California Department of Transportation
Coronado Bridge Carquinez Bridge San Francisco/Oakland Bay Bridge Richmond San Rafael Bridge

Materials Engineering and Testing Services

Office of Roadway Materials Testing
Electrical Testing Branch


Program Overview

Changeable message signs (CMS’s) play increasingly important roles in improved operations, highway safety, and use of existing facilities. CMS’s have been used to provide advanced warning of major highway incidents and route diversion information. The use of CMS’s for work zones has been very effective in alerting motorists of downstream lane closures during nighttime operations.

CMS’s are full matrix display signs capable of displaying a variety of character heights and up to three lines of text. CMS’s display text messages in all capital letters, while the number of characters per line varies from 9 to 16, depending on need. Some situations require messages that are longer than a sign is capable of displaying at one time. These situations require sequenced messages (also known as extended mode messages), which means the message is spilt into two or more parts that are sequenced on the CMS.

Properly written specifications is Caltrans safeguard to ensure quality CMS’s are being purchased and used. The Electrical Testing Branch exercises 100% quality assurance testing at the manufacturer’s facilities. This verifies all CMS are functioning properly before delivery to the warehouse and installation in the field.


TEES Chapter 8 - Specifications For Changeable Message Sign System
Quality Assurance and Testing Guideline (PDF)
Post Installation Start-Up Service (PDF)
Qualified Products List (QPL) LED Pixel Matrix Modules list

Contact:, Transportation Engineer (Electrical)
(916) 653-3068

Contact for technical issue:, , Transportation Engineer (Electrical)
(916) 227-6495