Research And Application Of Traffic Assignment By Paired Alternative Segments

Bar-Gera proposed a new algorithm for the traffic assignment problem that promises to produce highly precise solutions by identifying and keeping a list of paired alternative segments(PAS) on origin-based sub-networks and shifting flow on PAS. The high efficiency algorithm was named the traffic assignment by paired alternative segments. This algorithm has huge advantage so it is a pressing job for us to study it. The purpose of this paper is theory of PAS algorithm, especially to introduce these key steps of the algorithm. This algorithm was tested with different sizes of road network and its performance was evaluatedThe paper is divided into three parts.In the first part, the paper presented the procedure of PAS algorithm including establishing PAS structure and shifting flow and equalizing proportions between origins. And for one of the key steps such as breadth first search and the method of shift flow value, the instance is used to describe the process in detail. Based on the principles of fully grasp algorithm, PAS algorithm is easy to lay the foundation for program implementation.In the second part, in order to achieve algorithm, data storage structure was designed to store road network information and traffic demand information. The calculation strategy of the key steps was also designed. Based on these, the main program of the algorithm was write by c# programming language, and the PAS algorithm was realized on the computer.In the third part, the paper tested the algorithm with different sizes of road network then had a intuitive understanding on efficiency and convergence precision of the algorithm. Before the test, the convergence criteria and convergence precision of the algorithm is designed, and the average excess cost is easier to implementation of the algorithm.In the end, the PAS algorithm and GP algorithm.were compared. The paper analyzed the two algorithm's efficiency and convergence precision and got that when the accuracy is not high, the efficiency of them is same, but when the accuracy is high, the PAS algorithm is better.