Model - based speed limit control with different traffic state measurements ∗

In this paper, traffic flow is controlled using dynamic speed limits, obtained by Model Predictive Control (MPC). MPC is a model-based approach, where the states of the system, influenced by control actions, are predicted over a certain time span. The states of the system are the mean speeds and densities on the motorway. Traffic flow models typically use space mean speeds, while measurements on motorways are often time mean speeds. Several methods for obtaining estimates of the space mean speed based on the time mean speeds are discussed, and the possible performance loss of using another mean speed than the space mean speed for model-based traffic control is investigated. The resulting controllers, using the different estimates, are evaluated for a scenario where speed limits are used to eliminate a shock wave from a motorway by comparing the achieved reduction in the total time that the vehicles spend on the motorway (TTS). The result show that the performance for the different estimation methods is comparable, and lead to an improvement of the TTS of around 14%.