Detecting erroneous loop detector data in a freeway traffic management system.

The reliability of detector data is critical to efficient and effective transportation management through a freeway traffic management system (FTMS). An error detection algorithm is developed for the FTMS in the Seattle area. Although the current system includes some rudimentary data error checking, many detector failures and data errors remain undetected. The new algorithm uses volume-to-occupancy ratios to test 20-sec volume and occupancy data. The algorithm was tested by changing detector amplifier settings and producing manual actuations in the field to simulate detector malfunction states. The algorithm produced few false alarms when tested under simulated conditions. It reliably identified short-pulse (hanging-off) malfunctions during the simulation tests. The algorithm provides a relatively simple and affordable improvement to the Washington State Department of Transportation's existing freeway data screening methods.