Traffic Signal Timings For Sustainable Urban Development

Traffic signal timing plays a pivotal role in the management of urban traffic. In the previous relevant studies, the traffic signal timings aimed usually to ease traffic congestion, reduce vehicle delays and improve road capacity. In recent years, the climate change, global warming and energy shortage issues seriously affect the survival environment of human beings. It has widely been recognized that transportation is an important source of these urban issues. Therefore, it is an important and timely task for the community to establish an energy and environmental sustainable traffic signal control system. The main contributions of this study are as follows.Firstly, the traffic signal timing problems with environmental and equity considerations are studied. An inequity phenomenon underlying the traffic signal timing problems is first unveiled. A multi-objective bi-level programming model is then proposed to optimize the traffic signal settings with explicit consideration of the equity issue. The upper-level problem seeks to maximize the reserve capacity of a road network and to minimize the total amount of traffic emissions in the network. The lower level is a deterministic user equilibrium problem that considers the vehicle delays at signalized intersections. To solve the proposed model, an approach for converting incommensurable objective functions into the same unit is presented, and a penalty function method that is embedded by a simulated annealing algorithm is developed. It shows that the reserve capacity expansion and the green time proportion have significant effects on the network flow distribution and traffic emissions.Secondly, an energy sustainable traffic signal timing model for a congested road network with heterogeneous users is proposed. In the proposed model, two types of agents, namely the authority and road users, are considered together with interaction between traffic signal settings and energy policy (e.g. fuel surcharges), and route choice behavior of heterogeneous users. A multi-class stochastic traffic network equilibrium problem that considers vehicle delays at signalized intersections and travel demand elasticity is presented and formulated as a variational inequality formulation. It is assumed that the authority aims to maximize social welfare of the transportation system by optimizing the traffic signal timings and fuel surcharges. A simulated annealing based solution algorithm is developed to solve the proposed model. The findings show that the implementation of the fuel surcharge policy can cause spatial and social inequity issues.Finally, an environment and energy oriented pre-signal timing model with considering bus priority is proposed. The objective of the proposed pre-signal timing model is to minimize the total fuel consumption or the total amount of traffic emissions subject to bus priority constraint. With use of the proposed model, the coordination between pre-signals and main signals, and the changes in the vehicle delays, fuel consumption and traffic emissions due to introduction of the pre-signals are examined. Findings show that the pre-signal scheme can reduce the average delays of all vehicles, average bus fuel consumption and average bus pollutant emissions, but also increase the average fuel consumption and traffic emissions of social vehicles (i.e. private cars and trucks). In addition, there is an optimal pre-signal setting with bus priority that minimizes the total fuel consumption or total traffic emissions of the system.This study provides a useful tool for creating a green urban traffic signal system, and for promoting the coordination among urban transportation, energy and environment systems.