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原文传递 DBCENTRAI.IZBD Algorithms FOR THE MXNAOEHENT AND CCMJTROIi OF TRANSPORTATION SYSTEMS

题名：	DBCENTRAI.IZBD Algorithms FOR THE MXNAOEHENT AND CCMJTROIi OF TRANSPORTATION SYSTEMS
作者：	CHABINI. ISMAIL
关键词：	Algorithms, Networks, Road Networks. Intelligent transportation Systems
摘要：	When a person asks for travel directions to go from point O to point D, the advice he often gets Is ''from O get on to highway H and travel till you reach exit E2; get off the highway and travel along streets S3, S4, etc. till you reach D". This advice usually results in a path with a small number of turns and which is easy to follow. The reason is the person giving this advice recognizes that traffic networks contain highways, expressways, freeways which span longer distances and are faster than street roads and minor arterials. Since a major portion of the travel Is done on faster arcs, the total travel time may also be close to optimum. As described above traffic networks exhibit a hierarchical behavior in their are sat. Computer and communication networks also exhibit such behavior. Based on the ideas in the above advice, we develop a single source to single sink shortest path algorithm which operates on a two-level hierarchical network. By solving the shortest path problem mainly on the high level subnetwork, this algorithm may achieve significant computation time savings when compared to optimal shortest path algorithms. But this algorithm nay give non-optimal paths. To study this trade off, we formulate a simple mathematical model of hierarchical networks. We theoretically analyze the errors in path lengths, run times, run time improvements and optimal sizes of high and low level subnetworks for this model. Our study indicates that if the cost of arcs in the high level subnetwork is at most half the cost of arcs in the low level subnetwork, then the Hierarchical Algorithm is optimal for all source-sink pairs in the model. Further we test the algorithm performance on data from real traffic networks. The results of this testing indicate that significant computation time savings can be achieved with only small errors in path length. We also propose two extensions to the above algorithm for finding the shortest paths for a large number of source-sink pairs.
报告类型：	科技报告