Khaled A. Al-Sahili and William C. Taylor

ABSTRACT

            With the emergence of Intelligent Transportation System technologies, there has been a renewed interest in the study of bus priority signals (BPS). However, at present there is no convenient method of conducting these studies since existing models are not capable of simulating various BPS strategies and then restoring the original signal settings after bus preemption is awarded.

            The NETSIM graphic animation feature was used in this study to detect the bus arrival, award preemption, and the signal timing plan was then restored to the original signal setting manually. The green extension / red truncation with and without compensation, the skip phase with and without compensation, and the conditional preemption plans were evaluated. The most appropriate preemption strategy at each intersection along the study corridor in Ann Arbor, Michigan was established. The sensitivity of BPS was tested under different network traffic volumes and different main to cross street traffic ratios for an isolated intersection. The signal preemption for carpools and the impact of random traffic fluctuation were also tested.

            It was found that maintaining progression is critical under heavy traffic conditions. The traffic volume criteria that warrant signal preemption were established. There appears to be advantages to providing carpools with preemption capability up to between 5 and 10% of the main street traffic volume. In any corridor there is likely to be random fluctuations in the traffic demand, and this variation may be as large as the measured effect of BPS.