Modeling sustainable traffic assignment policies using bilevel programming

Abstract

Urban transport systems play a crucial role in maintaining sustainability. Recently, sustainable urban transportation has become a major research area. Most of these studies propose evaluation methods that use simulation tools to assess the sustainability of different transportation policies. Though there are some recent studies, the mathematical programming approaches to determine the optimal policies is still an open research area. The conventional mathematical programming techniques have been used in several transportation problems such as toll pricing and traffic assignment problems. We propose a bilevel structure for several optimization models that incorporate the measurement of gas emissions throughout a traffic network. The upper level of the problem represents the decisions of transportation managers that aim at making the transport systems sustainable, whereas the lower level problem represents the decisions of the network users that are assumed to choose their routes to minimize their total travel cost. By using emission factor tables provided by California Air Resources Board, we determine the emission functions in terms of traffic flow to reflect the accumulated emission amounts in case of congestion. The proposed emission functions are plugged into bilevel mathematical programming models that incorporate several policies, namely, toll pricing, zone charging and capacity enhancement. We conduct a computational study with the proposed models on a testing network by a state-of-the-art solver