Understanding the Dynamics of Heavy Vehicle Interactions in Car-Following

Heavy vehicles and passenger cars differ in their maneuverability and acceleration capabilities. Heavy vehicles thus influence other traffic in a different manner than passenger vehicles, causing different levels of traffic instability. Increasing number and proportion of heavy vehicles in the traffic stream may result in quite different traffic flow characteristics. Over the last five decades many studies have investigated passenger car drivers’ car-following behavior. However, the existence of heavy vehicles in the traffic stream has not received the same attention. This paper investigates the different car-following behavior of drivers in congested heterogeneous traffic conditions. It specifically focuses on the existence of heavy vehicles in general traffic and their interaction with other vehicles. Four different combinations of passenger car and heavy vehicle were considered. These combinations include passenger car-following a passenger car, passenger car-following a heavy vehicle, heavy vehicle following a passenger car, and heavy vehicle following another heavy vehicle. A data set from a freeway in the United States was used to show the different car-following behavior of drivers for each combination. This study analyzes space and time headways, drivers’ reaction times, and vehicle accelerations. It also introduces different car-following thresholds for each car-following combination. It was found that the presence of heavy vehicles causes larger space and time headways, longer reaction time, and more robust car-following behavior. It also shows that the car-following thresholds are of the four combinations studies. The findings of this paper indicate that further research is required to develop a generalized car-following model that can be used when different vehicle types are in the traffic stream.