Overview
The human factors studies planned for Tasks 6‐10 were presented and approved by the panel in June 2010. They consisted of focus groups and a usability study. As conceived at that time, the usability study would employ computer‐based multiple choice testing of terminology and website interface features. This objective testing allows rapid testing of large numbers of participants because data entry and scoring can be automated.
The computer survey was developed and deployed in the fall of 2010 as described in a separate interim report. The computer survey had presented test items asking participants to select departure times in response to a sample traveler information website which provided total trip time estimates. After approximately half the participants were tested, researchers reviewed interim results and found that a large portion of people were adding their own buffer time on top of the total trip time recommended by the system. Unfortunately, it is not clear whether this was due to a lack of interest in the terms used or a lack of understanding of how to apply them conceptually in the survey environment. The research team decided to add an open‐ended aspect to the survey to investigate this critical question in more depth. This open‐ended survey should be considered as an extension of the computer‐survey and is reported separately in these interim reports for convenience since the interview method and data analysis are distinctly different than the computer surveys.
The objective of the open ended survey was to determine whether the presentation of both an indicator of the normal (average, typical, estimated, expected) trip time and an indicator of reliability (added time, extra time, cushion time; 95%‐tile trip time) were correctly interpreted by drivers.
Conceptually, the total of a driver’s average or normal travel time plus the buffer time a driver adds for contingencies (uncertainty of conditions) is the driver’s estimated trip time for planning purposes:
Normal trip time + buffer time = total trip time estimate
Presently, no lexicon exists of the terms that should be used to convey each of these types of information. Furthermore, no clear evidence exists as to whether any or all of these information types can be adequately conveyed to, and correctly interpreted by, drivers. Therefore, TTI researchers developed the open‐ended, paper‐based survey to determine which combinations of terms representing an average trip time, a buffer time, and/or the ultimate trip time to plan for would be best for conveying trip time reliability information.