Effectiveness of Disseminating Traveler Information on Travel Time Reliability: Implement Plan and Survey Results Report
CHAPTER 3. LEXICON SELECTION
The Travel Time Reliability (TTR) terms and the alternate phrases for these terms that were tested in this study were initially generated in the Strategic Highway Research Program 2 (SHRP2) L14 research project and Lexicon document. The terms included in the SHRP2 Lexicon document were selected after analyzing results from a robust series of human factors experiments. The individual terms were selected because they performed well under all combinations of the scenarios and experiments. Furthermore, the information conveyed with each of the terms was discrete and independent of the other terms with respect to the intent of the information delivery and the desired outcome of the user.
The research in SHRP2 L14 found that it was difficult to determine if one phrase for a particular TTR term was significantly better than another and drastically outperformed another. However, that study did offer an opportunity to identify phrases that were bad, unclear, and/or needed to be avoided for numerous reasons. The differences in the performance of phrases in the original study were not major. If a term was identified as "best," in almost all cases it was only slightly better than those in the "adequate" category. Thus, in many of the Lexicon tables, there are two, three, and even four options for the "adequate" category.
The alternate phrases 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.
The Lexicon phrases for Recommended Route" were not tested because an alternate route was available in only one of the three test sites. The phrases were divided into two assemblies, denoted as Assembly A and Assembly B. The intent of dividing the phrases into two assemblies was to attempt to determine if one set of phrases performed better than the other with respect to user behavior and preference. Assembly A included the "best" alternate phrase for each travel time reliability term from the original SHRP2 report. In most instances, Assembly B included terms from the "adequate" list because only one phrase was in the "best" category. In the case of Alternate Travel Time, the second "best" phrase of Approximate Travel Time was tested. In the case of "Departure Time," the alternate phrase of "What time will you start your trip?" was used for Assembly B because the other "best" phrase of "Leave at" was so similar to the "best" phrase of "Departing at" that the study team did not think any difference in performance would be seen.
| Travel Time Reliability Phrase | Alternate Phrase: Assembly A | Alternate Phrase: Assembly B |
|---|---|---|
| 95th Percentile | Majority of the time1* | Most of the time2* |
| 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** |
1*Alternate phrase originally identified as "best" in SHRP2 L14 Lexicon. [Return to 1* Link]
2*Alternate phrase originally identifies as "adequate" in SHRP2 L14 Lexicon. [Return to 2* Link]
It is important to note that it was highly unlikely that a participant would see all of the individual Lexicon terms in an assembly together at one time, but rather would be far more likely to see only one or two terms at a time based on their individual preference. For example, different phrases were used if participants constrained their trip planning by departure time vs. arrival time. Finally, the differences between the terms used in the two assemblies in many cases were so minor (i.e., only one or two words added or replaced – "majority of the time" vs. "most of the time"), that any interdependency between the terms was expected to be negligible.
Overall, the study team did not expect to see drastic differences between the two assemblies, because they were two sets of terms that the SHRP2 L14 study found were reasonably well understood by a substantial portion of the population. The primary intent of the field study was to learn whether the TTR information itself had an effect on behavior in a real-life setting.
The application and use of these assemblies, their assignment to subject groups, and their evaluation is discussed later in this report.
