Comparing Freeways Capacity Analysis Based on Reliability Parameters with Traditional Methods

Traditional methods for analyzing freeway capacity are a common tool for decision making about demand and supply management for roads. Freeway capacity in traditional point of view can be defined as the highest number of vehicles which pass a road section in particular time. According to this definition, and Highway Capacity Manual 2000, for the defined situation, Capacity is defined as a constant measure. But on the other hand, this method can not reveal the actual performance of facility. Indeed, it shows an overall estimation of real flow. For detailed analysis of traffic flow, it is necessary to consider the variations of maximum flow of expected values. Freeway capacity in traditional view can be defined as the highest number of vehicles which pass a road section in particular time. According to this definition, and Highway Capacity Manual 2000, for the defined situation, Capacity is defined as a constant measure. But on the other hand, this method can not reveal the actual performance of facility. Indeed, it shows an overall estimation of real flow. For detailed analysis of traffic flow, it is necessary to consider the variations of maximum flow of expected values. In this research, a case study was performed in one of highways in city of Tehran. The results in two consecutive hours (6 to 8 Am) showed that the V/C ratio in preliminary hours increase but more detailed analysis confirmed that reliability in preliminary hours is more. Also, the basics for selecting performance measures for freeways was discussed and estimated for the case study.