Modeling Driver Compliance to VSL and Quantifying Impacts of Compliance Levels and Control Strategy on Mobility and Safety

Abstract

Variable speed limits (VSL) aim to improve freeway mobility and safety by influencing collective behaviors of drivers. Thus, VSL benefits should be positively correlated with the VSL compliance level (CL). Surprisingly, a number of heuristic VSL control strategies have shown that VSL with increased CLs can, in fact, increase travel time. However, it has yet to be analyzed whether or not that outcome is because of the control strategy design or the CL. Some recent studies have shown that, regardless of CL, a proactive optimal VSL control provides mobility benefits; however, no evidence has been found to indicate which CL is most achievable in practice, nor has a description been found for the distribution of speed of a given VSL. The objective of this paper is to quantify the relative contribution of CLs with a proactive optimal VSL control toward improving mobility and safety. In this study, several CL-to-VSL strategies have been modeled after real-world driver behavior. To quantify the impact of CLs only, speed distributions are altered with the static speed limit. Then, the benefits are quantified by implementing a proactive optimal VSL control strategy with CLs. The simulation evaluation shows that both VSL mobility and safety benefits are positively correlated with increasing CLs. Specifically, the travel time, throughput, and collision probability are improved in the CL ranges of 5–15%, 6–8%, and 50–60%, respectively. The study findings will help guide transportation agencies in deploying VSL control by considering CL, so as to achieve maximum mobility and safety benefits.