California Partners for Advanced Transportation Technology

District 10 of the California Department of Transportation (Caltrans) encompasses an area of seasonal fog and dust-related visibility problems that have been the cause of numerous multi-car traffic collisions, many fatal. In 1990, motivated by the expansion of State Route 120 (SR 120) connecting Interstate Highway 5 (I-5) and State Route 99 (SR 99), Caltrans proposed a sophisticated multi-sensor automated warning system as a means for reducing incidents in this high-traffic area. This proposal, and the significant development effort that followed, culminated in the implementation of Phase 1 of the Caltrans Automated Warning System, or “CAWS”, which entered service in November 1996. The system includes 36 traffic speed monitoring sites, 9complete remote meteorological stations including visibility detectors, and nine changeable message signs for warning drivers. The system is controlled by a network of three computers in the District 10 Transportation Management Center (TMC), running specialized software developed by Caltrans Operations. This system is believed to be one of the most advanced of its kind in the world.