Health of California’s Loop Detector System

The California Department of Transportation (Caltrans) freeway sensor network has two components: the sensor system of 25,000 inductive loop sensors grouped into 8,000 vehicle detector stations (VDS) and covering 30,500 freeway direction-miles; and the communication network over which the sensor measurements are transported to Caltrans Traffic Management Centers. The sensor network is virtually the only source of data for use in traffic operations, performance measurement, planning and traveler information. However, the value of these data is greatly reduced by the poor reliability of the sensor network: On a typical day in 2005, only 60 percent of the statewide sensor network provided reliable measurements. This is the report of an empirical study of the reliability of the sensor network based on two data sets.