Start-Up Delays of Queued Vehicles


Gary Long

Document Type

Journal Article

Publication Date


Subject Area

operations - traffic, infrastructure - vehicle, infrastructure - bus/tram priority, infrastructure - traffic signals, mode - rail, mode - bike


Traffic signal priority systems, Traffic signal preemption, Traffic queuing, Start-up delay, Railroad grade crossings, Queue length, Preemption (Traffic signals), Mathematical models, Level crossings, Highway railroad grade crossings, Highway rail intersections, Grade crossings, Field studies, Data collection, Data acquisition, Clearance interval (Traffic signal cycle), Calibration, Calibrating


Start-up delays of queued vehicles have been studied in past research for evaluation of their impacts on saturation flow rates at downstream traffic signals. A more crucial issue, however, can be the effect of start-up delays of queued vehicles at upstream locations where queued vehicles back up from a traffic signal across a railroad crossing. The relationship between queue start-up delays and track clearance times is important in establishing traffic signal preemption settings. This paper presents models that are developed for prediction of the expected maximum time required to mobilize a queue of any length. The models consider not only the average delay times but also the limiting delay times that are expected to accommodate high proportions of queues. For design convenience, queue lengths are converted into distance from the leading edge of a queue rather than being described only by the number of vehicles in a queue. Because the variations in start-up times, in addition to the average times reported in the literature, are needed, two sets of field studies were used to obtain data for model calibration and to investigate various traffic operation effects. Other factors that might be expected to influence queue start-up times are also analyzed.