE = 8%)

Cost and Economic To estimate benefit-cost ratios, assumed installation costs for painting supplementary 

Benefits pavement markings (i.e., STOP AHEAD) on a stop-controlled approach to an intersection 

ranged from $300-$750. The assumed cost for installing supplementary pavement markings 

on both uncontrolled approaches to an intersection with thermoplastic markings was $10,000 

(cost per intersection treatment). Benefit-cost ratios calculated for installing supplementary 

pavement markings (i.e., STOP AHEAD) on stop-controlled approaches to intersections 

ranged from 1.8 to 528.9, and benefit-cost ratios for installing supplementary pavement 

markings on uncontrolled approaches to intersections ranged from 15.1 to 138.7. 

Where to 

Implement 

The treatment should be considered at intersections with a crash pattern related to a lack of 

driver awareness of the presence of the intersection. 

Additional Factors 

for Consideration 

Supplementary pavement markings may not be visible during winter conditions with snow 

and ice. Supplementary pavement markings may have a lower coefficient of friction 

compared to the rest of the intersection approach, especially during wet conditions (5). 

TREATMENT DESCRIPTION 

Supplementary pavement markings may be used as a safety treatment at unsignalized 

intersections with minor-road stop control on rural two-lane roads. This study considered two 

distinct types of supplementary pavement markings: markings on stop-controlled approaches and 

markings on uncontrolled approaches. These two types of markings are discussed in greater 

detail below. 

Supplementary pavement markings installed on stop-controlled approaches alert drivers of the 

presence of the intersection and the need to stop before proceeding into the intersection. At all of 

the study locations included in the evaluation of supplementary pavement markings installed on 

stop-controlled approaches to an intersection, the supplementary pavement markings read 

“STOP AHEAD.” Figure 15 shows two images of supplementary pavement markings on stopcontrolled approaches. 

MRIGlobal-ISR\110818-01-005_R 50 
 

 

 

 

 

 

Figure 15. Photo. Aerial view and street view of supplementary pavement markings on stopcontrolled approach (Image credit: Google EarthTM Mapping Service).(21)

At uncontrolled approaches, the Pennsylvania Department of Transportation deployed a unique 

set of supplementary pavement markings on the major-road approaches (i.e., uncontrolled 

approaches) at intersections with minor-road stop control. These markings are intended to alert 

drivers of the presence of the intersection and of the potential for vehicles and other road users 

entering or exiting the roadway at that location. Figure 16 shows the pavement markings on the 

uncontrolled approach to an intersection that is located over the crest of the vertical curve. The 

treatment consists of two sets of pavement markings. In the direction of travel, the first set of 

markings warns drivers to slow to the speed limit of the roadway (e.g., “SLOW, XX MPH,”). 

The second set of markings illustrates the configuration of the upcoming intersection as either 4 

legs or 3 legs with one of the following symbols: ┼, ├, or ┤. For 3-leg intersections, the symbol 

indicates the side of the roadway from which the minor road intersects the major road. In 

MRIGlobal-ISR\110818-01-005_R 51 
 

 

 

 

Figure 16, the supplementary pavement markings warn drivers to slow down to a speed of 30 

mph as they are approaching a 4-leg intersection. 

Figure 16. Photo. Supplementary pavement markings on uncontrolled approach. 

(Image credit: Pennsylvania DOT) 

SAFETY EVALUATION 

The safety effectiveness of supplementary pavement markings was evaluated separately for 

markings installed on stop-controlled approaches of intersections and those installed on 

uncontrolled approaches, because the two types of installations are very different in their 

mechanism for reducing crashes. In the first case, drivers are being reminded that they must take 

action at the intersection—the treatment is aimed at reducing crashes related to a failure to stop 

at the intersection. In the second case, drivers are being warned to use caution while approaching 

the intersection as other vehicles or road users may be entering the roadway, slowing to exit the 

roadway, or making a left-turn in front of the driver; however, no specific action is necessarily 

required. The EB before-after analysis approach was used in both cases, as discussed in Chapter 

2 (Analysis Approach). The descriptive statistics, research methodology, and analysis results of 

the safety evaluations are presented below. 

MRIGlobal-ISR\110818-01-005_R 52 
 

 

 

 

 

Descriptive Statistics 

A total of 76 treatment and 140 nontreatment sites in four states—Arkansas, Minnesota, 

Nebraska, and Vermont—were available for analysis of the safety effectiveness of 

supplementary pavement markings on stop-controlled intersection approaches. Their breakdown 

by state, number of intersection legs, and number of treated approaches is shown in Table 20. 

The treatment was always installed on one minor-road approach at 3-leg intersections and either 

one or two minor-road approaches at 4-leg intersections. Traffic volumes at the treatment sites 

ranged from 90 to 5,700 veh/day (3-leg intersections) and from 105 to 4,800 veh/day (4-leg 

intersections) on the major-road approaches and from 40 to 3,000 veh/day (3-leg intersections) 

and from 25 to 1,770 veh/day (4-leg intersections) on the minor-road approaches. 

In Pennsylvania, 11 treatment sites and 28 nontreatment sites were available for analysis of 

supplementary pavement markings on uncontrolled intersection approaches. Supplementary 

pavement markings were installed on both major-road approaches at all intersections included in 

the evaluation. Their breakdown by number of intersection legs and number of treated 

approaches is also shown in Table 20. Traffic volumes at the treatment sites ranged from 1,890 

to 14,020 veh/day (3-leg intersections) and from 2,310 to 16,270 veh/day (4-leg intersections) on 

the major-road approaches and from 180 to 5,380 veh/day (3-leg intersections) and from 330 to 

3,480 veh/day (4-leg intersections) on the minor-road approaches. 

Table 20. Supplementary pavement markings: number of sites by State, number of intersection 

legs, and number of treated approaches. 

State 

Number of 

Intersection 

Legs 

Number of 

Treated 

Approaches 

Number of Sites 

Treatment Nontreatment 

Treatment on Stop-Controlled Approach(es) 

AR 

3 1 1 11 

4 

1 1 

19 

2 1 

MN 

3 1 29 21 

4 

1 21 

40 

2 9 

NE 

3 1 3 13 

4 

1 4 

17 

2 2 

VT 

3 1 2 9 

4 2 3 10 

All sites 76 140 

Treatment on Uncontrolled Approaches 

PA 

3 

2 

3 8 

4 8 20 

All sites 11 28 

MRIGlobal-ISR\110818-01-005_R 53 
 

 

 

 

 

 

 

 

 

Crash and traffic volume data were obtained for varying periods before and after treatment 

installation, depending on the treatment installation date at the individual sites and crash data 

availability. Three crash types were considered in the analyses: all collision types combined, 

angle crashes, and rear-end crashes. 

Table 21 (treatment intersections) and Table 22 (nontreatment intersections) summarize the crash 

data incorporated into the analysis of supplementary pavement markings installed on stopcontrolled approaches to intersections on rural two-lane roads. They present total, angle, and 

rear-end crash data summed across all intersections of a given configuration (number of 

intersection legs) within each state. 

Table 23 (treatment intersections) and Table 24 (nontreatment intersections) summarize the 

corresponding data incorporated into the analysis of supplementary pavement markings installed 

on uncontrolled approaches to intersections on rural two-lane roads. 

Methodology 

The safety effectiveness of installing supplementary pavement markings was evaluated using an 

EB method similar to that discussed in the EB evaluation of installing transverse rumble strips in 

Chapter 4. The safety effectiveness of supplementary pavement markings was evaluated 

separately for markings installed on stop-controlled approaches of intersections and those 

installed on uncontrolled approaches. Prior to implementing the EB method, the following points 

were addressed: 

1. Select appropriate SPF: The SPFs for intersections on rural two-lane roads from

Chapter 10 of the HSM were selected. These are given for total crashes only. The

coefficients of these SPFs vary by number of intersection legs. Use of the intersection

SPFs from Chapter 10 of the HSM provide an estimate of the intersection-related

predicted crash frequency for sites included in the analysis in the absence of the

treatment.

2. Obtain the proportion of target crashes for total, FS, FI, and PDO crashes (PR1): The

proportions of target crashes (angle and rear end) to all crashes for each severity level

(total, FS, FI, and PDO) were calculated using all crashes from nontreatment sites and

from the before-period years of treatment sites. These proportions were calculated

separately for 3- and 4-leg intersections. These proportions scale the total crash

predictions (i.e., all crash types) to predictions for the target crashes (i.e., angle and rearend crashes).

3. Obtain the proportions of FS, FI, and PDO crashes (PR2): These proportions were

calculated as the ratio of all FS, FI, or PDO crashes over total crashes using all crashes

from the nontreatment sites and from the before-period years of treatment sites. These

proportions were calculated separately for 3- and 4-leg intersections. These proportions

scale the total crash predictions (i.e., all severity levels combined) to predicted crashes

for specific severity level crashes (i.e., FS, FI, and PDO).

4. Calibrate the SPFs to the local jurisdiction: Calibration was performed using all crashes

(all collision types combined), separately for each intersection configuration within a

MRIGlobal-ISR\110818-01-005_R 54 
 

 

 

 

 

 

 

 

 

 

 

given state, again using all nontreatment intersections and before treatment intersections 

combined. Total crash counts were used rather than target crashes due to the scarcity of 

target crashes, especially FS and FI angle and rear-end crashes. The calibration factor 

adjusts the HSM SPFs for varying conditions in the local jurisdiction such as crash 

reporting thresholds, environmental, etc. 

Table 21. Supplementary pavement markings installed on stop-controlled approaches: summary 

crash statistics for the before and after treatment periods for treatment intersections by State and 

number of intersection legs. 

Number of 

Intersection 

Legs State 

Before Period After Period 

Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts 

Total FS FI PDO Total FS FI PDO 

ALL CRASHES 

3 

AR 5 1 5 1 1 1 0 9 1 9 0 0 0 0 

MN 5 29 145 14 0 7 6 9 29 261 17 0 10 7 

NE 3 3 9 2 1 2 0 16 3 48 13 2 5 8 

VT 5 2 10 8 1 1 7 1 to 2 2 3 2 0 0 2 

4 

AR 4 to 5 2 9 4 1 1 3 9 to 12 2 21 27 6 16 11 

MN 5 30 150 24 6 17 4 9 30 270 26 1 14 12 

NE 3 6 18 10 1 7 3 16 6 96 40 7 24 16 

VT 5 3 15 11 0 3 8 2 to 7 3 11 7 0 3 4 

ANGLE CRASHES 

3 

AR 5 1 5 1 1 1 0 9 1 9 0 0 0 0 

MN 5 29 145 1 0 0 1 9 29 261 1 0 1 0 

NE 3 3 9 0 0 0 0 16 3 48 2 1 2 0 

VT 5 2 10 1 1 1 0 1 to 2 2 3 0 0 0 0 

4 

AR 4 to 5 2 9 0 0 0 0 9 to 12 2 21 14 5 12 2 

MN 5 30 150 11 0 8 2 9 30 270 7 0 5 2 

NE 3 6 18 7 0 4 3 16 6 96 22 6 17 5 

VT 5 3 15 5 0 1 4 2 to 7 3 11 3 0 0 3 

REAR-END CRASHES 

3 

AR 5 1 5 0 0 0 0 9 1 9 0 0 0 0 

MN 5 29 145 1 0 0 1 9 29 261 0 0 0 0 

NE 3 3 9 0 0 0 0 16 3 48 2 0 1 1 

VT 5 2 10 0 0 0 0 1 to 2 2 3 0 0 0 0 

4 

AR 4 to 5 2 9 2 0 0 2 9 to 12 2 21 4 0 2 2 

MN 5 30 150 2 2 2 0 9 30 270 4 0 3 1 

NE 3 6 18 0 0 0 0 16 6 96 3 0 2 1 

VT 5 3 15 3 0 0 3 2 to 7 3 11 1 0 1 0 

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Table 22. Supplementary pavement markings installed on stop-controlled approaches: summary 

crash statistics for the entire study period for nontreatment intersections by State and number of 

intersection legs. 

Number of 

Intersection 

Legs State 

Entire Study Period 

Range of 

Years of 

Data in 

State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts 

Total FS FI PDO 

ALL CRASHES 

3 

AR 15 11 165 119 14 64 55 

MN 15 21 315 56 2 24 30 

NE 20 13 260 71 5 23 48 

VT 8 9 72 22 0 6 16 

4 

AR 17 19 323 161 35 96 65 

MN 15 40 600 106 4 47 55 

NE 20 17 340 123 22 65 58 

VT 13 10 130 58 1 27 31 

ANGLE CRASHES 

3 

AR 15 11 165 28 5 17 11 

MN 15 21 315 4 0 3 1 

NE 20 13 260 10 3 5 5 

VT 8 9 72 2 0 0 2 

4 

AR 17 19 323 98 24 63 35 

MN 15 40 600 31 2 17 11 

NE 20 17 340 70 18 44 26 

VT 13 10 130 35 0 18 17 

REAR-END CRASHES 

3 

AR 15 11 165 36 2 21 15 

MN 15 21 315 4 0 2 2 

NE 20 13 260 5 0 2 3 

VT 8 9 72 4 0 1 3 

4 

AR 17 19 323 16 3 8 8 

MN 15 40 600 21 1 8 13 

NE 20 17 340 14 2 7 7 

VT 13 10 130 5 0 0 5 

MRIGlobal-ISR\110818-01-005_R 56 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Predicted crashes/yr = exp[a + b(lnAADTmaj) + c(lnAADTmin)] 

 

Table 23. Supplementary pavement markings installed on uncontrolled approaches: summary 

crash statistics for the before and after treatment periods for treatment intersections by State and 

number of intersection legs. 

Number of 

Intersection 

Legs State 

Before Period After Period 

Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts Range

of Years 

of Data 

in State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts 

Total FS FI PDO Total FS FI PDO 

ALL CRASHES 

3 PA 5 3 15 14 3 11 3 2 3 6 6 0 5 1 

4 PA 4 to 5 8 37 94 8 50 44 2 to 12 8 52 156 5 74 82 

ANGLE CRASHES 

3 PA 5 3 15 7 1 5 2 2 3 6 3 0 2 1 

4 PA 4 to 5 8 37 62 7 38 24 2 to 12 8 52 122 5 62 60 

REAR-END CRASHES 

3 PA 5 3 15 1 0 1 0 2 3 6 1 0 1 0 

4 PA 4 to 5 8 37 13 0 5 8 2 to 12 8 52 19 0 7 12 

Table 24. Supplementary pavement markings installed on uncontrolled approaches: summary 

crash statistics for the entire study period for nontreatment intersections by State and number of 

intersection legs. 

Number of 

Intersection 

Legs State 

Entire Study Period 

Range of

Years of 

Data in 

State 

Number 

of Sites 

Number 

of 

Site-Years 

Crash Counts 

Total FS FI PDO 

ALL CRASHES 

3 PA 8 8 64 28 4 20 8 

4 PA 17 20 340 324 24 188 136 

ANGLE CRASHES 

3 PA 8 8 64 5 1 3 2 

4 PA 17 20 340 201 20 121 80 

REAR-END CRASHES 

3 PA 8 8 64 5 0 4 1 

4 PA 17 20 340 39 0 22 17 

The SPFs presented in the HSM for intersections on rural two-lane roads for total severity level 

(i.e., all severity levels combined) have the general form: 

Figure 17. Equation. Base model for predicted crashes per year. 

MRIGlobal-ISR\110818-01-005_R 57 
 

 

 

Predicted crashes/yr = {exp[a + b(lnAADTmaj) + c(lnAADTmin)]} × PR1 × PR2 × CMFCombined ×Cr 

 

 

 

 

 

where a, b, and c are the regression coefficients shown in Table 25 for the analysis associated 

with markings installed on stop-controlled approaches of intersections and in Table 27 for the 

analysis associated with markings installed on uncontrolled approaches. These coefficients apply 

to base conditions and vary by number of intersection legs. For the intersection SPFs in Chapter 

10 of the HSM, the base conditions are: 

• Intersection skew angle: 0 degrees 

• Number of intersection left-turn lanes: None on approaches without stop control

• Number of intersection right-turn lanes: None on approaches without stop control

• Presence of lighting: None 

Crash modification factors (CMFs), calibration factors (Cr), proportions of angle and rear-end 

crashes (PR1), and proportions of FS, FI, and PDO crashes (PR2) were then used to adjust for 

local conditions as follows: 

Figure 18. Equation. Model for predicted crashes per year for specific crash types and 

severity levels, and accounting for local conditions. 

The CMFCombined is the product of the CMFs from Chapter 10 of the HSM for skew angle 

(CMF1i), number of major-road left-turn lanes (CMF2i), and number of major-road right-turn 

lanes (CMF3i), for a particular intersection configuration. 

SPF coefficients (a, b, and c and overdispersion parameter), target crash proportions (PR1), 

proportions of FS, FI, and PDO out of total crashes (PR2), and calibration factors (Cr) are shown 

for each intersection configuration in Table 25 and Table 26. Number of site-years, total crash 

counts (all severity levels), and target crash counts are also displayed. The tables also show the 

default proportions of PR1 and PR2 presented in Chapter 10 of the HSM (see Tables 10-6 and 10-

5, respectively). Note that PR2 is always equal to 1 for total crashes. The decision of which 

proportions to use—those calculated from the data or those provided by the HSM—was based on 

whether calculated proportions of target crashes (PR1) were nonzero for all severity levels. If 

they were not, then the HSM proportions (both PR1 and PR2) were used in the EB before-after 

analysis. The selections of which proportions were used are indicated in Table 25 and Table 26 

by an asterisk. 

Safety Effectiveness 

The EB before-after method was applied to estimate the safety effectiveness of installing 

supplementary pavement markings at rural stop-controlled intersections. The analysis of the 

safety effectiveness of supplementary pavement markings installed on stop-controlled 

approaches to intersections included treatment and nontreatment sites in Arkansas, Minnesota, 

Nebraska, and Vermont, and used HSM SPFs for 3- and 4-leg intersections on rural two-lane 

roads. The analysis of the safety effectiveness of supplementary pavement markings installed on 

uncontrolled approaches to intersections was based on treatment and nontreatment intersections 

in Pennsylvania. 

MRIGlobal-ISR\110818-01-005_R 58 
 

 

 

 

 

 

 

 

 

 

Table 25. Supplementary pavement markings installed on stop-controlled approaches: SPF coefficients, target crash proportions, and 

calibration factors by State and number of intersection legs. 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

AR 3 170 Total 120 Angle 29 

-9.86 0.79 0.49 0.54 

0.24* 0.24 1.00* 1.00 

13.68 

Rear End 36 0.30* 0.28 1.00* 1.00 

FS 15 Angle 6 0.40* 0.28 0.13* 0.06 

Rear End 2 0.13* 0.26 0.13* 0.06 

FI 65 Angle 18 0.28* 0.28 0.54* 0.42 

Rear End 21 0.32* 0.26 0.54* 0.42 

PDO 55 Angle 11 0.20* 0.21 0.46* 0.59 

Rear End 15 0.27* 0.29 0.46* 0.59 

4 332 Total 165 Angle 98 

-8.56 0.60 0.61 0.24 

0.59* 0.43 1.00* 1.00 

9.18 

Rear End 18 0.11* 0.24 1.00* 1.00 

FS 36 Angle 24 0.67* 0.53 0.22* 0.06 

Rear End 3 0.08* 0.21 0.22* 0.06 

FI 97 Angle 63 0.65* 0.53 0.59* 0.43 

Rear End 8 0.08* 0.21 0.59* 0.43 

PDO 68 Angle 35 0.52* 0.35 0.41 0.57 

Rear End 10 0.15* 0.27 0.41 0.57 

MRIGlobal-ISR\110818-01-005_R 59 
 

 

 

 

 

 

Table 25. Supplementary pavement markings installed on stop-controlled approaches: SPF coefficients, target crash proportions, and 

calibration factors by State and number of intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

MN 3 460 Total 70 Angle 5 

-9.86 0.79 0.49 0.54 

0.07 0.24* 1.00 1.00* 

1.35 

Rear End 5 0.07 0.28* 1.00 1.00* 

FS 2 Angle 0 0.00 0.28* 0.03 0.06* 

Rear End 0 0.00 0.26* 0.03 0.06* 

FI 31 Angle 3 0.10 0.28* 0.44 0.42* 

Rear End 2 0.07 0.26* 0.44 0.42* 

PDO 36 Angle 2 0.06 0.21* 0.51 0.59* 

Rear End 3 0.08 0.29* 0.51 0.59* 

4 750 Total 130 Angle 42 

-8.56 0.60 0.61 0.24 

0.32* 0.43 1.00* 1.00 

1.24 

Rear End 23 0.18* 0.24 1.00* 1.00 

FS 10 Angle 2 0.20* 0.53 0.08* 0.06 

Rear End 3 0.30* 0.21 0.08* 0.06 

FI 64 Angle 25 0.39* 0.53 0.49* 0.43 

Rear End 10 0.16* 0.21 0.49* 0.43 

PDO 59 Angle 13 0.22* 0.35 0.45* 0.57 

Rear End 13 0.22* 0.27 0.45* 0.57 

MRIGlobal-ISR\110818-01-005_R 60 
 

 

 

 

 

Table 25. Supplementary pavement markings installed on stop-controlled approaches: SPF coefficients, target crash proportions, and 

calibration factors by State and number of intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

NE 3 269 Total 73 Angle 10 

-9.86 0.79 0.49 0.54 

0.14 0.24* 1.00 1.00* 

8.80 

Rear End 5 0.07 0.28* 1.00 1.00* 

FS 6 Angle 3 0.50 0.28* 0.08 0.06* 

Rear End 0 0.00 0.26* 0.08 0.06* 

FI 25 Angle 5 0.20 0.28* 0.34 0.42* 

Rear End 2 0.08 0.26* 0.34 0.42* 

PDO 48 Angle 5 0.10 0.21* 0.66 0.59* 

Rear End 3 0.06 0.29* 0.66 0.59* 

4 358 Total 133 Angle 77 

-8.56 0.60 0.61 0.24 

0.58* 0.43 1.00* 1.00 

7.57 

Rear End 14 0.11* 0.24 1.00* 1.00 

FS 23 Angle 18 0.78* 0.53 0.17* 0.06 

Rear End 2 0.09* 0.21 0.17* 0.06 

FI 72 Angle 48 0.67* 0.53 0.54* 0.43 

Rear End 7 0.10* 0.21 0.54* 0.43 

PDO 61 Angle 29 0.48* 0.35 0.46* 0.57 

Rear End 7 0.12* 0.27 0.46* 0.57 

MRIGlobal-ISR\110818-01-005_R 61 
 

 

 

 

 

 

 Table 25. Supplementary pavement markings installed on stop-controlled approaches: SPF coefficients, target crash proportions, and 

calibration factors by State and number of intersection legs (continued). 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

VT 3 82 Total 30 Angle 3 

-9.86 0.79 0.49 0.54 

0.10 0.24* 1.00 1.00* 

1.82 

Rear End 4 0.13 0.28* 1.00 1.00* 

FS 1 Angle 1 1.00 0.28* 0.03 0.06* 

Rear End 0 0.00 0.26* 0.03 0.06* 

FI 7 Angle 1 0.14 0.28* 0.23 0.42* 

Rear End 1 0.14 0.26* 0.23 0.42* 

PDO 23 Angle 2 0.09 0.21* 0.77 0.59* 

Rear End 3 0.13 0.29* 0.77 0.59* 

4 145 Total 69 Angle 40 

-8.56 0.60 0.61 0.24 

0.58 0.43* 1.00 1.00* 

2.44 

Rear End 8 0.12 0.24* 1.00 1.00* 

FS 1 Angle 0 0.00 0.53* 0.01 0.06* 

Rear End 0 0.00 0.21* 0.01 0.06* 

FI 30 Angle 19 0.63 0.53* 0.44 0.43* 

Rear End 0 0.00 0.21 0.44 0.43* 

PDO 39 Angle 21 0.54 0.35* 0.57 0.57* 

Rear End 8 0.21 0.27* 0.57 0.57* 

NOTE: Asterisked proportions were those used in the analyses. 

MRIGlobal-ISR\110818-01-005_R 62
 

 

 

 

 

Table 26. Supplementary pavement markings installed on uncontrolled approaches: SPF coefficients, target crash proportions, and 

calibration factors by State and number of intersection legs. 

State 

Number 

of Legs 

Number of 

Site-Years 

Severity 

Level 

Number 

of 

Crashes, 

All 

Target

Crash 

Type 

Number 

of 

Target

Crashes 

Intercept

(a) 

lnAADTmaj

Coefficient (b) 

lnAADTmin 

Coefficient (c) 

Overdispersion 

Parameter 

Proportion 

of Target

Crashes 

(PR1) 

PR1 

HSM 

Proportion 

of FS, FI, 

or PDO of 

Total 

Crashes 

(PR2) 

PR2 

HSM 

Calibration 

Factor (Cr) 

PA 3 79 Total 42 Angle 12 

-9.86 0.79 0.49 0.54 

0.29 0.24* 1.00 1.00* 

1.05 

Rear End 6 0.14 0.28* 1.00 1.00* 

FS 7 Angle 2 0.29 0.28* 0.17 0.06* 

Rear End 0 0.00 0.26* 0.17 0.06* 

FI 31 Angle 8 0.26 0.28* 0.74 0.42* 

Rear End 5 0.16 0.26* 0.74 0.42* 

PDO 11 Angle 4 0.36 0.21* 0.26 0.59* 

Rear End 1 0.09 0.29* 0.26 0.59* 

4 377 Total 418 Angle 263 

-8.56 0.60 0.61 0.24 

0.63 0.43* 1.00 1.00* 

2.82 

Rear End 52 0.12 0.24* 1.00 1.00* 

FS 32 Angle 27 0.84 0.53* 0.08 0.06* 

Rear End 0 0.00 0.21* 0.08 0.06* 

FI 238 Angle 159 0.67 0.53* 0.57 0.43* 

Rear End 27 0.11 0.21* 0.57 0.43* 

PDO 180 Angle 104 0.58 0.35* 0.43 0.57* 

Rear End 25 0.14 0.27* 0.43 0.57* 

NOTE: Asterisked proportions were those used in the analyses. 

MRIGlobal-ISR\110818-01-005_R 63 
 

 

The EB before-after analysis results are shown for the following crash types and severity levels: 

• Total crashes (all collision types combined)

○ Total crashes

○ FI crashes

○ PDO crashes

• Angle crashes

○ Total crashes

○ FI crashes

○ PDO crashes

• Rear-end crashes

○ Total crashes

○ FI crashes

○ PDO crashes

Although the analyses for FS injury crashes were performed, the analysis results were not 

considered reliable and are therefore not shown. The occurrence of FS crashes was too rare 

across all intersections in the study (both treatment and nontreatment sites). 

For the analysis of the safety effectiveness of supplementary pavement markings installed on 

stop-controlled approaches to intersections, the EB method was applied to all states combined 

based on the following reasoning: (1) a small number of treatment sites were available in 

Arkansas and Vermont—individually, they could not have been used for evaluation; and (2) all 

EB intermediate calculations (up to the final effectiveness calculations) are performed on a 

state/site basis, thus using SPFs, proportions (PR1 and PR2), combined CMFs, and calibration 

factors (Cr) specific to that state/site. This approach, to some extent, took state-to-state variability 

into account while increasing site and crash sample sizes. Additionally, the EB method was 

initially applied separately to 3-leg and 4-leg intersections and whether the treatment was 

installed on one or two stop-controlled approaches to the intersection. However, due to sample 

size issues, it was decided to pool across the number of treated approaches and perform the EB 

analysis separately for 3- and 4-leg intersections for the pooled data from the four states. 

For the analysis of the safety effectiveness of supplementary pavement markings installed on 

uncontrolled approaches to intersections, the data for 3- and 4-leg intersections were combined 

and analyzed together to have a sufficient sample size for analysis. 

The analysis results of the safety effectiveness estimates for supplementary pavement markings 

installed on stop-controlled approaches to intersections are shown in Table 27. The statistics 

shown for each crash severity are: 

• Number of treatment intersections

• Percent change in crash frequency due to the treatment: estimate and standard error

• An indication of whether the treatment had a statistically significant effect on the crash

types and severity level of interest at the 95-percent confidence level

A negative percent safety effectiveness indicates that crash frequencies decreased due to the 

treatment. 

MRIGlobal-ISR\110818-01-005_R 64 
 

 

 

The analysis results of the safety effectiveness estimates for supplementary pavement markings 

installed on uncontrolled approaches to intersections are shown in Table 28. 

Table 27. Supplementary pavement markings installed on stop-controlled approaches: safety 

effectiveness on target crashes by number of intersection legs. 

Crash 

Severity 

Number of 

Treatment 

Sites 

Safety

Effectiveness 

(%) 

SE of 

Treatment 

Effect (%) Significance 

ALL STATES COMBINED; 3-LEG INTERSECTIONS 

ALL CRASHES 

Total 

35 

-67 7 Significant at 95% CL 

FI -76 7 Significant at 95% CL 

PDO -72 7 Significant at 95% CL 

ANGLE CRASHES 

Total 

35 

-92 5 Significant at 95% CL 

FI -88 7 Significant at 95% CL 

PDO -100a NC NC 

REAR-END CRASHES 

Total 

35 

-95 4 Significant at 95% CL 

FI -96 5 Significant at 95% CL 

PDO -97 3 Significant at 95% CL 

ALL STATES COMBINED; 4-LEG INTERSECTIONS 

ALL CRASHES 

Total 

41 

-66 4 Significant at 95% CL 

FI -69 5 Significant at 95% CL 

PDO -77 4 Significant at 95% CL 

ANGLE CRASHES 

Total 

41 

-74 4 Significant at 95% CL 

FI -71 5 Significant at 95% CL 

PDO -88 3 Significant at 95% CL 

REAR-END CRASHES 

Total 

41 

-89 3 Significant at 95% CL 

FI -86 5 Significant at 95% CL 

PDO -95 2 Significant at 95% CL 

a Crashes recorded in before period; none in after period. 

NC=Not Calculated; standard error and significance could not be 

estimated. 

MRIGlobal-ISR\110818-01-005_R 65 
 

 

 

 

 

 

 

 

 

 

 

 

Table 28. Supplementary pavement markings installed on uncontrolled approaches: safety 

effectiveness on target crashes. 

Crash 

Severity 

Number 

of 

Treatment 

Sites 

Safety

Effectiveness 

(%) 

SE of 

Treatment 

Effect (%) Significance 

3- and 4-Leg Intersections Combined

All Crashes 

Total 

11 

-46 5 Significant at 95% CL 

FI -49 7 Significant at 95% CL 

PDO -50 6 Significant at 95% CL 

Angle Crashes 

Total 

11 

-38 7 Significant at 95% CL 

FI -42 8 Significant at 95% CL 

PDO -35 10 Significant at 95% CL 

Rear-End Crashes 

Total 

11 

-69 7 Significant at 95% CL 

FI -76 9 Significant at 95% CL 

PDO -75 8 Significant at 95% CL 

In general, the EB analysis results for supplementary pavement markings installed on stopcontrolled approaches to intersections yielded statistically significant results for most of the crash 

types and severity levels analyzed for both 3- and 4-leg intersections. The results show that the 

overall effectiveness of this treatment (for all crash types and severities combined) is nearly 

identical for 3-leg and 4-leg intersections. Also, greater reductions were estimated for target 

crashes (i.e., angle and rear-end crashes) than for total crashes (i.e., all crash types combined). 

The EB analysis results for supplementary pavement markings installed on uncontrolled 

approaches to intersections also show statistically significant reductions in crashes for all of the 

crash types and severity levels analyzed. The analysis results also show greater reductions in 

rear-end crashes compared to total (i.e., all crash types combined) and angle crashes. 

ECONOMIC ANALYSIS 

An economic analysis was conducted to estimate the economic benefits of installing 

supplementary pavement markings at unsignalized intersections with minor-road stop control on 

rural two-lane roads. Separate economic analyses were conducted for supplementary pavement 

markings installed on stop-controlled approaches and uncontrolled approaches. The Economic 

Analysis discussion in Chapter 2 describes the procedure for estimating the benefit-cost ratios of 

the treatments. The economic benefits of these treatments were estimated using the safety 

effectiveness estimates developed in this research. 

The economic analysis produced two separate benefit-cost ratio tables for installing 

supplementary pavement markings on stop-controlled approaches: one for 3-leg intersections and 

the second for 4-leg intersections on rural two-lane roads. The safety evaluation produced CMFs 

for total crashes on both 3-leg and 4-leg intersections, and these CMFs were used to determine 

MRIGlobal-ISR\110818-01-005_R 66 
 

 

 

 

 

the expected annual benefit. This particular analysis assumes that one STOP AHEAD 

supplementary pavement marking is installed on each stop-controlled approach. 

Kansas Department of Transportation reports the average cost of a STOP AHEAD pavement 

marking to be $750 per approach. For the sake of the analysis, a 1-yr service life was assumed. 

Longer service lives will only increase the benefit of a treatment, so assuming a shorter service 

life is conservative for a benefit-cost analysis. Table 29 and Table 30 present the benefit-cost 

ratios for installing a STOP AHEAD pavement marking on the stop-controlled approaches of a 

3-leg and 4-leg rural intersection, respectively. The AADTs in the table cover the range of

AADTs of the study sites used for the estimation of the CMF. For both intersection types, the

benefit-cost ratio exceeds 1.0 for all AADT combinations, indicating that installation of a STOP

AHEAD pavement marking on stop-controlled approaches is economically justified at all AADT

levels. At higher-volume intersections, the benefit can be 100 or more times the cost.

Table 29. Benefit-cost ratios for installing STOP AHEAD pavement marking on the stopcontrolled approach of a 3-leg intersection for $750 installation cost and 1-yr service life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 80% 90% 

200 N/A N/A N/A 1.8 2.0 2.2 2.5 2.8 3.1 3.3 3.5 3.7 

1,000 7.1 10.0 12.2 14.0 15.6 17.1 19.7 22.0 24.0 25.9 27.6 29.3 

2,000 17.3 24.2 29.6 34.0 38.0 41.5 47.8 53.3 58.3 62.9 67.1 71.1 

3,000 29.0 40.7 49.7 57.2 63.8 69.8 80.3 89.6 98.0 105.7 112.8 119.5 

4,000 41.9 58.9 71.8 82.7 92.2 100.8 116.1 129.5 141.6 152.7 N/A N/A 

5,000 55.8 78.3 95.5 110.0 122.7 134.1 154.5 172.3 N/A N/A N/A N/A 

5,200 58.6 82.3 100.4 115.6 129.0 141.1 162.4 181.2 N/A N/A N/A N/A 

CMF = 0.33 (total crashes) 

Installation cost = $750 (i.e., $750 per approach) 

Service life = 1 yr 

Shaded cells indicate the combination of major- and minor-road AADTs was not represented in the study 

Table 30. Benefit-cost ratios for installing STOP AHEAD pavement markings on the stopcontrolled approaches of a 4-leg intersection for $1,500 installation cost and 1-yr service life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 80% 90% 

200 N/A N/A N/A 1.9 2.2 2.5 3.0 3.4 3.8 4.2 4.5 4.8 

1,000 5.8 8.9 11.4 13.6 15.6 17.4 20.7 23.7 26.5 29.1 31.6 34.0 

2,000 13.5 20.6 26.3 31.4 36.0 40.2 47.9 54.9 61.4 67.4 N/A N/A 

3,000 22.0 33.6 43.0 51.3 58.8 65.7 78.3 89.7 N/A N/A N/A N/A 

3,600 27.5 41.9 53.7 64.0 73.3 81.9 97.6 N/A N/A N/A N/A N/A 

CMF = 0.34 (total crashes) 

Installation cost = $1,500 (i.e., $750 per approach) 

Service life = 1 yr 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study 

MRIGlobal-ISR\110818-01-005_R 67 
 

 

 

 

Vermont Department of Transportation reports the average cost of a STOP AHEAD pavement 

marking to be between $300 and $500 per approach with a service life of 2 years. Table 31 and 

Table 32 present the benefit-cost ratios for installing a STOP AHEAD pavement marking on the 

stop-controlled approaches of a 3-leg and 4-leg intersection, respectively. The AADTs in the 

table cover the range of AADTs of the study sites used for the estimation of the CMF. For both 

intersection types, the benefit-cost ratio exceeds 5.0 for all AADT combinations. 

Table 31. Benefit-cost ratios for installing STOP AHEAD pavement marking on the stopcontrolled approach of a 3-leg intersection for $500 installation cost and 2-yr service life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 80% 90% 

200 N/A N/A N/A 5.2 5.8 6.4 7.3 8.2 8.9 9.6 10.3 10.9 

1,000 20.7 29.1 35.5 40.9 45.6 49.9 57.5 64.1 70.1 75.6 80.7 85.5 

2,000 50.4 70.7 86.3 99.4 110.8 121.2 139.5 155.7 170.2 183.6 196.0 207.6 

3,000 84.6 118.9 145.0 167.0 186.2 203.7 234.5 261.6 286.0 308.5 329.3 348.9 

4,000 122.3 171.8 209.6 241.3 269.2 294.3 338.9 378.0 413.4 445.8 N/A N/A 

5,000 162.8 228.6 278.8 321.1 358.1 391.6 450.9 503.0 N/A N/A N/A N/A 

5,200 171.1 240.4 293.2 337.6 376.6 411.8 474.1 528.9 N/A N/A N/A N/A 

CMF = 0.33 (total crashes) 

Installation cost = $500 (i.e., $500 per approach) 

Service life = 2 yrs 

Shaded cells indicate the combination of major- and minor-road AADTs was not represented in the study 

Table 32. Benefit-cost ratios for installing STOP AHEAD pavement markings on the stopcontrolled approaches of a 4-leg intersection for $1,000 installation cost and 2-yr service Life. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 80% 90% 

200 N/A N/A N/A 5.6 6.4 7.2 8.6 9.8 11.0 12.1 13.1 14.1 

1,000 16.9 25.8 33.1 39.4 45.1 50.4 60.1 68.9 77.0 84.6 91.8 98.6 

2,000 39.1 59.7 76.5 91.1 104.4 116.7 139.1 159.4 178.1 195.7 N/A N/A 

3,000 63.9 97.5 124.9 148.8 170.5 190.6 227.2 260.3 N/A N/A N/A N/A 

3,600 79.7 121.6 155.7 185.6 212.6 237.7 283.3 N/A N/A N/A N/A N/A 

CMF = 0.34 (total crashes) 

Installation cost = $1,000 (i.e., $500 per approach) 

Service life = 2 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study 

The Pennsylvania Department of Transportation was the only state in the study that installed 

supplementary pavement markings on uncontrolled approaches to intersections. The 

Pennsylvania Department of Transportation reports the average cost of installation to be $10,000 

with a service life of 5 years. This cost is based on the use of thermoplastic pavement marking 

material and cost of the treatment for the entire intersection. Table 33 shows the benefit-cost 

ratios for the supplementary pavement markings on uncontrolled approaches at a 4-leg stopcontrolled intersection on rural two-lane roads. The ranges of the AADTs in the table are within 

MRIGlobal-ISR\110818-01-005_R 68 
 

 

 

 

 

the minimum and maximum AADTs of the study sites used in the safety evaluation. All the 

benefit-cost ratios exceed 15, meaning the installation of supplementary pavement markings on 

uncontrolled approaches is economically justified across the entire AADT range evaluated in this 

study. 

Table 33. Benefit-cost ratios for installing supplementary pavement markings on uncontrolled 

approaches at 4-leg stop-controlled intersections. 

MajorRoad 

AADT 

% of Major-Road AADT on Minor Road 

5% 10% 15% 20% 30% 40% 50% 60% 70% 80% 90% 

2,400 N/A N/A 15.1 18.0 23.0 27.4 31.4 35.1 38.6 41.8 45.0 

3,000 N/A N/A 19.7 23.5 30.1 35.9 41.1 46.0 50.5 54.8 58.9 

4,000 N/A 21.8 28.0 33.3 42.7 50.9 58.3 65.1 N/A N/A N/A 

5,000 N/A 28.6 36.6 43.7 55.9 66.6 76.3 N/A N/A N/A N/A 

6,000 N/A 35.7 45.7 54.4 69.7 83.1 N/A N/A N/A N/A N/A 

7,000 28.2 43.0 55.0 65.6 84.0 N/A N/A N/A N/A N/A N/A 

8,000 33.1 50.5 64.7 77.1 98.7 N/A N/A N/A N/A N/A N/A 

9,000 38.2 58.2 74.6 88.9 113.8 N/A N/A N/A N/A N/A N/A 

10,000 43.3 66.2 84.7 101.0 N/A N/A N/A N/A N/A N/A N/A 

11,000 48.6 74.2 95.1 113.3 N/A N/A N/A N/A N/A N/A N/A 

12,000 54.0 82.5 105.6 125.9 N/A N/A N/A N/A N/A N/A N/A 

13,000 59.5 90.9 116.4 138.7 N/A N/A N/A N/A N/A N/A N/A 

14,000 65.1 99.4 127.3 N/A N/A N/A N/A N/A N/A N/A N/A 

CMF = 0.54 (total crashes) 

Installation cost = $10,000 

Service life = 5 yrs 

N/A indicates the combination of major- and minor-road AADTs was not represented in the study 

IMPLEMENTATION 

The primary purpose of installing supplementary pavement markings on stop-controlled 

approaches to intersections on rural two-lane roads is to alert drivers of a stop ahead. The 

treatment is intended to increase drivers’ awareness of the intersection and to the traffic control. 

Supplementary pavement markings should be considered for installation on stop-controlled 

approaches to intersections with a pattern of crashes related to a lack of driver recognition of the 

presence of the intersection (e.g., angle crashes related to stop sign violations).(5) In particular, 

supplementary pavement markings should be considered for installation along the stopcontrolled approach to an intersection that is hidden from view due to horizontal or vertical 

curvature or where the traffic control is hidden from view as the driver approaches the 

intersection. 

The primary purpose of supplementary pavement markings on uncontrolled approaches to 

intersections on rural two-lane roads is to increase driver awareness of the intersection and 

reduce speeds of vehicles on the major road near the intersection. Supplementary pavement 

markings on uncontrolled approaches to intersections should be considered on approaches to 

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intersections where it is difficult to recognize the presence of the crossroad(s) and/or at 

intersections where speeds on the major-road approaches are higher than desired for the 

conditions. 

The economic analyses provided above show that both types of supplementary pavement 

markings are economically justifiable, even along roads with low traffic volumes. 

Both types of supplementary pavement markings should be implemented in accordance with the 

Manual on Uniform Traffic Control Devices (MUTCD). The MUTCD gives little guidance about 

the design and placement of supplementary pavement markings. Section 3B.20 of the MUTCD 

gives support for the use of markings, stating, “These pavement markings can be helpful to road 

users in some locations by supplementing signs and providing additional emphasis for important 

regulatory, warning, or guidance messages, because the markings do not require diversion of the 

road user’s attention from the roadway surface.(27)” Section 3B.20 also includes recommended 

sizes for words on the pavement and states that “STOP AHEAD” may be used to supplement 

signs. 

The following paragraphs present several example design details on the use of supplementary 

pavement markings. The information was provided by several state agencies. 

As indicated, the MUTCD permits the use of the phrase “STOP AHEAD” on pavement to warn 

drivers of an upcoming stop. Figure 19 and Figure 20 are from the Minnesota Traffic 

Engineering Manual and provide guidance on the placement of the supplementary pavement 

marking. Figure 19 shows that the placement of the pavement marking is dependent on the 

placement of the W3-1a advance warning sign. Figure 20 indicates the placement of the W3-1a 

sign relative to the location of the stop bar. 

Vermont Department of Transportation recommends installing the STOP AHEAD pavement 

marking at the location of the W3-1a sign (stop ahead sign). The distance to the stop bar is 

usually 200-250 ft; however, engineering judgment in the field is used to make sure sight 

obstructions such as crest vertical curves do not warrant longer distances. 

Figure 21 shows design details for the placement and size of the supplementary pavement 

markings on the uncontrolled approach. It is recommended that this treatment not be used in 

areas with significant grade differences. The placement of the markings relative to the 

intersection is dependent on the posted speed of the roadway (see Table 34 for distances). These 

markings are part of a comprehensive intersection treatment that includes unique signage. See 

Appendix A for additional guidance from the Pennsylvania Department of Transportation 

regarding this treatment. 

MRIGlobal-ISR\110818-01-005_R 70 
Figure 19. Diagram. Minnesota guidance for placement of STOP AHEAD pavement marking 

relative to W3-1a sign.(28) 

MRIGlobal-ISR\110818-01-005_R 71 
 

Figure 20. Diagram. Minnesota guidance for placement of W3-1a sign relative to stop bar.(28)

Figure 21. Diagram. Placement guidance for supplementary pavement markings on uncontrolled 

approach.(29)

Table 34. Placement of supplementary pavement markings relative to intersection by posted 

speed.

(29)

Posted Speed 

(mph) 

d, Pattern Length 

(ft) 

Y, Distance to Sign 

(ft) 

25 265 340 

30 300 380 

35 340 450 

40 375 500 

45 410 550 

50 450 600 

55 485 650 

MRIGlobal-ISR\110818-01-005_R 72 
CHAPTER 6. CONCLUSIONS 

 

 

 

 

 

 

 

 

 

 

 

The objective of this research is to advance efforts to improve safety at intersections with minorroad stop control along rural two-lane roads. The safety effectiveness of three low-cost safety 

treatments was evaluated to estimate their expected effectiveness in reducing crashes. The lowcost safety treatments included: 

• Single luminaire intersection lighting

• Transverse rumble strips in advance of stop-controlled approaches

• Supplementary pavement markings on intersection approaches

The effectiveness of each treatment in reducing crashes was estimated using the Empirical Bayes 

(EB) observational before-after safety evaluation analysis approach. In addition, economic 

analyses were performed to estimate the benefit-cost ratio of each treatment, incorporating safety 

effectiveness results from the EB analyses. 

The safety and economic analyses show that the treatments are effective in reducing crashes of 

different types and severity levels and are economically justifiable for installation at intersections 

with patterns of crashes that suggest drivers are unaware of the presence of the intersection. The 

expected safety effectiveness (and standard error) of each treatment in reducing crashes of 

different types and severities are shown in Table 35. 

Table 35. Summary of treatment effectiveness by treatment and intersection type and crash type 

and crash severity level. 

Intersection 

Type Crash Type 

Severity 

Level 

Crash Reduction (%) 

(SE (%)) 

Single Luminaire 

3 or 4 Legs Total 

nighttime 

Total 71 (29) 

Transverse Rumble Strips 

3 Legs All FI 37 (20) 

Angle PDO 61 (28) 

Rear End FI 60 (29) 

4 Legs All Total 13 (7) 

FI 29 (8) 

Angle FI 25 (10) 

Rear End Total 56 (8) 

FI 78 (8) 

PDO 54 (10) 

MRIGlobal-ISR\110818-01-005_R 73 
 

 

 

 

 

 

 

 

 

Table 36. Summary of treatment effectiveness by treatment and intersection type and crash type 

and crash severity level (continued). 

Intersection 

Type Crash Type 

Severity 

Level 

Crash Reduction (%) 

(SE [%]) 

Supplementary Pavement Markings on Stop-Controlled Approaches 

(i.e., STOP AHEAD) 

3 Legs All Total 67 (7) 

FI 76 (7) 

PDO 72 (7) 

Angle Total 92 (5) 

FI 88 (7) 

Rear End Total 95 (4) 

FI 96 (5) 

PDO 97 (3) 

4 Legs All Total 66 (4) 

FI 69 (5) 

PDO 77 (4) 

Angle Total 74 (4) 

FI 71 (5) 

PDO 88 (3) 

Rear End Total 89 (3) 

FI 86 (5) 

PDO 95 (2) 

Supplementary Pavement Markings on Uncontrolled Approaches 

3 or 4 Legs All Total 46 (5) 

FI 49 (7) 

PDO 50 (6) 

Angle Total 38 (7) 

FI 42 (8) 

PDO 35 (10) 

Rear End Total 69 (7) 

FI 76 (9) 

PDO 75 (8) 

The information in this research can be combined with information on other strategies to reduce 

crashes at intersections with minor-road stop control along rural two-lane roads. With this 

information, agencies can make informed decisions about planning and programming safety 

improvements at intersections under their jurisdiction 

MRIGlobal-ISR\110818-01-005_R 74 
CHAPTER 7. REFERENCES 

 

 

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MRIGlobal-ISR\110818-01-005_R 76 

For More Information: 

Visit http://fhwa.safety.dot.gov/intersection/ 

FHWA, Office of Safety 

Jeffrey Shaw 

Program Manager 

jeffrey.shaw@dot.gov 

202.738.7793

FHWA-SA-16-003 

Revised June 2020