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Abstract : |
The reliability and effectiveness of the TRANSYT model depend primarily on the ability of its platoon dispersion algorithm to accurately predict the flow pattern from one signal to another. The algorithm is based on the theory that a platoon of vehicles starting from an upstream intersection will continuously disperse as it travels downstream along the link. The amount of dispersion in the traffic flow pattern, as predicted by this algorithm, depends on the proper value of an empirical constant in the algorithm referred to as the ''Platoon Dispersion Factor'' (PDF). The objective of this study was to determine the value of PDF which best simulates the traffic conditions in the study area. The study was conducted along two major arterials in areas of mixed residential and commercial activities, Each arterial consisted of four signalized intersections with four approaches to each of them. The signals at these intersections were pre-timed with four protected phases. It was concluded that the average best fit (calibrated) PDF values in the study area were 28 and 40 for low and moderate friction links, respectively. On the other hand, the TRANSYT-7F manual suggests a value of 25 for low friction links and 35 for moderate friction links. Nevertheless, the change in performance measures resulting from using the calibrated PDF value over the suggested ones was small and seems to be within the accuracy of the TRANSYT-7F model., |
