A safety spacing policy and its impact on highway traffic flow

This paper proposes a Safety Spacing Policy (SSP) that can ensure safe operation while at the same time improving traffic flow for Adaptive Cruise Control (ACC) system. The proposed SSP, a nonlinear function of vehicle velocity, uses both the information of vehicle´s state and braking capacity to adjust the position and velocity of the controlled vehicle. String stability, traffic flow stability and traffic capacity of the proposed policy are analyzed. The SSP can ensure vehicle string stability and it can also yield stable traffic flow and higher traffic capacity that are superior to the traditional Constant Time Gap (CTG) system. Especially in the high-density traffic conditions, the proposed new policy can provide higher traffic capacity to relief traffic congestion while the CTG policy fails to do so. In addition, traffic simulations show that SSP can ensure vehicle safety in hard brake and acceleration scenarios. The proposed new spacing policy is a promising alternative to the traditional CTG policy.