Dynamic areas strategy design for variable speed limiting at fixed freeway bottlenecks

Abstract

Variable speed limit (VSL) control of freeway traffic is expected to improve traffic mobility and safety, especially at bottlenecks. However, unstable input flow makes the VSL less effective when the number of speed limit areas is fixed. In this paper, we first analyze the speed limit effect of the fixed speed limit area, then strengthen the VSL control effect by changing the number of speed limit areas, and finally propose a dynamic speed limit area strategy. This strategy redefines the speed limit areas and divides them into three types: normally open speed limit area, auxiliary speed limit area, and buffer speed limit area, which takes into account the transmission capability of the road and alleviates the speed difference. The effects of the VSL control strategy are evaluated using a cell transmission model. The proposed strategy uses the predictive control method to optimize the speed limit value and the number of speed limit areas. Two scenarios that considered both stable and fluctuating traffic demands are evaluated. The results show that the dynamic speed limit areas strategy can improve the safety and efficiency of the freeway.