An Extension to the Incremental Traffic Assignment Algorithm Based on Variable Step Sizes: Case Study of Mashhad

One of the most complicated steps in transportation planning is traffic assignment due to its long mathematical calculations for which some heuristic methods have been devised. Because of its simplicity and short calculations, incremental traffic assignment is a frequently used method though offering low accuracy. In this paper, the assumption of equal step size in the traditional incremental traffic assignment is ignored. The results indicate that intelligently assuming variable step sizes increases the efficiency of the method, meaning that adequate accuracy is obtainable with shorter iterations. The proposed algorithm has been applied to the city of Mashhad as a real size case study. An increase in the accuracy of the results has been achieved within shorter time and calculation. Results indicate that for a certain number of iterations and a fixed size for the first step, the best solution appears when the other steps vary less in size. Also, a linear relationship has been observed between the number of iterations and the size of the first step.