UNDERSTANDING THE NEED FOR HEAVY VEHICLE RESEARCH ON TRAFFIC FLOW

The different performance of heavy vehicles in traffic flow is the initiator of some traffic flow problems like decreasing the capacity and increasing delays. The different behaviour is the result of different characteristics and capability of heavy vehicles. The effect of these differences is more apparent since the number of heavy vehicles and their proportion in traffic stream are increasing in many countries. Notwithstanding the increasing proportion and the impacts of heavy vehicle on traffic flow, little is known about their microscopic. This paper aims to show the different microscopic behaviour of heavy vehicle and passenger car drivers in the traffic stream. A real data set was used to assess the car following and lane changing behaviour of the vehicles as the two fundamental microscopic vehicular movements. It was found that the behaviour of heavy vehicles differs from that of passenger cars. Heavy vehicle drivers keep a larger space headway and longer time headway when following another vehicle. They also seek for a larger gap to execute a lane changing manoeuvre. The acceleration and deceleration rates applied by heavy vehicles were also lower than passenger cars’. These differences assist in explaining the negative impacts of heavy vehicles on traffic flow.