Effects of Adaptive Cruise Control System on Traffic Flow and Safety Considering Various Combinations of Front Truck and Rear Passenger Car Situations

Existing studies on the heterogeneity in traffic flow have considered either conventional car–truck or conventional vehicle–automated vehicle combinations. Nevertheless, these assumptions are not realistic as there will be possible combinations of cars–trucks and conventional–automated vehicles in the future. This study aims to investigate heterogeneous traffic flow with or without an adaptive cruise control (ACC) system for the pair of a front truck and a rear passenger car. Vissim microscopic traffic simulation software and the HighD dataset were applied. The major findings include the following. (1) The greater the penetration rate of ACC vehicles in the same speed interval, the smaller the space headway of the rear car. (2) Both conventional and ACC cars accelerate or decelerate frequently when their speeds exceed that of the front truck in the car-following state. In the free-flow state, a conventional car keeps a constant speed or accelerates, while an ACC car mainly adopts an acceleration strategy. (3) The variation of speed differences and space headways is smallest when both the front truck and rear car have ACC. (4) The probability of conflicts between the front truck and rear car pair decreases with the increase of market penetration of ACC vehicles. Compared to conventional cars, the rear car equipped with ACC exhibits a lower probability of conflicts. Statistical tests further confirmed the significant differences between any two of the four combinations based on the ACC equipment.