Traffic jams are an economic and environmental problem in many countries. When traffic demand exceeds the motorway capacity, shock waves can be caused by small disturbances in traffic flow. Since it is not always desirable or feasible to add more lanes on motorways to overcome capacity shortage, alternative methods have been developed to reduce and dissolve traffic jams. One of these methods is using model-based traffic control on motorways.
The model-based methods use traffic flow models, in which the speeds are typically space mean speeds, while the measured speeds on a motorway are often time mean speeds (measured by loop detectors). The difference between using space mean speeds an time mean speeds for model-based methods has not been addressed in literature before. In this paper, we investigate the possible performance loss caused by using another mean speed type as the space mean speed, for model-based traffic control.
Methods for approximating the space mean speed based on local measurements are discussed, together with the time mean speed and geometric mean speed. The suitability of six mean speed types is investigated, using microscopic simulation. The three most suitable mean speed types for model-based traffic control are used to determine dynamic speed limits on a motorway using a model predictive control approach. Based on these investigations, conclusions are drawn on the suitability of the different types of mean speeds for model-based traffic control.