Stair-Like Control Strategies of Variable Speed Limit for Bottleneck Regions on Freeway

The traffic flow operation at bottleneck sections on freeway mainlines is usually deteriorated by heavy traffic load, resulting in an increase in travel time and a decrease in traffic efficiency. By analyzing the space-time characteristics of the traffic flow at bottleneck sections on freeway mainlines, the cell transmission model was expanded to describe the traffic flow in the bottleneck area under variable speed limit (VSL) control. On this basis, a VSL control model for bottleneck region was established, and stair-like strategies were proposed to prevent the long queue from interrupting the vehicles operation at upstream on-and off-ramps. The proposed methods were tested through a case study, and the results demonstrate that the proposed stair-like strategies for VSLs can effectively reduce the travel time and decrease the average delay. Compared with no control and the strategy of using mainline control on single sections, the proposed strategies can reduce the average delay by about 13.78% and 1.60%, respectively.