Variable Speed Limits System: A Simulation-Based Case Study in the city of Naples

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The development of Intelligent Transportation Systems (ITS) aims to improve the performance of transport systems in terms of efficiency, safety and energy saving. Among these services, the Variable Speed Limit (VSL) systems are widely used to mitigate the problem of traffic congestion by changing the road speed limits in response to traffic, incidents, and/or weather conditions. This paper investigates the effects of a VSL system on a freeway road segment of the city of Naples. The control strategy leverages volume, occupancy and average speed data, provided by loop detectors located along the road, for adapting dynamically the road speed limit. Numerical simulations were carried out by exploiting VISSIM microscopic traffic simulator, which embedded the control strategy, for two different scenarios: with and without the VSL system. Results disclose the effectiveness of the VSL control strategy in improving road efficiency by reducing speed variance and increasing both average speed and volume of vehicles. Moreover, the VSL system has also proved to have environmental benefits, since it allows reducing fuel consumption.