impacts of lead vehicle class on driver’s following behaviour

car-following models play a key role in the traffic microscopic simulations. they have a significant impact on accuracy of replicating real world traffic behaviour. over the last five decades many studies have investigated passenger car drivers’ car-following behaviour. however, the existence of heavy vehicles in the traffic stream has not received the same attention while it may result in quite different traffic flow characteristics. this neglect could become very crucial with attention to the increasing number and proportion of heavy vehicles in the traffic stream. this paper investigates the different car-following behaviour of drivers in congested traffic conditions while following different class of vehicles (passenger car and heavy vehicle). a real world data set obtained from a freeway in usa was used to analyse space and time headways, driver’s reaction times and vehicle accelerations. it was showed that drivers keep longer headways in front, need longer time to react and follow the lead vehicle with less speed changes when the leader is a heavy vehicle compared to the time in which the leader is a passenger car. the findings indicate that further study is required to develop a generalised car-following model in order to capture these fundamental differences.