Advanced Evaluation Methods for Variable Speed Limit Systems

The variable speed limit (VSL) system has been implemented on many freeways and urban arterials as a link control strategy. Objectives for deploying VSL systems may include giving advance warning, stabilize and smooth traffic (i.e. harmonization). Accuracy and reliability of the messages displayed by VSL systems can “make or break” its successful implementation. The aim of this paper was to present methods for evaluating VSL systems. As VSL systems may be implemented with different control strategies, an approach for assessing different features of the system independently was adopted. In this way, systems with different control strategies can be evaluated. Methods for assessing incident detection, warning and harmonization abilities were presented. A case study on the VSL system on the Autobahn A99 near Munich, Germany was also discussed.