Changeable Message Sign Displays During Non-Incident, Non-Roadwork Periods (2008)

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Permanently mounted changeable message signs (CMSs), sometimes referred to as variable message signs or dynamic message signs, are used primarily to display real-time messages for non-recurrent, environmental, special event traffic, and other special operational problems. CMSs are also used for AMBER (America’s Missing: Broadcast Emergency Response) alerts. (Permanently mounted CMSs are referred to as CMSs in this synthesis). When the CMSs are not used for the aforementioned problems, the traditional wisdom has been to leave the CMSs blank; however, some state departments of transportation (DOTs) and agencies that operate toll roads are using their CMSs to display other types of messages during non-incident/ non-roadwork periods as an alternative to leaving the signs blank. Guidelines for the design and display of CMS messages for incidents and roadwork are available. However, guidelines do not exist for messages displayed during non-incident/non-roadwork periods. This synthesis was prepared to provide the state of the practice concerning the display of messages during non-incident/non-roadwork periods as a first step toward developing guidelines. Addition- ally, the state of the practice concerning AMBER alert messages also was examined. The content of this synthesis is based on information from an extensive literature review and a survey of state DOT traffic management centers (TMCs) and in agencies that operate toll roads. Responses to the survey were received from 100 TMCs in urban and rural areas. Responses were received from 40 state DOTs and 6 toll road agencies with a total of 100 TMCs. The TMCs operated 3,023 CMSs in urban areas and 821 CMSs in rural areas. Forty-two TMCs operated CMSs only in urban areas, 8 only in rural areas, and 50 in both urban and rural areas. During the past 10 years, there has been an increase in the number of transportation agencies that display messages on CMSs during non-incident/non-roadwork periods instead of leav- ing the signs blank. Part of this increase is the result of the greater use of travel-time infor- mation on CMSs. Travel-time messages are recommended by FHWA and in current CMS message design and display guidelines. However, congestion, speed, safety campaign, public service announcements (PSAs), and/or traffic law or ordinance messages are also displayed by some TMCs. A division in opinion still exists among TMCs that do not have the capabil- ity, or need to display travel time as to whether it is best to leave the CMS blank during non-incident/non-roadwork periods or to display messages. The results of the survey indicated that the decisions by TMCs to display congestion, speed, safety campaign, PSA, and/or traffic law or ordinance messages in lieu of leaving the CMSs blank are based primarily on administrative and upper management preference, TMC manager and supervisor preference—or both—rather than on objective research data. As in the past, the rationale of some TMCs that leave CMSs blank is that drivers will notice the essential messages when they are displayed and the messages will be more effective. The rationale expressed by some TMCs that display messages is that the public appreciates that the CMSs are being used, thus justifying the expensive investment in the signs. In addition, requests from administrators or management to display messages strongly influences the decision. One of the concerns and challenges of TMCs that leave the CMSs blank is uncertainty as to the best way to convince motorists that the signs are functional. For the TMCs that display SUMMARY CHANGEABLE MESSAGE SIGN DISPLAYS DURING NON-INCIDENT, NON-ROADWORK PERIODS

messages other than travel time, there is uncertainty as to the best type of messages that should be displayed during non-incident/non-roadwork periods. There is a trend in urban areas toward increased use of travel-time messages as an alter- native to leaving CMSs blank during non-incident/non-roadwork periods. A majority of the TMCs that display travel-time messages reported very favorable or favorable public response. Travel time is generally not displayed on all of the system CMSs, just on selected CMSs. Some CMS locations in a system are not conducive for displaying travel time. A review of the travel-time messages currently displayed by TMCs indicated that there is little uniformity with respect to message format. Also, many of the travel-time messages exceed the recommended maximum of four units of information per message. Thus, it is expected that unfamiliar drivers will not be able to read and recall the messages while traveling at typical freeway speeds. Some of the TMCs reported that drivers reduced speed to read the travel-time messages. TMCs are experiencing difficulty in accurately measuring and displaying travel times during rapidly deteriorating freeway operating conditions such as during the transition from off-peak to peak periods or when incidents occur. During these times, the calculated travel time that is displayed is significantly lower than the actual time it takes to traverse the section of freeway. Therefore, credibility of the CMSs is adversely affected. Current travel-time messages are based (at best) on recent data. Predictive models and algorithms are needed to enhance credibility. There is inconsistency among TMCs regarding the frequency at which travel times are updated on the CMSs, and guidance is needed by TMCs regarding the frequency at which travel times should be updated. Other conclusions drawn from the survey of TMCs are as follows: • When used, travel times should be displayed and updated automatically. • Several TMCs in urban areas do not currently display travel time because of inadequate infrastructure or software to accurately compute travel time. • The cost of added infrastructure and/or software to implement the capability to display travel-time messages varies widely among TMCs. Although several TMCs surveyed display messages during non-incident/non-roadwork periods, the percentage of TMCs that regularly display messages during non-incident/ non-roadwork periods as an alternative to leaving the CMSs blank is: congestion (12%), safety campaign (8%), PSA (3%), speed (2%), and traffic law or ordinance (2%) messages. Higher percentages of TMCs display these messages often, sometimes, or rarely. The basis for displaying congestion, speed, PSA, safety campaign, and traffic law or ordi- nance messages during non-incident/non-roadwork periods as an alternative to leaving the CMSs blank was found to be primarily (and, in some cases, solely) administrative/upper-management preference, TMC manager/supervisor preference, or both. Very little, if any, objective data from focus groups or other research studies were used in the decision-making process for dis- playing the messages. A significant percentage of TMCs that display these types of messages did not know the public’s attitude about the messages; therefore, there is uncertainty among TMCs as to the effectiveness of these messages and whether they are beneficial. CMS messages that indicate the levels of traffic congestion are discouraged by the authors of CMS message design and display guidelines because of the difficulty in finding adequate words to describe the large continuum of congested traffic conditions during the peak period. The problem with finding adequate descriptors during the peak period is compounded when incidents occur. The survey results, however, indicated that some TMCs display congestion messages. Some TMCs expressed concern that the differences between the various levels of congestion (e.g., heavy, moderate, or light) are not clear to drivers. 2

Messages that provide the beginning and end of traffic congestion are helpful to the motorists. Because the locations and limits of congestion change very quickly, several TMCs experience difficulty in displaying accurate messages. Results of research reported in the literature revealed that speed messages are not ranked high among the information needs of motorists when incidents occur on the freeway or when roadwork is affecting traffic flow and may be easily misinterpreted. Therefore, the display of speed information on CMSs during incidents or roadwork is not recommended. The major concern and challenge expressed by the TMCs when displaying speed messages dur- ing non-incident/non-roadwork periods was to display accurate speed information and to change the speed message when traffic flow and weather conditions change. Credibility can be an issue. The display of PSAs is discouraged by FHWA. There are strong arguments against dis- playing PSAs, including adverse public response, credibility, and the possibility of change blindness—the failure to see the CMS message change—when important messages are dis- played. One consequence of displaying PSAs is that this leads to requests from other agencies to display non-traffic-related messages. The display of safety messages associated with a safety campaign is allowable under pro- visions of the Manual on Uniform Traffic Control Devices (MUTCD). Safety campaign messages should be current and displayed for a limited time. The results of the survey revealed that safety campaign messages are currently displayed by a large majority of TMCs. Comparable to PSAs, display of safety campaign messages often leads to requests from other agencies to display non-traffic-related messages. Few TMCs reported on their experiences, lessons learned, concerns, and challenges with displaying traffic law or ordinance messages. There is some indication that law enforcement agencies favor the display of these types of messages. AMBER alert messages are displayed by 100% of the TMCs that responded to the survey. The majority of the TMCs reported very favorable or favorable public response to such messages, although 16% of the TMCs did not have sufficient information to comment on the public’s response. Many of the TMCs reported that they are not certain as to the most effective message con- tent for AMBER alert messages. Some TMCs recognized that the messages they posted were too long for drivers to read and recall; drivers tended to slow down to read the messages. Research results reported in the literature indicated that there is a hierarchy of CMS message elements and specific terms for each message element preferred by motorists. Most of the TMCs display AMBER alert messages that exceed current effective message design guidelines concerning the maximum number of units of information in a message. Therefore, it is expected that drivers will not be able to read and recall the messages, partic- ularly license plate numbers and 10-digit telephone numbers. Many TMCs encounter problems with getting complete and timely information from law enforcement agencies. Therefore, they are concerned about not being able to display accurate and timely information. 3