Headway Compression during Queue Discharge at Signalized Intersections

Abstract

Current methodologies for estimation of intersection capacity are based mainly on the concept of saturation flow. Saturation flow is the steady maximum queue discharge rate after the green light is turned on. According to the U.S. Highway Capacity Manual, this steady maximum rate is generally reached after the fourth queuing vehicle is discharged. Two recent studies conducted in Hawaii and Taiwan, however, have found that queue discharge headways tend to undergo compression for a considerable time as more vehicles in the same queue are discharged. Consequently, queue discharge rates often kept rising even after the 15th vehicle has entered the intersection. If this queue discharge characteristic is common in the United States, then there is a need to assess the implications of con-tinued use of the traditional concept of saturation flow rate for capacity analysis of signalized intersections. To provide insight into this potential problem, this study examines the queue discharge characteristics at three intersections on Long Island, New York. The queue discharge characteristics at all three intersections were found to be similar to those observed in Taiwan and Hawaii.