The dynamic optimisation of variable speed limit interval on mainline combined with Ramp Metering

With the rapid growth of vehicles, congestion on highways and expressways has become increasingly apparent. However, few studies considered the association between the Variable Speed Limits (VSL) boundary and congestion propagation, which may induce control hysteresis effects. Therefore, this paper proposes a cooperative control framework considering both VSL optimisation of mainline and Ramp Metering (RM) control. The specific VSL area of mainline is determined according to the predicted congestion propagation length. And the Dynamic-Interval (DI) VSL and RM control strategies are established by considering the capacity of VSL safety and the ramp regulation of each control subarea. Simulation experiments demonstrated significant performance improvements of the proposed control method, achieving 35.73% reduction in Total Travel Time (TTT) and 45.38% decrease in average delay compared to Fixed-Interval (FI) VSL with RM control strategies.