Exploring the effectiveness of variable speed limits: a multi-dimensional systematic review

This is the authors' abstract. We don't add key points for this paper.

Variable Speed Limit (VSL) has received widespread attention over the years as a measure to improve traffic operations and safety, due to its ability to dynamically adjust speed limits based on current road and weather conditions. Therefore, it was necessary to review the existing literature related to VSL. Following the PRISMA guidelines, the relevant literature was identified through multiple databases. Studies were selected based on PICOS criteria, focusing on those that assessed the impact of VSL implementation using software simulations, driving simulators, or on-field experiments. Field evaluations indicate potential safety and operational benefits of VSL under specific deployment conditions, while simulation studies suggest system-level improvements in traffic efficiency and emissions under modelled conditions. Driving simulator studies provide insights into driver compliance and perception of VSL systems. Various control strategies, ranging from reactive to proactive, have been employed, with prediction models supporting decision-making. Integration of VSL with other Intelligent Transportation Systems (ITS) technologies has also been explored, and the findings indicate notable improvements over standalone VSL systems. Driver compliance and acceptance of technology were identified as critical factors influencing the effectiveness of VSL systems and were influenced by factors such as sign clarity, the distance between consecutive signs, drivers' perceptions of whether the posted limits are reasonable, surrounding traffic conditions, etc. The review synthesises current knowledge on VSL systems across multiple dimensions, highlights gaps in existing evaluation approaches, and provides directions for future research.