Traffic Control Strategy Optimization With Environmental Concern

With the improvement of people's living standards,motor vehicle ownership has increased year by year,but also led to a series of problems such as traffic congestion and environmental pollution.In recent years,Beijing has repeatedly issued heavy red air pollution warning,which aroused widespread concern.Although traffic emergency response measures including vehicle ban and restriction have played a remedial role in the short term,it is impossible to implement them for a long time taking account of their containment of traffic demand.How to design a more reasonable and lasting control strategy that can be used in daily traffic assignment to reduce vehicle exhaust emissions by traffic guidance instead of restrictions is an urgent problem.In this paper,signal timing and emission pricing are adopted as control measures and the optimization model and method of traffic control strategy considering environmental benefits are studied.The main work is as follows:(1)Based on the theory of bilevel programming,a traffic emission control model is established with the combination of intersection-based signal timing and road-based emission pricing to optimize the timing scheme and toll rate.The upper layer is an optimization model aiming at minimizing total emissions and total travel time of the system,and the lower layer is a traffic assignment model which takes traffic mode sharing into account.The upper multi-objective problem is transformed into a single objective problem with the help of weight coefficient that represents a preference for different goals.Particle Swarm Optimization(PSO)algorithm and Frank-Wolfe algorithm are combined to solve the problem.The case study shows that total emissions and total travel time are two conflicting goals that can not be optimized simultaneously,but the reduction of emission is more significant than the increase of time,so it is reasonable to sacrifice part of the efficiency of the road network in exchange for environmental benefits.(2)Based on the stochastic network equilibrium theory,an emission control model with stochastic characteristics is established taking into account travelers' estimation error on the road resistance.System optimal(SO)is achieved under stochastic user equilibrium(SUE)by second best pricing.Method of Successive Averages(MSA)and PSO are combined to solve the problem.Numerical examples show that previous model(SO + UE)is a special case of the improved model(SO + SUE)whose application is much more extensive.(3)An emission control model considering turning delay is established,in which turning delay at the intersection is added to the calculation of the travel time which makes it possible to obtain turning flow and design signal timing scheme of any phase.In order to solve this problem,the traffic network is expanded by replacing one actual node which represents an intersection with four virtual nodes and the Frank-Wolfe algorithm is improved.Finally,a case study with two-way street and four-phase signal timing is carried out.