Seeing the wood and the trees: simulation-based evaluation of the effect of variable speed limit signs on capacity and user safety

This article describes how a simulation-based evaluation methodology was applied on a variable speed limit signs (VSLS) system designed for a heavily-traveled roadway around Lausanne, Switzerland. Using the MITSIM Laboratory, the evaluation focused on determining the impacts that variable speed limit signs would have on capacity, traffic flow and user safety. In evaluating the efficacy of the VSLS on capacity and congestion, no clear improvement in performance was shown. In terms of the impact on user safety, it was found that a decrease in speed limits for high flow levels and congestion near an intersection led to an increase in safety. However, simulations showed that in the case of an accident which greatly reduced roadway capacity, VSLS did not seem to improve network performance.