Resilient Ramp Control for Highways Facing Stochastic Perturbations.

Highway capacity is subject to stochastic perturbations due to weather, traffic mixture, driver behavior, etc. However, systematic approaches to traffic control with performance guarantees in the face of such perturbations are still limited. In this paper, we develop a novel control-theoretic method for designing perturbation-resilient ramp metering. We consider a cell-transmission model with 1) Markovian cell capacities and 2) buffers representing on-ramps and upstream mainline. Using this model, we analyze the stability of on-ramp queues by constructing piecewise Lyapunov functions motivated by the nonlinear traffic dynamics. Then, we design ramp controllers that guarantee bounds for throughput and queue sizes. We formulate the coordinated ramp metering problem as a bi-level optimization with non-convex inner problems. To address the computational issue, we also consider a localized and a partially coordinated reformulation. A case study of a 18.1-km highway in Los Angeles, USA indicates a 7.6\% (resp. 8.8\%) reduction of vehicle-hours-traveled obtained by the localized (resp. partially coordinated) control, both outperforming the 5.4\% reduction obtained by the classical ALINEA policy.