Behavioral Traffic Safety Messaging on Variable Message Signs (2022)

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S-1   BTSCRP Project BTS-02 was initiated to develop a guide for the use of variable message signs (VMS) to deliver behavioral traffic safety (BTS) announcements, covering policy develop- ment through implementation. The Guide (Part 1) summarizes the fundamental human factors and traffic engineering principles that govern the design and display of all types of VMS messages, including BTS messages. In addition, the Guide incorporates the results of human factors testing done under this project to determine how characteristics unique to BTS messages influence motorist comprehension and performance when viewing such messages (Part 2). The project consisted of a thorough review of U.S. and international literature on the topic; collection, collation, and analysis of BTS messages that have been displayed on VMS across the country as well as the processes used to develop and display those messages; and a computer-based laboratory study designed to aid the research team in determining accept- able BTS message design parameters for display on VMS. The literature identified various ways in which BTS messaging can be targeted by utilizing a range of content and execution strategies. Such messaging must be credible, trustworthy, consistent, clear, persuasive, relevant, and appealing to the target audience. BTS messages can present a “gain” to be had by avoiding some behavior or by adopting a safer behavior (i.e., a gain-framed message) or a “loss” to be experienced by engaging in the undesirable behavior or failing to adopt the safer behavior (i.e., a loss-framed message). Messages can also be designed to appeal to driver emotions (i.e., fear-based or comfort-based emotional- appeal messages) or to simply present facts (nonemotional appeal messages). Males tend to be less influenced by loss-framed, fear-based emotional-appeal messages than do females. However, the use of humor in BTS messages appears to be somewhat more effective in influ- encing males to adopt safer driving behaviors. Yet, excessively humorous BTS messages may entertain those viewing the message without getting them to accept or understand the safety analogy being presented. Likewise, parodies and plays on words need to be familiar and liked by the target drivers to be effective. Messages that attempt to shame or label certain target drivers may not be effective, as those target drivers may not identify with those being mocked or insulted in the message. The driving public considers the display of BTS messages on VMS as worthwhile so long as it does not supersede other real-time traffic information that may be pertinent at that moment. However, studies to date are mixed as to the actual effects that BTS messages dis- played on VMS have on driving behavior. The effect of such messages is likely influenced by their content (including the behavior being targeted), as well as the design of the message itself. Drivers have limited time to detect, read, and process information on VMS. Poorly designed BTS messages increase information processing times, which can cause motorists S U M M A R Y Behavioral Traffic Safety Messaging on Variable Message Signs

S-2 Behavioral Traffic Safety Messaging on Variable Message Signs to slow down to allow more time to view and read the messages. Formatting issues, such as splitting message thoughts across different VMS phases, using unfamiliar abbreviations, or not starting new message thoughts on a new line can all contribute to difficulties in quickly reading and processing the VMS message. The FHWA has provided basic guidance regard- ing VMS message design in the Manual on Uniform Traffic Control Devices (MUTCD) and in a recent official ruling. The review of current practices regarding BTS message design and display on VMS revealed a range of approaches being taken. Some agencies only display national slogans during times of national campaigns, whereas others develop their own messages and display them on a more frequent basis. Multidisciplinary teams are sometimes used to develop messages, and some agencies have even held contests to allow the public to offer message ideas. A review of over 1,000 BTS messages that have been displayed on VMS across the country targeted a wide range of safety topics. Practices also varied in terms of the frequency of message displays, the duration of those displays, and the number of VMS used to display those messages. A review of the messages themselves found several that violated one or more principles of good VMS message design. The literature review and current practices demonstrated that several questions remain about what constitutes acceptable BTS message design criteria for display on VMS. For example, should BTS message length be limited to a maximum number of words? Is it accept- able to present more than one traffic safety topic in the VMS message (such as seat belt use and no cell phone use) or to combine a BTS message with a travel time or other general message? Is the incorporation of humor or pop culture references detrimental to BTS messages displayed on VMS? Although discouraged in the FHWA official ruling, several agencies have received positive feedback from the public as well as media coverage about humorous BTS messages they displayed on VMS in the past. To address these questions, a laptop-based laboratory study was developed and performed in Texas and Pennsylvania. The study presented subjects with BTS messages that varied in length; number and types of safety topics; and use of humor, wit, or pop culture references. Participants were asked to simultaneously perform a secondary task to mimic the cogni- tive load of driving. Study results indicated that a significant proportion of drivers did not understand the safety topics of BTS messages that included humor, wit, or pop culture references. More importantly, those drivers that did not understand the safety topic of BTS messages using humor, wit, or pop culture references performed significantly worse on the secondary control task while viewing the message than did those drivers who did under- stand the message. Study results also suggested that long BTS messages and BTS messages focusing on multiple traffic safety topics adversely affected driver secondary task perfor- mance and message comprehension. Based on the results of this research, it is recommended that agencies not attempt to incorporate humor or pop culture references into BTS messages that are displayed on VMS. Furthermore, it is recommended that BTS messages comply with the following principles of good VMS message design: • Messages should be limited to no more than two VMS phases. • Messages should be tailored to the types of safety issues that occur on the type of roadway where the VMS are located. • Messages should be limited to no more than 16 words total. If driver workload conditions are high, messages should be limited to no more than 11 words. • Messages should only target one specific safety topic. The message can target a specific safety topic on one phase and a general information statement (travel times, a generic

Summary S-3   “drive safely” statement, etc.) on a second phase so long as the total length of the message does not exceed the limits described above. • Messages should not include websites, domain names, hashtags, or electronic device appli- cation names. • Messages should not include telephone numbers. • Messages should not include scrolling lines, animation, flashing displays, punctuation, or graphic symbols or icons not included in the MUTCD. • Each phase of a two-phase VMS message should be understandable by itself regardless of the order in which the phases are viewed. • A BTS message thought or phrase should not be split between two VMS phases. • Each line of a message should be centered on VMS. • Each new thought in the message should start on a new line on VMS. • Nonstandard or texting abbreviations should not be used in a BTS message displayed on VMS. Although outside the scope of this study, the literature review indicated mixed results from other studies that have attempted to evaluate the effectiveness of BTS messages dis- played on VMS. It is recommended that additional studies be designed and conducted to determine which BTS topics are most effective at reducing undesirable driver behaviors and traffic crashes.