Evaluation of a Freeway Work-zone Advance Speed Advisory System

The Quixote IntelliZone is a work zone speed advisory system. Three mobile count units (which can measure flow, speed, and density) are placed in each lane where queues could form due to the construction zone. Two variable message signs (VMS units) are placed approximately two miles and five miles upstream from the detectors. One mobile command unit is placed between the detectors and the VMS units. The command units take information from the sensors on average speed and send signals to the VMS units to indicate an appropriate message, using either line-of-sight or cellular communication. Under free flow conditions the message would provide a standard warning of the construction zone. When queues cause significant speed reductions the VMS units can warn of the reduced speed ahead by displaying the downstream speed, based upon a rolling 3- to 5-minute average. The study site for the evaluation of the IntelliZone system was Eastbound I-70 near Wentzville Pkwy. and Pearce Blvd. which is just west of St. Louis, Missouri. One important conclusion from the study was that there was some evidence that the IntelliZone system did positively affect speeds of vehicles during congested periods.