Alicia Nelson

Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability

A key component to addressing the reliability issue related to urban mobility is conveying this reliability-related information to system users so that they can make informed decisions about their travel. The goal of the Strategic Highway Research Program 2 (SHRP 2) L14 project, Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability, is to examine what combination of words, numbers, and other features of user information messages, along with communications methods and technology platforms, best communicate information about travel time and reliability to travelers so they can make optimal travel choices from their point of view, such as whether to take a trip, departure time, mode choice, and route choice. This final report documents the research conducted as part the SHRP 2 L14 project. One of the main work products from the L14 project is the Lexicon for Conveying Travel Time Reliability Information, which offers recommendations to system operators on appropriate ways to provide travel time reliability information to travelers so that the information is most likely to be understood and used by travelers to influence their travel choices. The research team identified several key elements of a lexicon entry that were deemed necessary to completely present each term and how it might be used within the transportation community. One purpose of this final report is to describe the process that led to the development of the lexicon. The research began with a literature review to document existing practices and lessons learned regarding the communication of both travel and non-travel-related reliability information. The team then focused on conducting expert interviews and a technology and innovation scan to further examine the state of the practice in communicating information to travelers. The team also conducted a series of human factors experiments, including focus groups and surveys, to assess travelers’ comprehension and preferences for various reliability-related words and phrases. Finally, two laboratory experiments developed a utility function for travel time reliability information by observing participants’ use of reliability information during simulated commute trips and soliciting their opinions about the monetary value of that information. The lexicon was developed as the final task of this project.

Traffic sign legibility for different sign background colors: results of an open road study at freeway speeds

Transportation agencies have been considering the use of a purple sign background color to denote that the roadway is tolled. Prior studies have shown a driver preference for a unique color for the toll road category. Concerns about the legibility of purple signs have been raised due to their brightness and contrast ratio with a white legend. The current study performed an evaluation of the legibility and recognition of purple and green freeway guide signs during daytime and nighttime driving in the Houston, TX area. Forty-eight participants drove an instrumented vehicle in open traffic and read traffic signs along a toll road with purple signs on one segment and green signs on another. Results showed no significant difference in legibility distance between signs with purple and green backgrounds. An analysis of recognition distances for advance guide signs marking ramps to the toll road also showed no difference between purple and green signs. These results support the implementation of this new color without any loss in legibility.

Path Guidance Information in Advance of Work Zones at Urban Freeway Interchanges

Work activities at complex urban freeway interchanges often result in modified lane assignments and the temporary misalignment of existing overhead guide signs with the travel lanes. Researchers conducted a driving simulator study to determine whether the location and accuracy of driver lane changes made before major freeway-to-freeway interchanges were affected by temporarily misaligned permanent guide signing, temporary guide signing, and route shield pavement markings. The results of this study verify that when the lane assignment arrows on existing overhead guide signs are covered and the signs are temporarily misaligned with the travel lanes, drivers are not clear about which lane they need to be in to reach their destination; thus they wait to make a lane change until they are closer to the exit ramp gore area. Additional path guidance information presented to drivers before the interchange can be beneficial. The results of the study also indicate that smaller temporary lane assignment signs, route shield pavement markings upstream of the interchange, or both encourage drivers to make their lane change further upstream of the exit ramp gore area. Either of these devices or a combination should be used to provide drivers with additional path guidance information in work zones in which the existing overhead guide signs are temporarily misaligned with the travel lanes and the lane assignment arrows are covered.

Lexicon for Conveying Travel Time Reliability Information

The primary goal of Strategic Highway Research Program 2 (SHRP 2) Reliability research is to improve the reliability of highway travel times by mitigating the effects of events that cause travel times to fluctuate unpredictably. A key component to addressing the reliability issue related to urban mobility is conveying reliability-related information to system users so that they can make informed decisions about their travel. The goal of the SHRP 2 L14 project, Effectiveness of Different Approaches to Disseminating Traveler Information on Travel Time Reliability, is to examine what combination of words, numbers, and other features of user information messages, along with communications methods and technology platforms, best communicate information about travel time and reliability to travelers so that they can make optimal travel choices from their point of view, such as whether to take a trip, departure time, mode choice, and route choice. This lexicon is one of the main L14 project work products. It offers recommendations to system operators on appropriate ways to provide travel time reliability information to travelers so that the information is most likely to be understood and used by travelers to influence their travel choices. On the basis of the results of human factors studies and current traffic engineering practices regarding communicating to drivers, recommendations were made in the lexicon for using the following terms related to travel time reliability: 95th percentile, arrival time, average travel time, buffer time, delay time, departure time, free-flow travel time, peak travel time, planning time, planning time index, recommended departure time, recommended route, and reliability. There is also input from a literature review, expert interviews, and a technology and innovation scan done as part of the research project. For each of the travel time reliability terms listed, the lexicon includes a technical travel time reliability term, the definition of the term or 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. Finally, the lexicon identifies appropriate media and technology interfaces for each listed term, phrase, or graphic.