An Evaluation of the Consequences and Effectiveness of Using Highway Changeable Message Signs for Safety Campaigns

Changeable Message Signs (CMSs), which are also called dynamic or variable message signs, are programmable signs used on highways worldwide to provide drivers with real-time information, such as traffic updates, roadwork warnings, and other traffic and safety-related information. CMSs allow motorists to take immediate action in response to information—to slow down or change routes, for example, which leads to safer driving conditions and less congestion. More recently, in California and throughout the U.S., CMSs have been used as part of public campaigns to promote roadway safety by posting messages that encourage drivers to use seat belts, not to drink and drive, and not to speed. These messages are typically displayed on CMSs during designated time periods that coincide with broader safety campaigns.This study was sponsored by the California Department of Transportation (Caltrans) to examine the following questions about displaying safety campaign messages on CMSs: (1) How attentive is the public to messages displayed on CMSs? (2) Is there a public safety benefit from displaying safety campaign messages on CMSs? (3) Do travelers slow down to read CMS messages and, as a result, interrupt traffic flow? This study employed a range of sources to evaluate these questions including: (1) a review of the relevant published literature on CMSs; (2) interviews with experts and stakeholders; (3) focus groups with California drivers; (3) statewide telephone and intercept surveys; (4) analysis of speed data from California highway loop detectors (taken from the PeMS database). The results suggest the following: (1) driver inattention to CMS messages does not appear to be a significant problem among California drivers; (2) positive safety effects may be derived from public safety campaigns messages on CMSs when the public is familiar with and understands the messages displayed; and (3) a small percentage of drivers may slow in the presence of safety campaign messages displayed on CMSs, but this does not appear to cause disruptions in the overall flow of traffic.