Bi-objective simulation-based optimization for real-time coordinated ramp metering under traffic demand uncertainty

This paper proposes a real-time coordinated ramp metering (RCRM) method to simultaneously maximize the number of vehicles entering the expressway mainline from on-ramps and space mean speed of the expressway mainline. This method applies a proportional-differential (PD) controller to adjust vehicular flow entering the expressway mainline from on-ramps. It also utilizes shockwave analysis to dynamically determine the upstream on-ramps that have to be coordinated. In order to ensure the RCRM method can withstand traffic demand uncertainty in real-time, we establish a ramp metering stochastic simulation-based optimization (RMSSO) model to fine-tune the weighting coefficients for on-ramps and PD gains and solve it by a bi-objective surrogate-based promising area search (BOSPAS) algorithm. Simulation experiments in Edmonton show that the optimized RCRM schemes improve the space mean speed of the mainline by around 40% almost without sacrificing the number of vehicles entering the mainline from on-ramps. The outperformance and robustness of the optimized RCRM scheme by BOSPAS are also validated under traffic demand uncertainties.