Effect of Vehicle Types on Capacity of Signalized Intersections: An Urban Street Performance Case Study Using Mini Buses as Main IPT in Libya

摘要

The effect of traffic factors on the capacity of an intersection approach is usually allowed by the use of weighting factors referred to as passenger car equivalents assigned to different vehicle categories. Signalized intersections performance is impeded mainly due to unavoidable impedance to traffic flow. Despite the fact that how well a signal is timed, maintained and adapted to instantaneous conditions some vehicles arrive during the red interval. These vehicles form a queue that needs to be dissipated during the ensuing green interval. The presence of large vehicles in the queue increases the headway as well as delay of other vehicles. This paper highlights strategies to improve the performance of signalized intersections in capital city of Tripoli in Libya based on limited data from a case study that reflects the impacts of different Intermediate Passenger Transport (IPT) like minibuses (MBs) on capacities of two signalized intersections. A regression analysis is generated to present estimates of mean headways of IPTs involving various categories of MBs, as well as passenger cars. Using these estimates optimal headways of Passenger Car Equivalents (PCEs) is calculated. These calculations reveal that the impacts of MBs need to be given special consideration when analyzing the capacity of signalized intersections. Results show that a long MB (LMB) in through traffic is equivalent to 1.81 passenger cars and a small MB (SMB) is equivalent to 1.52 passenger cars. This indicates that such long headways diminish the signalized intersections performance by reducing its capacity with consequent increased urban congestion.