A Safety Service Patrol Case Study in the Use of Vehicle-Mounted Message Boards to Promote Move-Over Behavior

Move over, slow down laws have been enacted in all 50 U.S. states, plus the District of Columbia and Puerto Rico, to make safety service patrol (SSP) personnel safer. Emergency vehicle lighting and markings are treatments aimed at improving driver compliance. Portable changeable message signs (CMSs) and vehicle-mounted arrow boards are typically used by SSP vehicles to enhance visibility and provide advance warning. This research sought to understand the effect that vehicle-mounted message and arrow boards have on driver move-over behavior by observing motorists approaching a staged roadside event. By altering the text and graphic message on the SSP vehicle signboard, changes in driver behavior could be observed, and subsequent analysis provided insights into the most promising practices. More than 4,000 vehicles passed the roadside incident, 1,536 of which were in the lane adjacent to the response vehicle, creating a requirement to move over. It was determined that the use of an arrow pointing to the left (24%) and text messages such as “Caution, Slow Down” (9%) and “Move Over, It’s The Law” (8%), were all more effective than the four-dots displayed in the typical vehicle-mounted CMS caution mode. Procedures for SSP operators should include options for the use of text and arrow sign displays for shoulder events, in addition to the typical caution modes. Furthermore, FHWA’s Manual on Uniform Traffic Control Devices might clarify the language for this particular use case, since traffic incidents are emergency road user occurrences where responders do not have the resources available of work zones.