Traffic-Responsive Linked Ramp-Metering Control

A new traffic-responsive ramp-metering strategy is presented that coordinates local ramp-metering actions, thus enabling the linked control of the inflow from two (or more) consecutive on-ramps to the freeway mainstream. The proposed linked ramp-metering scheme is simple and utterly reactive, i.e., based on readily available real-time measurements without any need for real-time model calculations or external disturbance prediction. The well-known feedback strategy, known as Asservissement LINeaire d´Entree Autoroutiere (ALINEA), is used at a local level. Simulation results are presented for a hypothetical freeway axis with two successive on-ramps. Some pitfalls and misapplications of the local ramp metering are also illustrated via appropriately designed simulation scenarios. The proposed linked strategy is demonstrated to outperform the uncoordinated local ramp metering and, thus, to increase the achievable control benefit over the no-control case. In fact, the new strategy is shown to reach the efficiency of sophisticated proactive optimal control schemes.