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...