Model predictive control for ramp metering of motorway traffic: A case study

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Model predictive control for ramp metering of motorway traffic: A case study

Bellemans, T. / Schutter, B. De / Moor, B. de

The motorway E17 Ghent-Antwerp in Belgium is studied and a comparison is made between a simulation of a morning rush hour situation without control and a simulation of a morning rush hour situation with ramp metering implemented. Two types of controllers are compared: a traditional ALINEA PID (Proportional plus Integrating plus Derivating) like based controller and a model predictive control based ramp metering controller. In order to evaluate the controllers in a realistic framework, the simulations presented are based on real-life traffic measurements, and constraints on the maximal allowed queue lengths at the on-ramps are imposed. The presented simulations are indicative for the reduction in the total time spent (on the studied motorway and on the on-ramps) that can be achieved by ramp metering during a typical morning rush hour. It was observed that with ALINEA based controllers the metering rates oscillated due to the constraints on the maximal queue lengths overriding the controller. This resulted in oscillations in the traffic density and the average speed in the section fed by the on-ramp. These oscillations need to be suppressed as much as possible. A very strong point of ALINEA is its limited computational complexity. The computational complexity of the predictive controllers is larger than the computational complexity of ALINEA due to the optimization problem that needs to be solved at every iteration step. By appropriately choosing the prediction and the control horizons, a trade-off was made between the performance and the computational complexity of the predictive control based ramp metering.