Travel Time Displays At Freeway Entrance Approaches

Executive Summary

Transportation agencies are investing resources in systems that provide real-time travel time information to motorists through the use of changeable message signs (CMSs). However, research suggests these sophisticated systems have relatively little impact on actual driver decisionmaking and route.^(1–3) The Federal Highway Administration (FHWA), as well as State and local agencies, face the challenge of providing real-time travel time information to motorists in a manner that allows them to take full advantage of it. One factor contributing to the limited effects of current systems is that the travel time displays are not optimally located. This project explored the best means of providing travel time information to drivers as they approach a freeway entrance and evaluated how this influences route choice and diversion.

The purpose of this project was to investigate motorist response to real-time travel time displays at freeway approaches. The research aimed to determine the benefits and effectiveness of travel time signs on arterial approaches to freeways and develop recommendations for the design and use of such displays, including information content, format, sign location, and warrants. The focus was freeway travel time (FTT) information (the current state of practice), but some experimental attention was also directed to provision of arterial route travel time estimates.

Overview

The project consisted of two experimental tasks. The first task was a laboratory-based experiment in which participants were presented with scenarios and video of arterial travel time (ATT) displays and then were asked to provide ratings and to offer location recommendations. The second task was a field implementation over 11 weeks investigating behavior, ratings, and use of both freeway and ATT information provided near a freeway entrance approach. Information was provided via a CMS and in-vehicle. A main goal of both studies was to better understand optimal ways and preferred locations of presenting both freeway and ATT information to commuters.

Laboratory Task

The laboratory task was a within-subjects design with one group of commuters. Sign message content and scenario were manipulated throughout the task. In addition, participants provided ratings, qualitative responses, and sign location mapping preference.

The primary purpose of the laboratory study was to investigate the effectiveness of CMS travel time displays on arterial approaches to freeways. A secondary purpose was to examine the effectiveness of travel time information for arterial routes. Key measures included stated route preference and subjective ratings. Using a four-part method in a laboratory setting, the research team showed participants many different types of signs with different formats and features and determined their preferences, perception of ease of use, and perception of usefulness. In addition, the team gained an understanding of where, along their everyday commuting route, participants would find travel time signs most useful in making route decisions.

Signs with various features were presented to participants to examine preferences for presentation of travel time information. The best format appeared to be the “hybrid” signs; participants rated this sign format as high in ease and usefulness. In addition, participants seemed to have a strong mental model suggesting that ATT signs should include the time it would take them to get to the freeway. From the final part of the study in which participants selected the ideal location for travel time signs, it was evident that people had a preference for ATT signs rather than FTT signs, and they wanted those signs placed nearer downstream choice points.

Field experiment

The primary purpose of the field study was to test a field implementation of travel time information presented on an arterial. The field evaluation was conducted with a before/after assessment on an experimental site (U.S. Route 1 North (US-1N) in Virginia). Participants were not provided with any travel time information during the pre-implementation stage (2 weeks) and provided with both arterial (via in-vehicle device) and freeway (via roadway sign) travel time following implementation for 9 weeks. The methodology was designed to be forward looking and allow testing of the display of travel time messages in locations that might not even have travel time signs. It also allowed for more accurate tracking of trip patterns to complement the usual approach of self-reported travel logs. In addition, using smartphone apps to provide this information was relevant because people rely more on smartphones.

Participants shifted route choices after being provided with freeway and ATT information. They used travel time information from the roadway sign and in-vehicle device but also continued using traditional media such as the radio. Participants reported that their routes were influenced by the roadway travel time sign but not much by the in-vehicle device and questioned the accuracy of the information or their ability to make the best decisions.

The results of this study were consistent with the laboratory experiment in the ways that participants desired receiving both freeway and arterial information when making route choices—with the usefulness of a sign decided by its placement at a key decision point. In addition, participants had difficulty understanding the sign format.

Recommendations

The following recommendations for the design and use of nonfreeway-based travel time displays are based on the current research and previous project findings detailed in the FHWA report Driver Use of En Route Real-Time Travel Time Information.⁽¹⁾ It should be noted that these general recommendations might not be consistent with some local signing practices and so might need to be adapted. Regardless, these recommendations should be taken into consideration when developing an ATT program when possible.

Also note that the size of ATT signs varies by location and jurisdiction. The Manual on Uniform Traffic Control Devices (MUTCD) provides guidance on CMS sign size (sections 2L.04, 2A.07, and 6F.52), providing a maximum length of 20 characters over three lines (for a total of 60 possible characters).⁽⁴⁾ There is no specific guidance given for arterial signs. Most examples described in this section are based on the full-sized freeway-type sign (e.g., 20-character lengths) that is often used over freeways but occasionally used on arterials. If a smaller sign is required, the examples can be adjusted accordingly—removing the extra spaces or, if necessary, elements such as “MIN” after travel times.

Overall, a well-positioned sign should contain messages with the following elements to be the most effective:

• Position the sign at a key decision point (i.e., 0.5 mi from the freeway onramp) that allows the driver to switch lanes before approaching the onramp.
  
  
• Display destinations, not travel speeds or congestion descriptions, and indicate time units (MIN).
  
  
• Left-justify destinations and right-justify times.
  
  
• Use street names or towns for destinations (not exit numbers).
  
  
• Limit message text to three lines or five to six information units.
  
  
• Use simple linear diagrammatic signs if needed (no more than three destinations).
  
  
• Convey frequent updating using a fixed-sign component.
  
  
• Maximize route diversion by using the following elements:
  
  
  • Recommended alternate route (e.g., USE ALT RTE).
  • Specific route (e.g., VIA RTE 355).
  • Major delay or incident information (e.g., MAJOR DELAY).
  • Open-ended travel time estimate (e.g., 30+ MIN).
  • Travel times for both current and alternate route.

Example signs that use the optimal format and follow this guidance are shown in chapter 4, Summary and Recommendations.

Travel time information presented at key decision points, such as freeway entrance approaches, can be a powerful tool for operators and managers to better inform travelers. In turn, travelers can make better decisions and take proper actions based on this information. In addition to placing the sign in the best location, the information must be presented optimally for the traveler to use it properly. The studies presented in this report provide both laboratory and field insights into message format and location, as well as resulting behaviors by commuters. It is hoped that the guidance distilled from these studies will help operators and managers provide better travel time information to the traveling public.