Variable Speed Limit Control Based on Extended Link Transmission Model

In this paper the link transmission model (LTM) is extended to include the effects of variable speed limit (VSL) and consequently to provide VSL control for traffic networks modeled by the LTM. The LTM was recently developed for route assignment, but in this study the LTM was modified to be used for control purposes. This modification achieved a model that provides a balanced trade-off between accuracy and computational complexity, and therefore the model is useful for online model-based traffic control. Nevertheless the extension of the model for ramp metering and speed limit control needed careful attention. Because the LTM lacks explicit velocity equations, the focus was on other potential sources that could imitate the influences of VSL. The delays inside the model were manipulated to achieve the mentioned goal. Moreover, different situations were taken into account that might occur in reality on the basis of changes in VSL and different traffic conditions. Finally, the total extensions were verified with simulation and real data. For that aim to be achieved, the VSL extension integrated in the LTM was verified with simulations for a benchmark case study (to show the performance of the extended LTM clearly). Next, the LTM was calibrated by real data collected from the A12 freeway in the Netherlands. The optimal parameters of the model were identified with a global optimization method. Comparison with real data from a period of time when VSL installed on the freeway was active showed the acceptable performance of the total extended and calibrated LTM.