Changeable Message Sign


A changeable message sign (CMS) is primarily used to give motorists real-time traffic safety and guidance information about planned and unplanned events that significantly impact traffic on the State's highway system. At times, traffic congestion or America's Missing: Broadcast Emergency Response (AMBER) Alert information is displayed on CMS.

Changeable Message Signs are also used to inform motorists of unexpected conditions and should not be used until such conditions warrant their use. Caltrans recognizes the benefits of properly using CMS to manage traffic and inform motorists. Caltrans is also aware that improper use of CMS can adversely affect travel on our highways. In areas where both permanent and portable signs are used, it is important that no conflicting messages are displayed. CMS should be used as a supplement for conventional traffic control devices and not as a substitute.

CMS Resources