Optimal Variable Speed Limit Control for Real-time Freeway Congestions

It is well recognized that proper control of traffic speed can contribute to both a reduction in accidents and improved efficiency of freeway operations. Regarding the real-time traffic congestions, a variable speed limit (VSL) control system along freeway is able to improve the capacity of the downstream bottleneck. To respond to this need, this study firstly proposed a VSL control model, based on a macroscopic traffic flow model. Due to the inaccurate prediction of the macroscopic model, an enhanced module is further introduced, adopting the concept of Kalman Filter. Also, considering the fact that drivers may not follow the displayed VSL in real-world applications, the computed optimal VSL value would be adjusted according to the detected compliance rate. Our extensive simulation analysis with a VISSIM simulator has revealed the benefits of the proposed VSL control model, compared with the case without VSL. Also the results indicated that the compliance rate of drivers can served as a important factor which may impact the operational efficiency of the VSL system. (C) 2013 The Authors. Published by Elsevier Ltd.