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45 The primary purpose of this synthesis was to present the state of the practice of state departments of transportation (DOTs) and agencies operating toll roads that display messages on changeable message signs (CMSs) during non-incident/ non-roadwork periods as an alternative to leaving the signs blank. A secondary objective was to present the state of the practice of displaying AMBER alert messages. Information for this synthesis was obtained from an extensive literature review and a survey of transportation agencies that operate CMSs. Responses were received from 40 state DOTs and 6 toll road agencies with a total of 100 traffic management centers (TMCs). The TMCs operated 3,023 CMSs in urban areas and 821 CMSs in rural areas. Forty-two TMCs oper- ated CMSs only in urban areas, 8 in rural areas, and 50 in both urban and rural areas. The intent of the literature review was to provide a brief summary of basic principles for effective CMS message de- sign and display. The results of the survey were compiled and presented to establish the types and extent of CMS messages displayed during non-incident/non-roadwork periods. In addition, experiences, lessons learned, concerns, and chal- lenges for displaying CMS messages during non-incident/ non-roadwork periods were summarized. CURRENT APPLICATIONS OF CHANGEABLE MESSAGE SIGNS The eight most common applications of CMSs based on the percentage of the TMCs are as follows: AMBER alert (100%), incidents (99%), roadwork (98%), floods (85%), advance notice of upcoming roadwork (84%), ice on road (83%), snow on road (77%), and planned special events (73%). MESSAGES DURING NON-INCIDENT/ NON-ROADWORK PERIODS Blank Changeable Message Signs versus Display of Messages Since 1997, there has been an increase in the number of agen- cies that display messages on CMSs rather than leave the signs blank during non-incident/non-roadwork periods. Of the 100 TMCs that responded to the survey, 55% leave the CMSs blank, whereas 45% display messages. There is a di- vision among the TMCs over whether it is best to leave the CMS blank during non-incident/non-roadwork periods or to regularly display messages. The vast majority (more than 90%) in each group do not intend to change their current policy. The issue as to whether CMSs should be blank or contain a message during non-incident/non-roadwork periods is complicated by reported contrasting public reaction. The California DOT (Caltrans) in Los Angeles received adverse public reaction to public service messages. There was a belief among the traffic operations professionals that such use led to a public disregard of CMS messages, thus making the signs less effective when traffic operational messages were dis- played. The practice was discontinued, and the CMSs are now used only for travel time and for messages pertaining to unusual real-time traffic flow conditions. In contrast, the New York DOT received adverse public reaction because of delay in posting messages after the CMSs were installed during the construction of the INFORM Proj- ect on Long Island. This prompted the agency to adopt a pol- icy of displaying some type of message on the freeway CMSs at all times. Blank Changeable Message Signs Several of the 55 TMCs that leave the CMSs blank reported that they did not receive any adverse comments from the public and believed the process to be satisfactory. Several TMCs believed that by leaving the CMSs blank, drivers pay more attention to the message when one is displayed and so the CMSs are thus more effective. There was some fear that frequent display of non-essential messages will result in drivers ignoring important messages. The reported public response to blank CMSs among the TMCs ranged between very favorable to neutral, although a high percentage of the TMCs (37%) did not have sufficient information to comment on the publicâs response. The pri- mary concerns and challenges to leaving the CMSs blank centered on (1) ways to convince motorists that the signs are functional, and (2) pressures from administrators/upper-level management and others to display messages rather than leav- ing the CMSs blank. Some TMCs illuminate one or more pixels as a means of informing drivers that the CMSs are operable. However, the effectiveness of this process of informing drivers is not known. CHAPTER FIVE CONCLUSIONS
The types of messages that are displayed during non- incident/non-roadwork periods as an alternative to leaving the CMSs blank are travel time, congestion, speed, safety campaign, PSAs, and/or traffic law or ordinance messages. Fifty-one percent of the 45 TMCs that regularly or periodi- cally display messages during non-incident/non-roadwork periods reported a very favorable (22%) or favorable (29%) public response. Several of these TMCs currently display travel-time information. Comparable to TMCs with blank CMSs, 27% reported that they had insufficient information to comment on the publicâs response. The primary concerns expressed and challenges noted with displaying the afore- mentioned types of messages (excluding travel time) were (1) uncertainty as to the best type of messages that should be displayed, and (2) when displayed, the messages are not usu- ally changed often enough. The experiences and lessons learned by the TMCs displaying messages other than travel time were mixed. TMCs reported that some motorists prefer messages, some do not. There is concern by some that display of repetitive infor- mation during non-incident/non-roadwork periods will re- sult in many drivers failing to read the CMS when important information is given owing to the psychological visual change detection phenomenon referred to as change blind- ness, in which a person viewing a visual scene apparently fails to detect large changes in the scene. Change blindness can result in a credibility problem. The issue of change blindness has caused some agencies to use or consider using flashing beacons on CMSs to attract the attention of motorists when incident, roadwork, or other important messages are displayed, even though CMSs, particularly light-emitting signs, are designed to attract the attention of motorists. Whether the practice of using flashing beacons does im- prove motorist attention to the CMS message is not known at this time. To date, no research has been conducted to eval- uate the effects of change blindness with respect to CMS messages. Travel Time There is a trend toward increased use of travel-time messages as an alternative to leaving CMSs blank during non-incident/ non-roadwork periods. Travel time is currently displayed by 30% of the TMCs (representing 20 different agencies). A few other TMCs reported that they would display travel time in lieu of blank CMSs if they had the necessary infra- structure and/or software. A majority (60%) of the reported public response to travel-time messages was very favorable or favorable. Thirty percent of the TMCs display travel time during the peak period and 23% display travel time during the off-peak period. All of the TMCs are in urban areas. Travel time is generally not displayed on all of the system CMSs; some CMS locations are not conducive to displaying travel time. 46 Three travel-time message formats are currently being used by TMCs nationally. These are travel time to 1. A single destination, 2. Two destinations, and 3. A single destination by means of two alternative routes. A review of the travel-time messages displayed indicated that there is little uniformity with respect to message format among the TMCs. Also, many of the travel-time messages currently being displayed 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 messages, verifying concerns regarding information overload with these types of messages. TMCs are experiencing difficulty in accurately measuring and displaying travel times during rapidly deteriorating free- way operating conditions, during the transition from off-peak to peak periods, or when incidents occur. The travel time experienced by drivers can be longer than that shown on the CMS. The problem occurs because travel time is based (at best) on recent data; predictive models do not currently exist. Accuracy is also adversely affected because of poor reliability of detectors, loss of communications, or inadequate spacing of detectors. Thus, credibility can be adversely affected. There is inconsistency among the TMCs regarding the fre- quency at which travel times are updated on the CMSs, although the update interval for 77% of the TMCs is within 5 min. Seventeen percent update every minute, 20% every 2 min, 27% every 3 min, and 13% every 5 min. Meanwhile, 13% of the TMCs reported changing the travel times when traf- fic conditions change. Interestingly, 3% of the TMCs update every 10 min, 3% every 15 min, and 3% update every 30 min. TMCs that display travel times manually (i.e., an operator physically calculates the travel times on the routes and/or posts the message on the CMS) encounter difficulty in changing the messages when traffic conditions change. Displaying travel time manually is difficult and often results in inaccurate in- formation being displayed on the CMSs. Several TMCs in urban areas do not currently display travel time because of inadequate infrastructure or software to accurately compute travel time. TMCs in rural areas gen- erally do not have the infrastructure or the need (i.e., no con- gestion) to display travel time. The cost to implement the capability (i.e., additional in- frastructure and/or software) to display travel-time messages varied widely among TMCs, and was reported to be between $30,000 and $250,000. The differences were primarily the result of the amount of new infrastructure and/or software needed to implement travel-time messages.
47 Congestion, Speed, Public Service Announcement, Safety Campaign, and Traffic Law or Ordinance Messages General The types of messages other than travel time that the TMCs displayed during non-incident/non-roadwork periods rather than leaving the CMSs blank are congestion (35%), speed (15%), public service announcement (PSA) (30%), safety campaign (83%), and traffic law or ordinance (36%). How- ever, only a small percentage of TMCs regularly display one or more of these non-incident/non-roadwork messages. The percentage of TMCs that regularly display messages is as fol- lows: congestion (12%), speed (2%), PSA (3%), safety cam- paign (8%), and traffic law or ordinance (2%) messages. The other TMCs display the messages often, occasionally, or rarely. Administrative/upper-management preference, TMC manager/supervisor preference, or both, was cited as the basis for making the decision to display specific types of messages for the following percentages of TMCs: congestion (62%), speed (100%), PSAs (93%), safety campaign (99%), and traf- fic law or ordinance (92%). Very little, if any, objective data from focus group or other research studies were used in the decision-making process. A significant percentage of the TMCs did not know the publicâs attitude about the messages that are displayed dur- ing non-incident/non-roadwork periods. About one-half of the TMCs that display congestion messages reported very favorable or favorable public response, 7% that display speed reported favorable public response, 17% reported favorable response to PSAs, 12% reported favorable response to safety campaign messages, and 12% reported very favorable/ favorable response to traffic law or ordinance messages. Congestion Messages Research results reported in the literature point to the diffi- culty in designing congestion messages that motorists will be able to understand. The major problem is because it is dif- ficult to find adequate words for CMS messages because of the large continuum of congested traffic states during the peak period. The problem is compounded during the peak period when incidents occur. Some of the potential traffic state mes- sages such as CONGESTION AHEAD, NORMAL TRAFFIC, or EXPECT DELAY do not offer meaningful or useful infor- mation to travelers. Thus, these messages can adversely affect credibility. However, messages that provide the begin- ning and end of traffic congestion are helpful to the motorist in assessing the degree of congestion and the location where the motorist can reenter the freeway should he/she decide to leave the freeway and detour around the congestion. Some of the TMCs surveyed also expressed difficulty in understanding the differences between the various levels of congestion (e.g., heavy, moderate, and light). Several TMCs emphasized the importance of accurate congestion messages. Experiences and lessons learned with displaying congestion messages, however, indicated that it is difficult to post accu- rate messages because traffic conditions change rapidly. That is, the locations and limits of congestion change too quickly to keep the information current. Therefore, one challenge of TMCs that display congestion messages is ensuring that accurate information is displayed at all times. Speed Messages Research results reported in the literature indicated that speed messages on CMSs are not ranked high among the informa- tion needs of motorists during incidents or roadwork. Also, some motorists may misinterpret speed messages and some may react in adverse ways. The results in the literature indi- cate that travel speed should not be used as part of an incident or roadwork CMS message. The major concern and challenge expressed by TMCs with displaying speed during non-incident/non-roadwork periods was maintaining credibility. It is difficult to keep the speed message synchronized with traffic flow and weather condi- tions. Also, it is difficult to convey that the speed displayed is an average, and that the speed may differ along the freeway. PSAs The display of general public information or other non- essential information is discouraged by FHWA. There are strong arguments against displaying PSAs on CMSs, includ- ing adverse public response, credibility, and the possibility of change blindnessâthe failure to see the CMS message changeâwhen important messages are displayed. TMCs that display PSAs (1) emphasized that the PSAs must be relevant and must convey a clear message, (2) rec- ommended that PSAs should not be displayed during the peak direction of traffic flow and that the duration of display should be short, and (3) emphasized that the TMC should coordinate posting PSAs with other agencies. Concerns and challenges expressed by the TMCs included the lack of clear guidance as to what messages constitute PSAs and how to display consis- tent messages. In addition, concern was expressed about re- quests to display non-traffic-related messages from agencies not related to transportation once PSAs are posted. Safety Campaign Messages The display of safety messages associated with a safety cam- paign is allowable under MUTCD provisions. Safety campaign messages should be current and displayed for a limited time. Of all the non-incident/non-roadwork messages included in the survey, the most comments regarding experiences and
lessons learned were with displaying safety campaign mes- sages. The responses from the TMCs focused on the concept that the safety campaign messages (1) resulted in requests from agencies to display other non-traffic-related messages, (2) created uncertainty about the effectiveness of the messages, (3) should be displayed for short periods of time, and (4) gen- erated negative feedback. Concerns and challenges noted by TMC personnel about these messages were as follows: ⢠Insufficient research is available to determine whether the messages are beneficial, ⢠Guidance is needed on the appropriate time to display the messages, ⢠Guidance is needed to establish consistency and credi- bility for these types of messages when used, and ⢠Policies and procedures on how to handle requests for other types of non-traffic-related messages are needed, given that safety campaign messages are displayed. Traffic Law or Ordinance Messages Only a few TMCs reported on their experiences and lessons learned with displaying traffic law or ordinance messages (e.g., SLOW DOWN OR MOVE OVER FOR EMERGENCY VEHICLES). The TMCs that responded reported positive feedback from law enforcement agencies and cautioned about overuse and problems with displaying these messages at in- appropriate times. The main concern and challenge reported dealt with making sure that the messages were consistently designed and applied. AMBER ALERT 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. The mes- sage elements and terms from one scenario follow in order of importance: 1. Situation descriptor: AMBER ALERT, 2. Vehicle descriptor: BLUE MAZDA 05 PICKUP, 3. License plate number: LIC # SR8-493, 4. Telephone number: CALL 511, and 5. Tune to radio action descriptor (highway advisory radio or local radio station): TUNE TO 530 AM. The results of the survey revealed that all of the 100 TMCs that responded to the questionnaire display AMBER alert messages. The most frequently displayed situation descriptors were AMBER ALERT (39%), CHILD ABDUCTION (18%), and CHILD AMBER ALERT (12%). Research results from the literature review indicated the following: (1) a license plate number is equivalent to more than three units of information, and (2) a 10-digit telephone number is equivalent to more than three units of information. 48 Thus, a message with a license plate number will exceed cur- rent effective message design guidelines that specify a maxi- mum of four units of information in a message. Likewise, a message with a 10-digit telephone number will exceed current effective message design guidelines. Therefore, drivers will not be able to read and recall AMBER alert messages that contain a license plate number, 10-digit telephone number, or both. A review of message content revealed that 88% of the TMCs include a license plate number, 10-digit telephone number, or both and, therefore, exceed the recommended maximum of four units of information. It is expected that most drivers will not be able to read and recall the informa- tion contained in these AMBER alert messages. Seventy-five percent of the TMCs stated that they received very favorable or favorable responses from the public for the messages, whereas 16% indicated that they did not have suf- ficient information to comment on the publicâs response. Many of the TMCs reported positive experiences with AMBER alert messages. Some TMCs highlighted the impor- tance of obtaining complete information from the law enforce- ment agencies as quickly as possible to ensure that accurate information is displayed in a timely manner. However, many TMCs encounter problems with getting complete and timely information from the law enforcement agencies. Many TMCs expressed uncertainty as to the correct mes- sage content and format for AMBER alert messages. Some TMCs recognized that the messages that they posted were too long for drivers to read and recall. Some drivers tended to slow to read the messages. Some TMCs emphasized the im- portance of including the vehicle license plate number in the CMS message (unless it is reported by means of radio or from a telephone contact). CHANGEABLE MESSAGE SIGN MESSAGE DESIGN AND DISPLAY POLICIES AND GUIDELINES Seventy-five percent of the TMCs reported that they have a written policy or guidelines regarding the design and display of CMS messages. Sixty-four percent have a written policy or guidelines to assist CMS operators in making decisions as to the priority of messages when two or more events occur on the freeway (e.g., incident and planned special event). SUGGESTIONS AND FURTHER RESEARCH NEEDED TO ADVANCE THE STATE OF THE PRACTICE Based on the results of the literature review and information gathered from the survey, it is suggested that the following actions be taken or research conducted relative to CMS mes- sages during non-incident/non-roadwork periods to assist TMCs in more effective operation of CMSs.
49 General Procedures should be developed to ensure that existing CMS message design and display manuals are available to TMCs. Blank Changeable Message Signs versus Display of Messages Objective data are needed to assist TMCs in their decision to either leave the CMSs blank or to display messages. Blank Changeable Message Signs Research is needed to determine the most effective ways to inform drivers that the CMSs are functional when no mes- sage is displayed. Public information campaigns and driver understanding of illuminating one or more pixels should be considered in the evaluations. Display of Messages Research should be conducted to evaluate the effects of change blindness when messages are regularly or periodi- cally displayed and the need and effectiveness of flashing beacons mounted on CMSs should be evaluated. Travel Time Predictive computer algorithms are needed to accurately dis- play travel times, particularly during rapidly deteriorating traffic conditions such as the transition from off-peak to peak traffic flows and during the occurrence of incidents. Studies should be conducted to provide guidance to TMCs regarding the (1) best content and format for travel-time messages to enhance uniformity among TMCs; (2) frequency that travel times should be updated during congested periods; and (3) the most effective detector spacing for various levels of traffic operations. Congestion, Speed, Public Safety Announcements, Safety Campaign, and Traffic Law or Ordinance Messages General The need, benefit, driver understanding, and effectiveness of various congestion, speed, PSA, safety campaign, and traffic law or ordinance messages should be evaluated. Guidance is needed to establish message consistency, uni- formity, and credibility when these types of messages are used. Guidelines are needed to assist TMCs in distinguishing the difference between PSAs and safety campaign messages. Computer algorithms and guidelines for detector spacing are needed to ensure that the limit of congestion is accurately displayed at all times. If effective computer algorithms exist, efforts should be taken to share the technology with other TMCs. PSA Messages Guidance is needed regarding the specific message content that constitute PSAs, and procedures for displaying consis- tent messages. Policies and procedures are needed to assist TMCs in re- sponding to requests for other types of non-traffic-related messages once PSAs are displayed. Safety Campaign Messages Guidance is needed on the appropriate times to display safety campaign messages. Policies and procedures are needed to assist TMCs in re- sponding to requests for other types of non-traffic-related messages once safety campaign messages are displayed. AMBER Alert Messages Guidance is needed on the most effective message content and format for AMBER alert messages, and display duration for AMBER alert messages. Guidance is needed regarding the display of license plate and telephone numbers given that their use results in a mes- sage exceeding the recommended maximum number of units of information. Procedures should be recommended to TMCs to assist them in improving the accuracy and timeliness of informa- tion from law enforcement agencies. Procedures should be recommended to TMCs to assist them in improving notification from law enforcement agen- cies when AMBER alert is no longer necessary.
