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Final Report 

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4. TITLE AND SUBTITLE

Impact of Data Link Technology on Railroad Dispatching Operations 

5. FUNDING NUMBERS

 R2103/RR204 

6. AUTHOR(S)

Nicolas Malsch, Thomas Sheridan, and Jordan Multer 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Department of Transportation 

Research and Special Programs Administration 

John A. Volpe National Transportation Systems Center 

Cambridge, MA. 02142 

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DOT-VNTSC-FRA-04-04 

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U.S. Department of Transportation 

Federal Railroad Administration 

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13. ABSTRACT (Maximum 200 words) 

This study examined data link communication as an alternative channel to voice radio for railroad dispatchers. The goal was to compare how data 

link affected performance compared to voice radio only communications on measures related to safety, productivity, communication efficiency, 

and situation awareness. A data link system with two addressing options was compared to radio. The discrete message capability enabled the 

dispatcher to send a message to one individual at a time. The broadcast message capability enabled the dispatcher to send a single message to 

multiple recipients. The experiment was run on a human-in-the-loop railroad dispatcher simulator. 

Overall, data link proved superior to the voice radio environment, in terms of safety. Safety of maintenance workers was improved by both data 

link systems while train safety was improved only for broadcast messages. No increase in dispatching productivity (train and track maintenance) 

was observed with data link. For communication efficiency, the results depended upon message complexity. Dispatchers spent less time 

exchanging simple messages with voice radio. Conversely, dispatchers exchanged complex messages more quickly in the data link environment. 

The differences in communication efficiency as a function of message complexity can be attributed to the type of interface: visual or auditory.

14. SUBJECT TERMS

cognitive task analysis, radio communications, data link, decision-making, displays, intelligent railroad 

systems, railroad dispatcher, track allocation, train routing 

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 ii 

METRIC/ENGLISH CONVERSION FACTORS 

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE) 

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in) 

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in) 

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft) 

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd) 

 1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE) 

1 square inch (sq in, in2) = 6.5 square centimeters 

(cm2

) 

1 square centimeter (cm2

) = 0.16 square inch (sq in, in2) 

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, 

yd2

) 

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2) 

1 square mile (sq mi, mi2) = 2.6 square kilometers 

(km2

) 

10,000 square meters (m2

) = 1 hectare (ha) = 2.5 acres 

1 acre = 0.4 hectare (he) = 4,000 square meters (m2) 

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE) 

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz) 

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb) 

1 short ton = 2,000 pounds 

(lb) 

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg) 

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE) 

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz) 

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt) 

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt) 

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal) 

1 pint (pt) = 0.47 liter (l) 

 1 quart (qt) = 0.96 liter (l) 

1 gallon (gal) = 3.8 liters (l) 

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3) 

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT) 

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 34 5

Inches

Centimeters 01 3 2 6 11 4 5 7 13 8 9 10 12

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSION

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286
 iii 

PREFACE 

Voice radio channels have become increasingly congested as railroad traffic has increased and 

railroads centralize their operation centers. Dispatchers control increasingly large territories and 

their communication load has increased as a result. The ability of dispatchers to communicate 

effectively with train crews and roadway workers will impact the safety and productivity of 

railroad operations. 

Digital (data link) communications systems can alleviate the burden of communication 

congestion by using a larger bandwidth, capable of displaying information in visual and auditory 

forms. The effectiveness of data link systems to assist dispatchers will depend upon how the 

interface is designed and the degree to which the design addresses human performance limitation 

and abilities. This report focuses on the safety, efficiency, and productivity issues associated 

with the introduction of a visually based (graphical and textual) data link interface for railroad 

dispatchers. 
 iv 

ACKNOWLEDGMENTS 

This research was part of a program initiated by the Federal Railroad Administration (FRA) to 

examine the use of digital data link communications in the railroad environment. This work was 

performed as part of an ongoing research program at the John A. Volpe National Transportation 

Systems Center, in collaboration with the Human-Machine System Laboratory at the 

Massachusetts Institute of Technology (MIT). The FRA’s Office of Research and Development 

supported this study, as part of its activities to develop intelligent railroad systems (Federal 

Railroad Administration, 2002). 

The authors would like to thank Dr. Thomas Raslear of the FRA and Dr. Donald Sussman of the 

Volpe Center for their interest and support over the course of this research. 

We also would like to express our deep gratitude to all the people who helped us during the past 

2 years. Dr. Emilie Roth provided insightful comments on the dispatchers’ strategies. Stephen 

Jones supported our study by making railroad dispatchers available to participate. John Pollard 

provided the expertise to solve many of our technical challenges. Sarah Miescher, Frank 

Sheelen, and Drew Kendra showed keen interest in our study and participated in many 

discussions. Santanu Basu provided the essential expertise to build and program the simulator. 

We thank Nicolas Oriol for his invaluable comments during earlier drafts of this study. Finally, 

we thank all the dispatchers who participated in our study, for their valued time and energy. 
 v 

TABLE OF CONTENTS 

Section Page

Executive Summary....................................................................................................................ix

1. Introduction..........................................................................................................................1

1.1 The Railroad Environment Today .................................................................................1 

1.2 The Existing Environment of the Dispatcher ................................................................1 

1.2.1 The Dispatcher’s Strategies .......................................................................................2 

1.2.2 Voice Radio Congestion ............................................................................................3 

1.3 Data Link Communication and the Dispatcher..............................................................3 

1.4 Research Goals ..............................................................................................................4 

2. Method ..................................................................................................................................5

2.1 Overview........................................................................................................................5 

2.2 Simulator Description ....................................................................................................6 

2.2.1 The Dispatcher’s Interface.........................................................................................6 

2.2.2 The Experimenter’s Interface ....................................................................................7 

2.2.3 Equipment..................................................................................................................8 

2.3 Routing Interface ...........................................................................................................8 

2.4 Communication Environments ....................................................................................11 

2.4.1 Voice Radio Environment........................................................................................11 

2.4.2 Data Link Environment............................................................................................11 

2.4.3 Discrete Data Link and Broadcast Data Link ..........................................................14 

2.5 Scenario Description....................................................................................................15 

2.5.1 The Train Schedule..................................................................................................17 

2.5.2 The Hazard Schedule ...............................................................................................17 

2.5.3 The MOW Schedule ................................................................................................17 

2.6 Experimental Design....................................................................................................18 

2.7 Participants...................................................................................................................19 

2.8 Procedures....................................................................................................................19 

3. Results and Discussion.......................................................................................................21

3.1 Train Safety..................................................................................................................21 

3.2 Mow Safety..................................................................................................................22 

3.3 Communication Efficiency ..........................................................................................23 

3.3.1 Performance Varies with Message Content.............................................................23 

3.4 Situation Awareness ....................................................................................................28 

3.5 Productivity..................................................................................................................29 

3.6 Dispatchers’ Preferences..............................................................................................30 

4. Conclusions.........................................................................................................................33

4.1 Future Research ...........................................................................................................35 

Appendix A. Message Trees......................................................................................................37

Appendix B. Event Schedules ...................................................................................................43

Appendix C. Questionnaires .....................................................................................................49

Appendix D. Experiment Documents.......................................................................................53
 vi 

Glossary ......................................................................................................................................59

References...................................................................................................................................61
 vii 

LIST OF FIGURES 

Figure Page

1. Simulator Configuration ............................................................................................................6 

2. Dispatcher’s Workstation ..........................................................................................................7 

3. Active Track Layout. ...............................................................................................................10 

4. Dispatcher Message Console...................................................................................................12 

5. Dispatcher Message Menu Hierarchy......................................................................................13 

6. Preprogrammed Message.........................................................................................................14 

7. First Level of Experimenter’s Message Tree...........................................................................15 

8. Track Layout............................................................................................................................16 

9. Number of Transactions by Time and Environment................................................................24 

10. Distribution of Transactions by Time and Type of Message.................................................25 

11. Mean Task Completion Time for Simple and Complex Type Messages by Communication 

Environment...........................................................................................................................26 

LIST OF TABLES 

Table Page

1. Meaning of Track Color Coding................................................................................................8 

2. Menu Structure of Messages Initiated by Dispatcher..............................................................13 

3. Territory Elements ...................................................................................................................15 

4. Experimental Design................................................................................................................18 

5. Safety of Trains and MOW Crews by Communication Environment.....................................21 

6. Mean Transaction Completion Time by Communication Environment..................................23 

7. Characteristics for Selecting Modality in which to Present Information ................................27 

8. Situation Awareness by Activity and Communication Environment......................................28 

9. Productivity by Communication Environment ........................................................................29 

10. Dispatcher Ratings of Workload, Comfort, and Simulator Realism .....................................30 

11. Dispatcher Comments on the Use of Data Link ....................................................................31 

 ix 

EXECUTIVE SUMMARY 

The ability of dispatchers to communicate effectively with train crews and roadway workers 

impacts the safety and productivity of railroad operations. Voice radio channels have become 

increasingly congested as railroad traffic has increased and operations centers become more 

centralized. Data link represents a potential solution to supplement voice radio. Data link 

communication differs from voice radio because the information is digitally coded and discretely 

addressed. Digital coding allows many new options in providing communications better tailored 

to employee needs. 

The additional channel capacity of data link will allow more information to be communicated. 

However, the use of data link poses challenges, as the dispatcher must be able to manage the new 

communications medium without experiencing information overload. 

The goal of this study was to evaluate how data link affects dispatcher performance compared to 

the radio. Two data link environments were designed and evaluated against the current voice 

radio environment. The level of improvement was evaluated in terms of safety, efficiency, and 

productivity. Also examined were the dispatcher’s attention allocation strategies. 

Method 

A visual (text-based) data link interface was designed as an alternative to the current voice radio 

communication environment. This data link system was compared to voice radio for common 

information transmissions using a railroad dispatcher simulator to evaluate its impact on 

dispatcher performance. 

The data link interface was modeled after an e-mail application. To send a message, the 

dispatcher used a mouse to select from a set of message templates related to the task being 

performed. Keyboard entry was needed only to tailor the message. A data link system was 

designed with discrete and broadcast addressing capabilities. The discrete message capability 

enabled only private “one to one” communications in which the dispatcher could send a message 

to a single recipient. The broadcast message capability enabled the dispatcher to send a single 

message to multiple recipients. 

The dispatcher’s workstation enabled the dispatcher to route trains and communicate with 

workers in the field. The dispatcher used two or three monitors depending on the communication 

environment. Two of these monitors displayed the track layout (routing interface), and one 

served as the dispatcher’s data link display (communication interface). In the voice radio 

environment, a two-way radio was used in place of the data link display. The dispatcher 

interacted with the routing (track layout) monitors using a mouse. For the data link display, a 

keyboard and mouse were used. For communication in the data link condition, the dispatcher 

used only the data link interface to initiate communication requests or to reply to people in the 

field. 

Two scenarios were designed using 15 scheduled trains in each. To evaluate safety, each 

scenario included two types of hazards: trespassers on the track and children stoning the train. 

Each scenario also included maintenance-of-way (MOW) activities. Using the track layout 

screens, the dispatcher routed trains, blocked track, cleared routes, and took other actions to 

control equipment in the field. 
 x 

The following three safety measures were collected: percent of trains alerted in response to a 

hazardous event, the percent of MOW crews properly protected, and situation awareness scores. 

The questionnaire was divided into four groups of questions: routing, hazards, MOW activities, 

and communications. 

To evaluate communication efficiency, total transaction time was measured. Total transaction 

time represented the duration of a transaction between the dispatcher and the respondent. A 

single transaction could include multiple exchanges of information. 

MOW activity and the “on time” performance of the routed trains were evaluated. The number 

of late trains entering the stations were recorded, as well as the number of trains that were more 

than five minutes late. MOW activity was evaluated by recording the number of granted MOW 

requests. 

The participants were six professional dispatchers: one woman and five men. Three participants 

had 7 to 9 years dispatching experience, while the other three had less than 2 years. Participants 

were paid the same hourly rate they received for performing their usual job duties. 

Each dispatcher participated in two scenarios, with a different communication environment each 

time. Before each trial, dispatchers were trained on the interface they would use. After the 

experiment, there was a short debriefing session. Each trial lasted one hour, and was interrupted 

once after 30 minutes so the participant could complete a situation awareness questionnaire. The 

participant’s task was to perform their usual dispatching task given the constraints imposed by 

the new environments. At the conclusion of each scenario, the dispatcher completed a brief 

questionnaire. 

Data Link Improves Communication 

Our results suggest that data link can improve communication efficiency, safety, and situation 

awareness. The differences between conditions were not always statistically significant, but in 

almost every case, they favored data link. Compared to voice radio, both data link systems 

improved safety and situation awareness. For productivity, no differences were observed 

between data link conditions and voice radio. 

With data link, dispatchers protected a greater percentage of trains and MOW crews as compared 

to the radio. By providing information in a visual format, data link eliminated readback errors 

and hearback errors associated with the auditory modality. Translating track requests from 

alphanumeric text to a graphic display on the track layout display made the request even easier to 

process. The visual presentation of information in the data link systems minimized the demand 

placed on the dispatcher’s memory. Anecdotal comments by the participants suggested it also 

reduced stress by giving the dispatcher the opportunity to respond to messages when time 

allowed, providing a quieter environment in which to work. 

The advantage of communicating information in visual form was evident in the evaluation of 

situation awareness. Situation awareness for data link was better than voice radio for routing, 

hazard awareness, and communication. While the dispatcher devoted more resources to 

processing visual information with data link than with radio (there were three displays to 

monitor, instead of two), no adverse impact was evident. MOW activity was the only category in 

which performance was as good or better than the radio condition. Dispatchers had a visual form 

of information to assist them in situation awareness. 
 xi 

Overall, the differences between the discrete data link condition and the broadcast data link 

condition were small. The broadcast version showed a greater improvement in train safety than 

the discrete version. The broadcast version minimized communication workload by providing a 

simple way to reach multiple recipients, allowing the dispatcher to attend to other tasks. For 

example, the dispatcher could use a single message to alert all trains along a particular branch, 

while the discrete system required the dispatcher to contact each train individually. 

Communication efficiency for voice radio and data link varied as a function of the characteristics 

of each medium. Information communicated by voice radio was presented in an auditory format. 

Information communicated via data link was presented in a visual format. Each form proved 

better suited for presenting some kinds of information than others. 

Voice radio proved better suited to communicating short and informal communications as well 

as time-critical messages that required immediate action (i.e., a dispatcher reporting no speed 

restrictions when a locomotive engineer called to request a temporary speed-restriction bulletin, 

or alerting a locomotive engineer to the presence of a trespasser). For these types of 

communications, data link doubled the communication times over voice radio. These results 

were due to the auditory format in which the information was presented. 

In this experiment, data link was better suited for communications whose length or complexity 

imposed a significant burden on memory. In railroad operations, these characteristics are typical 

of safety critical messages that require formal acknowledgement procedures (i.e., granting a Foul 

Time request or authorizing a train movement using a Form D). Data link provided an efficient 

channel for these communications. As a result, communication times were reduced by a factor of 

two. The concept of not having to repeat a message multiple times was also appealing to the 

dispatchers in our study. 

In the voice radio and data link conditions, the performance differences observed between the 

two types of messages were due to the modality or format in which the information was 

presented, not the communication medium. While information sent over voice radio is presented 

in an auditory form, digital communications systems like data link provide more options for 

presentation. Data link supports both auditory and visual modalities. 

The differences identified between radio and data link also depended upon the details of how 

each interface was implemented. Had the data link interface required the dispatcher to make 

heavier use of the keyboard to enter messages than with the current design, the results might 

have been quite different. Successful implementation of a data link interface will depend upon 

applying principles of good human factors design and usability testing to meet the needs of 

dispatchers who use this communication interface. 

The current study suggests that dispatchers benefit from both voice and data link communication 

modes. In recommending the conditions under which each medium should be used, this study 

suggests that voice radio is best suited for communicating simple, time-sensitive messages to one 

recipient. Data link system is best suited for communicating lengthy messages. Sending discrete 

messages works best where privacy is important or the message content would benefit only the 

recipient for which the message is intended. Sending broadcast messages works best when there 

is a need to communicate the same information to multiple recipients. 

1 

1. INTRODUCTION 

1.1 The Railroad Environment Today 

Railroad traffic has increased in recent years. As a result, railroads have improved their 

infrastructure by investing in faster trains and new technologies to enhance train movements. 

Between 1992 and 1995, railroads bought more than 800 new locomotives (Railroad Facts, 

1996). The Federal Railroad Administration (FRA) and the railroad industry are working 

together on the development of intelligent railroad systems that include new computer and 

communications technologies in train control and the scheduling of railroad operations (FRA, 

2002). 

One consequence of these changes is the movement toward more efficient communication. 

Dispatchers must work closely with train crews and roadway workers to manage track use. 

Managing the communication process is a challenge, given the current voice radio channel 

availability. Using voice radio as the primary communication channel in the railroad 

environment has resulted in communication congestion. Data link communication can provide 

capabilities not available through voice radio. However, the use of data link itself poses 

challenges, as the dispatcher must be able to manage the additional communications. 

Currently, the dispatcher acquires information from parties in the field by way of voice radio and 

telephone. By what criteria will a dispatcher select the communication medium, when data link 

becomes available for sending and receiving information? What kind of information is 

appropriate for each medium? To address these questions it is important to first understand how 

the dispatcher acquires and shares information in the current environment. To begin answering 

these questions, the current communication environment of the dispatcher was analyzed. 

1.2 The Existing Environment of the Dispatcher 

Railroad dispatchers are responsible for managing track use, ensuring that trains are routed 

safely and efficiently, and ensuring the safety of the maintenance-of-way (MOW) personnel 

working on and around the track (Devoe, 1974). These tasks require integrating multiple sources 

of information, projecting track use into the future, and balancing multiple demands from various 

sources. The railroad dispatcher is responsible for the safety of people and equipment on the 

track as well as the efficient use of railroad resources. By contrast, in the aviation environment, 

these two job functions are divided between the air traffic controller whose primary concern is 

safety and the airline dispatcher whose primary concern is productivity. 

Successful performance of the train routing task depends on the ability of the dispatchers to 

monitor train movements beyond their territory, balance multiple demands placed on track use, 

and factor in unplanned events in allocating track. This requires monitoring train positions and 

MOW activities. In CTC territories, the dispatcher monitors train position via signals 

communicated by track circuitry, on a visual display (i.e., a computer display or mimic board) 

and monitors events through two-way radio communications with railroad crews in the field. In 

territories, where information about train position is not available (either Automatic Block Signal 

territory or dark territory), the dispatcher must rely upon voice radio communications with 

railroad personnel in the field as the only means to monitor train movements. 
2 

Voice radio traffic places significant demands on the dispatcher’s attention and memory. To stay 

informed and in control the dispatcher performs a variety of tasks. These tasks include: 

answering requests, determining the current state of railroad operations (delays, speed 

restrictions, and track outages), informing railroad entities of the current state of operations, 

coordinating with other railroad “supervisors” (e.g., train masters and yard masters), and filling 

out paperwork. 

These tasks contribute to three types of demands on the dispatcher: 

• Demands on attention associated with monitoring the radio channel and responding to 

radio requests. 

• Demands on memory, associated with the need to keep track of many more elements than 

the ones actually displayed on the routing or communication interface. 

• Demands on decision-making strategies associated with the assignment of track to trains 

or MOW crews. 

1.2.1 The Dispatcher’s Strategies 

Dispatchers have developed several strategies for meeting their job demands (Roth, Malsch and 

Multer, 1999). Awareness of dispatcher strategies is important for designers considering new 

aiding technologies. Strategies can signal problems in the current dispatching environment that 

dispatchers are compensating for, and may suggest ideas for new aids. When introducing new 

technologies, designers need to be careful not to inadvertently create conditions that prevent the 

dispatchers from implementing their strategies, especially if there is no replacement strategy. 

One strategy consists of off-loading memory requirements. A great amount of information needs 

to be considered when making track allocation or routing decisions. Some of this information 

can be found in rulebooks, schedules, memos, and daily bulletins. Dispatchers have developed 

techniques to extract key pieces of information in a more accessible form. One example is the 

“cheat sheet,” which is a piece of paper summarizing the most relevant information in the 

schedule. Another example is the desk book, a clipboard including formal memos, speed 

bulletins, scheduled track outages, or informal notes written by the dispatcher. Both tools 

provide the dispatcher with a convenient way of keeping track of changes and updates. 

A second set of strategies is to anticipate unplanned events and plan ways to address these 

events. These strategies include coordination with the dispatchers for abutting territories and 

from the people in the field (i.e., asking adjoining dispatchers about changes in the usual routing 

and alerting them to changes caused by unplanned events). The dispatcher develops a “game 

plan” to work out meets and passes depending on train schedules and priorities for each shift and 

territory ahead of time. Dispatchers may summarize parts of the game plan in their cheat sheets. 

To maintain the “big picture” they monitor activity beyond their territory. If an overview display 

showing track use for all territories is available, they monitor where trains are on the track even 

before they enter their territory. Dispatchers also take advantage of the party line feature of the 

voice radio. Dispatchers listen for information on the radio channel not directly addressed to 

them. This information can provide important clues to potential delays or problems. Typically, 

dispatchers listen for “train out of station” messages, equipment problems, (when a locomotive 

engineer is talking to the mechanical department), and other dispatcher commitments that might 

have an impact on their territories. 
3 

Dispatchers plan by developing contingencies for unplanned events such as engine failures and 

late or unscheduled trains. Planning includes taking advantage of the windows of opportunity for 

track usage. If track that was previously in use becomes available earlier than expected, 

dispatchers will call up a MOW crew to let them know it is available. In the same manner, they 

will call locomotive engineers before a train is scheduled to leave the station to give them the 

speed bulletin for the trip. 

A third strategy is to level workload. Dispatchers try to shift the work from high workload 

periods to lower workload periods. For example dispatchers will pre-name trains, clear routes in 

anticipation of needs, and give provisional authority (giving track away until further notice). 

Other methods include reducing the amount of communication (especially for work crews), and 

performing multiple tasks in parallel (e.g., clearing a route for a train and answering the radio for 

a MOW person). 

1.2.2 Voice Radio Congestion 

There was consensus among the interviewed dispatchers that the voice radio channel is often 

overloaded. Furthermore, there was agreement that voice radio is not well suited for some 

communication tasks. For example, long dialogues intended to convey detailed information such 

as exact location, should be conducted on a more private voice channel (i.e., telephone). 

1.3 Data Link Communication and the Dispatcher 

Data link technology provides an alternative that can supplement voice radio and telephone 

communications. Data link communication differs from voice radio because the information is 

digitally coded. This makes it possible to discretely address individual receivers or multiple 

recipients. 

Data link would benefit the railroad industry by making data available in real time, while 

improving information in terms of quantity, reliability, and quality (Vanderhorst, 1990). Real 

time transmission of information could improve the dispatcher decision-making process. The 

contribution of real time information can be understood when one observes the current 

dispatching environment. For example, at one dispatching center, with passenger trains 

comprising the majority of traffic, the system shows delays for each train. However, the 

information is not displayed in real time. As a result, the dispatchers cannot rely on this 

information for time-critical decisions. They need to solicit additional sources of information and 

use strategies for allocating track that depends upon a coarser level of information. Current data 

link technologies could help. 

Additional channel capacity of data link means that more information can be communicated. 

However, increasing the amount of data could lead to information overload. To use the new 

technology efficiently, data link must provide additional data that can be turned into useful 

information. Information normally provided aurally could be displayed visually. This feature 

would assist dispatchers in managing their workload. 

Data link also has the potential to address the voice radio congestion problem. Data link will 

reduce congestion in the radio environment by providing an alternative, higher bandwidth 

communication channel. Currently, only one person can transmit over a given voice radio 

channel. When someone transmits a message, other parties are blocked from transmitting their 

messages over the same channel. Data link enables many people to transmit multiple messages 
4 

simultaneously. Data link may also change the order in which messages are answered. Currently, 

the order in which messages are answered depends upon the dispatcher’s implicit, situationally 

dependent priority. The ability to store and display messages will require that messages are 

organized to facilitate the dispatcher’s tasks. This organization can make explicit (observable) 

the dispatcher’s priorities. Thus, data link changes the nature of the communication problem for 

the dispatcher. Instead of answering messages in the order they arrive, now the dispatcher or the 

system must prioritize the order in which messages are answered. In the current radio 

environment, the dispatcher faces a similar situation because there are several frequencies over 

which people can communicate. Data link highlights this challenge for the dispatcher. Designers 

will need to consider ways to help the dispatcher prioritize the order in which messages are 

answered. 

Data link also provides the ability to design flexible interfaces (either visual or aural) for 

delivering information. However, the success of this communication channel is likely to depend 

upon its implementation. Simply adding data link technology without considering how 

information will be presented may create new problems. Advantages present in the current voice 

radio environment can be lost if designers do not understand their importance. 

Using data link, information can be presented aurally or visually. Each modality has advantages 

and disadvantages. What information should be sent via data link and what information should 

be communicated by voice? This study seeks to answer this question by examining how data link 

affects railroad dispatcher performance. As the focal point for communications in the railroad 

control environment, the benefits and drawbacks of implementing data link in the dispatcher’s 

working environment were investigated. 

1.4 Research Goals 

The goal of this study was to evaluate how data link affected dispatcher performance compared 

to the current voice radio channel. Using a railroad dispatcher simulator, two data link 

environments were designed and evaluated against the current voice radio system. The level of 

improvement in terms of safety, efficiency, and productivity within this new environment was 

evaluated. The dispatcher’s attention allocation strategies were also examined. 
5 

2. METHOD 

2.1 Overview 

The performance differences between data link and voice radio were measured using a humanin-the-loop railroad dispatcher simulator. In the voice condition, messages were communicated 

by two-way radio. Transactions communicated by radio were synchronous; the transaction 

between sender and receiver took place at the same point in time. Use of a voice radio channel 

by a sender blocked its use by other potential senders. Therefore, a message could only be sent 

by one person at time. However, anyone in range of the communication could listen to the 

message. 

A user interface for a data link system was created to operate similarly to an email system. The 

dispatcher interacted with the data link system using a computer monitor, keyboard, and mouse. 

Unlike voice radio, the data link system was asynchronous. Transactions communicated by radio 

were asynchronous; transactions between senders and receivers could take place at different 

points in time. The sender of a message could send a message to one recipient or to many 

recipients. 

Although a real-world system would have both capabilities, in the current study, these two ways 

of sending messages were separated into two experimental data link conditions to evaluate their 

impact on dispatcher performance. The two data link conditions were called discrete and 

broadcast. In the discrete condition, messages were sent to a single recipient. In the broadcast 

condition, messages were sent to multiple designated recipients. Each type of message 

distribution has advantages and disadvantages. Sending a single message to multiple recipients 

in one transaction by the dispatcher requires less work than sending the same message multiple 

times. The challenge is determining who received the message. For safety critical transactions, 

the dispatcher needs confirmation that the recipient received the message. Sending messages to 

recipients who don’t need this information may overload the recipients with unnecessary 

information. Conversely, failing to send it to a recipient who should have received this 

information could contribute to a mishap. 

In the two data link conditions, voice radio was not used. The two communication environments 

were evaluated separately to identify the effects of each communication environment on 

dispatcher performance. 

Dispatchers performed their normal duties routing trains and allocating track to maintenance of 

way (MOW) crews. Each participant was exposed to two scenarios in which a variety of events 

occurred such as trespassers on the tracks, delayed trains, and requests from track personnel for 

Foul Time. Participant performance was measured in terms of efficiency (minimizing 

communication time), productivity (minimizing train delays and maximizing maintenance work), 

safety (avoiding collisions), and attention allocation. 
6 

Figure 1. Simulator Configuration 

2.2 Simulator Description 

The simulator was divided into two parts as shown in Figure 1: the dispatcher’s workstation and 

the experimenter’s workstation. Each workstation was composed of two display elements, 

reflecting the two main activities of the dispatcher: routing and communication. The routing 

interface displayed the track layout and was modeled after a Central Traffic Control (CTC) based 

signal system. It simulated routing activity for a track network on the Northeast Corridor. The 

communication interface was either a portable two-way radio or a data link display, depending 

on the experimental condition. 

2.2.1 The Dispatcher’s Interface 

The dispatcher’s workstation enabled the dispatcher to route trains and communicate with 

workers in the field. The dispatcher used two or three monitors depending on the communication 

environment. Two of these monitors displayed the track layout (routing interface) and one served 

as the dispatcher’s data link display (communication interface) as seen in Figure 2. In the voice 

radio environment, a two-way radio was used in place of the data link display. The dispatcher 

interacted with the routing (track layout) monitors using a mouse. For the data link display, a 

keyboard and mouse were used. 
7 

Figure 2. Dispatcher’s Workstation 

Using the track layout screens, the dispatcher routed trains, blocked track, cleared routes, and 

took other actions to control equipment in the field. For communication in both data link 

environments, the dispatcher used the data link interface to initiate communication requests or to 

reply to people in the field. 

2.2.2 The Experimenter’s Interface 

The experimenter’s workstation enabled the experimenter to monitor the experiment and to play 

the roles of other entities with whom the dispatcher would interact. These entities included: train 

crews, MOW crews, yardmasters, trespassers, and other dispatchers. For example, the 

experimenter could halt, reverse direction, or derail a train. Although the experimenter’s 

workstation consisted of the same three monitors as the dispatcher’s workstation (as shown in 

Figure 2), the experimenter’s workstation did not allow dispatching activities. The experimenter 

controlled the routing interface and data link interface with the appropriate keyboard and mouse. 

Two monitors displayed the track layout. The third monitor displayed the data link interface. In 

the radio environment, the experimenter used three portable radios in place of the data link 

display. Playing the role of other railroad staff involved the use of assistants communicating with 

each other and the dispatcher about events taking place. 

In the data link environment, the experimenter used the message console to communicate with 

the dispatcher. Preprogrammed messages were created to play the part of other railroad operating 

personnel. However, the type of preprogrammed messages differed from those available to the 

dispatcher. In the voice radio environment, the experimenter(s) still used the message console 

because it provided the appropriate message to read aloud on the radio. For more details about 

the operation of the simulator, see Basu (1999). 
8 

2.2.3 Equipment 

The railroad dispatcher simulator was comprised of six personal computers (PCs) connected via 

a local area network (LAN), and a set of four portable radios. Each was a WindowsTM based 

machine with a PentiumTM II class processor. Seventeen-inch cathode ray tube (CRT) type 

monitors were used. The simulation was programmed using JavaTM. 

The dispatcher’s workstation consisted of three PCs. The experimenter’s workstation was 

located in an adjacent room, and consisted of three PCs. The three PCs in the dispatcher’s room 

were connected via a LAN to the three PCs in the experimenter’s room. The experimenter 

initiated actions or created conditions to which the dispatcher responded. Alternatively, the 

experimenter, playing the role of locomotive engineer, roadway worker, or another dispatcher, 

responded to events or action initiated by the dispatcher. 

Four Motorola HT/MT1000 portable radios were used to simulate voice radio communication. 

One radio was present in the dispatcher’s room, and the experimenter and two assistants used the 

remaining three radios. In the voice radio condition, three people simulated the communications 

of the operating personnel amongst themselves and with the dispatcher. A video camera located 

in the participants’ room recorded all experimental trials. 

2.3 Routing Interface 

The routing simulation was modeled on an Amtrak passenger railroad dispatching system. It 

showed a color-coded track display with text to display the current track state. 

Color-coding - The color of individual track segments (referred to as blocks) represented how 

the track was allocated. The color-coding conformed to the conventions as seen in Table 1. 

Table 1. Meaning of Track Color Coding 

Color Meaning

Red Indicates the presence of a train. Other trains are not 

allowed in this block. 

Green Cleared route. Train has permission to enter this block. 

Blue Indicates track work is occurring. Trains are not allowed to 

enter without permission of MOW workers. 

White Track is currently unallocated. 

Text information - Train numbers were displayed above the track if traveling outbound and 

below the track if traveling inbound. Inbound trains had even numbers and outbound trains had 

odd numbers. In addition, an arrow was located on the left or on the right of the train number to 

indicate travel direction. Finally, a plus or minus sign was displayed on the left of the train 

number to indicate whether the train was ahead of or behind schedule. This display was only 

updated when a train passed an interlocking. Stations and interlockings were named. 

Track layout - The track consisted of a terminal station named Boston, with ten platforms from 

which four branches departed towards New York City as shown in Figure 3. The four branches, 

labeled A, B, C, and D respectively, varied in length and number of stations. 
9 

Routing activities - The main routing tasks were accomplished using mouse-activated buttons 

located at the bottom of the screen; clearing and unclearing a route as well as blocking and 

unblocking tracks. Clearing a route enabled a train to move over that section of track. Other 

trains were prohibited by the signal system from entering track sections occupied by the train. 

Unclearing a route made the previously cleared track available for other uses. The track 

uncleared automatically after the train went through. The unclearing delay typically encountered 

by dispatchers when correcting a mistake was not implemented. If a switch was changed while 

the train was in an interlocking, the change did not affect the train’s movement. A two-aspect 

signal system (clear route or route occupied) was implemented. The dispatcher blocked a track to 

enable roadway workers and their equipment to occupy the track. Unblocking the track removed 

this protection for the roadway worker crew and equipment and made the track available for 

train movements or other MOW crews. The simulator propagated the state of the signal to the 

adjacent block. Hence, trains slowed down and eventually stopped if a cleared route was not 

available. 
10 

Control buttons

Train number and

representation

Blocked section

of track

Tracks running

South towards

New York

Interlocking

Boston South Station

- Platforms

Cleared

interlocking

Figure 3. Active Track Layout 
11 

2.4 Communication Environments 

2.4.1 Voice Radio Environment 

The experimental communication procedures were modeled after a communication protocol used 

at a scheduled train operations dispatching center. Messages transmitted to the dispatcher were 

computer generated in accordance with the dispatcher’s routing decision. If the simulator was 

programmed to act on the presence of a trespasser within a given time span, and the dispatcher 

was routing a train through the area where the trespasser was, the simulator would then send a 

message to the experimenter. The experimenter, playing the role of the locomotive engineer on 

that particular train, then called the dispatcher on the radio to warn of the trespasser’s presence. 

If the dispatcher routed no trains through the territory while trespassers were supposedly present 

there, these trespassers went unnoticed by the dispatcher. 

Communications were not always directed to the dispatcher. To simulate communications 

among field personnel, the experimenter and several assistants used a set of computer-generated 

cues to talk amongst themselves using the three radios. The experimenters used the same 

communication protocol as the dispatcher. 

2.4.2 Data Link Environment 

The data link environment was displayed visually using an e-mail-like interface. The data link 

interface contained a menu of preprogrammed messages. The voice radio was unavailable in the 

data link conditions. The data link interface consisted of a monitor with a mouse and keyboard 

for information input. To send a message, the dispatcher used a mouse to select from a set of 

message templates (containing text) relating to the task being performed. Keyboard entry was 

needed only to tailor the message. This approach minimized the need for time-consuming 

keyboard use. Two ways of sending messages using the data link system were designed: discrete 

and broadcast. The discrete message capability enabled only private “one to one” 

communications in which the dispatcher could send a message to a single recipient. The 

broadcast message capability enabled one to many communications in which the dispatcher 

could send a message to multiple recipients. The screen was split into four windows as shown in 

Figure 4. 

Received messages window - The upper left window of Figure 4 displays the list of received 

messages. With each incoming message, an additional line was added to the list specifying the 

sender. Messages were sorted by arrival time. If unselected, messages were preceded by a series 

of four question marks. Once highlighted, messages were preceded by a series of stars. If the 

dispatcher used the reply button to answer a message, the message was preceded by a series of 

“Rs.” 

Text message window for received messages - The lower left window of Figure 4 displays the 

entire text of the selected message. If this message referred to a track location, this location was 

highlighted in yellow on the track layout display. 
12 

Received message 

window 

Sent message 

window 

Received message 

Full text

Sent message 

Full text

Figure 4. Dispatcher Message Console 

Sent message window - The upper right window in Figure 4 displays the list of outgoing 

messages. With each sent message, another line was added to the list. Each line contained the 

recipient and the subject of the message. 

Text message window for sent messages - The lower right window shown in Figure 4, displays 

the entire text of the message the dispatcher highlighted in the sent message window. This text 

window lacked the track location-highlighting feature. 

Message creation: the dispatcher’s message-tree - To facilitate message creation, the most 

frequently used message types were preprogrammed. The dispatcher scrolled within a 

hierarchical menu to select a message. The menu contained a small number of fundamental 

messages. Clicking the reply button or the send message button at the bottom of the receivedmessages window displayed a menu. The menu consisted of a four level tree, through which the 

sender proceeded in sequence, from level one to level four. The menu hierarchy is shown in 

Table 2 and Figure 5. 
13 

Table 2. Menu Structure of Messages Initiated by Dispatcher 

Level Content Example

1 Message Priority High, medium or low 

2 Recipient Engineer, MOW 

3 General subject Trespasser, Kids throwing stones 

4 Detailed message content Track Work – Foul Time Granted 

Track Work – Foul Time Refused 

Clicking a button in the fourth level of the message tree hierarchy displayed a window with the 

desired message. If the dispatcher wanted to send a message not found in the message tree, a 

“blank message” could be created. 

Third level of message tree 

First two levels of message tree 

Fourth level of message tree 

Figure 5. Dispatcher Message Menu Hierarchy 

The entire dispatcher message tree used in the data link environments is shown in Appendix A. 

To complete a message, the dispatcher filled in the blanks using the mouse or keyboard (see 

Figure 6). Typically, the dispatcher filled in a location, time, and train number. To specify 
14 

location or train number, the dispatcher used the mouse. By selecting the location or train 

number on the track layout display, the blank fields in the message were completed 

automatically. Once a field was filled in, the cursor moved to the next blank field. In the final 

step, the dispatcher pressed the send button to deliver the message. Once sent, messages were 

always acknowledged. 

Figure 6. Preprogrammed Message 

2.4.3 Discrete Data Link and Broadcast Data Link 

With the discrete data link condition, messages were sent to only one recipient. In the broadcast 

data link condition, messages were always sent to multiple recipients. To send a message, the 

dispatcher specified one primary recipient and a group of secondary recipients (see Appendix A 

for the list of the groups). It was assumed that recipients always properly acknowledged 

messages. 

The experimenter’s data link interface was identical to the dispatcher’s message console. To 

create a message, the experimenter used the same procedure as the dispatcher. However, the 

experimenter had message trees available for all railroad entities such as a dispatcher tree, an 

engineer tree, a MOW tree, and a “miscellaneous” tree as shown in Figure 7. The message trees 

were similar in structure to the previously described dispatcher message tree. The experimenter 

message tree can be found in Appendix A. 
15 

Figure 7. First Level of Experimenter’s Message Tree 

2.5 Scenario Description 

Two scenarios were designed. Each experimental run started at the beginning of a new shift and 

lasted one hour. Figure 8 represents the territory for which the dispatcher was responsible. The 

territory for both scenarios was the same. The territory contained the elements shown in Table 3. 

The top track layout shows the terminal on the left. The track at the right side of the top track 

layout is located south of the track to the left. On the bottom display, the left side of the track 

layout continues the display shown on the right hand side of the top track layout.1

 

Table 3. Territory Elements

Territory Elements 

Four branches: A, B, C, D 

One Terminal station 

Four intermediate stations: A, BL, BR, D 

One drawbridge (not displayed, between D7 and D8) 

 

1

 The track is not displayed to scale. 
16 

Figure 8. Track Layout 
17 

2.5.1 The Train Schedule 

Fifteen scheduled trains were used during each scenario. The schedule and the territory were 

designed so that if the dispatcher routed the trains perfectly, all trains could arrive on time or 

slightly early. If the dispatcher made a significant routing mistake (i.e., forgetting about a train 

for five minutes or longer), the affected train could not make up for the delay. Small routing 

mistakes (one or two minutes) did not appear in the data. This was done to simulate the fact that 

engineers will try to make up for their delays. During the experiment, dispatchers had a copy of 

the schedule readily available. 

Trains outside of the stations were moving when the simulation began. All trains were on time 

and had sufficient track to move at full speed for the first three minutes of the simulation without 

any action by the dispatcher. The entire train schedule is shown in Appendix B. 

2.5.2 The Hazard Schedule 

To evaluate safety, two types of hazards were used; each scenario included five hazards. The 

first type of hazard was the presence of trespassers on the track. Two or three times during each 

experiment, trespassers were present on the track for a certain period. If during that period of 

time a train passed through the area, the locomotive engineer saw the trespassers and the 

dispatcher was alerted. The dispatcher was expected to relay the trespasser alert to all other 

trains that would travel through that area. The second type of hazard was children stoning the 

train, which occurred twice during each experiment. If trains were routed into the hazardous area 

at the “right” time, the dispatcher was alerted and had to relay the information to the other trains 

near the hazard. 

To collect enough data, these two types of hazards were scheduled to take place in an area with 

heavy train traffic. The appropriate hazard occurrence time was chosen so that delays between 

five and ten minutes would not prevent the experimenter from gathering enough data. The 

territory was busy enough and the hazard schedule designed to account for variations in routing. 

For details on the hazard presence times and on the expected “alerter trains,” see Appendix B. 

2.5.3 The MOW Schedule 

Each scenario included MOW activities. To provide enough data points to compare performance 

between conditions and to create a moderately stressful workload, the number of MOW requests 

a dispatcher would normally face was exaggerated. After preliminary testing, 12 track requests 

were made during each scenario. These 12 requests included: 

• 2 bridge lifting requests 

• 2 management-scheduled track outages 

• 8 unscheduled MOW requests 

At the beginning of each experiment, the dispatcher took over the protection of two MOW crews 

who were granted permission by the previous dispatcher on the shift. 

There were two types of unscheduled MOW activity. The first activity was signal work. Signal 

workers requested protection for work on the signals near an interlocking. The second type of 

activity was track work. Track work was requested and performed either by track cars (special 

trucks riding on the track and checking its condition) or by repair crews. In the data link case, 
18 

there were two different answer messages, one for each type of MOW crew. Dispatchers were 

expected to use the appropriate reply message, depending on the type of request. In the radio 

condition, dispatchers were instructed to use the “Form D” movement authority for all MOW 

requests. 

The MOW schedule was designed to create challenging “meets and passes” problems for the 

dispatcher. At least one MOW request could not be granted if all trains were on time. 

Appendix B shows the MOW schedule. 

2.6 Experimental Design 

The type of communication environment was the independent variable. There were three levels: 

radio, discrete data link (DD), and broadcast data link (BD). The experimental design is shown 

in Table 4. A balanced incomplete block design (Lindman, 1992) was used. All dispatchers 

started with a data link scenario. 

Table 4. Experimental Design

Dispatcher Environment 

Radio Data link 

Discrete Broadcast 

1 Scenario 1 Scenario 2 

2 Scenario 2 Scenario 1 

3 Scenario 1 Scenario 2 

4 Scenario 2 Scenario 1 

5 Scenario 1 Scenario 2 

6 Scenario 2 Scenario 1 

The dependent variables (i.e., measured variables) can be classified into three groups: 

- Safety 

- Efficiency measurements of the communication system 

- Productivity 

Safety Measures

Three safety measures were collected. Two measures related to action taken by the dispatcher to 

warn or protect trains and MOW crews. The third safety measure concerned situation awareness. 

The two safety measures related to warning or protecting trains and MOW crews were: the 

percent of trains alerted in response to a hazardous event, and the percent of MOW crews 

properly protected. 

In the first safety measure for each hazard, a fixed number of trains were supposed to receive a 

warning message. For each train properly warned, the dispatcher earned one point.2

 All scores 

were converted into percentages. 

 

2

 The dispatcher could alert trains that did not need alerts. Participants received no credit when 

this event occurred, nor were they penalized. 
19 

The second safety measure was the number of MOW crews protected properly when Foul Time 

or Form D movement authority was granted. For each MOW request granted, the pieces of track 

asked for and the pieces of track given away were recorded. When MOW people were protected, 

the dispatcher earned one point. The number of points varied with each dispatcher. The 

percentage of MOW crews protected was calculated by dividing the number of properly 

protected MOW crews by the number of MOW requests granted for each dispatcher. 

The third safety measure was situation awareness, which was evaluated using the Situation 

Awareness Global Assessment Technique (SAGAT) developed by Endsley (1993). During the 

experiment, the simulation was paused so that the participant could complete a questionnaire. 

The questionnaire was divided into four groups of questions: routing, hazards, MOW activities, 

and communications questions. A dispatcher received one point for each correct answer. Partial 

credit was given if the answer was partially correct. For details about the questionnaire, see 

Appendix C. 

Communication Efficiency

To evaluate communication efficiency, total transaction time was measured. Total transaction 

time represented the duration of a transaction between the dispatcher and the respondent. A 

single transaction could include multiple exchanges of information. The duration was measured 

from the time at which an initial message was received by the dispatcher to the time at which 

final response was sent by the dispatcher. 

In the radio environment in this experiment, the initiation of the message and reception occurred 

simultaneously. In the data link environment, a delay could occur between the time the message 

was displayed on the monitor and the time the dispatcher observed and read the message. In the 

data link condition, the time at which the message was displayed on the monitor represented the 

initiating event for measuring total transaction time. The transaction was considered complete in 

the radio environment when the dispatcher completed the verbal response. In the data link 

condition, the transaction was completed after the message was sent and the experimenter 

forwarded the message to the appropriate recipient. 

Productivity Operations

MOW activity and the “on time” performance of the trains were evaluated. The number of trains 

entering a station was known for all dispatchers. The number of late trains entering the stations 

were recorded, as well as the number of trains that were more than five minutes late. MOW 

activity was evaluated by recording the number of granted MOW requests. 

2.7 Participants 

The participants were six professional Amtrak dispatchers: one woman and five men. Three 

participants had 7 to 9 years dispatching experience. Three others had less than 2 years 

experience. Participants were paid at the same hourly rate they received for performing their 

usual job duties. 

2.8 Procedures 

Each dispatcher was present in the laboratory for six to eight hours. Each dispatcher participated 

in two scenarios, with a different communication environment each time. Before each trial, 
20 

dispatchers were trained on the interface they would use. After the experiment, there was a short 

debriefing session. 

A short training program was designed to familiarize each participant with the simulator and the 

communication environments they would experience. The training consisted of two phases. In 

the first phase, the dispatcher learned how the simulator operated (approximately 30 minutes). 

During the second phase of training, dispatchers learned the schedule (approximately 90 

minutes). 

The voice radio communication equipment was different from what participants were 

accustomed to and so training was given. In the data link environments, training was necessary 

to introduce the dispatcher to the data link interface, to gain familiarity with the message tree and 

learn the rules (when to alert a train and how to alert it). During this first training phase, the 

experimenter explained the routing procedures. On a training scenario, the dispatcher practiced 

routing trains (with eight trains, four inbound trains and four outbound trains, and a yard move). 

Then, the experimenter walked the dispatcher through the voice radio or the data link system. 

Next, the participant practiced routing and communicating on the training scenario modified by 

adding hazards and MOW requests. During this training, the experimenter sat next to the 

dispatcher to answer questions about the system. Dispatchers were given the structure of the 

message tree in written form (Appendix A). 

During the second phase, the experimenter prepared the dispatcher for the experimental trials. 

The experimenter trained each dispatcher on the schedule for the next scenario. Dispatchers were 

given up to an hour and a half to become familiar with the schedule by practicing with the 

routing part of the simulator. Familiarization training was repeated before the second trial, as the 

scenario was different. 

Just before the experiment began, the experimenter reviewed all the rules (transmission rules for 

voice radio and message handling for data link) with the dispatcher. The participant was allowed 

to use any notes prepared during the training. The document showing the structure of the 

message tree, and the Form Ds were made available. The documents provided to the dispatchers 

in addition to the schedule for each scenario can be found in Appendix D. 

Each trial lasted one hour and was interrupted once after 30 minutes to complete the situation 

awareness questionnaire. The participant’s task was to perform their usual dispatching task given 

the constraints imposed by the new environments. At the conclusion of each trial, the dispatcher 

completed a brief questionnaire. Dispatchers were asked to evaluate workload, comfort with the 

system, and the usefulness of data link. Questionnaires for all three environments can be found in 

Appendix C. After completing the second trial, the dispatcher also answered some open-ended 

questions about the two environments and ranked the environments by preference. 
21 

3. RESULTS AND DISCUSSION 

3.1 Train Safety 

Train safety was evaluated by calculating the ratio of actually alerted trains to the number of 

trains that needed to be alerted. Table 5 shows these ratios for each communication environment. 

Table 5. Safety of Trains and MOW Crews by Communication 

Environment 

 Environment 

 Data link 

Safety Measure Voice Radio 

(%) 

Discrete (%) Broadcast (%) 

Trains Alerted 33 45 93 

MOW crews protected 64 94 97 

The broadcast data link was the safest environment. The percent of trains alerted was highest in 

the broadcast condition, followed by the discrete data link environment and the radio 

environment. The differences observed between the broadcast data link case and the two other 

conditions were statistically significant (t(6) = 6.02, p.< .05 comparing discrete to broadcast data 

link and t(6) = 9.36, p.< .05 comparing voice radio to broadcast data link). The better 

performance of the broadcast data link case was due to the ease with which multiple designated 

trains could be notified. In this environment, dispatchers were free to broadcast the alerting 

message to all trains on one branch or to all trains on their territory. Thus, the dispatcher could 

alert all trains entering the hazardous area with only one message. The drawback of the broadcast 

environment was that forgetting to send one alert message endangered multiple trains. In one 

case, a dispatcher neglected to warn trains of a hazard, which resulted in 20 percent of the trains 

failing to receive the warning. A second drawback could occur if warnings resulted in false 

alarms. If the train never encountered the trespasser, but received the warning, the crew might 

give less credence to this type of warning in the future. 

In the radio and discrete conditions, the dispatcher alerted each train individually. If the 

dispatcher was busy when notified of the hazard, the dispatcher might delay alerting some or all 

of the trains. The differences between the voice radio and discrete data link condition were not 

statistically significant. Although the differences were not statistically significant, the direction 

of the differences favors the discrete condition. Dispatchers alerted a greater percentage of trains 

in the discrete data link condition than in the voice radio condition. The train closest to the 

hazardous area was notified in 83 percent of the cases for the voice radio, and 100 percent of the 

cases in the discrete environment. In the voice radio environment after alerting the closest train, 

the dispatchers may have allocated their attention to other tasks and forgotten to alert the other 

trains. Alternatively, the dispatcher’s criterion for which trains should be notified in the voice 

radio condition may have differed from their criterion in the discrete data link condition. The 

dispatcher may have decided that only some trains traveling on a specific branch were at risk and 

therefore only notified the trains perceived to be at risk. 
22 

3.2 Mow Safety 

Dispatchers normally control the entire track territory for which they are responsible. However, 

when maintenance is necessary on or near the track, dispatchers give temporary control of the 

track section to the MOW crew. To make sure the track section under repair is protected, the 

dispatcher blocks that track section so that other trains are denied permission to enter. Trains 

cannot enter the protected track without the permission of the MOW crew. However, sometimes 

there is confusion about the exact track section the MOW crew requests. For example, where 

there are two tracks the MOW crew may request authority to work on track one, but the 

dispatcher may inadvertently give them authority to work on track two. Alternatively, after 

receiving permission to work on a section of track, the MOW crew may inadvertently work on 

unprotected track instead of the protected track. Both of these situations can compromise safety 

for the MOW crew. 

The number of MOW crews properly protected during each experiment was recorded. Whenever 

dispatchers blocked the track requested or a portion of track greater than requested, MOW crews 

were assumed safe. A dispatcher who granted a track request, but failed to physically block the 

track, resulted in an unprotected MOW crew. Table 5 shows the results in percentages for each 

environment. In the voice radio environment, 24 MOW crews were protected properly out of 37. 

In the discrete environment, 29 MOW crews were protected properly out of 31, and in the 

broadcast environment, 25 out of 26 MOW crews were protected properly. 

Both data link systems were clearly superior to the voice radio communication environment. The 

differences observed were statistically significant (t(6) = 5.98, p. < .05 comparing voice radio to 

discrete data link and t(6) = 7.32, p. < .05 comparing voice radio to broadcast data link). The two 

data link environments did not exhibit a significant difference. In the voice radio condition, the 

process of listening to a track request and transcribing it was time-consuming and error prone. If 

the voice radio transmission was unclear, the dispatchers asked the sender to repeat the message. 

If an error was detected during the initial transmission or during the acknowledgement, the 

process was repeated. Dispatchers made errors in hearing and transcribing the message. These 

kinds of errors are typical of the errors that occur in voice radio environments. They have also 

been documented in the aviation environment (Monan, 1983; Monan 1988; and Golaszewski, 

1989). 

In the data link conditions, the MOW foreman (represented by the experimenter in our study) 

requested authority to work on selected portions of the track by sending an email message to the 

dispatcher. The location and duration of the track request was displayed in a text format. The 

location was also displayed on the track layout display, color-coded in yellow. 

Errors in the data link environment usually came from a peculiarity of track layout interface. 

When the dispatcher viewed a message requesting work authority on a particular section of 

track, the track layout interface displayed this information by showing the requested track 

section in yellow. When a dispatcher granted a MOW crew’s authorization to work on a track 

section (blocking the track for use by others), the track section was color-coded blue on the track 

layout display. If the request message was still displayed in the text message window of the data 

link interface, the operator could not see if the track was properly blocked because the yellow 

color-coding of the MOW request masked the blue color-coding of the granted authorization. 
23 

The results illustrate that a visual display has the potential to improve safety by minimizing data 

entry errors and reducing memory load for the recipient. However, the details of how the 

interface is implemented will also impact safety. 

3.3 Communication Efficiency 

The average transaction time for each environment was calculated. The results are summarized 

in Table 6. Lower transaction times were observed for the two data link environments, compared 

to the radio. The difference observed between the broadcast data link environment and the voice 

radio environment was statistically significant (t(157) = 2.28, p < .05, comparing voice radio to 

broadcast data link). The difference between the discrete data link and the voice radio condition 

was not statistically significant, although the trend was in the same direction as the broadcast 

data link condition. 

Table 6. Mean Transaction Completion Time by Communication 

Environment 

 Environment 

 Data link 

 Voice Radio Discrete Broadcast 

Mean Transaction Time (s) 227 174 135 

3.3.1 Performance Varies with Message Content 

To understand why transaction times were lower for both data link conditions, the distribution of 

messages by transaction time was examined. Figure 9 shows the distribution of message 

transactions by time. For all three conditions, the majority of transactions were completed in two 

minutes or less. In each condition, there were a small number of messages that took longer to 

complete. For the voice radio condition, there were more of these lengthy transactions compared 

to the data link conditions. In the voice radio environment, the percentage of messages 

completed after five minutes was 85 percent. By contrast, in the data link conditions the 

percentage of messages processed was 97 percent or greater. Thus, some messages took longer 

to communicate in the voice radio condition. Similarly, 9 percent of messages were never 

answered (presumably forgotten) in the voice radio condition. By contrast, in the data link 

conditions, dispatchers forgot significantly fewer messages. None of the messages were 

forgotten in the broadcast condition, and only 1 percent of the messages were forgotten in the 

discrete condition. 

The difference between voice radio and data link may be partly explained by the additional 

memory load required to process messages in the voice radio condition. Dispatchers were heard 

asking at least once during each voice radio condition, “Who was that on the voice radio a 

couple of minutes ago?” In the data link interface, the visual display provided an easy way to 

remember who called. 
24 

Figure 9. Number of Transactions by Time and Environment 

To understand what type of message might account for the longer transaction time, messages 

were divided into categories by content. Figure 10 shows the transaction time distribution by the 

type of message. The message types included: denied MOW requests, granted MOW requests, 

messages between train crews and the dispatcher, miscellaneous messages, and messages that 

were not forwarded. Figure 10 shows that granted MOW requests accounted for the difference 

between the data link conditions and the voice radio condition. There were a comparatively large 

number of granted MOW requests that took longer than 500 seconds compared to the two data 

link conditions. 

To clarify the distinction between message types and communication efficiency in the three 

communications environments, the communication transactions were separated into two types 

depending on the type of answer. The first type of communication, referred to as simple 

communications, included denied MOW requests (i.e., Foul Time), requests for bulletins on 

temporary speed restriction bulletins (TSRBs) when there were none, and the hazard alerts 

communications. The second type of communications called complex communications included 

only one type of communication - granting a MOW request. In each environment, simple and 

complex messages were compared and transmitted as a function of time. Figure 11 shows the 

average transaction time for the two communication types by environment. 

Radio

0

10

20

30

0 500 1000 1500 2000

Time (s)

Trans action

Discrete

0 500 1000 1500 2000

Time (s)

Broadcast

0 500 1000 1500 2000

Time (s)
25 

As expected, in all three environments the average transaction time was shorter for simple 

messages than for complex ones. For simple messages there were statistically significant 

differences between the voice radio condition and the two data link conditions (t(90)=3.36, p < .05 

comparing voice radio and direct data link and t(100) = 2.48, p < .05 comparing voice radio to 

broadcast data link). In both cases, the transaction times were lower in the voice radio condition. 

Radio

0 500 1000 1500 2000

Transaction Time (s)

Event Type

Denied MOW Request

Granted MOW Request

Train Message

Miscellaneous

Not Forw arded

Discrete

0 500 1000 1500 2000

Transaction Time (s)

Event Type

Denied MOW Request

Granted MOW Request

Train Message

Miscellaneous

Not Forw arded

Broadcast

0 500 1000 1500 2000

Transaction Time (s)

Event Type

Denied MOW Request

Granted MOW Request

Train Message

Miscellaneous

Not Forw arded

Figure 10. Distribution of Transaction by Time and 

Type of Message 
26 

The average transaction time was 62 seconds in the voice radio condition compared to 111 

seconds in the discrete data link condition, and 161 seconds in the broadcast data link condition. 

For complex messages, the voice radio condition performed worse than the two data link 

conditions. The average transaction time was 463 seconds in the voice radio condition compared 

to 199 seconds in the discrete data link condition, and 197 seconds in the broadcast data link 

condition. Again, these differences were statistically significant (t(55) = 3.07, p. < .05 comparing 

voice radio to discrete data link and t(53) = 2.95, p. < .05 comparing voice radio to broadcast data 

link). There were no statistically significant differences between the discrete and broadcast 

conditions. 

Figure 11. Mean Task Completion Time for Simple and Complex Type Messages by 

Communication Environment 

In general, the differences in performance between voice radio and data link can be related to the 

way information in different sensory modalities is processed, and the design of the two 

communication interfaces. In the voice radio environment, information was presented in auditory 

form. In the data interface, information was presented in a visual form. 

Van Cott and Kinkade (1972) provide guidance on message format. They indicate that short 

simple messages are more effectively presented in auditory form. Lengthy and complex 

messages are more effectively presented in visual form. Table 7, adapted from Van Cott and 

Kinkade shows the criteria for selecting the form information should take - either auditory or 

visual. In the voice radio environment, the simple messages met several of the criteria for 

selecting the auditory channel. The simple messages were generally short addressed events in 

time that needed to be acted upon immediately. By contrast, the complex messages were lengthy 

and needed to be available to the dispatcher for a longer period. 

111

62

161

197

463

199

550 450 350 250 150 50 50 150 250 350 450 550

Broadcast

Discrete

Radio

Communication 

Environment

Average Response Time (s)

Simple communications Complex communications
27 

The advantage of the data link environments over the radio in processing complex messages can 

be attributed to the reduced memory needed to process information displayed visually. The data 

link systems gave a visual representation of train and MOW crew locations in text form and on 

the track layout display. MOW crews did not need to repeat which section of track was needed 

because of a failure to hear, transcribe, or understand the track section being described. The 

dispatcher could read the information in the text message or see the section requested on the 

track layout display color-coded in yellow. 

Table 7. Characteristics for Selecting Modality in which to Present 

Information 

Auditory Visual 

Simple Complex 

Short Long 

Message not referred to later Message referred to later 

Addresses events in time Addresses events in space 

Message acted upon immediately Message not acted upon immediately 

Visual system is overburdened Auditory system is overburdened 

Environment is too bright or dark 

adaptation is necessary 

Environment is too noisy 

Receiver must move about Receiver remains stationary 

Adapted from Van Cott and Kinkade (1972) 

By contrast, the dispatcher in the voice radio environment dictated specific information to MOW 

workers when they were granted Foul Time (i.e., dispatcher name, date, time span granted, 

location, and number of work crew among others). While the dispatcher dictated the authority to 

work on the track, MOW people transcribed the information on paper. Then, the MOW person 

acknowledged the transmission by reading back that same information to the dispatcher. For 

Form Ds, dispatchers verified the readback by writing this information on paper. This process 

was time-consuming and prone to errors. With the data link interface, the dispatcher filled in the 

form directly on the computer and transmitted the message to the roadway worker. Upon 

receiving the message, the roadway worker read and acknowledged the message by sending a 

written confirmation back to the dispatcher. The time-consuming process of listening to the 

message and repeating it back to the sender was minimized because the visual display of the 

work authority was available to the dispatcher and could be acted upon more quickly. 

Favorable comments by the dispatchers indicated that the visual representation of location 

information on the track layout display was particularly helpful in supporting the dispatcher’s 

communication task, as well as managing the territory. The graphic representation lowered 

memory load by making information about the track visible over time. By displaying this 

information directly on the track display, the dispatcher could also see how it would impact the 

movement of trains or allocation of track to other MOW crews. 

Specific aspects of the visual interface also facilitated the completion of complex transactions. 

During the design of the data link interface, interviews with dispatchers indicated they would not 
28 

use an interface that required use of a keyboard to enter information. The development of 

message templates facilitated the data entry process. The dispatcher simply chose the appropriate 

message type from a menu of message types and filled in the key information. This procedure 

minimized transaction time by reducing the amount of data entry by the dispatcher. A system 

that required greater keyboard entry would have reduced the benefits of the visual interface 

compared to the auditory interface inherent with voice radio. 

3.4 Situation Awareness 

Table 8 shows the percentage of questions answered correctly, and summarizes the evaluation of 

situation awareness. While none of the differences between scores were statistically significant, 

an examination of the data is interesting. For voice radio, situation awareness scores were best 

for MOW activity followed by hazard awareness, communications, and routing. For both data 

link conditions, situation awareness scores were best for hazard awareness followed by MOW 

activity, communications, and routing. For both voice radio and data link conditions, routing 

ranked last. This finding suggests that dispatchers were devoting more resources to 

communication activities than to routing activities. Given the higher workload demands 

associated with this experiment compared to normal railroad operations, this seems reasonable. 

However, it is also reasonable to expect that the competition for visual resources in the data link 

condition by the visual presentation of text might result in a performance decrement in the data 

conditions compared to voice radio. Because vision requires selective attention, the dispatcher 

can focus on only one display at a time. However, a performance decrement for data link did not 

occur. Routing situation awareness scores were actually better in both data link conditions, 

although these differences were not statistically significant. 

For three of the four activities measured, routing, hazard awareness, and communication 

performance were better with data link than with voice radio. The dispatchers demonstrated 

better knowledge of the train schedule, current train location, hazard location, and also when 

messages were sent and their content. Although the results were not statistically significant, the 

trend suggests that data link does not impair situation awareness compared to the use of voice 

radio. It may actually improve situation awareness. 

Table 8. Situation Awareness by Activity and Communication Environment

 Percent Correct Response by Environment 

 Data link 

Activity Voice Radio (%) Discrete (%) Broadcast (%) 

Routing 43 63 63 

Hazards 57 85 74 

Communication 56 71 66 

MOW activity 82 85 72 
29 

A number of factors may have contributed to the improved performance trends in the data link 

conditions for these three measures. The visual persistence of messages enabled dispatchers to 

examine this information at their leisure while lowering memory load at the same time. 

Displaying information about routing and hazard location on the track layout display provided a 

method for relating this information to the train schedule. For example, in the data link 

conditions the dispatchers saw the hazardous area highlighted in yellow on the track layout 

display when they viewed the alerting message. In the voice radio environment, dispatchers 

relied on memory to retrieve this information. In current railroad operations, dispatchers write a 

personal note or report it in a “desk book.” The visual display found in the data link interface 

saves time and resources by avoiding the process of putting this information in a visual form. By 

saving the cognitive and physical resources for other activities, dispatchers can devote more time 

to other tasks. 

For MOW activity, situation awareness scores were similar for voice radio and data link 

conditions. Here, situation awareness for voice radio was slightly worse than the discrete 

condition and better than the broadcast condition. Of the four measures of situation awareness, 

MOW activity was the measure for which dispatchers showed the best performance in the voice 

radio condition. In the voice radio and data link conditions, the dispatcher made use of a visual 

display to process information about MOW activity. In current railroad operations, the dispatcher 

must prepare paperwork when granting a MOW request. This paper work (i.e., Form D) 

describes in visual form the track location and time for which the track authority is requested. In 

our experiment, dispatchers followed these procedures. Thus, the information received by voice 

radio was translated early on into a visual form. When the dispatcher put the MOW request into 

effect, this track authority was also displayed on the track layout display. This provided an 

additional visual cue, similar to what was displayed in the data link conditions. Thus, in both 

voice radio and data link conditions, a visual aid was available to assist the dispatcher. 

These results suggest that data link does not impair situation awareness. Overall, a trend towards 

better situation awareness in the two data link conditions was observed compared to the voice 

radio condition. This improvement was attributed to the lower memory demands associated with 

information that was made available in visual form. Although the visual interface in the data link 

conditions increased attention to communication activities, routing situation awareness did not 

suffer. 

3.5 Productivity 

Two measures were used to assess productivity: the number of trains entering a station late (i.e., 

with a delay more than five minutes), and the number of MOW requests granted. 

Table 9. Productivity by Communication Environment 

 Environment 

 Data link 

Productivity Measure Voice Radio (%) Discrete (%) Broadcast (%) 

Late Trains 27 24 13 

MOW requests granted 63 65 54 
30 

Table 9 shows the percent of trains more than five minutes late by environment and the 

percentage of MOW requests granted for each environment. For both measures, the results were 

not statistically significant. For both measures, the voice radio and the discrete data link 

environment show similar results. The broadcast data link condition shows the smallest 

percentage of late trains compared to the two other conditions. Having fewer alerting messages 

in the broadcast case might have lead to more free time to route trains. However, dispatchers 

granted fewer MOW requests in the broadcast condition. Overall, the data suggests that the data 

link interface did not adversely affect productivity compared to the voice radio interface. 

3.6 Dispatchers’ Preferences 

The debriefing questionnaire gave the dispatchers an opportunity to comment on our data link 

designs as well as on the voice radio condition. Table 10 summarizes the answers to the 

debriefing questionnaires. The numbers in Table 10 represent average scores across participants 

on a scale from one to seven. A score of one represents a low or negative value (low workload, 

uncomfortable, unrealistic compared to revenue service). A score of seven represents a high or 

positive value (high workload, comfortable, realistic compared to revenue service). No 

statistically significant differences were observed. 

Table 10. Dispatcher Ratings of Workload: Comfort 

and Simulator Realism 

 Environment 

 Data link 

 Voice Radio Discrete Broadcast 

Workload 6.3 6.0 5.8 

Comfort 5.9 5.0 4.3 

Realism 2.1 N/A N/A 

The dispatcher rated workload high in all three environments with an average score around six. 

The workload was perceived slightly lower in both data link environments. Dispatchers rated the 

realism of the voice radio environment 2.1 out of 7. Dispatchers commented, “No way is a 

territory that busy...” One dispatcher said, “No way can a man deal with that during eight hours. 

It is totally unrealistic.” This rating can be attributed to the high workload. No dispatcher 

criticized the voice radio environment for lack of similarity with the current environment in 

respects other than workload. 

All dispatchers felt relatively comfortable with the data link environments (see Table 10). Before 

the experiment began, most dispatchers expressed a negative attitude towards data link. 

However, after the experiment the dispatchers felt it would be very useful in addition to voice 

radio. The dispatchers also gave comments on the use and implementation of data link. These 

comments are summarized in Table 11. 
31 

Table 11. Dispatcher Comments on the Use of Data Link

Category Comment 

Data link would be good for communicating TSRBs (with speed 

restrictions announcements), Form Ds for MOW crews and engineers, 

Foul Time, train crew and consist information, car placement 

information, planned track outage information, and emergency phone 

numbers. 

Choice of 

communication 

channel 

Choose voice radio for emergencies and when an immediate response is 

required. 

A sound alert for incoming messages would be welcome in the data link 

environment. 

Provide capability to print paper copies of messages. 

Distinguish answered from unanswered messages. 

Use voice recognition. 

Interface 

The highlighting feature makes a MOW request very clear, however, 

blocking actions should remove the yellow color code. 

The dispatcher needs to know whether the recipient read the message. 

The acknowledgment procedure requires further work. 

When Foul Time is given back, dispatcher should acknowledge the 

message. 

Data link allows messages to be acknowledged when one has the time. 

There is no audio pressure to respond immediately. 

Safety 

The broadcast feature could be misused in the same way as voice radio. 

MOW crews might take advantage of information about train and 

equipment movements to work without permission. 

33 

4. CONCLUSIONS 

Voice radio congestion is a significant problem in the current dispatching environment. Data link 

has been proposed as an alternative communication channel to solve this problem. In particular, 

information presented orally over the radio can be presented in visual (text and graphic) or aural 

form with data link. The objective of this study was to evaluate how the introduction of data link 

technology might affect dispatcher performance. The results suggest that data link can improve 

communication efficiency without adversely affecting productivity, situation awareness, or 

safety. Even where the results were not statistically significant, they favored data link. Compared 

to voice radio, data link improved safety and situation awareness. For productivity, no 

statistically significant differences were observed between data link and voice radio. 

Data link improved safety compared to the voice radio. In data link, dispatchers protected a 

greater percentage of trains and MOW crews compared to the voice radio. By providing 

information in a visual format, data link eliminated readback errors and hearback errors 

associated with the auditory modality. Eliminating these errors helped shorten the duration of 

complex, safety critical messages like temporary speed restrictions. Translating track requests 

from alphanumeric text to a graphic display on the track layout display made the request even 

easier to process. The visual nature of information presented in the data link systems reduced the 

demand placed on the dispatcher’s memory. The dispatchers were much less likely to forget to 

respond to messages with data link than with voice radio. Anecdotal comments by the 

participants suggested it also reduced stress by providing a quieter environment in which to 

work, giving the dispatcher greater control over when messages were answered. 

Communicating information in visual form did not negatively impact situation awareness scores. 

Where the differences between the data link and voice radio conditions were not statistically 

significant, the trends showed a positive impact for data link. Situation awareness scores for both 

data link conditions were better than voice radio for routing, hazard awareness, and 

communication. While the dispatcher devoted more resources to processing visual information 

with the data link conditions than with voice radio, (there were three displays to monitor instead 

of two), no adverse impact was evident. The dispatcher appeared to benefit by having a visually 

persistent display of information that reduced memory load. MOW activity was the only 

category in which performance was as good or better than the voice radio condition. Dispatchers 

had a visual form of information to assist them in situation awareness. In the voice radio 

condition, dispatchers wrote the track requests on paper as part of the track authorization 

process, which helped in acknowledging the request. This finding reinforces the importance of 

the visually persistent forms of information in supporting the dispatcher in processing complex 

information. 

Overall, the differences between the discrete data link condition and the broadcast data link 

condition were small. The broadcast version showed a greater improvement in train safety than 

the discrete version. The broadcast version minimized communication workload by providing a 

simple way to reach multiple recipients and freed the dispatcher to attend to other tasks. For 

example, the dispatcher could use a single message to alert all trains along a particular branch. 

The discrete system required the dispatcher to contact each train individually. 

However, implementing broadcast data link in revenue service will require addressing two issues 

related to information distribution and acknowledgment procedures. If a dispatcher failed to send 
34 

a message as happened in one instance, or the message failed to reach the intended recipients, the 

consequences were larger since multiple parties were affected. Failure to send a single message 

placed multiple trains at risk. Thus, a single error can increase the risk of harm, compared to a 

system that only allows messages to be sent to one party at a time. System designers will need to 

consider how to minimize the impact of these types of errors. 

A second issue for broadcast data link concerns acknowledging the receipt of messages. 

Acknowledgement means that the train crew has read and understood the message. Since 

dispatchers alert multiple trains simultaneously, they need to determine whether all trains 

received the message. Therefore, the dispatcher will need a method to keep track of 

acknowledgments. Designing the data link interface to support tracking of multiple 

acknowledgements will be an important requirement. 

Communication efficiency for voice radio and the two data link conditions varied as a function 

of the characteristics of each medium. Information communicated by voice radio was presented 

in an auditory format. Information communicated via data link was presented in a visual format. 

Each form proved better suited for presenting some kinds of information than others. Voice radio 

proved to be better suited for communicating short and informal communications as well as 

time-critical messages that required immediate action (i.e., a dispatcher reporting no speed 

restrictions when a locomotive engineer called to request a temporary speed-restriction bulletin 

or alerting a locomotive engineer to the presence of a trespasser). For these types of 

communications, data link doubled the communication times over voice radio. These results 

were due to the auditory format in which the information was presented. 

In this experiment, data link proved better suited for communications whose length or 

complexity imposed a significant burden on memory. In railroad operations, these characteristics 

are typical of safety critical messages that require formal acknowledgement procedures (i.e., 

granting a Foul Time request or authorizing a train movement using a Form D). Data link 

provided an efficient channel for these communications; transaction times were reduced by a 

factor of two. The idea of not having to repeat a message multiple times was also appealing to 

the dispatchers in our study. 

In voice radio and data link conditions, the differences observed between the two types of 

messages were due to the modality or format in which the information was presented, not the 

communication medium. While information sent over the radio is presented in an auditory form, 

digital communications systems like data link afford more presentation options. Thus, data link 

supports both auditory and visual modalities. The properties listed in Table 7 suggest what 

format a message should take. 

The differences identified between voice radio and data link also depended upon the details of 

how each interface was implemented. Had the data link interface required the dispatcher to make 

more use of the keyboard to enter messages than with the current design, the results might have 

been quite different. Pilot testing indicated that heavy use of a keyboard was unacceptable to the 

dispatcher population, and would have resulted in longer response times. Similarly, the ability to 

show track-related information in text or graphic format reduced communication errors and 

dispatcher response time. This feature also generated positive comments from the dispatchers. 

Successful implementation of a data link interface is dependent upon applying principles of good 

human factors design and usability testing to meet the needs of dispatchers who use this 

communication interface. 
35 

The current study suggests that dispatchers benefit from both voice radio and data link 

communication modes. In recommending the conditions under which medium should be used, 

this study suggests that voice radio is best suited for communicating simple, time-sensitive 

messages to one recipient. Data link system is best suited for communicating lengthy messages. 

Sending discrete messages works best where privacy is important or the message content would 

benefit only the recipient for which the message is intended. Sending broadcast messages works 

best when there is a need to communicate the same information to multiple recipients. 

4.1 Future Research 

This study suggests that data link technology has the potential to improve the safety and 

communication efficiency of the dispatching environment. However, the introduction of new 

technology and new interfaces raises new issues along with solving old problems. The current 

study compared voice radio to data link where each was the only medium. However, in actual 

operations both types of communication systems will be available. Currently, data link affords 

more flexibility in terms of how information is presented. The challenge for designers of future 

railroad communication and information systems will be deciding the format that different kinds 

of information should take. 

As an example, consider the acknowledgment procedures for granting train movements or 

authorizing track use by MOW crews. For safety reasons, the acknowledgment procedure is 

needed to assure the sender that the message was received and understood. This issue is 

particularly important for messages concerning train movement authorization and track 

allocation procedures that are governed by formal operating procedures. The kinds of errors 

associated with the verbal acknowledgement procedures are less likely to occur when this 

information is presented in a visual format. Nevertheless, different methods of entering 

information (e.g., keyboard, mouse, or touch screen) will create new errors as well. Keyboard 

entry may result in transposition errors while mouse and touch screen entry may contribute to 

selection errors. Identifying these error types will be important to their mitigation. 

Another example concerns how dispatchers allocate their attention to incoming messages. The 

temporal nature of messages received by voice radio calls for an immediate response by the 

dispatcher. In practice, however, the dispatcher does not immediately answer all calls (Roth, 

Malsch, and Multer, 2001). The dispatcher constantly evaluates whether to continue with the 

current task or switch to a different activity. When there is more than one call to answer, the 

dispatcher must decide which call will be attended to first. In this experiment, simples messages 

from train crews were acted upon more quickly than messages from MOW crews requesting 

track in the radio condition. This behavior was not observed with data link. Did the lower 

workload associated with granting a MOW request in the data link condition change how the 

dispatchers allocated their attention? How will dispatchers allocate their attention when voice 

radio and data link are used together? More research will be needed to understand how the use of 

both voice radio and data link impacts the dispatcher’s attention allocation. 

Several related challenges for designers will come from the increasing complexity of these 

information systems. By increasing the bandwidth over which information is communicated, 

data link will increase the quantity of information available to the dispatcher. To handle the 

increasing quantity of information, the interface for managing this information and railroad 

operations will also increase in complexity. Data link technology offers the ability to create 

public (shared) and private communication channels. What information should remain private 
36 

and what information should be shared? For shared communication, how much information can 

be communicated before the operator becomes overloaded? How should the interface be 

designed to address information overload? 

Both visual and auditory interfaces have limits to the amount of information that can be 

effectively displayed. Thus, large amounts of information may be hidden from the dispatcher. 

One challenge concerns getting lost in this information space (Elm and Woods, 1985; Woods, 

Roth, Stubler, and Mumaw, 1990; and Burns, 2000). 

A second challenge concerns the management of the interface itself. As the information space 

increases in size, more cognitive resources will be devoted to dealing with the interface. Fewer 

resources will be devoted to cognitive activities directly associated with the operational task 

(e.g., deciding whether to authorize a train movement). Designers will need to carefully consider 

how the interface design impacts the dispatcher’s ability to quickly find information so that 

attention remains on the operational task. 

Finally, it is unclear from our results to what extent dispatchers are affected by the loss of 

information they acquire over voice radio that is not specifically directed to them. Roth, Malsch, 

and Multer (2001) observed that dispatchers in actual railroad operations took advantage of 

information overheard on the radio but not intended for them. The participants in this study did 

not appear to make use of this additional information. Further research will be necessary to 

determine the need for information now available through the party line and how that 

information could be provided in a data link system. 
37 

APPENDIX A. MESSAGE TREES 

This appendix shows the message trees for the dispatcher and experimenter. In addition, the 

distribution list used by the dispatcher to specify the group of secondary recipients in the data 

link broadcast environment was included. 

The Dispatcher Message Tree Used During the Experiment

High Priority 

To Engineer- Fatalities 

Trespasser hit Train derailment 

Notified RT – protection set up. 

Med. Assistance – help underway. 

Notified RT help underway. 

To other trains – routing delays. 

To MOW – train derailed –busy time. 

To Rescue Team

Trespasser hit Train derailment 

Alert rescue team. Alert rescue team. 

Medium Priority 

To Engineer – Danger Warning 

Trespasser Obstruction – train stalled Kids throwing stones 

Trespassers on track ahead. 

Trespassers are gone. 

Trespassers have been taken 

care of. 

Vehicle on track. 

Train stuck on track. 

Information request about 

stalled train. 

Locomotive is coming. 

Kids are playing. 

Kids are gone. 

To MOW –Danger Warning

NOW on the wrong track 

Notification 

Low Priority 

To Engineer – Standard Communication

Temporary Speed 

Restrictions (TSR) 

Track Problem State of Engine Special Train Movement 

No TSRB 

TSRB follows 

TSRB update 

Special speed restrictions 

Track repaired – 

reduced speed 

Track out of service 

– delay and reroute 

Special routing due 

to risk of total 

failure 

Special movement 

Dispatcher to MOW – Standard Communication To Yard Routing preferences To Lifting Bridge 

Track Work Signal Work Track Wishes Need Locomotive Bridge Lifting 

Foul Time granted. 

Foul Time refused. 

Other Foul Time 

proposal 

Foul Time ends. 

Foul Time granted. 

Foul Time denied. 

Not possible – other 

track or wait. 

Okay for required 

track. 

Can we have a 

locomotive? 

Okay to lift bridge. 

Impossible to lift 

bridge. 
38 

Broadcast Group Selection 

The broadcast group selection has two layers. The first layer is the type of recipient and 

the second is the location of these recipients. The broadcast group selection tree used in the 

experiment has the following structure: 

(Recipient) Trains

(Location) On branch A 

 On branch B 

 On branch C 

 On branch D 

 All 

 Trains and MOW 

 On branch A 

 On branch B 

 On branch C 

 On branch D 

 All 

 MOW 

 On branch A 

 On branch B 

 On branch C 

 On branch D 

 All 

 Everybody 
39 

Experimenter’s Message Tree

ENGINEER MESSAGE TREE

High priority

 Engineer to Dispatcher 

 Trespasser hit 

 Train hit a trespasser 

 Medical help is needed 

 Passenger dead/injured 

 Assistance in station 

 Assistance right away? 

 Train derailed 

 Need help 

Medium priority

 Engineer to Dispatcher 

 Trespasser 

 Seen on track 

 Engine failure 

 Train stuck on track 

 Freight train stuck 

 Power insufficient – need power/loco 

 Threat for people in the train 

 Chemicals released 

 Bomb on the track 

 Kids throwing stones 

 Kids throwing stones 

 Not there any more 

 Obstruction 

 Engine failure - train stuck on track 

 Trees across the track 

 No trees any more 

 Additional locomotive needed – freight train 

 Failures 

 Total power loss – Train stuck 

 In cab system failure 

 Re-crewing 

 Crew outlawed 

 Re-crewing position OK 

 What is up? 

 Need information – What are you doing? 

Low priority

 Engineer to Dispatcher 

 Engine state 

 Engine OK 

 Engine state – serious trouble 

 Track problem 

 Track damaged 

 Bad weather 

 Thunderstorm – reduce speed 

 Leaves on the track – reduce speed 

 Special events 

 Dignitaries on the train 
40 

 Bulletin 

 Bulletin request 

 Warning 

 Long/large/high train! 

 Position report 

 Current position 

 Engineer to Support staff 

 Engine state 

 Engine OK 

 Engine state – serious trouble 

MISCELLANIOUS MESSAGE TREE

High priority

 Police to Dispatcher 

 Police intervention 

 Stop the train 

 Corpse near the track 

 Rescue Team to dispatcher 

 Fatality 

 Everything under control 

 Train derailment 

 Everything under control 

 Passenger dead/injured 

 Everything under control 

 MOW fatality/injury 

 Everything under control 

 System to Dispatcher 

 MOW in danger 

 Protection forgotten 

 Gave Foul Time but unprotected! 

Medium priority

 System to Dispatcher 

 MOW person on the wrong track 

 Worker not protected 

 Trespasser 

 Trespasser on track 

 Obstruction 

 Vehicle stranded on grade crossing 

 Unprotected station 

 Station with no bridge crossing 

 Electrification problem 

 Power cable failure 

 Loss of electrification/power 

 Re-crewing 

 Crew outlawed 

 Loco power problem 

 Power insufficient 

 CETC problem 

 Not updating – shift to radio communication 

 Field signal problem – messaging routing 
41 

 Electrification Department to Dispatcher 

 Power loss 

 Power outage on track. 

 Power problem repaired 

Low priority

 System to Dispatcher 

 Engine state 

 Engine OK 

 State of the engine – serious trouble 

 Information 

 Rescue operation – World information 

 Unprotected station – World information 

 Notified - Height limitation on given track 

 Notified - Speed limitation on given track 

 Emergency phone numbers 

 Special events 

 Dignitaries on train 

 Special train 

 Special car 

 Delays 

 Slow crew 

 Scheduled meet not possible 

 Bulletin 

 Bulletin request 

 Warnings 

 Long/large/high train! 

 Operation at limit capacity 

 Reminder – Train priorities 

 Signal workers on track 

 Two meets and passes at same time 

 Time to recover - alert 

 Possible dispatching mistakes 

 Omitted a warning 

 Unnecessary route cleared 

 Routing mistake – Lack of protection? 

 Too much track given away 

 Routing mistake – No power! 

 Yard to Dispatcher 

 Train servicing 

 Request particular track 

 System to Engineer 

 Engine state 

 Engine OK 

 State of the engine – serious trouble 

 Bulletin 

 No bulletin 

 Bulletin – restrictions 

 Bulletin – update 

 Bridge Lifting to Dispatcher 

 Bridge Lifting 

 Ship waiting for bridge 

 The ship passed 
42 

MOW MESSAGE TREE

High priority

 MOW to Dispatcher 

 MOW fatality/injury 

 Railroad person dead (heart attack) 

 Medical assistance needed 

Medium Priority

 MOW to Dispatcher 

 Track Work 

 Track Work permission request 

 Track Work protection request 

 Work completed 

 Additional time requested 

 Signal Work 

 Signal Work permission request 

 Signal Work protection request 

 Track car failure 

 Track car stuck 

 Track car out of the way 

 Track problem 

 Track damaged 

 Work performed – Speed restrictions 

 Power loss 

 Power outage on track. 
43 

APPENDIX B. EVENT SCHEDULES 

Appendix B contains the schedules for the trains, hazards, and MOW work. The train schedule 

was provided to dispatchers during the experiment. 

The following is the train schedule for Scenario #1 
44 

The following is the train schedule for Scenario #2 
45 

The following is the hazard schedule for scenario #1 (with MOW crew calling times). The gray 

area indicates the presence of a trespasser in a specific area of the track. Under each hazard are 

the identification numbers of the trains that would pass through this area if the trains ran on 

schedule. The first number in the gray area represents the number of the “alerter train”; the other 

numbers in the gray area represent the trains the dispatcher had to alert. 
46 

Bridge Messages MOW MOW out Total Mess.

1:00 PM 221

1:01 PM SW #1 1

1:02 PM

1:03 PM

1:04 PM

1:05 PM

1:06 PM

1:07 PM 100 1 2

1:08 PM

1:09 PM

1:10 PM Disp 2 3

1:11 PM 300 RC #5 4

1:12 PM

1:13 PM 113 SW #1 5

1:14 PM 443 3 6

1:15 PM SW #3 7

1:16 PM 223 331 4 8

1:17 PM RC #1 9

1:18 PM

1:19 PM

1:20 PM

1:21 PM 400 5 10

1:22 PM

1:23 PM

1:24 PM RC #6 RC #2 11,12

1:25 PM

1:26 PM

1:27 PM 102 200 6,7 RC #3 13,14,15

1:28 PM

1:29 PM SW #3 16

1:30 PM

1:31 PM

1:32 PM

1:33 PM

1:34 PM TC #2 17

1:35 PM

1:36 PM

1:37 PM 225

1:38 PM SW #4 18

1:39 PM

1:40 PM

1:41 PM

1:42 PM 115 8 TC #3 19,20

1:43 PM

1:44 PM

1:45 PM RC #4 21

1:46 PM

1:47 PM

1:48 PM

1:49 PM 117 302 9 22

1:50 PM 333 Disp 10 23

1:51 PM SW #5 24

1:52 PM

1:53 PM

1:54 PM TC #2 25

1:55 PM

1:56 PM

1:57 PM

1:58 PM 104

1:59 PM

2:00 PM

Tresp. Kids
47 

The following is the hazard schedule for scenario #2 (with MOW crew calling times) 

Bridge Number of M MOW MOW End Total Mess.

4:00 PM

4:01 PM SW #1 1

4:02 PM

4:03 PM

4:04 PM 240 491 1 2

4:05 PM RC #2 3

4:06 PM

4:07 PM

4:08 PM RC #1 4

4:09 PM

4:10 PM Disp. 2 5

4:11 PM 291 391 RC #5 6

4:12 PM 120 3 7

4:13 PM 242

4:14 PM

4:15 PM 191 RC #3 8

4:16 PM

4:17 PM 360 480 4.5 SW #1 9,10,11

4:18 PM

4:19 PM

4:20 PM

4:21 PM RC #6 12

4:22 PM

4:23 PM

4:24 PM

4:25 PM TC #2 13

4:26 PM

4:27 PM 362

4:28 PM

4:29 PM 244 6 RC #8 14,15

4:30 PM 393 493

4:31 PM

4:32 PM

4:33 PM 293

4:34 PM

4:35 PM TC #1 RC #2 16,17

4:36 PM

4:37 PM

4:38 PM RC #7 18

4:39 PM

4:40 PM 482

4:41 PM

4:42 PM

4:43 PM

4:44 PM 293 7 19

4:45 PM RC #4 20

4:46 PM 122 8 21

4:47 PM 193 RC #5 22

4:48 PM 364 9 23

4:49 PM

4:50 PM Disp. 10 24

4:51 PM

4:52 PM TC #3 25

4:53 PM

4:54 PM

4:55 PM

4:56 PM TC #2 26

4:57 PM

4:58 PM

4:59 PM

5:00 PM

Tresp. Kids
48 

The following are the MOW schedules respectively for scenario #1 and scenario #2 

Id - Scenario #1 where asking starting ending type

Repair Crew #1 before A3 0 17 FT

Repair Crew #2 between Term and B1 0 24 FT

Repair Crew #3 between B1 and B2 27 32 180 Form D

Repair Crew #4 between B3 and B6 45 50 90 FT

Repair Crew #5 before C2 and at C2 11 16 180 FT

Repair Crew #6 between C4 and C5 24 29 240 Form D

Track Car #2 before D2 and at D2 34 39 54 FT

Track Car #3 at D6 42 47 75 FT

Signal Worker #1 at B3 1 6 13 FT

Signal Worker #3 between D3 and D4 15 20 29 FT

Signal Worker #4 at C3 38 43 70 FT

Signal Worker #5 at B7 51 56 65 FT

bridge @10 between D7 and D8 20

bridge @50 between D7 and D8 50

Id - Scenario #2 where asking starting ending type

Repair Crew #1 between A2 and A3 0 8 FT

Repair Crew #2 between term and B1 5 10 35 FT

Repair Crew #3 between B1 and B2 15 20 120 Form D

Repair Crew #4 between B3 and B6 45 50 95 FT

Repair Crew #5 between C1 and C2 11 16 47 FT

Repair Crew #6 between C4 and C5 0 21 FT

Repair Crew #7 between D1 and D2 38 43 180 FT

Repair Crew #8 at C4 29 34 180 Form D

Track Car #1 and between D3 and D4 35 40 60 FT

Track Car #2 between D6 and D7 25 30 56 FT

Track Car #3 at B7 52 56 75 FT

Signal Worker #1 before station A 1 6 17 FT

bridge @10 between D7 and D8 20

bridge @50 between D7 and D8 50
49 

APPENDIX C. QUESTIONNAIRES 

Appendix C includes all the questionnaires: the situation awareness questionnaire, the 

post-experiment questionnaires for all three environments, and the final debriefing questionnaire. 

Situation Awareness Questionnaire 

Please answer the following questions as best as you can. Keep your answers as short as 

possible. You will have very little time and will not be allowed to use the dispatching system; 

hence, you are not expected to answer all questions properly. 

1. What is the number of the most delayed train? 

2. Can you estimate the time delay for that train? 

3. What is the number of the least delayed train? 

4. Can you estimate the time delay for that train? 

5. When is your next train due out of the terminal? 

6. Do you see any routing conflicts? 

7. Do you have “hazards” somewhere on the territory? 

8. Where? 

9. Any particular restrictions on the track usage? 

10. Where are your MOW crews? 

11. Which MOW crew will complete its work next? 

12. What track could you give away for a 15 minute span to a MOW crew? 

13. Whom did you last talk to? 

14. When did you last talk? 

15. What was the subject of your communication? 

16. What was the last message you heard that wasn't intended for you directly? (used only in the 

radio environment and in the DB environment) 
50 

Post Experiment Questionnaire 

Radio environment

Please answer the following questions as best as you can. If you have any problems, we are here 

to help. Don’t feel limited by the questions. 

− Did you route before answering the messages, answer messages before routing, or neither – it 

depends on the situation? 

− How realistic do you think the replica of the radio environment? 

Very Unrealistic Very Realistic

1 2 3 4 5 6 7 

− How would you rank the workload during the experiment? 

Very Low Very High

1 2 3 4 5 6 7 

− How comfortable were you in the radio communication environment? 

Very Uncomfortable Very Comfortable

1 2 3 4 5 6 7 

− Any suggestions to make the system better. Improvements. Any comment is welcome. Feel 

free to write anything, especially critiques! 

DD environment

− Would you like the data link directed environment in addition to your current radio 

environment? Why?3

− Did you route before answering the messages, answer messages before routing, or neither – it 

depends on the situation? 

− How would you rank the workload during the experiment? 

Very Low Very High

1 2 3 4 5 6 7 

− How comfortable did you feel with the data link directed system? 

Very Uncomfortable Very Comfortable

1 2 3 4 5 6 7 

− How helpful would it be to have such data link capacities in your current environment? 

Very Unhelpful Very Helpful

1 2 3 4 5 6 7 

− Any suggestions to make the system better. Improvements. Any comment is welcome. Feel 

free to write anything, especially critiques! 

 

3

 The term discrete was used in place of directed in the body of the report because it more aptly 

describes the characteristics of this data link environment. 
51 

DB environment

− Would you like the data link broadcast environment in addition to your current radio 

environment? Why? 

− Did you route before answering the messages, answer messages before routing, or neither – it 

depends on the situation? 

− How would you rank the workload during the experiment? 

Very Low Very High

1 2 3 4 5 6 7 

− How comfortable did you feel with the data link broadcast system? 

Very Uncomfortable Very Comfortable

1 2 3 4 5 6 7 

− How helpful would it be to have such data link capacities in your current environment? 

Very Unhelpful Very Helpful

1 2 3 4 5 6 7 

− Any suggestions to make the system better. Improvements. Any comment is welcome. Feel 

free to write anything, especially critiques! 
52 

Final Debriefing Questionnaire 

Please answer the following questions as best as you can. If you have any problems, we are here 

to help. Don’t feel limited by the questions. 

− Which environment did you like most (Data link Directed, Data link Broadcast or radio)? 

Why? 

− Would you like the data link directed system in addition to your current radio environment? 

Why? 

− Could you please rank the following starting with the best? 

Radio only 

Data link Directed only 

Data link Broadcast only 

Radio and Data link Directed 

Radio and Data link Broadcast 

− Would any environment be good for training? Why? 

− Any suggestions to make the system better. Improvements. Any comment is welcome. Feel 

free to write anything, especially critiques! 
53 

APPENDIX D. EXPERIMENT DOCUMENTS 

Appendix D contains all the documents provided to the dispatcher during the two one-hour 

experiments, except the train schedules and the message tree structure. Train schedules for the 

experiments can be found in Appendix B and the message tree structure can be found in 

Appendix A. In order, we have the explanatory text for the use of the simulator, the train 

schedule for the training scenario, the transfer sheets, the Form D sheets, and the Foul Time 

sheets. 

Simulator quick user’s manual 

About the routing:

1. A red track is a track occupied by a train. When there is no train, the track is white. 

2. Every train leaving the terminal has to be sent a bulletin before he/she can leave. Assume 

that, in any other station, the train has already started the ride and received a TSRB. 

3. To clear the route, click first on the “clear route” button at the bottom of the screen. Then 

click on the entry and exit signals of the interlocking according to the route you want the 

train to take. The color of the track changes to green. 

4. To unclear a route, click first on the “unclear” button at the bottom of the screen. Then click 

on entry or exit signal of the interlocking according to the route you want the train to take. 

The color of the track changes back to white. 

5. The route will unclear automatically if a train has used it. The color of the track will change 

back to white. 

6. To block a route for MOW activity, click first on the “block” button at the bottom of the 

screen. Then click on the part of the track you are giving away. You have to repeat the 

process if you want to block more track. 

7. To unblock a route, click first on the “unblock” button at the bottom of the screen. Then click 

on the part of the track you want to unblock. You have to repeat the process if you want to 

unblock more track. 

Names:

The territory has four main branches named A, B, C, and D respectively. Stations on these 

branches have the name of the branch. There are four stations: station A, station BR, station BL, 

and station D. 

Interlockings have names composed of a letter (the branch) and a number, the number 

representing the order of the interlocking from left to right. 
54 

To identify blocks during communications, we use a set of three elements. First, the general 

position i.e. the interlocking, the station or interlockings on the left and on the right. Second, the 

number of the track - knowing that tracks are numbered from top to bottom and third, the 

number of the block. 

About the messaging system:

1. The message console is divided in two parts: the left window handles received messages and 

the right window shows the messages that were sent out. In each of these windows, there are 

two elements: a list of all appropriate messages and the message, currently highlighted in the 

list displayed at the bottom of the window. 

2. The dispatcher would answer a message by pressing the “send message” or “reply” button, 

and a list of preprogrammed messages will appear. These messages are sorted into a message 

tree. The tree has four levels: the priority, the recipient, the subject of the message and the 

preprogrammed message itself. A layout of the tree will be provided and explained to you. 

3. To fill in the blanks in the messages, you can use either the keyboard or the mouse. Most 

blanks can be specified by double clicking on the adequate field and by clicking the target 

train or by using the keyboard directly (without double-click). This is valid for train numbers, 

MOW crew identifiers, and name of block to be worked on. The cursor automatically moves 

from one field to the next. When a message is highlighted, i.e., read, the blocks specified in 

the text of the message turn yellow on the routing screen. 

About the work allocation:

There are two groups of messages related to work request. Each group is described below: 

1. Track work- Track Cars or Repair Crews usually perform track work. We expect the 

dispatcher to answer their request using the correct branch of the message tree. The type 

of work will be indicated in the work request message. 

2. Signal work- Signal Workers usually perform repairs on signal. They expect to receive 

answers from the signal work sub tree. Here again the type of work in the request 

message will help decide which branch of the tree to use. 

About the message “replying,” sending, and forwarding requirements: 

1. Any update about hazards has to be transmitted to all other trains scheduled to ride the 

branch on which the hazard is located. These messages include: trespasser on the track and 

trespasser are gone, kids throwing stones and kids are gone, and finally, bad weather zone 

and bad weather zone is gone. 

2. Overweight events and engine state messages are for your personal information. 
55 

Training Scenario Train Schedule 

Transfer Sheets 

Dispatchers take over the track given away by the previous dispatcher on the shift when they 

start their experiment. Dispatchers also get written information about the scheduled work during 

their shift. This information is usually found on a transfer sheet. The following are our transfer 

sheets (Note that the only similarity with the real world is the name and the type of information. 

The same is true for the Form Ds that follow.). 

Transfer Sheet for scenario #1 

Scheduled work information (provided when the dispatcher start the experiment): 

1. Track outage is scheduled at 1:30 p.m. between interlocking B1 and B2 on track 1 and 

track 2 block 2, at interlocking B2 T11, at interlocking B2 T12, and at interlocking B2 

T22 block 1. Repair Crew #3 will ask for protection around 1:25 p.m. Form D required. 

2. Track outage is scheduled at 1:30 p.m. between interlocking C4 and C5 on track 3 block 

1 and at interlocking C5 T33 block 1. The MOW crew will ask for protection around 1:25 

p.m. Form D required. 

Please follow the platform indications as closely as possible. As at South Station, some trains 

have a longer consist and might not fit everywhere. The schedule has been drafted accordingly. 
56 

Also, you might want to pay particular attention to the incoming train appearing during the 

simulation given that you don’t have a big overview display. 

Transfer Sheet for scenario #2 

Scheduled work information (provided when the dispatcher starts the experiment): 

1. Track outage is scheduled at 4:38 p.m. at interlocking C4 T32, interlocking C4 T22, block 2, 

and interlocking C4 T33, block 2. Repair Crew #8 will ask protection around 4:33 p.m. Form 

D is required in the radio environment. 

2. Track outage is scheduled at 4:19 p.m. between interlocking B1 and B2 on track 3 block 1 

and 2 and on track 4 block 1 and 2. Repair Crew will ask for protection around 4:15 p.m. 

Form D is required in the radio environment. 

Please follow the platform indications as closely as possible. As at South Station, some trains 

have a longer consist and might not fit everywhere. The schedule has been drafted accordingly. 

Also, you might want to pay particular attention to the incoming train appearing during the 

simulation given that you don’t have a big overview display. 
57 

Form D 

Form D 

Work Crew # _______________________ 

Date _______________________________ Dispatcher’s name ____________________ 

Starting Time ________________________ Ending Time_________________________ 

Location ________________________________________________________________ 

________________________________________________________________________ 
58 

Foul Time form 

Foul Time Request 

Work Crew # _______________________ 

Date _______________________________ Dispatcher’s name ____________________ 

Starting Time ________________________ Ending Time_________________________ 

Location ________________________________________________________________ 

________________________________________________________________________ 

________________________________________________________________________ 
59 

GLOSSARY 

Block: A length of track with defined limits on which train movements are governed by block 

signals, cab signals, or Form D. 

Broadcast data link: A form of data link in which a message is sent to multiple designated 

parties. 

Cognitive Task Analysis (CTA): Analysis of the cognitive demands of a complex task. This 

includes the knowledge, mental processes, and decisions that are required to perform the task. 

The goals of a CTA are (1) to identify what factors contribute to cognitive performance 

difficulty; (2) to uncover the knowledge and skills that expert practitioners have developed to 

cope with task demands; and (3) to specify ways to improve individual and team cognitive 

performance in a domain through new forms of training, user interfaces, or decision-aids. 

Consist: The make-up of a train, including locomotives and cars. Also described by its 

locomotive power, tonnage, number, and type of cars, and location and type of hazardous 

materials. 

Crossover: A combination of two switches connecting two adjacent tracks. When aligned, this 

switch combination allows movements to cross from one track to the other. 

Centralized Traffic Control (CTC): A signal system that allows the dispatcher to know which 

blocks are occupied by trains and roadway workers, and to control switches and signals remotely 

from the dispatch center. 

Data link: A digital communications capability which supports moving information between 

office-based and field-based computers and their operators. In the railroad environment, 

operators include: dispatchers, train crews, and roadway workers. Information is digitally coded 

and messages can be discretely addressed to individuals or multiple recipients. Information can 

be presented in multiple sensory modalities (e.g., visual or auditory). 

Discrete data link: A form of data link in which a message is sent to a single party. 

Form D: A track usage authority form that is issued by a railroad dispatcher. A Form D contains 

written authorization, restrictions, or instructions issued by the dispatcher to specified 

individuals. Form Ds permit trains and other track users to occupy specific segments of track 

identified by the railroad dispatcher. 

Foul Time: Time during which track is temporarily obstructed for work on or around the track. 

The term “Foul Time” is used by railroads that follow the NORAC operating rules. Other 

railroads use different terms (e.g., track and time) to refer to the same condition. 

Interlocking: A configuration of switches and signals interconnected to direct trains along 

different routes, the limits of which are governed by interlocking signals. 

Maintenance-of-Way (MOW): On-track maintenance for repairing, testing, and inspecting 

track or wayside apparatus such as signals and communication devices. 

NORAC: Northeast Operating Rules Advisory Committee. 
60 

Operating Rules: A book of rules that govern a particular railroad’s operating procedures and 

practices. 

Roadway worker: Any employee of a railroad or of a contractor to a railroad whose duties 

include the inspection, construction, maintenance or repair of railroad track, bridges, roadway, 

signal and communication systems and electric traction systems on or near the track. This 

definition also applies to employees or contractors who have the potential to foul the track and 

employees responsible for their protection. 

Shunt: Activate automatic block or interlocking signals when present on track. 

Territory: A section of railroad for which a dispatcher is responsible for the safe and efficient 

movement of trains and other on-track equipment.

TGV: Train à Grande Vitesse, the French high-speed train.

Track car: Equipment, other than trains, operated on a track for inspection or maintenance. 

Track cars might not shunt track circuits. 

Track and Time: Time during which track is temporarily obstructed for work on or around the 

track. Other railroads use different terms (e.g., Foul Time) to refer to the same condition. 

TSRB: Temporary Speed Restriction Bulletin(s). 
61 

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