Disseminating Traveler Information on Travel Time Reliability

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.
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 Twitter^™, 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.

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:

95^th 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	Alternate Phrase: Assembly B
95^th 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.

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".

Technical Term: 95^th 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.

**Table 2. Travel time reliability Lexicon for *95^th PERCENTILE.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Web	Information Technology Platforms: Mobile Web^	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Majority of the time	"The majority of the time, your trip will take X minutes or less."			+	+	X
Best	Majority of the time	MAJORITY OF TIME TRIP TO [DESTINATION] X MIN OR LESS					>
Best		Graphical representation of the average and 95^th percentile.			X		X
Adequate	Most of the time	"Most of the time, your trip will take X minutes or less."			+	+	X
Adequate	Most of the time	MOST OF THE TIME TRIP TO [DESTINATION] X MIN OR LESS					>
Adequate	Travel time for planning	"Travel time for planning is X minutes or less."			+	+	X
Adequate	95^th percentile trip time	"The 95^th 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
Avoid	Most common trip time	Transportation Agency concerns regarding liability and credibility.	N/A	N/A	N/A	N/A	N/A
Avoid	Worst-case trip time	Transportation Agency concerns regarding liability and credibility.	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.

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.

**Table 3. Travel time reliability Lexicon for *ARRIVAL TIME.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Text / 511	Information Technology Platforms: Dynamic Message Sign
Best	Arrive by	"Arrive by X:XX am/pm"		X
Best	Arrive by	ARRIVE BY X:XX AM/PM		> % #
Adequate	Arrive at	"Arrive at X:XX am/pm"		X
Adequate	Arrive at	ARRIVE AT X:XX AM/PM		> % #
Adequate	What time do you want to get there?	This question would be used by a traveler to enter a preferred arrival time into a travel time calculator to receive a recommended departure time.	X	X
Adequate	What's the earliest you can arrive	This question would be used by a traveler to enter a preferred arrival time into a travel time calculator to receive a recommended departure time.	X	X
Adequate	What's the latest you can arrive?	This question would be used by a traveler to enter a preferred arrival time into a travel time calculator to receive a recommended departure time.	X	X
Avoid

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

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.

Table 4. Travel time reliability Lexicon for *AVERAGE ARRIVAL TIME (Adapted from ⁽³⁾).*
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Web	Information Technology Platforms: Mobile Web^	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Estimated travel time	"Estimated travel time is X minutes."			+	+	X
Best	Estimated travel time	"It is estimated that your trip will take X minutes."			+	+	X
Best	Estimated travel time	EST THAT TRIP TO [DESTINATION] WILL TAKE X MIN					>
Adequate	Approximate travel time	"It will take approximately X minutes to make your trip."			+	+	X
Adequate	Approximate travel time	APPROX X MIN TO [DESTINATION]					>
Adequate	Typical travel time	"Typical travel time is X minutes."			+	+	X
Adequate		Graphical representation of the average and 95^th percentile (typical day and bad day).			X		X
Adequate		Graphical representation of the 20^th percentile and average and 95^th percentile (good, typical, and bad day).			X		X
Adequate	Average travel time	"Average travel time is X minutes."			+	+	X
Adequate	Expected 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

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.

**Table 5. Travel time reliability Lexicon for *BUFFER TIME.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Web	Information Technology Platforms: Mobile Web^	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Extra time	"Extra time for trip is X minutes."			+	+	X
Best	Extra time	EXTRA TIME TO [DESTINATION] IS X MIN					X
Adequate	Added time	"Added time for trip is X minutes."			+	+	X
Adequate	Added time	ADDED TIME TO [DESTINATION] IS X MIN					X
Adequate	Recommended cushion	"Recommended cushion for trip is X minutes."			+	+	X
Avoid	Cushion	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Buffer time	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Departure window	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Leeway	Preference shown for other terms.	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.

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.

**Table 6. Travel time reliability Lexicon for *DEPARTURE TIME.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Text / 511	Information Technology Platforms: Dynamic Message Sign
Best	Departing at	"Departing at X:XX am/pm"		X
Best	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
Adequate	Leave by	"Leave by X:XX am/pm"		X
Adequate	Departing by	"Departing by X:XX am/pm"		X
Adequate	What'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
Adequate	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.

Technical Term: Recommended Departure Time
Definition: 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 given level of added delay.
Usage: To indicate the time a driver should depart for a trip to ensure he/she arrives at his/her destination on time.

**Table 7. Travel time reliability Lexicon for *RECOMMENDED DEPARTURE TIME.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Recommended departure time	"Recommended departure time is X:XX am/pm"	+	+	X
Adequate	Suggested departure time	"Suggested departure time is X:XX am/pm"	+	+	X
Adequate	Estimated departure time>>	"Estimated departure time is X:XX am/pm"	+	+	X
Adequate	95^th percentile departure time	"The 95^th percentile departure time is X:XX am/pm" Provide description such as "19 out of 20 days."	+	+	X
Avoid

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.

**Table 8. Travel time reliability Lexicon for *RECOMMENDED ROUTE.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Web	Information Technology Platforms: Mobile Web^	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Best route	"Best route is via [facility]."			+	+	X
Best	Best route	BEST ROUTE TO [DESTINATION] TAKE [FACILITY]					>
Adequate	Forecasted trip	"Forecasted trip is via [facility]."			+	+	X
Adequate	Forecasted trip	FORECASTED TRIP TIME VIA [FACILITY] X MIN					X
Adequate	Most reliable trip	"Most reliable trip is via [facility]."			+	+	X
Adequate	Most reliable trip	MOST RELIABLE TRAVEL TIME TO [DESTINATION] TAKE [FACILITY]					> %
Adequate	Most predictable trip	"Most predictable trip is via [facility]."			+	+	X
Adequate	Most predictable trip	MOST PREDICTABLE TRAVEL TIME TO [DESTINATION] TAKE [FACILITY]					>%
Adequate	Most consistent trip	"Most consistent trip is via [facility]."			+	+	X
Adequate	Most consistent trip	MOST 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
Avoid	Least variable time	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

^ 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.

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.

**Table 9. Travel time reliability Lexicon for *RELIABILITY.*⁽³⁾**
Recommendation	Alternate Phrase	Wording Context/Additional Information	Information Technology Platforms: Web	Information Technology Platforms: Mobile Web^	Information Technology Platforms: Text / 511	Information Technology Platforms: Mobile Application^	Information Technology Platforms: Dynamic Message Sign
Best	Predictable	"Most predictable trip."					X
Adequate	Reliable	"Most reliable trip."					X
Adequate	Consistent	"Most consistent trip."					X
Adequate	Vary	"Trip varies."					X
Avoid	Differ	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Fluctuate	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Change	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Go up or down	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Increase or decrease	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A
Avoid	Deviate	Preference shown for other terms.	N/A	N/A	N/A	N/A	N/A

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

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