Distributed ramp metering - a constrained discharge flow maximisation approach

Considered in this note is a novel model-based, coordinated ramp metering strategy. It aims at maximising the discharge flow in motorway networks by minimising the divergence of the traffic density from its critical value caused by unknown demand flow. The suggested synthesis algorithm casts the traffic control objective into the form of an induced $\mathcal{L}_2$ norm minimisation problem. Hence, we purport rejecting the effect of disturbance on the overall network performance output while the ramp input flow is subjected to constraints. With such a problem formulation, it is not required to know the disturbance input in order to find the proper control input. Without any central decision unit (traffic control centre), ramp meters coordinate by sharing their local variables with solely their neighbour units (upstream and downstream) to achieve the global performance goal. Under some network symmetry conditions, a compositionally inexpensive distributed flow control method is suggested to address scalability issues. The method is implemented in simulation environment and compared to other control algorithms in two comprehensive case studies