An investigation of the variability of start-up lost times and departure headways at signalized intersections in urban areas

Abstract

The number of waiting vehicles that can cross a signalized intersection in a given period of time depends basically on how soon the vehicles begin to move after the signal changes to green and how fast each individual vehicle in the queue reacts to the acceleration of the vehicle immediately ahead. This process continues until all cars in the queue are progressing or have progressed through the intersection. The dissipation of a queue of vehicles after the signal changes to green depends on the reaction time and acceleration characteristics of each individual driver and vehicle. Thus, the total time for a group of vehicles to pass through a signalized intersection can vary considerably depending on the alertness and aggressiveness of the individual drivers, their familiarity with the intersection in question, and the acceleration characteristics of the vehicles, which the drivers control. This paper attempts to give a new viewpoint on the calculation of the departure headways and of the start-up lost times at signalized intersections in urban areas. Departure headways are the time intervals between vehicles departing from the signalized intersection; start-up lost time is defined as the excess time that is needed for a number of vehicles to pass through the signalized intersection compared with that would be needed if the signal did not exist. Data was collected for a considerable number of signalized intersection approaches in the Athens, Greece area. Data collection through contemporary techniques included lane width, lane position (inside lane versus outside lane, etc.), time of day (morning-peak versus afternoon-peak) and the posted speed limit (48km/h, 56km/h, 64km/h, or 72km/h). Statistical analyses were performedin order to define the elements of the approaches that influence the time headway values. It was found that the lane width and the lane position (for the ranges that were studied) did not have a significant effect on the lost times and the vehicle headways. The combined effect of time of day and direction had in contrast a significant effect on the lost time and the vehicle headways. The combined effect of the posted speed limit and the area within the city had a significant effect for the lost time when the speed limit was, for example, 45 mph in an open area and for the vehicle headways when the speed limit was 30 mph in a business area. The final results can be useful for a more effective modeling of the traffic signal calculations performed in all usual traffic engineering techniques. © 2010 WIT Press.