Quantifying the impact of driver compliance on the effectiveness of variable speed limits and lane control systems

Variable speed limits (VSL) and lane control systems (LCS) are commonly applied active traffic management (ATM) strategies to improve traffic mobility and safety. These systems can be used for recurring congestion or for non-recurrent incident response settings. Regardless of the setting, it is naturally assumed that for such systems to be effective, the driver compliance rate must be reasonably high. In this work, we investigate the impact of a wide range of driver compliance rates on safety and mobility performance measures during incidents. We consider a microsimulation setup in which rule-based VSL and LCS systems are deployed, and we vary the number of complying drivers that adhere to the variable speed limits in response to an incident. Our main finding is that VSL and LCS systems can achieve a substantial benefit in key safety performance measures without reducing mobility measures significantly, even when the driver VSL compliance rates are as low as 5% in sufficiently dense traffic. This result can be explained by examining the impact of a small number of complying drivers on the surrounding traffic.