The Effect of Zone Size on Traffic Assignment Results, Case Study of Mashhad

Numerous worldwide studies have examined the effect of zone aggregation on the results of traffic assignment worldwide, but there are very few studies in the country have investigateding this effect on the various stages of transportation planning. Existing literature reveals the important role of zoning methods on different stages of transportation planning. In this paper, a quantitative research has beenis conducted on the effect of zone aggregation, particularly, on the results of traffic assignment for the a case study of in Mashhad. In the aggregation process, emphasize has beenis placed on homogeneity of zones and respect appreciating to the boundaries and physical barriers, where possible. For comparison purposes, predicted values for the four different research scenarios are have been plotted and analyzed statistically, based on statistical parameters, such as the coefficient of determination and t- test. Results show that aggregation (reducing the number) of zones for the case under study, does not improve traffic assignment model results expressed in link volumes, as expected.