Study And Application Of Urban Road Impedance Model

With economic development, people’s travel is becoming more and more diversified. The assignments of traffic flow in the network depend on many factors. In these factors, impedance of traffic plays the most important role in improving road capacities, balancing flows, and reducing congestions. For rational organization and distribution of traffic flow, it is necessary to calculate road impedance accurately. Road impedance model shows the relationship between traffic conditions and flow speeds, thus, how to accurately determine impedance is one of the urgent problems in traffic assignment.The impedance model is developed and studied in large numbers at home and abroad, but most of them just considered a single factor in the most influencing factors, such as the U.S. BPR model which only consider the impact of traffic flow, as it is not consistent with the real result. With many factors, building reasonable impedance can accurately calculate road impedance.Firstly, this paper describes several existing road-impedance models universally, including U.S. BPR model, Davidson Road impedance model, the linear impedance model in Japan and Germany. The most influencing factors are analyzed on the basis of traffic-speed-density relationship (Green Shields). With the tool of SPSS, these factors are classified by factor analysis to seven common factors, and then, the common factors have been explained, and the contribution rates of them are calculated.Secondly, after comparing these impedance models, we decide to improve the impedance model on the basis of BPR model. Studying the defects of BPR model, several improvements are taken, including the statistical sample, free travel time to, capacity, Q/C and the performance of the model. The theoretical application and practical significance of the model have discussed, and the importance of impedance model has been cleared in transportation planning.Finally, traffic flows in Dalian are surveyed, after determining the methodology, time and location. The data have been collated such as standardizing the vehicles——transfer the real vehicles to equivalent vehicles——and then according to the improved BPR model, the model parameters have been calibrated respectively as the rank of urban roads such as expressways, major roads, minor roads and tertiary roads by non-linear regression. Meanwhile, the comparisons of different methods and different rank roads have finished. The result shows that the improved model is able to reflect the Dalian urban roads impedance better.