Optimal Speed Limits And Signal Control Of Traffic Assignment In Saturated Road Networks

In recent years, urban traffic congestion problems have become increasingly prominent while vehicle numbers continue to escalate with the development of urban modernization.The city continues to introduce traffic control measures like developing rail transit,promoting mess transit and enacting the "odd-even" traffic restrictions or others. However,all the measures have failed to effectively pinpoint the root cause of the crux of the problem.Reasonable speed limit can improve the service level of the road network as much as possible based on security. Failure for traffic management to keep up with the construction of urban transport facilities will lead to traffic chaos and frequent traffic accidents. Thus, to understand the optimized synergies of basic road network control facilities becomes a matter of urgency to solve the problem.In view of the above, this paper establishes a bi-level programming model with double objectives to optimize the limit speed and the optimal timing of the traffic lights. The main research works are as follows:(1) Based on the current situation of urban traffic congestion in China, this paper firstly summarizes the necessity of speed limit setting and the effect of regulation of speed limit for road network traffic. Secondly the selection of urban road network limit speed is explained in detail especially the safety speed. Then this paper sketches out the concept and method of signal control of intersections with illustrating the timing parameter and evaluation methods which paves the way for the following model and algorithm construction.(2) A bi-level programming model is established to optimize the speed limit and signal timing of the double target with the minimum of total delay and the total amount of the accident. Firstly, the lower model of user equilibrium distribution with a signal phase saturated flow taken as the capacity limit is established under the road speed limit. The lower model can better react the signal phase of the intersection, and comprehensively responses to the delay of each section with a certain speed limit. Secondly, the upper double objectives model which has minimal total delay and traffic accidents in the road network is established. The upper model can clearly determines the optimal speed limit and intersection signal timing.(3) The upper and lower algorithms are designed for the multi-objective and bi-level programming model, and an example is designed to analyze the effect and its validity. The multi-objective genetic algorithm by the parallel selection method is selected for the upper model. While the algorithm for lower model chooses the Augmented Lagrangean dual algorithm combined with MSA iterative updating algorithm. At last, MATLAB R2014a is used to coding so as to calculate and analyze the optimization results.