Travel Time Displays At Freeway Entrance Approaches

Chapter 1. Problem Background and Objectives

Transportation agencies have been investing resources in systems that provide real-time travel time information to motorists through the use of CMSs. However, research suggests these sophisticated systems have relatively little impact on actual driver decisionmaking and route.^(1–3) 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. There has been little research or evaluation on this issue. This project explored the best means of providing travel time information to drivers as they approach a freeway entrance and evaluated how this influenced route choice and diversion.

One additional factor raised in past research that is related to this project’s objectives is the provision of travel time or related information for arterial route alternatives to freeway routes. Studies have shown that drivers are more likely to divert from a planned route if they have information on travel time or congestion on the alternative route as well. Unfortunately, while many agencies have good real-time information on freeway travel, they do not have comparable information on surface streets. Furthermore, different agencies (State, county, local) are often responsible for operating various types of roadways. While the efficiency of the overall roadway system in an area is the overarching goal, the narrower interests of these various agencies may be in conflict. For example, diverting traffic off of an interstate highway may increase congestion on a roadway operated by a municipality or may cause neighborhood traffic to increase, resulting in resident complaints. It is beyond the scope of this project to try to resolve these sorts of operational issues. However, it is entirely appropriate to consider the potential benefits of providing travel time estimates for arterial routes. Because this sort of information is not typically available to motorists, there is little data on its actual benefits.

Many transportation agencies now provide real-time travel time information to motorists by means of CMSs. Travel time is an important item of information that is valued by travelers, and travel time displays are generally viewed positively by the public. In current practice, the provision of travel time by CMS is generally limited to information about travel times on freeway routes, provided by signs located on the freeway. However, past work has had difficulty identifying substantial effects of travel time displays on driver route choice and diversion. One possible reason is that the location of displays only on the freeway itself may not be optimal. Key driver decisions may be made before entering the freeway, and once on a particular freeway, it may be difficult to get people to divert. This may be especially so if there is no information about travel times on alternative routes, particularly arterial alternatives.

The purpose of this project was to compare and quantify motorist response to real-time travel time displays at freeway approaches compared with their response to displays located on the freeway itself. 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 FTT information (the current state of practice), but some experimental attention was also directed to provision of arterial route travel time estimates.

All parts of the study were conducted on behalf of the Transportation Management Center (TMC) Pooled Fund Study and FHWA.

Background on ATT Displays

Technology makes it feasible to provide drivers with real-time information about how long it will take to reach a given destination. Many jurisdictions within the United States provide such information on CMS displays. In almost all cases, these signs are located on freeways and provide text messages about travel time to upcoming exits, roadways, or landmarks. Cases where the information display is provided on nonfreeway roads, or where travel times on alternative routes are given, are rare. Figure 1 shows an example of typical practice.

©Lerner et al. (2009)
Figure 1. Photo. Travel time information display in Atlanta, GA.⁽¹⁾

Practices for the design and use of travel time displays vary considerably across the country, and little is known about what options are most effective. For this reason, the TMC Pooled Fund Study, through FHWA, funded a study to assess the impacts of travel time displays on drivers, define the effective options, and develop preliminary guidance for practitioners. This study found that commuting drivers valued travel time information and were generally positive about travel time sign systems.⁽¹⁾ However, it was difficult to identify much influence of these signs on route choice and diversion. This is not to say that drivers did not use the travel time information but that such information, by itself, generally has limited effects.

These results parallel those of other studies using different survey and experimental methods.^(2,3,5) Based on research and focus group findings, Lerner et al. suggested that one major reason for the absence of a stronger influence on route choice was that current practice does not locate the displays in such a way that the information is fully usable by the motorist.⁽¹⁾ Travel time is only displayed to drivers after they are already on the freeway. The problems with this include (1) key choice points for many commutes occur before entering the freeway, particularly choices between freeway and surface street routes; (2) once on the freeway, alternative route options may be very limited; (3) once drivers are on the freeway, inertia makes it difficult to get them to reroute, and greater motivation is required; and (4) information on the congestion and times of alternate routes is not available, so there is little confidence in rerouting decisions.

Recently, there has been greater interest in displaying travel times, not only on freeways, but on arterial approaches to freeways. Probably the most ambitious program is in the Chicago area, where the Illinois Department of Transportation has initiated a systematic program of travel time displays on approaches to freeways, with 14 sites implemented and more planned. Although various agencies have expressed interest in travel time signs at arterial locations, at this point, there is no guidance, or good basis for guidance, on what the displays should include, how information should be formatted, where displays should be located (relative to freeway entrances and/or commuter choice points), distraction and safety concerns, and so forth. Thus, the research team identified two general needs: (1) to assess the effectiveness of travel time signs at locations other than on freeways and (2) to develop recommendations for the optimal design, placement, and use of these nonfreeway displays. These are the primary issues this project addresses.

One additional factor raised in past research is related to this project’s objectives—the provision of travel time or related information for arterial route alternatives to freeway routes. Studies have shown that drivers are more likely to divert from a planned route if they have information on travel time or congestion on the alternative route as well.⁽¹⁾ Unfortunately, while many agencies have good real-time information on freeway travel, they do not have comparable information on surface streets. Furthermore, different agencies (State, county, local) are often responsible for operating various types of roadways. While the efficiency of the overall roadway system in an area is the overarching goal, the narrower interests of these various agencies may be in conflict. For example, diverting traffic off an interstate highway may increase congestion on a roadway operated by a municipality or may cause neighborhood traffic to increase, resulting in resident complaints. It is beyond the scope of this project to try to resolve these sorts of operational issues. However, it is entirely appropriate to consider the potential benefits of providing travel time estimates for arterial routes as a supplementary objective. Because this sort of information is not typically available to motorists, there is little data on its actual benefits.

Objective and Scope

The purpose of this project was to compare and quantify 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 in a laboratory study and a field study. For the field study, both freeway and ATT information was provided to participants, including the provision of ATT information with an in-vehicle device triggered near to a roadway sign.