Travel Time Displays At Freeway Entrance Approaches

Chapter 2. Review of Current Practice and Research

Review of Practice

Note that these review activities were initially conducted as part of a previous project detailed in the FHWA report Driver Use of En Route Real-Time Travel Time Information.⁽¹⁾ These findings are only briefly reviewed here. The research team began the review of practice by sending formal requests for information to the heads of various committees and professional associations to be disseminated among their members. The request was sent to the chairperson of each of the following committees and organizations:

• TMC Pooled Fund Study Group.
  
  
• Transportation Research Board (TRB) Intelligent Transportation Systems (ITS) Committee.
  
  
• Transportation Research Board Freeway Operations Committee.
  
  
• TRB Effects of Information and Communication Technologies on Travel Choices Committee.
  
  
• Institute of Transportation Engineers Management & Operations/ITS Council.
  
  
• American Association of State Highway and Transportation Officials Standing Committee on Highways.

These requests yielded responses from 13 individuals who either have implemented ATT systems or have considered doing so. Additional requests for information were sent to individuals who were identified as perhaps having knowledge of the state of practice.

In addition to the requests, the research team conducted keyword Internet searches to identify locations where ATT displays were present. Emails and telephone calls were also placed to key individuals who were expected to be knowledgeable about the current state of ATT practice.

The review of practice ultimately identified more than a dozen ATT implementations in the United States and abroad as well as a number of additional jurisdictions that were considering the use of ATT. Key individuals at seven jurisdictions with ATT were interviewed by telephone for further information, and others were contacted by email.

FTT Displays: Recent Developments

While FTT literature was not the focus of this review, it is important to consider the implications of FTT knowledge on ATT. The review of recent developments in FTT found that the use of FTT displays expanded in recent years. According to FHWA, as of 2014, travel time signs were used in 66 areas in the United States, and there were plans to begin using travel time signs in 11 additional areas.⁽⁶⁾ Practice for the display of travel times on CMS remains diverse, with no apparent movement toward convergence of practice. Many State transportation departments have their own guidelines or policies for the display of travel times and other messages on CMSs, and the MUTCD provides Federal requirements and guidelines for some aspects of CMS message display, but no consensus or best practices have emerged for the display of travel times.⁽⁴⁾ Similarly, no major evaluations of travel time implementations or research-based guidelines appear to have been published since the 2009 Lerner et al. review (see also Robinson, Lerner, Singer, Jenness, and Huey; and Singer, Robinson, Krueger, Atkinson, and Myers).^(7,8)

ATT Displays

Most current ATT systems use CMSs located on arterial approaches to freeway entrance ramps to show FTTs. A smaller number of ATT systems, however, show travel times for arterial roads instead of or in addition to FTTs. Regardless of which road travel times are shown, ATT implementations have the potential to overcome many of the limitations of FTT displays because they are presented before drivers commit to a freeway route while they have more routing options available and can avoid freeway congestion simply by remaining on arterial roads.^(9–13)

Drivers are largely in favor of ATT displays. Benson surveyed drivers in the Washington, DC, area and found that roughly 90 percent approved of the idea of ATT signs because they wanted to be alerted to freeway conditions when alternative routes were still available.⁽¹⁴⁾ Likewise, a survey of Milwaukee-area drivers found that 76 percent believed ATT displays were useful in providing travel information, and 62 percent reported getting information from ATT displays more than once a week.⁽¹⁰⁾

Research suggests that drivers want to know travel times for various route options so they can make their own routing decisions rather than simply receive prescriptive routing instructions or qualitative statements.⁽²⁾ In a stated preference survey, Polydoropoulou, Ben-Akiva, Khattak, and Lauprete found that as many as 58 percent of respondents would divert from a freeway if quantitative travel times provided for both freeway and an alternate route showed that the alternate route was faster.⁽¹⁵⁾ High diversion rates have the potential to reduce freeway congestion by encouraging drivers to use alternate routes when the freeway is congested, although there is also the possibility that high rates of diversion could cause congestion on the arterial alternatives as well.^(11–13)

Despite promising evidence from various research efforts, there have been very few formal evaluations of actual ATT displays or systems. Although some implementing agencies feel that their ATT displays benefit drivers and improve traffic flow, they lack data on these issues. One survey effort, however, has found positive effects of ATT displays. An Internet survey of drivers in Chandler, AZ, found that 76 percent believed the ATT displays (which showed travel times for major commuter routes that included both arterial roads and freeways) were helpful, 86 percent found the information easy to understand, and 88 percent considered the information to be accurate.⁽¹⁶⁾

Summary of Practice

The review of practice identified more than a dozen domestic jurisdictions where travel time displays were located on arterial or other off-freeway roads, as well as three jurisdictions with plans to begin displaying ATT soon. All implementations have been active for fewer than 10 years, and many have only existed for a few months or a few years at the time of this writing. Most ATT implementations show only FTTs, but some jurisdictions have taken advantage of new and improved vehicle detection and speed calculation technologies to be able to provide travel times for arterial roads themselves. Table 1 summarizes a subset of sites of implementation found in this literature review for which the research team was able to obtain detailed information from contacts.

Literature Review Conclusions

The review of literature on ATT revealed that very little research has directly addressed the effects of ATT displays and systems. While evaluations of ATT are scarce, there is a broader base of literature on related topics such as route choice behavior. Research has generally found that drivers are hesitant to divert from their planned route, particularly once they are on a freeway, unless they receive clear and trustworthy information that an alternative route will save a meaningful amount of time. ATT systems that provide drivers with travel time information before they commit to a freeway have the potential to provide drivers with the information and motivation they need to make informed route choice decisions. Surveys have found that drivers generally desire ATT information and like having it. Similarly, ATT implementers believe that their systems are working well and benefitting drivers. Despite these promising indicators, however, there are no clear empirical data that show measurable benefits of ATT such as driver time savings, improved traffic flow, or safety benefits, nor is there any evidence comparing various options for ATT systems such as display features, sign locations, and so forth. While the presentation of ATT information in any form may result in some benefits, particular system or message features could potentially result in greater benefits than others.

ATT is an emerging application of ITS technology and has only been implemented in a few States. The review of practice revealed a diverse range of practices for the display of travel times on arterial-based CMSs with no signs of convergence of practice. In fact, no two implementations summarized in the review of practice took the same approach to ATT display. This diversity is due in part to the different strategies of each implementation. While all implementations shared the common goals of informing drivers and improving the use of the roadway system, specific strategies included displaying the following information:

• FTTs to one or more destinations in the same direction.
• FTTs to one or more destinations in different directions.
• ATTs to one or more destinations.
• Travel times for a route that includes both freeway and arterial roads.
• Travel time via two routes to a common destination.
• Travel times via two modes (car and bus) to a common destination.
• Average speed or incident information as a supplement to travel times.

In addition to the variety of ATT strategies employed by various implementing agencies, other possible reasons for the diversity of practice include the following:

• Constraints imposed by existing technologies (e.g., pre-existing CMS), funding, and broader agency objectives.
  
  
• Lack of guidelines for ATT deployment (while the MUTCD provides standards and guidance for the use of CMSs, there are no guidelines specific to travel time messages).⁽⁴⁾
  
  
• Lack of implementers’ knowledge about deployments in other regions.

The different approaches of various jurisdictions resulted in significant differences among jurisdictions in terms of the content and appearance of travel time information, including the following:

• Number of information elements per message.
• Message context (e.g., inclusion of freeway name).
• Message syntax (i.e., order of information elements).
• Message layout (e.g., centered versus left/right justified).
• Use of capitalization.
• Phrasing of messages.
• Sign dimensions and character height.
• Mounting (i.e., roadside versus above roadway).
• Color coding.

Although there are significant differences between ATT implementations in different areas, there are also the following noteworthy commonalities (as of 2012):

• All U.S. ATT systems use dynamic elements that feature amber characters on a black legend. The two implementations that use static/dynamic signs (Minneapolis and Utah County) both provide static sign information using white characters on a green legend in compliance with MUTCD Standard 2D.03.02.⁽⁴⁾ As full-color, full-matrix CMSs become more common, other practices may emerge.
  
  
• In the United States, all ATT implementations show a maximum of two destinations per sign, whether on a single phase or two phases.
  
  
• Locations that show FTTs on ATT displays typically have ATT CMSs placed from 0.2 to 1 mi from the freeway interchange, with the location optimized to allow drivers to choose a nonfreeway route as an alternative. In Chandler, AZ, where ATT CMSs are up to 2 mi from the freeway interchange, travel time estimates include the travel time to the freeway entrance.

Despite some promising evidence of driver satisfaction from surveys, no empirical evaluations of ATT displays have been conducted in the United States. As a result, it is difficult to determine how various ATT systems, as well as the particular features of those systems and the roadway environment in which they exist, affect route selection, driver comprehension, safety effects (e.g., distraction), and roadway network performance. The subsequent tasks in the present research effort (task 3, Evaluation of Alternative Displays, and task 4, Evaluation of Field Implementation) will seek to provide data to address many of these questions.