Methodology for Evaluating Effectiveness of Traffic-Responsive Systems on Intersection Congestion and Traffic Safety

In 1986, the city of Milwaukee applied for and received approval for a hazard elimination grant to reduce congestion and traffic accidents at the intersection of two major and one minor arterial on the northwest side of the city. The intersection complex had several approaches at or above capacity, associated long queues of traffic, and an annual traffic-accident rate of more than three per 1 million entering vehicles. The hazard elimination grant called for the installation of a closed-loop, traffic-responsive signal system to manage the congestion and to reduce traffic accidents. The intersection complex presented many constraints on traffic-responsive operation, the most critical of which was that the three arterials formed a signal triangle (three separate signalized intersections) with intersection spacing as short as 27.4m (90 ft). FHWA realized the unusual nature of this project and designated it an experimental project in 1987. The development of the traffic-responsive signal system within the many constraints of the location is described. After a lengthy process, the traffic-responsive system became operational in September 1993 and proved to be an operational success by reducing the length of traffic queues. After extensive data collection, an analysis and evaluation confirmed that the traffic-responsive signal system reduced the occupancy levels per vehicle on the system detectors and reduced the incidence of congestion-related traffic accidents.