Safety and mobility trade-off assessment of a microscopic variable speed limit model

In this paper a three part traffic simulation environment is utilized to quantify the multi-objective optimization frontier of variable speed limit (VSL) control. Specifically the trade-off between safety and mobility performance is quantified for a VSL control algorithm designed to homogenize vehicle speeds within a freeway incident region. A microscopic driver model for VSL traffic previously developed by the authors is implemented in VISSIM's API module and simulation is controlled via a MATLAB COM interface. Results indicate an inverse relationship between safety and mobility performance, forcing jurisdictions designing VSL systems to either conduct multi-objective optimization or set a dominant policy objective (safety versus mobility). Control algorithm parameters that invoke VSL adjustment more frequently produce greater safety benefits but also greater mobility impairments. Freeway volume had no significant effect on VSL performance in this study.