Dynamic speed limits can be used to eliminate shock waves on freeways. Shock waves are typically short traffic jams that emerge at bottlenecks and travel in the upstream direction on the freeway. These shock waves lead to increased travel times and possibly to unsafe situations. The paper will present a speed limit control approach to resolve shock waves, that is based on a distributed controller design technique. The controller is distributed in the sense that each speed limit sign has its own controller. The controller parameters are optimized by numerical optimization, assuming that the controller structure and parameters are the same for each controller. The resulting performances are compared for several designs, differing in (1) the controller order and (2) the extent that the upstream and downstream traffic states are used as inputs for the controller. Other controllers known from literature are based on switching schemes using local information only, or are centralized model-based controllers with high computational loads. The proposed method gives a systematic way to design distributed controllers, using the appropriate amount of upstream and downstream traffic information. The resulting controllers attractive from the implementation point of view as they are very efficient: they do not require extensive on-line computations, and use only information from the neighborhood. For the design scenario used in this paper the controller successfully resolves the shock wave and reduces the total time spent by approximately 20% compared to the uncontrolled case, which is comparable to the performance of the best controllers known from literature.
Abstract