This paper proposes a simulation-based optimization (SO) method that enables the efficient use of complex stochastic urban traffic simulators to address various transportation problems. It presents a metamodel that integrates information from a simulator with an analytical queueing network model. The proposed metamodel combines a general-purpose component (a quadratic polynomial), which provides a detailed local approximation, with a physical component (the analytical queueing network model), which provides tractable analytical and global information. This combination leads to an SO framework that is computationally efficient and suitable for complex problems with very tight computational budgets.We integrate this metamodel within a derivative-free trust region algorithm. We evaluate the performance of this method considering a traffic signal control problem for the Swiss city of Lausanne, different demand scenarios and tight computational budgets. The method leads to well-performing signal plans. It leads to reduced, as well as more reliable, average travel times.Key words : Simulation-based optimization, Traffic control, Metamodel, Queueing
IntroductionMicroscopic urban traffic simulators embed the most detailed traffic models. They represent individual vehicles and can account for vehicle-specific technologies/attributes. They represent individual travelers and embed detailed disaggregate behavioral models that describe how these travelers make travel decisions (e.g. departure time choice, mode choice, route choice, how travelers respond to real-time traffic information, how they decide to change lanes). They also provide a detailed representation of the underlying 1 Osorio and Bierlaire: A simulation-based optimization framework for urban transportation problems 2 Article submitted to Operations Research; manuscript no. (Please, provide the mansucript number!) supply network (e.g. variable message signs, public transport priorities). Thus, these traffic simulators can describe in detail the interactions between vehicle performance (e.g. instantaneous energy consumption, emissions), traveler behavior and the underlying transportation infrastructure, and yield a detailed description of traffic dynamics in urban networks.These simulators can provide accurate network performance estimates in the context of what-if analysis or sensitivity analysis. They are therefore often used to evaluate a set of predetermined transportation strategies (e.g., traffic management or network design strategies). Nevertheless, using them to derive appropriate strategies, i.e., to perform simulation-based optimization (SO), is an intricate task.We focus on transportation problems of the following form:The objective function f is usually the expected value of a stochastic network performance measure, F . The probability distribution function of F depends on the deterministic decision or control vector x and on deterministic exogenous parameters p. The feasible space Ω consists of a set of general (e.g., nonconvex) constraints that lin...