Development of Optimal Variable Speed Limit Control System for Freeway Work Zone Operations

Operational safety and efficiency of VSL system are the two core control objectives at work zone areas. In response to such need, this study presents a proactive VSL control model for freeway work zone operations. The proposed model uses embedded macroscopic traffic flow model to predict the traffic state evolutions over the projected time horizon and computes the optimal speed limit values. To improve the safety of operations, this study selects a new control objective function to smooth the speed reduction curve along the target freeway sketch by minimizing the difference between actual speeds and ideal speeds. Also, the smoothness of speed reduction can help to prevent the formation of shockwave and thus enhance the operational efficiency of the system. The authors’ extensive simulation analysis with a VISSIM simulator has revealed that the proposed VSL system can significantly reduce the speed variance along the freeway sketch. Also, the evaluation of several MOEs has shown the promising results of the VSL system on the efficiency improvements.