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Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
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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 4. Summary and Recommendations

This chapter presents key findings of the study and recommended practices for nonfreeway-based travel time displays.

Key Findings

The primary purpose of the laboratory study was to compare the effectiveness of CMS travel time displays on arterial approaches to freeways compared with freeway-based signs. A secondary purpose was to examine the effectiveness of travel time information for arterial routes. Using a four-part method in a laboratory setting, the research team was able to show participants many different types of signs with different formats and features and determine their preferences, perception of ease of use, and perception of usefulness. In addition, the team was able to differentiate whether participants had a clear understanding about information provided on ATT signs—that is, whether the travel time included the route to the freeway or started at the freeway ramp. The team was then able to gain an understanding of where along their everyday commuting route participants would find travel time signs most useful in making route decisions.

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 commuters in a before/after assessment on an experimental site ((US-1N) in Virginia). Participants were tracked for 9 weeks and exposed to FTT information presented on a roadway sign and ATT information presented on an in-vehicle device. The methodology was designed to be forward looking and allow for testing the display of travel time messages in locations that might not even have travel time signs. It also allowed 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 are becoming more accustomed to using their telephones while driving for a variety of tasks.

Apart from the methodological advancements, the following themes were found throughout the responses provided by participants:

The following additional options would be important to investigate in future research using this method: (1) various sign formats similar to the laboratory experiment, (2) comparisons of additional sign locations relative to the freeway entrance, and (3) diversion behavior based on various congestion levels and nonrecurring events. The current study had resource, logistical, and jurisdictional constraints that did not allow for these investigations. However, the research team sees these investigations as vital to better developing an efficient ATT program.

Overall, this study provides a field example of providing travel time information on freeway entrance approaches along with a novel methodology for testing sign location that can be used to investigate these and other research topics of interest for future applications.

Recommended Practices for NonFreeway-Based Travel Time Displays

A summary and discussion of information content, as well as recommendations for the design and use of nonfreeway-based travel time displays, follow and are based on the current research as well as the findings of previous research discussed in the FHWA report Driver Use of En Route Real-Time Travel Time Information.(1) This discussion and recommendations provide the practitioner with specific guidance based on recent research as well as supporting data for use in discussions about which recommendations to adhere to in his or her local community. It should be noted that these general recommendations may not be consistent with some local signing practices and so may have to be adapted according to the local conventions. Regardless, where possible, the information content discussion and CMS recommendations should be considered when developing an ATT program.

Note that in contrast to some foreign applications, travel time displays in the United States are typically provided via CMSs that are not specifically dedicated to travel time messages. Travel time information may be the default when other higher-priority messages are not warranted (e.g., incidents, adverse weather, or Amber alerts). This may preclude the use of fixed-sign elements that simplify the sign and allow additional sorts or amounts of information. The recommendations in this chapter are based on normal U.S. practice and the available findings.

Finally, the size of ATT signs varies by location and jurisdiction. The MUTCD includes guidance on CMS sign size (sections 2L.04, 2A.07, and 6F.52), providing a maximum length of 20 characters over 3 lines (for a total of 60 possible characters), but no specific guidance is given for arterial signs. Most examples described in this report’s recommendations are based on a 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, practitioners can adjust the example signs accordingly—removing the extra spaces or, if necessary, elements such as “MIN” after travel times.

Information Content Summary and Discussion

This section presents a summary and discussion of recommendations regarding information content for ATT displays.

Message Content

The results of the current study’s laboratory experiment showed that drivers who received only information via a freeway route were more likely to divert onto the highway even when the highway is potentially congested. When drivers were provided with both a freeway and an ATT, drivers were more likely to stay on their current route when it was an arterial (i.e., not choose the highway route, which was often considered the default). This is consistent with the research team’s earlier work that found a higher propensity to divert if given alternative route information. (The arterials can be considered alternative routes in the current situation.) It is also consistent with the current field study that found individuals were willing to take alternative routes (i.e., arterial roads) when provided with that information, and the travel times were less than the highway times.

Effect of Receiving Freeway-Only Information Versus Freeway and Arterial Information

Travel time signs displaying information about just one location may not provide drivers with enough information to divert their route. When given more information (i.e., travel time information about both a freeway and an arterial), drivers were more likely to stay on their current route when it was an arterial. In other words, drivers who receive only information via a freeway route are more likely to divert and continue onto the highway, which may be potentially congested. In addition, drivers had higher ratings in confidence of knowledge of best route, ease of use, and willingness to divert when given more information (two potential routes).

Conclusion: Travel times to a destination for both arterial and freeway routes are clearly the preferred type of information, as opposed to average travel speeds or levels of congestion.

Effect of Color Coding Travel Times

Some of the signs presented to participants during the laboratory study were color coded, with red indicating bad traffic and green indicating lighter traffic. The data indicated no significant differences between drivers on an arterial receiving color-coded travel time information about that arterial versus non-color-coded travel time information. However, when presented with color-coded travel time information about a freeway while on an arterial versus non-color-coded information, 16 percent more drivers stayed on their current route (the arterial).

Conclusion: It appears possible that color coding has the greatest effect when drivers cannot visually confirm traffic conditions (e.g., on a roadway other than the one they are currently traveling). Also, color-coded travel time information may be more influential to drivers on arterial roads when they receive freeway information rather than arterial road information.

CMS Findings Summary and Recommendations

CMS displays can include many different types of information, including travel time, average speed, distance, and information about delays and incidents on the roadway. These features do not necessarily need to be independent of each other; CMS displays can include several of these information features at one time. The data indicate that travel time (in minutes) is the most desired information on these CMS displays. In terms of displaying information about delays and incidents, more participants indicated that they wanted general information versus specific location information (see figure 48).

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Figure 48. Chart. Type of information on personalized CMS signs chosen by participants.

To maximize route diversion in response to a freeway-based travel time display, the display features depicted in table 16 should be considered.

Table 16. Display features to consider.
Display Description Display
Recommend using an alternate route (USE ALT RTE)
TRAVEL TIME TO
FALLS RD   16 MIN
USE ALT RTE
Indicate a specific alternate route (VIA RTE 355)
TRAVEL TIME TO
FALLS RD   16 MIN
USE ALT RTE
VIA RTE 355   12 MIN
or
TRAVEL TIME TO
DEMOCRACY   24 MIN
HOV SAVES   5 MIN
Indicate major delay or incident (MAJOR DELAY)
MAJOR DELAYS AHEAD
DETOUR SHADY GROVE
Provide an open-ended travel time estimate (30+MIN)
TRAVEL TIME TO
SHADY GROVE   10 MIN
GW PKWY   30+ MIN
Show travel times for both current and alternate route
TRAVEL TIME TO
PEACHTREE   18 MIN
USE ALT RTE
VIA RTE 33   7 MIN

Information Limits and Visibility/Legibility

Messages should be concise and to the point. Messages should be limited to no more than three lines of text (where possible) or five to six information units. Lengthy messages consisting of more than six words are discouraged because drivers are unable to read, process, and make a decision about the information all within a few seconds. Although this recommendation is based on freeway speeds and scenarios in earlier work, similar concerns hold for arterial traffic. Drivers may be approaching more slowly (although some arterials can see speeds of 50+ mi/h), but there is also more competing signage, richer environmental cues, and more closely spaced traffic, so drivers may also be limited in how long they can attend to a sign. Therefore, it is recommended that message content consist of only necessary but still coherent information with no more than six words. Each word should consist of less than eight letters. Finally, the use of abbreviations is encouraged. Figure 49 shows an example sign that contains many of these features.

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Figure 49. Illustration. Travel time display featuring concise information.

Note that the discussion of information units is based on CMSs and stems from the research that resulted in the FHWA report Driver Use of En Route Real-Time Travel Time Information.(1) The MUTCD recommends four or five units, depending on the speed and visibility (see table 17).(4)

Table 17. MUTCD maximum information units and legibility distance by speed.
Speed (mi/h) Maximum Units Legibility Distance (mi)1
25
5 .5
35
5 .5
45
4 .5
55
4 .5

1Legibility distance is the maximum distance at which a driver can first
correctly identify letters and words on a sign. The minimum legibility
distance is 600 ft for daytime conditions and 800 ft for nighttime
conditions. (Taken from 910.3.2.5, Legibility and Visibility of CMS
(MUTCD 2L.03).)(4)

According to the 2009 MUTCD, for the more common CMS, the longest measured legibility distances on sunny days occur during midday when the Sun is overhead.(4) Legibility distances are much shorter when the Sun is behind the sign face (facing the driver), when the Sun is on the horizon and shining on the sign face, or at night. Visibility is the characteristic that enables a CMS to be seen without necessarily having the message processed by the driver. Visibility is associated with the point where the CMS is first detected, whereas legibility is the point where the message on the CMS can be read. Environmental conditions such as rain, fog, and snow affect the visibility of CMSs and can reduce the available legibility distances. During these conditions, there might not be enough viewing time for drivers to read the message, so taking into account environmental conditions is important. When environmental issues cause reduced visibility and legibility or when the legibility distances stated earlier cannot be practically achieved, messages composed of fewer information units should be used, and consideration should be given to limiting the message to a single phase.

In addition, the 2009 MUTCD (see paragraphs above and sections 2L.04, 2A.07, and 6F.52) also provides the following guidance for text size and spacing:(4)

Display Recommendations

This section presents a summary and discussion of recommendations regarding format for ATT displays.

Format Type

Simple hybrid signs that include travel times are an acceptable alternate format (see figure 50). These are signs with certain fixed display parts as well as dynamically changing sections. Although simple diagrammatic signs with a static linear depiction of the roadway and that include a dynamic display of travel time and congestion severity are recommended as acceptable, preference for nondiagrammatic hybrid signs has been observed. Nondiagrammatic hybrid signs are the preferred means for receiving travel time information compared with diagrammatic and trailblazer signs.

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Figure 50. Illustration. Dynamic travel time information display.

Effect of Alternative Formats

The “hybrid” format received the highest ratings on confidence in knowledge to make the best decision, ease of use, and willingness to divert to another route. The trailblazer-formatted sign received the lowest ease of use rating. Based on the ratings for different sign formats, it seems that participants preferred the “hybrid” sign as a means for receiving travel time information.

More complex display configurations with more than three destinations appear to be too difficult to readily interpret under driving conditions (signs #2 and #3, in figure 51 and figure 52, respectively). These diagrammatic signs are dynamic and represent travel times as well as color-coded congestion information that changes based on conditions. It is important to note that acceptability is limited to no more than three destinations in either format. Note the difference between sign #2 (figure 51) and sign #1 (figure 53).

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Figure 51. Illustration. Dynamic travel time sign #2.

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Figure 52. Illustration. Dynamic travel time sign #3.

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Figure 53. Illustration. Dynamic travel time sign #1.

Destination Information

Overall, it was evident that information regarding destination was highly variable among participants dependent on their own personal commute or desired destination. See figure 31 for the data describing the participants’ destination information.

Destinations

As illustrated in the following figures, signs with four destinations (figure 54, sign3) took longer to process than signs with three destinations (figure 55, sign 2), which in turn took longer to process than signs with two destinations (figure 56, base 1, and, figure 57, sign 19). This relative ordering also held for ease of use and confidence.

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Figure 54. Illustration. Sign 3.

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Figure 55. Illustration. Sign 2.

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Figure 56. Illustration. Base 1.

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Figure 57. Illustration. Sign 19.

In addition, the public should be made aware that travel times are updated frequently but the CMS should not be used for this purpose. Consider a fixed-sign component (e.g., UPDATED EVERY 3MINUTES) and/or a public education campaign (see figure 58).

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Figure 58. Illustration. Updated sign example.

Text Positioning

There was a clear preference for text positioning consisting of a centered heading, left justified destinations, and right justified travel times (see figure 59). This structure allows for clear organization of information into separate categories and quick recognition while approaching the sign.

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Figure 59. Illustration. Example of a sign with left and right justifications.

Number of Elements

Limit displays to three lines of text with no more than six units of information and two units of information per line (see figure 60).

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Figure 60. Illustration. Example of a sign featuring concise information.

Wording of Messages

Describe arterial destinations as street names or towns and freeways as their jurisdictional designation, assuming the display is intended primarily for regular commuters. When displaying travel times on arterials, include the words “TRAVEL TIME TO” for the ATTs and “I-___ TIME TO” for FTTs. The use of exit numbers for FTTs presented on arterials is not recommended.

Destination Type

Results from Lerner et al. indicate that drivers process signs that show street names and town labels faster than signs that label destinations using route numbers, exit numbers, or specific expressway locations (such as a split in the expressway or a State border).(1)

Capitalization and Abbreviations

All of the text should be in capital letters. Standard street abbreviations such as RD, BLVD, etc., should be included in the destination. In addition, the abbreviation MIN should be used to indicate the time units in minutes for travel times (see figure 61).

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Figure 61. Illustration. Example of a sign demonstrating recommended capitalization and abbreviation.

Sign Placement Relative to Freeway Entrances Recommendations

This section presents a summary and discussion of recommendations regarding sign placement location for ATT displays.

Distance to Freeway Onramp

Sign position should be at a key decision point that allows the driver to switch lanes before approaching the onramp. Results of the current study indicate that drivers would like travel time CMSs to be placed approximately 0.5 mi from the freeway onramp. Note that this is the participants’ preferred location and not the recommended location based on engineering and roadway considerations. Each jurisdiction will have to evaluate its own constraints to find the most optimal locations. However, if all else is equal, participants would prefer to see signs at this distance.

Sign Placement

In addition, drivers indicated that CMS displays of travel time would be most valuable on their final approaches to the freeway. It seems that people want travel time information at a vital decision point in their drive and would prefer to see it on an arterial approaching the freeway onramp rather than on a freeway. Participant responses also suggested that personally optimal sign location is not necessarily in the most densely populated areas. See figure 26 through figure 29 for a more detailed description of the participants’ preferred location of personalized signs and for figures describing sign placement and population density surrounding the sign placements.

Concluding Recommendations

In conclusion, the following brief overview presents the qualities and elements of signs that can yield the most effective displays. Several recommendations are provided to improve the dissemination of travel time messages on ATT signs. Overall, a well-positioned sign should contain messages with the following elements to be the most effective:

Figure 62 and figure 63 are example signs that use the optimal format and follow this guidance.

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Figure 62. Illustration. Travel time information display with optimal format (example #1).

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Figure 63. Illustration. Travel time information display with optimal format (example #2).

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, 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.

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