Intervehicle Spacings and Queue Characteristics

The lengths of queues of stopped vehicles are important in the design of storage bays for left- and right-turning traffic, for timing signal phases to clear queues, for simulation of traffic operations, and for other purposes. Queue lengths depend on the numbers and types of vehicles stored, the lengths of vehicles, and the spacings allowed by drivers between vehicles. The lengths of both trucks and passenger vehicles have been changing over the past two decades. On the basis of recent observations of queue component lengths, guidance was developed for estimating queue lengths for the current vehicle fleet. It was found that the 7.6 m (25 ft) per vehicle, including an intervehicle gap that is often assumed for design, and 0.915 m (3 ft) between vehicles used by CORSIM, are severe under-estimations for determining queue lengths. From observations measured at a variety of sites, intervehicle spacings were found to average 3.66 m (12 ft) and were not found to differ significantly at different sites. Models were devised for estimating average queue lengths and maximum lengths at a given probability.