Disseminating Traveler Information 

on Travel Time Reliability

January 2017
Notice

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

Transportation in the interest of information exchange. The U.S. Government assumes no 

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The U.S. Government does not endorse products or manufacturers. Trademarks or 

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objective of the document.

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Technical Report Documentation Page 

1. Report No.

FHWA-HOP-16-067

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

4. Title and Subtitle

Disseminating Traveler Information on Travel Time Reliability

5. Report Date

January 2017

6. Performing Organization Code

7. Author(s)

Beverly Kuhn, Alan Pate, Laura Higgins, Robert Krile, Michael Vickich

8. Performing Organization Report No.

9. Performing Organization Name and Address

Battelle, 505 King Avenue, Columbus, OH 43201

Texas A&M Transportation Institute, 3135 TAMU, College Station, TX 77843

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-12-D-00046-T5017

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

Federal Highway Administration

Office of Operations

1200 New Jersey Avenue, SE

Washington, DC 20590

13. Type of Report and Period Covered

Final Report 10/14-12/16

14. Sponsoring Agency Code

HOTM

15. Supplementary Notes

Jimmy Chu, FHWA, Office of Transportation Management, Government Task Manager (GTM)

16. Abstract

Travel time variability is that characteristic of the transportation system that means a traveler’s trip will vary from what 

is normally expected and will potentially take longer than planned. By helping travelers make travel choices that take 

into account travel time variability, agencies have the potential to reduce roadway congestion.

Travel Time Reliability (TTR) information includes static data about traffic speeds or trip times that capture historic 

variations from day to day and enable individuals to understand the level of variability in traffic. A key component to 

addressing the reliability issue related to urban mobility is conveying this TTR information to system users so that they 

can make informed decisions about their travel. The challenge for transportation professionals lies in selecting the best 

means of conveying that information so that it is usable and effective to the traveler and other stakeholders.

The Strategic Highway Research Program (SHRP2) Reliability Project L14 established a preliminary set of suggested 

terminology and guidelines for conveying TTR information to road users so that they may make optimal travel choices 

from their point of view, such as whether to take a trip or not, departure time, mode choice, and/or route choice. 

Specifically, a Lexicon of phrases was developed for each of eight TTR terms, which contained detailed guidelines for 

TTR information that would most likely be understood and used by travelers. To help agencies and other transportationrelated entities better deploy and use the recommended Lexicon terminology, a field study was conducted to test the 

phrases to demonstrate the technical and institutional feasibility of their use and determine the potential costs and 

benefits of using these products of L14.

Overall, the field study found that the particular Lexicon phrases tested performed similarly. Only one survey question 

resulted in statistically significant differences between the Lexicon phrases. The biggest finding of the field study was 

that dissemination of TTR information via the 511 information channel was less preferred than via the Web or App 

access channels. In a few instances, the App access demonstrated superior responses over both the Web and 511 access.

17. Key Words

Travel time reliability, traveler information, arrival time, average travel time, 

buffer time, departure time, recommended departure time, recommended route

18. Distribution Statement

No Restrictions

19. Security Classif.(of this report)

Unclassified

20. Security Classif.(of this page)

Unclassified

21. No. of Pages

42

22. Price

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

iii

TABLE OF CONTENTS

EXECUTIVE SUMMARY 1

CHAPTER 1. OVERVIEW 3

THE CONCEPT OF TRAVEL TIME RELIABILITY 3

CHAPTER 2. COMMUNICATING TRAVEL TIME RELIABILITY 7

FIELD STUDY RESULTS 9

CHAPTER 3. A LEXICON FOR COMMUNICATING TRAVEL TIME RELIABILITY 11

LEXICON FORMAT 11

TRAVEL TIME RELIABILITY LEXICON 13

CHAPTER 4. DEPLOYMENT OF THE TRAVEL TIME RELIABILITY LEXICON 23

USE CASES FOR TRAVELERS 23

DATA NEEDS 24

Delivery Platform Data Interface Technical Description 25

INFORMATION DELIVERY PLATFORMS 26

COMBINING REAL-TIME AND RELIABILITY INFORMATION 27

CHAPTER 5. FINAL REMARKS 29

WEBSITE / MOBILE APPLICATION DESIGN 29

GRAPHICAL MESSAGES 29

AUDITORY MESSAGES 29

REFERENCES 31

v

LIST OF FIGURES

Figure 1. Graphic. Average travel time used by professionals.(1) 3

Figure 2. Graphic. Traveler travel time experiences.(1) 4

Figure 3. Graphic. Web service architecture. 26

LIST OF TABLES

Table 1. Assemblies of travel time reliability lexicon alternate phrases for testing. 13

Table 2. Travel time reliability Lexicon for 95th PERCENTILE.(3) 15

Table 3. Travel time reliability Lexicon for ARRIVAL TIME.(3) 16

Table 4. Travel time reliability Lexicon for AVERAGE TRAVEL TIME (Adapted from (3)). 17

Table 5. Travel time reliability Lexicon for BUFFER TIME.(3) 18

Table 6. Travel time reliability Lexicon for DEPARTURE TIME.(3) 19

Table 7. Travel time reliability Lexicon for RECOMMENDED DEPARTURE TIME.(3) 20

Table 8. Travel time reliability Lexicon for RECOMMENDED ROUTE.(3) 21

Table 9. Travel time reliability Lexicon for RELIABILITY.

(3) 22

1

EXECUTIVE SUMMARY

Travel time variability is that characteristic of the transportation system that means a traveler’s 

trip will vary from what is normally expected and will potentially take longer than planned. 

This transportation system characteristic is important for travelers and shippers. It also is a 

component of the congestion problem for which transportation agencies can make significant and 

measurable gains, even as travel demand grows. By providing the means to help travelers make 

travel choices that take into account travel time variability, agencies have the potential to reduce 

roadway congestion. This reduced congestion has the added benefit of reducing primary and 

secondary crashes, vehicle emissions, and fuel use, as well as yielding other benefits.

One measure of travel time variability is Travel Time Reliability (TTR). Transportation 

professionals describe TTR in terms of historical average travel times calculated over periods 

of a year or longer. TTR information includes static data about traffic speeds or trip times 

that capture historic variations from day to day and enable individuals to understand the level 

of variability in traffic. TTR information is considerably different from real-time travel time 

information and may have different uses. A traveler can use reliability information to plan and 

budget in advance for a trip rather than simply react to current conditions. A key component 

to addressing the reliability issue related to urban mobility is conveying this TTR information 

to system users so that they can make informed decisions about their travel. The challenge for 

transportation professionals lies in selecting the best means of conveying information so that it is 

usable and effective to the traveler and other stakeholders.

The Strategic Highway Research Program 2 (SHRP2) Reliability Project L14 established a 

preliminary set of suggested terminology and guidelines for conveying TTR information to road 

users so that they may make optimal travel choices from their point of view, such as whether 

to take a trip or not, departure time, mode choice, and/or route choice. Specifically, a Lexicon 

of phrases was developed for each of eight TTR terms, which contained detailed guidelines for 

TTR information that would most likely be understood and used by travelers. To help agencies 

and other transportation-related entities better deploy and use the recommended Lexicon 

terminology, a field study was conducted to test the phrases to demonstrate the technical and 

institutional feasibility of their use and determine the potential costs and benefits of using these 

products of L14. Two Lexicon assemblies and three dissemination platforms were tested in the 

field study.

Overall, the field study found that the particular Lexicon phrases tested performed similarly. 

Only one survey question resulted in statistically significant differences between the Lexicon 

phrases. The biggest finding of the field study was that dissemination of TTR information via the 

511 information channel was less preferred than via the Web or App access channels. In a few 

instances, the App access demonstrated superior responses over both the Web and 511 access.

Agencies considering dissemination of TTR information to their system users should consider 

various scenarios in which travelers and other stakeholders might find that information valuable. 

Some of these scenarios are individual trip planning for familiar trips, individual trip planning 
Disseminating Traveler Information on Travel Time Reliability

2

for unfamiliar trips, individual trip changes, alternate route comparisons, employment center 

locations, and overall system reliability. Agencies also will need to obtain historical traffic 

datasets as a source for determining the TTR calculations. These calculations can then be 

utilized by information dissemination platforms so that travelers can make informed decisions 

about their trip.

If an agency determines that TTR information will be valuable to its system users, it is important 

to clearly explain to them the difference between real-time information and TTR information. 

It is highly likely that system users will be familiar with existing real-time traveler information 

for the region from the plethora of sources available to them across providers and information 

dissemination platforms. They may not intrinsically understand what TTR information is telling 

them, so an explanation is important for comprehension. Furthermore, providing examples of 

how travelers might use TTR information for trip planning (e.g., unfamiliar trips, familiar trips 

at unusual times, etc.) may help increase awareness and overall use of the information 

by travelers. If the transportation agency already provides real-time traveler information, 

then comparing the two types of information in a side-by-side comparison might help with 

comprehension and usage.
3

CHAPTER 1. OVERVIEW

Travel time variability is that characteristic of the transportation system that means a traveler’s 

trip will vary from what is normally expected and will potentially take longer than planned. 

This transportation system characteristic is important for travelers and shippers. It also is a 

component of the congestion problem for which transportation agencies can make significant and 

measurable gains, even as travel demand grows. By providing the means to help travelers make 

travel choices that take into account travel time variability, agencies have the potential to reduce 

roadway congestion. This reduced congestion has the added benefit of reducing primary and 

secondary crashes, vehicle emissions, and fuel use, as well as yielding other benefits.

THE CONCEPT OF TRAVEL TIME RELIABILITY

Transportation professionals typically describe Travel Time Reliability (TTR) in terms of 

historical average travel times calculated over periods of a year or longer, as shown in Figure 1. 

A typical definition for TTR would be the following: 

The consistency or dependability in travel times, as measured from day to day and/or across 

different times of the day.(1)

How traffic conditions have

been communicated

Annual average Travel

Time

Jan July Dec

Figure 1. Graphic. Average travel time used by professionals.(1)

Source: http://ops.fhwa.dot.gov/publications/tt_reliability/brochure/index.htm#fig1m

However, most system users do not experience the same average travel time each day. Rather, 

they experience and remember something much different than the average throughout a year 

of commute trips (see Figure 2). Their travel times vary greatly from day to day, and they are 

more likely to remember a few bad days during which they suffered longer-than-typical travel 

times than a good day or a typical day.(1) Research has shown that TTR information can provide 
Disseminating Traveler Information on Travel Time Reliability

4

transportation system users with a more complete picture of expected travel times along 

a particular route. The challenge is how to communicate that reliability information 

effectively to system users so that they understand it clearly and respond appropriately 

to improve their trip experience.

What travelers experience...

Travel

Time

Jan July Dec

...and what

they remember

Travel times vary

greatly day-today

Figure 2. Graphic. Traveler travel time experiences.(1) 

Source: http://ops.fhwa.dot.gov/publications/tt_reliability/brochure/index.htm#fig1m

Real-time travel time messages have been in use in the U.S. since traffic monitoring and 

integration systems became reliable more than a decade ago. Typically, the most commonly 

used media for these messages are Dynamic Message Signs (DMSs) and transportation agency 

websites. However, the widespread use of cell phones and other mobile devices has resulted in 

an explosion of new mechanisms for transportation agencies and third-party providers to offer 

real-time updates on transportation conditions and options via e-mails, text messages, mobile 

application push notifications, and Twitter feeds.(2)

Real-time travel time estimates are most often provided for a particular roadway segment, 

facility, or transit route based on recent travel speeds or conditions. Some agencies also provide 

travel time comparisons among two or more routes/roadways to help travelers make decisions 

about the route or transportation mode to take. More recently, agencies are beginning to provide 

TTR information for facilities: the likelihood that the estimated travel time for a particular trip or 

trip segment will be dependable.

As discussed previously, travel time variability describes how a traveler’s trip will vary from 

what is normally expected. One measure of travel time variability is travel time reliability. TTR 

information includes static data about traffic speeds or trip times that capture historic variations 

from day to day or over a specified period of time and enable individuals to understand the level 

of variability in traffic.(2) TTR information is considerably different from real-time travel time 
5

information and may have different uses. A traveler can use reliability information to plan and 

budget in advance for a trip rather than simply react to current conditions.

Typically, travelers might want to access TTR information for such purposes as: (a) trip planning 

for habitual trips such as commutes, or when new to an area and unfamiliar with routes and 

typical travel times; (b) pre-trip planning immediately prior to departure, to make decisions 

about departure time and/or mode based on real-time and historical travel time trends, especially 

if traveling at a time or to a destination that is not typical; and (c) changing their trip while in 

progress prior to a route or mode choice point (again based on both real-time and historical 

information regarding particular routes at particular times of the day).(1)

A key component to addressing the reliability issue related to urban mobility is conveying this 

TTR information to system users so that they can make informed decisions about their travel. 

Furthermore, transportation agencies can use TTR information to assess system performance and 

use that information to inform local decision makers about congestion challenges and/or needs 

in the region. The challenge for transportation professionals lies in selecting the best means of 

conveying that information so that it is usable and effective to the traveler and other stakeholders.

7

CHAPTER 2. COMMUNICATING TRAVEL TIME RELIABILITY

Cognitive science has demonstrated that most people are not good at understanding complex 

statistical concepts, which is the foundation of Travel Time Reliability (TTR) information. As 

with other forms of traveler information communication like traffic signs, a Lexicon of phrases 

to convey TTR information should accomplish the following:

• Communicate a useful message.

• Improve on-time performance.

• Encourage trust in the message.

• Communicate the “riskiness” of a route.

• Distinguish TTR from real-time traveler information.(2)

Based on the results of the initial human factors studies conducted as part of the Strategic 

Highway Research Program 2 (SHRP2) L14 project and on current traffic engineering practices 

regarding communication to drivers, recommendations were presented regarding the use of 

various terms related to TTR concepts. This document is based on that original research, along 

with additional research funded by the Federal Highway Administration (FHWA) that validated 

the initial findings of the L14 project and fine-tuned the Lexicon of TTR terms to better represent 

motorists’ understanding and preference for various terms and access method.

The report, A Lexicon for Conveying Travel Time Reliability Information, developed as part of 

the SHRP2 Reliability Project L14—Effectiveness of Different Approaches to Disseminating 

Traveler Information on Travel Time Reliability—established a preliminary set of recommended 

terminology and guidelines for conveying TTR information to road users and stakeholders to 

reflect reliability conditions.(2,3) Specifically, a Lexicon of phrases was developed for each of the 

eight TTR terms:

• 95th percentile.

• Arrival time.

• Average travel time.

• Buffer time.

• Departure time.

• Recommended departure time.

• Recommended route.

• Reliability.(2)

Each Lexicon contained detailed guidelines for TTR information that would most likely 

be understood and used by the travelers. The Lexicon terminology and guidelines developed 

in L14 were based on a series of laboratory studies, and none of the terms were tested 

in a field environment.
Disseminating Traveler Information on Travel Time Reliability

8

To help agencies and other transportation-related entities better deploy and use the recommended 

Lexicon terminology, a field study was conducted to test the phrases to demonstrate the technical 

and institutional feasibility of their use and determine the potential costs and benefits of using 

these products of L14. The overall project objectives were to:

• Convey TTR information from theory to reality.

• Better understand travelers’ perceived value of TTR information.

• Better understand the current and future dimensions of the TTR information marketplace.

• Better understand what network travel and TTR information travelers require.

• Develop and implement a plan to test and evaluate the preliminary design guidelines 

and Lexicon phrases for disseminating TTR information.

• Develop guidelines based on the outcome of the test and evaluation.

• Lay out the barriers to communicating TTR information to travelers and steps 

to overcome barriers.

• Outline how different travelers will use TTR information differently (e.g., one-time visitor 

vs. regular commuter).

• Recommend and develop outreach activities in order to encourage use and adoption 

of the recommended Lexicon phrases and guidelines.

• Outline clear steps that agencies need to take to start getting the TTR information into 

travelers’ decision processes.

The field study was conducted in three different metropolitan areas—Houston, Texas; Columbus, 

Ohio; and Raleigh-Durham, North Carolina. At each of the three study locations, two separate 

assemblies of Lexicon terms for TTR information were delivered using three distinct methods: 

agency website, mobile smartphone application, and a traditional keypad response 511 system. 

The study was intended to assess the effectiveness and utility of TTR information to travelers 

in these three different areas of the United States and to help develop guidelines for agencies to 

disseminate this information in their jurisdictions.
9

FIELD STUDY RESULTS

The results of the field study are briefly summarized in this section. A complete discussion 

and presentation of the study results can be found in the final report from the study.

(4)

Local partners from each study location provided historical traffic datasets as a source for 

determining the TTR information that was provided to study participants in the field study. Using 

a custom Smartphone application, study participants collected Global Positioning System (GPS) 

and travel characteristic data for all trips made over a four-week period along specific travel 

corridors in each study location. The travel period was divided into two equal phases. Only travel 

data was collected during the first phase. In addition to collecting travel data during the second 

phase, TTR information was provided to participants according to their randomly assigned 

Lexicon assembly (A or B) and dissemination platform (i.e., App, Web, 511). 

Baseline and exit surveys were administered to study participants to obtain their typical travel 

patterns and perceptions of the provided TTR information. The data collection for the field study 

occurred during multiple rounds between April 2015 and April 2016. Depending on the round, 

participant recruitment was conducted in various manners, including targeted postcard mailings 

to randomly selected households in zip code areas near the study corridors, flyers and newsletter 

advertisements at major university campuses within the study corridor, and postings on social 

media and local partner websites.

A total of 762 participants across the three metropolitan areas completed the field study. 

Their aggregate information for the Baseline Survey, Phase 2 trip diaries, and Exit Survey 

were utilized to conduct an analysis for determining if TTR information dissemination Lexicon 

(A, B) or channel (App, Web, 511) generated a significant impact on the utility or satisfaction of 

trip planning and execution. The Baseline Survey results were analyzed to assess any preexisting 

differences between treatment groups, while the Exit Survey results were analyzed to establish 

the response probabilities associated with the TTR information dissemination channel and 

lexicon as a function of demographic and travel characteristic data.

Analysis of the baseline survey data found that there were no statistically significant associations 

between treatment group and demographic and travel characteristics variables. Given this result, 

subsequent differences between the treatment groups could be interpreted to be associated with 

the testing and not possibly reflective of an a priori bias in the panel composition.

Only one survey question resulted in statistically significant differences between the Lexicon 

assemblies. Those that were provided Assembly A were more likely to change their trip plans 

for a familiar trip than those provided Assembly B. However, it should be noted that across all 

the questions evaluated, no multiple comparison adjustments were made to the statistical test 

results. Therefore, each “statistically significant” result has a potential to have been reached in 

error. Across a large number of such results, it becomes likely that one or more of the significant 

results really represent only random variability in the responses. As such, this one result should 

be evaluated with caution.
Disseminating Traveler Information on Travel Time Reliability

10

Throughout the survey responses, there were several instances showing lower utility or 

satisfaction for the 511 information channel than either the Web or App access channels. In a few 

instances, the App access demonstrated superior responses than 511 or the Web.

Statistical models accounted for several exogenous factors, and this clearly seemed important to 

properly interpreting the results of interest for the Lexicon assemblies and information channels. 

The city of the participants only rarely appeared as a significant factor in the models, suggesting 

that location was not an important differentiator in the outcomes. Among other exogenous 

variables, education level and the number of Phase 2 trips taken with the TTR information were 

found to significantly correlate with responses for multiple questions. Specifically, participants 

with college degrees and those taking more trips in the TTR phase were less likely to report that 

they had made changes to either a familiar or unfamiliar trip as a result of the information. This 

finding was reinforced by the fact that in subsequent survey questions, these two groups were 

identified as finding TTR information less useful and reliable, and disagreeing that it reduced 

their travel time or their travel stress.
11

CHAPTER 3. A LEXICON FOR COMMUNICATING TRAVEL TIME RELIABILITY

As a result of the field study, the Lexicon tables presented in the original Strategic Highway 

Research Program 2 (SHRP2) L14 report were refined to better represent traveler preferences.(3)

Only nominal changes were made, because in most cases those terms noted as “best” remained 

so and if one of the “best” terms performed better than the other, the other term was moved to 

“adequate.” The one table that was modified (Table 4) is noted below as being adapted from the 

original report.

Each Lexicon entry in the following tables includes a technical Travel Time Reliability (TTR) 

term; the definition of the term/concept within the reliability framework; a description of when 

or for what purpose an agency might use the term; and recommendations for terminology, 

phrases, or graphics to be used, in order of preference. In some cases, alternate terms or phrases 

suitable for selected technology platforms also are provided. Finally, the Lexicon entries identify 

appropriate media and technology interfaces for each listed term, phrase, or graphic. However, 

it is important to note that graphical representations of the TTR data were not tested in either the 

original SHRP2 or follow-up Federal Highway Administration (FHWA) research. Additionally, 

the phrases were not tested on Dynamic Message Signs (DMSs) within the travel corridors for 

en-route access. The information for these presentations remains the same for all phrases based 

on the original guidance developed in the SHRP2 L14 project. Thus, these dissemination formats 

need additional research to confirm their usefulness to system users.

As noted previously, the goals for establishing a Lexicon to convey TTR information were 

the following:

• Communicate a useful message.

• Improve on-time performance.

• Encourage trust in the message.

• Communicate the “riskiness” of a route.

• Distinguish TTR from real-time traveler information.(2)

LEXICON FORMAT

The key elements of a Lexicon entry that are considered necessary to completely present each 

term are as follows:

• Technical Term—the formal TTR term to be defined.

• Definition—a definition of the term within the reliability framework.

• Usage—a general description of when an agency might use the reliability term or for what 

purpose it would use the term in the traveler information system. 
Disseminating Traveler Information on Travel Time Reliability

12

• Recommendation—the ranking of the messages and/or terms to be used in order 

of preference.

− Best—represents the term(s), phrase(s), and/or format(s) that performed the best and 

will most likely yield the desirable behavioral results when conveyed to system users or 

other stakeholders.

− Adequate—represents term(s), phrase(s), and/or format(s) that performed reasonably 

well and will not likely present significant comprehension problems for system users or 

other stakeholders.

− Avoid—represents terms(s), phrase(s), and/or format(s) that did not perform well or are 

recommended to avoid for noted reasons.

• Alternate Phrase—an alternative term or phrase of different length that is likely to be more 

easily understood than the technical term.

• Information Technology Platforms—identification of appropriate media and technology 

interfaces for each alternative. This list of technology platforms could continue to evolve 

as new media are introduced. These might include portable navigation devices, connected 

vehicle on-board equipment, and advanced car stereo or satellite radio systems. An initial 

list includes:

− Web—intended to mean full website format viewed from a full-sized personal computer 

screen in a full-featured Internet browser.

− Mobile Web—intended to mean a website format viewed from mobile devices such as 

smartphones and tablet computers.

− Text—includes short message service (SMS) text messages and social network text 

messages, such as TwitterTM, viewed on a mobile device.

− Mobile Application—specially designed user interfaces optimized to work on a specific 

smartphone operating system. These apps include user input and output screens and 

data entry mechanisms, such as drop-down text boxes and scrolling menus, specifically 

designed for the touchscreen or keyboard supported by that operating system.

− Dynamic Message Sign—roadside dynamic message sign.
13

TRAVEL TIME RELIABILITY LEXICON

The alternate phrases from the original SHRP2 research that were tested in this project are 

provided in Table 1. The Lexicon alternate phrases were tested for the following TTR terms:

• 95th percentile.

• Arrival time.

• Average travel time.

• Buffer time.

• Departure time.

• Recommended departure time.

• Reliability.

Table 1. Assemblies of travel time reliability lexicon alternate phrases for testing.

Travel Time 

Reliability Phrase

Alternate Phrase

Assembly A Assembly B

95th Percentile Majority of the time* Most of the time**

Arrival Time Arrive by* What time do you want to get there?**

Average Travel Time Estimated travel time* Approximate travel time*

Buffer Time Extra time* Recommended cushion**

Departure Time Departing at* What time will you start your trip?**

Recommended Departure 

Time Recommended departure time* Suggested departure time**

Reliability Predictable* Reliable**

*Alternate phrase originally identified as “best” in SHRP2 L14 Lexicon.

**Alternate phrase originally identifies as “adequate” in SHRP2 L14 Lexicon.

The SHRP2 L14 report identified only one “Best” phrase for six of the eight technical TTR 

terms.(3) For these cases, the two TTR assemblies tested in the field study were determined by 

selecting the “Best” phrase to be Assembly A and an option from the “Adequate” category to be 

Assembly B. A phrase from the “Adequate” category was selected that was somewhat different 

from the “Best” phrase, though with multiple options, this was not always the case. It was 

impractical to test all of the “Adequate” options because of the number of subjects that would 

be required to participate in order to get a statistically significant sample of responses. For the 

other two TTR terms (i.e., “Average Travel Time” and “Departure Time”), slightly different 

methods were used to determine Assembly A and Assembly B. Both of the “Best” phrases were 

tested for “Average Travel Time”, while one of the “Best” phrases and one from the “Adequate” 

list that was considerably different from the “Best” phrase were tested for “Departure Time”. 

The reason for the difference with “Departure Time” was that the two “Best” phrases were so 

similar in nature.
Disseminating Traveler Information on Travel Time Reliability

14

Table 2 through Table 9 present the specific Lexicon of phrases for each TTR term tested in the 

original SHRP2 L14 project through various human factors studies as well as in the succeeding 

field tests. The evaluation of the effectiveness of various messages was based in part on the 

improvement of travelers’ outcomes (reduction of early and late schedule delay, better on-time 

performance, and reduced delay) and preferences in the exit surveys. Because the Lexicon 

phrases were tested on a 511 platform in the field study, 511 was added to the tables as part of the 

Text information technology platform given that the messages were identical. Furthermore, the 

Mobile Web and Mobile Applications noted on the tables do not include auditory messages.

Only one table (Table 4) was changed from what was presented in the SHRP2 L14 report based 

on the findings of the field study. This change was the demotion of “Approximate travel time” 

from “Best” option to “Adequate” option for “Average Travel Time”.
Disseminating Traveler Information on Travel Time Reliability

15

Table 2. Travel time reliability Lexicon for 95th PERCENTILE.(3)

Technical Term 95th Percentile 

Definition The point on a travel time frequency distribution at which 95% of the trips made would be at or less than the identified time.

Usage To describe the longest time a driver can expect a trip to take.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Mobile Web^ Text / 511 Mobile Application^ Dynamic Message Sign

Best

Majority of the time

“The majority of the time, your trip will take X minutes or less.” √ √ √+ √+ XMAJORITY OF TIME TRIP TO [DESTINATION] X MIN OR LESS √ √ √ √ √>

6:45

8:308:158:007:457:307:15

6:50 6:55 7:00 7:05 7:10 7:15

Depature Time (AM)

Extra Time for Unexpected Delays

Arrival Time (AM) Estimated Travel Time Graphical representation of the average and 95th percentile. √ √ X √ X

Adequate

Most of the time

“Most of the time, your trip will take X minutes or less.” √ √ √+ √+ XMOST OF THE TIME TRIP TO [DESTINATION] X MIN OR LESS √ √ √ √ √>

Travel time for planning

“Travel time for planning is X minutes or less.” √ √ √+ √+ X

95th percentile trip time

“The 95th percentile trip time is X minutes or less.”Provide description such as “19 out of 20 days.”

√ √ √+ √+ X

Avoid

Maximum trip time Transportation Agency concerns 

regarding liability and credibility. N/A N/A N/A N/A N/A Most common trip time Worst-case trip time

^ Mobile Web and Mobile Applications did not include auditory messages.+ Underlined terms to be removed for this platform; other phrase shortening may be possible depending on user preference.> The formatting of this travel time message is very different from the standard messages used by state transportation agencies on DMSs.
Disseminating Traveler Information on Travel Time Reliability

16

Table 3. Travel time reliability Lexicon for ARRIVAL TIME.(3)

Technical Term Arrival Time 

Definition The time at which a traveler would arrive after a trip.

Usage To tell the driver when he/she can expect to arrive at his/her destination.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Web^ Mobile Text / 511 Mobile Application^ Message Dynamic Sign

Best Arrive by “Arrive by X:XX am/pm” √ √ √ √ X ARRIVE BY X:XX AM/PM √ √ √ √ √>%#

Adequate

Arrive at “Arrive at X:XX am/pm” √ √ √ √ X

ARRIVE AT X:XX AM/PM √ √ √ √ √>%#

want to get there?What time do you 

receive a recommended departure time. preferred arrival time into a travel time calculator to This question would be used by a traveler to enter a 

√ √ X √ X

you can arriveWhat’s the earliest 

receive a recommended departure time.preferred arrival time into a travel time calculator to This question would be used by a traveler to enter a 

√ √ X √ X

you can arrive?What’s the latest 

receive a recommended departure time.preferred arrival time into a travel time calculator to This question would be used by a traveler to enter a 

√ √ X √ X

Avoid

# Term is not a complete message and cannot stand alone in this platform. It needs to be anchored to specific destination information.% Term may present ambiguity to the viewer, as he/she would not see a specific destination.> The formatting of this travel time message is very different from the standard messages used by state transportation agencies on DMSs.^ Mobile Web and Mobile Applications did not include auditory messages.
17

Table 4. Travel time reliability Lexicon for AVERAGE TRAVEL TIME (Adapted from (3)).

Technical Term Average Travel Time 

Definition An average of historical travel times calculated over a specified time interval for a specified trip or roadway segment.

Usage To describe the typical travel time a driver can expect a trip will take.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Mobile Web^ Text / 511 Mobile Application^ Dynamic Message Sign

Best Estimated travel time

“Estimated travel time is X minutes.” √ √ √+ √+ X“It is estimated that your trip will take X minutes.” √ √ √+ √+ XEST THAT TRIP TO [DESTINATION]WILL TAKE X MIN √ √ √ √ √>

Adequate

Approximate travel time

“It will take approximately X minutes to make your trip.” √ √ √+ √+ XAPPROX X MIN TO [DESTINATION] √ √ √ √ √>

Typical travel time “Typical travel time is X minutes.” √ √ √+ √+ X

6:45

8:30

8:158:007:457:307:15

6:50 6:55 7:00 7:05 7:10 7:15

Depature Time (AM)

Extra Time for Unexpected Delays

Arrival Time (AM) Estimated Travel Time Graphical representation of the average and 95th percentile (typical day and bad day). √ √ X √ X

7:05

9:15

9:00

8:458:308:158:007:45

7:10 7:15 7:20 7:25 7:30 7:35

Depature Time (AM)

Arrival Time (AM)

Bad DayTypical DayGood Day

Graphical representation of the 20th percentile and average and 95th percentile (good, typical, and bad day).

√ √ X √ X

Average travel time “Average travel time is X minutes.” √ √ √+ √+ XExpected travel time “Expected travel time is X minutes.” √ √ √+ √+ X

Avoid Historical Travel Time Difficult to determine relevance with no comparison to real-time information. N/A N/A N/A N/A N/A

^ Mobile Web and Mobile Applications did not include auditory messages.+ Underlined terms to be removed for this platform; other phrase shortening may be possible depending on user preference.> The formatting of this travel time message is very different from the standard messages used by state transportation agencies on DMSs.
Disseminating Traveler Information on Travel Time Reliability

18

Table 5. Travel time reliability Lexicon for BUFFER TIME.(3)

Technical Term Buffer Time 

Definition The average travel time multiplied by the buffer index.

Usage To describe how much extra time a driver should plan for a trip he/she wishes to take.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Web^ Mobile Text / 511 Mobile Application^ Message Dynamic Sign

Best Extra time

“Extra time for trip is X minutes.” √ √ √+ √+ X[DESTINATION] IS X MINEXTRA TIME TO √ √ √ √ X 

Adequate

Added time

“Added time for trip is X minutes.” √ √ √+ √+ X[DESTINATION] IS X MINADDED TIME TO √ √ √ √ X

Recommended cushion

for trip“Recommended cushion 

 is X minutes.” √ √ √+ √+ X 

Avoid

Cushion

Preference shown for other terms. N/A N/A N/A N/A N/A

LeewayDeparture windowBuffer time

+ Underlined terms to be removed for this platform; other phrase shortening may be possible depending on user preference.^ Mobile Web and Mobile Applications did not include auditory messages.
19

Table 6. Travel time reliability Lexicon for DEPARTURE TIME.(3)

Technical Term Departure Time 

Definition The time at which a traveler would depart for a trip.

Usage To indicate the time a traveler departs for a trip. For DMS applications, message would need to be set in context with other information, 

such as destination, travel time, or route.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Mobile Web^ Text / 511 Mobile Application^ Dynamic Message Sign

Best Departing at “Departing at X:XX am/pm” √ √ √ √ X

Leave at “Leave at X:XX am/pm” √ √ √ √ X

Adequate

What time will you start your trip?

This question would be used by a traveler to enter a start time into a travel time calculator to receive an arrival time.

√ √ X √ X

Leave by “Leave by X:XX am/pm” √ √ √ √ XDeparting by “Departing by X:XX am/pm” √ √ √ √ XWhat’s the earliest you can start your trip?

This question would be used by a traveler to enter a start time into a travel time calculator to receive an arrival time.

√ √ X √ X

What’s the latest you can start your trip?

This question would be used by a traveler to enter a start time into a travel time calculator to receive an arrival time.

√ √ X √ X

Avoid

^ Mobile Web and Mobile Applications did not include auditory messages.
Disseminating Traveler Information on Travel Time Reliability

20

Table 7. Travel time reliability Lexicon for RECOMMENDED DEPARTURE TIME.(3)

Technical Term Recommended Departure Time 

Definition

given level of added delay.A time of departure displayed to a traveler that is calculated by a traveler information system and would ensure an on-time arrival for a 

Usage To indicate the time a driver should depart for a trip to ensure he/she arrives at his/her destination on time.

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Web^ Mobile Text / 511 Mobile Application^ Message Dynamic Sign

Best departure time Recommended “Recommended departure time is X:XX am/pm” √ √ √+ √+ X

Adequate

departure timeSuggested “Suggested departure time is X:XX am/pm” √ √ √+ √+ Xdeparture timeEstimated 

>>

“Estimated departure time is X:XX am/pm” √ √ √+ √+ X

95th percentile departure time

is“The 95th percentile departure time 

 X:XX am/pm”

“19 out of 20Provide description such as 

days.”

√ √ √+ √+ X

Avoid

>> Can be used if term is NOT being used to mean average trip time.+ Underlined terms to be removed for this platform; other phrase shortening may be possible depending on user preference.^ Mobile Web and Mobile Applications did not include auditory messages.
21

Table 8. Travel time reliability Lexicon for RECOMMENDED ROUTE.(3)

Technical Term Recommended Route

Definition A route between two points calculated by a traveler information system that would provide the best probability of on-time arrival to a 

specific destination.

Usage To describe the route a driver should take for a planned trip to ensure he/she arrives on time to his/her destination.

Recommendation Alternate Phrase Wording Context/Additional Information Information Technology Platforms Web Mobile Web^ Text / 511 Mobile Application^ Dynamic Message Sign

Best Best route

“Best route is via [facility].” √ √ √+ √+ XBEST ROUTE TO [DESTINATIONTAKE [FACILITY] √ √ √ √ √>

Adequate

Forecasted trip

“Forecasted trip is via [facility].” √ √ √+ √+ XFORECASTED TRIP TIME VIA [FACILITY] X MIN √ √ √ √ X

Most reliable trip

“Most reliable trip is via [facility].” √ √ √+ √+ XMOST RELIABLE TRAVEL TIME TO [DESTINATION] TAKE [FACILITY] √ √ √ √ √>%

Most predictable trip

“Most predictable trip is via [facility].” √ √ √+ √+ XMOST PREDICTABLE TRAVEL TIME TO [DESTINATION] TAKE [FACILITY] √ √ √ √ √>%

Most consistent trip

“Most consistent trip is via [facility].” √ √ √+ √+ XMOST CONSISTENT TRAVEL TIME TO [DESTINATION] TAKE [FACILITY] √ √ √ √ √>%

Avoid

Historical trip conditions

Difficult to determine relevance with no comparison to real-time information. Preference shown for other terms.

N/A N/A N/A N/A N/A

Least variable time

^ Mobile Web and Mobile Applications did not include auditory messages.+ Underlined terms to be removed for this platform; other phrase shortening may be possible depending on user preference.> It is unknown whether drivers will understand this message if displayed on a DMS. Field testing needed to assess comprehension.% The formatting of this travel time message is very different from the standard messages used by state transportation agencies on DMSs.
Disseminating Traveler Information on Travel Time Reliability

22

Table 9. Travel time reliability Lexicon for RELIABILITY.(3)

Technical Term Reliability

Definition A consistency or dependability in travel times between two points, as measured from day to day or across different times of day. 

Usage To describe the variability of travel times to drivers so they can plan their trip with more robust information. 

Recommendation Alternate Phrase Wording Context/Additional Information

Information Technology Platforms

Web Web^ Mobile Text / 511 Mobile Application^ Message Dynamic Sign

Best Predictable “Most predictable trip.” √ √ √ √ X

Adequate

Reliable “Most reliable trip.” √ √ √ √ X

Consistent “Most consistent trip.” √ √ √ √ X

Vary “Trip varies.” √ √ √ √ X

Avoid

Differ

Preference shown for other terms. N/A N/A N/A N/A N/A

Fluctuate

Change

Go up or down

Increase or decrease

Deviate

^ Mobile Web and Mobile Applications did not include auditory messages.
23

CHAPTER 4. DEPLOYMENT OF THE TRAVEL TIME RELIABILITY LEXICON

This chapter provides information to transportation agencies with respect to use cases, data 

needs, delivery platforms, and other important considerations when assessing the potential use 

of Travel Time Reliability (TTR) information in their jurisdiction. 

USE CASES FOR TRAVELERS

As discussed previously, travelers might find TTR information useful in a variety of situations 

related to trip planning. As agencies consider disseminating TTR information to their system 

users, they could consider various scenarios in which travelers and other stakeholders might find 

that information valuable and present it as such for ready use. These scenarios, which are by no 

means exhaustive, include the following:

• Individual Trip Planning – Habitual: Travelers may find TTR information valuable 

when planning habitual trips, such as daily commutes. TTR information may be 

particularly valuable when an individual is new to an area and unfamiliar with routes and 

typical travel times. They may also find it beneficial when moving to a new neighborhood 

or corridor within a community and need to assess commute times in new corridors. 

Explaining the potential use of the information for these habitual trips could be beneficial 

to the traveler and increase the overall value of the information to the target audience. 

• Individual Trip Planning – Unfamiliar: Travelers may find TTR information useful for 

pre-trip planning immediately prior to departure or to make decisions about departure time 

and/or mode based on real-time and historical travel time trends, especially if traveling 

at a time or to a destination that is not typical. Explaining the value of TTR information 

for unfamiliar trips and how someone might use the information could help increase the 

overall value and usage of the information by the target audience.

• Individual Trip Change: Travelers may find TTR information helpful en-route and 

consider changing their trip while in progress prior to a route or mode choice point 

(again based on both real-time and historical information regarding particular routes at 

particular times of the day). However, it is important to note that the traveler should not be 

encouraged to access the information in a moving vehicle as this increases distraction in 

the driving environment.

• Alternate Route Comparison: Travelers may need to decide between alternate routes for 

either familiar or unfamiliar trips. Making TTR information available for facilities with 

alternate routes might improve the usability of the information by the target audience.
Disseminating Traveler Information on Travel Time Reliability

24

• Employment Center Location: Corporations or large employers could utilize TTR 

information when considering employment center locations within corridors with reliable 

travel times for employees. Presenting TTR trends for facilities along with comparisons of 

regional facilities can make this information useful to these stakeholders.

• Overall System Reliability: Agencies can use TTR information and the Lexicon phrases 

to provide stakeholders and decision makers with valuable information on system 

reliability. This information can be used to assess the priorities of future projects as well 

as to assess the impacts of projects and operational strategies for corridors and the system 

as a whole. The target audiences for this information presentation could include, but not 

be limited to, regional planning organizations; transportation agency decision makers; 

local chambers of commerce; economic development organizations; travel and tourism 

organizations; local entities such as school districts and universities; and more.

DATA NEEDS

For an agency to present TTR information to system users, it will need to have historical traffic 

datasets as a source for determining the TTR calculations. These calculations are then utilized by 

information dissemination platforms so that travelers can make informed decisions about their 

trip. To ensure compatibility across all platforms and to provide information that can be easily 

understood by system users, historical traffic datasets benefit from the following:

• Average segment-based travel time data with origins and destinations corresponding to the 

majority of entry/exit points along each corridor by direction. These average values are 

used as the “typical” travel time for display in the traveler information applications.

• For each of the segments in a corridor and for each aggregation period, the 95th percentile 

travel time for use in determining the worst-case travel times.

• Travel time data aggregated by day of week in at least hourly intervals for a 6-month 

period or more. The aggregation time (e.g., 15 minutes, hourly) limits the resolution of the 

departure and arrival times in the traveler information applications.

• The most recent historical dataset possible in order to reflect the current traffic conditions 

as accurately as possible.

Based on the availability of data, as well as source, timeframe, and format, agencies likely 

will need to manipulate the data to generate a dataset that can be mined to calculate TTR 

information and disseminate that information to the traveling public. To illustrate the type of 

data manipulation that might be necessary, the manner in which the project team handled travel 

time and speed data from Houston is described below. It is important to note that the volume and 

type of data available in Houston is not typical, given that the region collects and manages its 

own flow data. Many other locations obtain flow data from third-party sources, which may have 
25

different levels of granularity. The manipulation and summary of those data likely will differ 

considerably from that in Houston; however, the format of the final resulting dataset would 

be similar.

The Houston region has an extensive deployment of Intelligent Transportation System (ITS) 

based sensors installed throughout each of the study corridors, which provide speed and travel 

time information through the region’s traffic management center, Houston TranStar®. The source 

of the Houston study data was the information collected by these sensors that utilize either 

Bluetooth or toll-tag-based re-identification for estimating travel times. The sensors are operated 

by the Texas Department of Transportation, which provided the data for the study’s usage for the 

I-10 Katy, I-10 Katy Managed Lanes, Westpark Tollway, I-45 North, I-45 North High-Occupancy 

Vehicle (HOV), and Hardy Toll Road study corridors.

The origins and destinations for each travel time segment were based on the locations of the 

roadside sensors. In most cases, the sensors were located near major entry and exit points along 

the corridors with 1- to 3-mile spacing. The software internal to Houston TranStar® collects and 

processes the travel time data in both real-time and historically, and aggregates the data into 

15-minute summaries by day of week. For each 15-minute period and for each day of the week, 

the dataset contained a location identifier (including the roadway name, direction of travel, origin 

cross street, and destination cross street), a timestamp indicating the time of the summary, an 

average travel time, and a 95th percentile travel time.

Delivery Platform Data Interface Technical Description

There are a variety of approaches to disseminating TTR information to travelers depending on 

the delivery platform that an agency intends to use for the dissemination or which they already 

manage. For example, a backend architecture for a pre-existing traveler information website can 

provide a data interface framework for any of the three information delivery platforms included 

in the Lexicon. Additionally, a web Application Programming Interface (API) can be developed 

to allow other applications to query the historical datasets that are developed for a region. 

Typically, the delivery platform (e.g., a traditional website, mobile application, 511 system) can 

make queries to a web interface to obtain the traffic conditions data.

To initiate a query to the web service, a client makes a call to a web address with the following 

parameters included:

• Starting Location ID.

• Ending Location ID.

• Time of Day.

• Date of Travel.

• Departure or Arrival Calculation.

• Lexicon Phrase Selection.
Disseminating Traveler Information on Travel Time Reliability

26

Based on the information passed via the parameters, the web service queries the appropriate 

historical dataset and returns a string of text containing the approximate travel time, buffer time, 

and predicted arrival or departure time. The different information channels are then able to relay 

this information in an appropriate format (e.g., webpage via the website and mobile application, 

via 511). A diagram of a typical web service architecture is shown in Figure 3. This particular 

architecture was used in the research study, but can be replicated for a particular location.

Traditional

Website

Historical

Traffic

Dataset

• Location

• Time of Day

• Calculation Type

• Travel Time

• Buffer Time

• Predicted Arrival/

 Departure

Mobile

Application

Web

Service

5-1-1

System

Figure 3. Graphic. Web service architecture.

Note that this web service architecture may vary depending on the traveler information website 

or service currently operated by an agency.

INFORMATION DELIVERY PLATFORMS

The research study tested three information platforms: a mobile application provided via 

smartphone, a traditional website, and a 511 telephone service.

• The mobile application was the platform most preferred by users in the study. This format 

can be the most convenient option for users to find TTR information at the point when 

they may be most likely to want it (i.e., just as they are beginning a trip). Designing the 

application so that users can enter and save personalized information such as their mostused departure point can help to maximize utility of this platform. Drivers should be 

encouraged to not enter any information while operating a vehicle.

• A traditional or mobile website may offer more options for customizing user inputs 

and/or output formats. This information platform ranked second in preference among 

study participants.
27

• The 511 telephone service was least preferred by study participants. It is therefore not 

recommended that an agency develop a 511 system solely for the purpose of providing 

TTR information. However, if an agency already has a 511 system for travel information 

and develops other platforms (e.g., mobile application, mobile website, traditional website) 

for deploying TTR information, the mechanism for transferring that TTR information to 

the 511 system is fairly straightforward.

COMBINING REAL-TIME AND RELIABILITY INFORMATION

The original research conducted in the Strategic Highway Research Program 2 (SHRP2) L14 

research project indicated that travelers consider real-time travel time information to be valuable 

and even necessary in addition to historical data when planning trips. However, this project did 

not assess the viability and/or best approach to combining those sources of information. Thus, 

additional research is needed to determine how best to combine real-time and historical travel 

time information to provide the most useful and accurate information to travelers. Some regions 

are beginning to provide this comparison information and future research could benefit these 

and other regions in ensuring that these two forms of information are combined in an effective 

manner to optimize the user travel experience. 

If an agency determines that TTR information will be valuable to its system users, it is 

important to clearly explain to them the difference between real-time information and TTR 

information. It is highly likely that system users will be familiar with existing real-time traveler 

information for the region from the plethora of sources available to them across providers 

and information dissemination platforms. They also are highly likely to be very familiar with 

the roadway network in the region, especially for their regular commute route. They may not 

intrinsically understand what TTR information is telling them, so an explanation is important for 

comprehension. Furthermore, providing examples of how travelers might use TTR information 

for trip planning (e.g., unfamiliar trips, familiar trips at unusual times, etc.) may help increase 

awareness and overall use of the information by travelers. If the transportation agency already 

provides real-time traveler information, then comparing the two types of information in a sideby-side comparison might help with comprehension and usage.

29

CHAPTER 5. FINAL REMARKS

The field study was beneficial in better refining the information originally developed as part 

of the Strategic Highway Research Program 2 (SHRP2) L14 research project. However, 

only one survey question resulted in statistically significant differences between the Lexicon 

terminologies. Overall, the particular Lexicon terminologies tested performed similarly. The 

biggest finding of the field study was that dissemination of Travel Time Reliability (TTR) 

information via the 511 information channel was less preferred than via the Web or App access 

channels. In a few instances, the App access demonstrated superior responses over both the Web 

and 511 access.

However, some questions remain unanswered regarding the dissemination of TTR information to 

travelers across a broad spectrum of delivery platforms. These limitations are discussed below.

WEBSITE / MOBILE APPLICATION DESIGN

The research study assessed the use of the Lexicon in three different dissemination platforms: 

website, mobile web application, and 511. In all three cases, the information presented was 

identical across all three platforms. However, the actual user interface of the website and mobile 

web application was not assessed. User interface best practices should be utilized to develop a 

website and mobile application that will be easy to use and minimize access time.

GRAPHICAL MESSAGES

Two graphical formats were tested in the original SHRP2 L14 study as alternatives for presenting 

reliability information to drivers. These two formats were rated by participants as being “more 

complex” and therefore less easy to use than the same information presented in a text format. 

However, other graphical formats may prove useful as alternative or supplemental methods for 

communicating reliability information to drivers. These graphical formats were not tested in 

this study, so further research is still necessary to assess the potential usefulness and usability of 

“star” ratings, Harvey Balls, and other graphical formats for conveying reliability information.

AUDITORY MESSAGES

While the research study assessed the use of the Lexicon in a 511 auditory platform, it did 

not test auditory messages in the vehicle. Auditory messages were included as one format for 

communicating reliability messages in the original SHRP2 L14 project, but future research 

should further examine auditory options for both message delivery and, potentially, verbal inputs 

by system users.
Disseminating Traveler Information on Travel Time Reliability

30

DYNAMIC MESSAGE SIGN MESSAGES

As indicated in the Lexicon tables, sample messages for Dynamic Message Signs (DMSs) are 

provided. It is important to note that the studies conducted in SHRP2 L14 and in this project did 

not test these phrases as being displayed on a DMS and as en-route information. Those phrases 

suggested for display on DMSs were developed by the original SHRP2 L14 research team 

based on the results discussed for the related terminologies.(3) The team developed these phrases 

using the general guidance for DMS message development provided in the Manual on Uniform 

Traffic Control Devices. It is important to note that the formatting of these TTR messages is very 

different from the standard messages used by state transportation agencies on DMSs. For many 

of the TTR terms, their use on a DMS would present various challenges to the traveler including:

• Drivers are conditioned to see real-time travel information displayed on DMSs on freeway 

corridors, and reliability information may confuse them when placed on a DMS.

• Any reliability information displayed on a DMS would need to be relative to the specific 

location of the sign on the freeway facility, as drivers would have begun their trips from 

various locations in the region’s transportation network.

• Messages providing departure time or buffer time information are not appropriate 

for DMSs since travelers would need to see these messages prior to starting their trip, 

not en-route.(3)
31

REFERENCES

1. Texas A&M Transportation Institute with Cambridge Systematics, Inc. Travel Time 

Reliability: Making It There On Time, All The Time. U.S. Department of Transportation, 

Federal Highway Administration, Washington, D.C., 2006.

2. Kuhn, B., L. Higgins, A. Nelson, M. Finley, G. Ullman, S. Chrysler, K. Wunderlich, V. Shah, 

C. Dudek. Effectiveness of Different Approaches to Disseminating Traveler Information 

on Travel Time Reliability. SHRP2 Reliability Project L14. SHRP 2 Report S2-L14-RW-1. 

National Academy of Sciences, 2014.

3. Kuhn, B., L. Higgins, A. Nelson, M. Finley, G. Ullman, S. Chrysler, K. Wunderlich, V. Shah, 

C. Dudek. A Lexicon for Conveying Travel Time Reliability Information. SHRP2 Reliability 

Project L14. SHRP 2 Report S2-L14-RW-2, National Academy of Sciences, 2014.

4. Kuhn, B., R. Krile, C. Ritter, L. Higgins, A. Pate. Effectiveness of Disseminating Traveler 

Information on Travel Time Reliability: Task 3 – Implement Plan and Survey Results Report. 

FHWA-HOP-16-066. Federal Highway Administration, 2016.


U.S. Department of Transportation

Federal Highway Administration

Office of Operations (HOP)

1200 New Jersey Avenue, SE

Washington, DC 20590

www.ops.fhwa.dot.gov 

FHWA-HOP-16-067

January 2017