Traffic Efficiency Comparative Analysis And Optimal Design Of Ramp Combinations In Urban Expressway

With the advancement of China’s urbanization process, urban expressways, as the backbone system of the urban road network, also speed up the construction pace accordingly. While, it still exists some problems in the process of construction and in operation, resulting in low traffic efficiency and unsatifying effect. In the urban expressway system, considering the mutual influence between traffic flows, two adjacent ramps should be regarded as a whole to be studied when the ramp distance is small. According to the ramp configuration and traffic impact, this paper divided ramp combinations into four types: on-off, on-on, off-on and off-off. Then, corresponding threshold values for four ramp combinations were obtained. Models were develoded by adopting microscopic simulation software TSIS. With the field data, simulation models were calibrated effectively.Taking ramp combinations(containing ramp distance) in urban expressway as research objective, this paper qualitatively and quantitatively analyzed the traffic efficiency of four ramp combinations under different traffic volumes. At first, changing regulations of blocking rate of traffic volume, average speed, delay travel per vehic le per distance traveled and arbitrary lane changes in combination area for four ramp combinations were revealed from the statistical s ignificance, at the same time, comparison and analys is were held accordingly. Obviously, this would provide theory basis for improving the traffic efficiency of urban expressway. Secondly, considering delay travel per vehicle per distance traveled in combination area was the concentrated reflection of traffic efficiency and service level, quantitative models between delay travel per vehic le per distance traveled and corresponding influenc ing factors for four ramp combinations were developed with mathematical statistics software SPSS. Then, the influence of factors on delay travel per vehic le per distance traveled was quantitatively analyzed. It’s found that ramp distance played an important role in traffic delay.From the perspectives of actual traffic operation and quantitative models of delay travel per vehic le per distance traveled in combination area, this paper put forward some measures to reduce the traffic delay. Reasonable ramp distances were recommended for four ramp combinations by transforming the form of quantitative models, which would provide a reference for engineering application.