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Coordinating, Developing, and Delivering Highway Transportation Innovations

 
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Publication Number:  FHWA-HRT-16-059    Date:  November 2017
Publication Number: FHWA-HRT-16-059
Date: November 2017

 

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:

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.

Table 1. Summary of travel time practice for select implementations.
State Minnesota Missouri Georgia Wisconsin
Area Minneapolis area St. Louis area Cobb County
(Atlanta area)
Milwaukee area
Number of arterial signs 12-16 28 4 13
ATT on arterials No Yes No No
FTT on arterials Yes Yes Yes Yes
FTT on freeways Yes Yes Yes Yes
Description Arterial signs show travel times to downtown Minneapolis via car versus bus Signs on three major arterial routes that provide travel times for arterial, freeway, or both Arterial signs that show FTT and average speed to destinations in the direction of Atlanta Arterial signs that show FTTs to destinations in the direction of Milwaukee
Type and features Static navigation-type sign with dynamic cutout for travel times, mounted on roadside Dynamic, pole-mounted on roadside; most signs can display up to 3 lines of text with up to 20 characters per line, 12-inch character height Dynamic, cantilever over roadway; 2 rows of 15 characters each; 18-inch character height Dynamic, cantilever over roadway; sizes vary
Road-type placement Major arterial roads 0.5-1 mi from freeway entrances; on approaches to park and ride lots Major arterial roads, at least 500 ft from any signaled intersection; allow for a 750-ft sight distance Major arterial roads on approaches to I-75 or on arterial alternative route High volume arterial routes on approaches to freeway, before key decision points
Number of phases 1 1 2 1, 2
Destinations per sign 1 2 1 1, 2
Example FWY TIME TO DOWNTOWN MPLS
CAR 20 MIN
BUS 15 MIN
FROM I-55 TO:
I-270 VIA 55N 5 MIN
RT M VIA 55S 8 MIN
Phase 1:
I-75 SOUTH FROM BARRETT TO I285
Phase 2:
TIME: 10-12 MIN SPEED: 40-50 MPH
FREEWAY TIME TO DOWNTOWN 8 MIN HWY F 8 MIN

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:

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

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:

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

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.

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