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IRoad inhomogeneities such as on- and off-ramps, lane increasing and decreasing are potential bottlenecks. Capacity of urban freeway during peak period is affected by these complex road structure and high traffic demand. Since the dense inhomogeneities are close to each other, investigation aiming at describing integrated effects of road inhomogeneities is needed. In this paper, based on real traffic data of Beijing urban freeway, relation between traffic demand, road structure and lane-specified traffic characteristics are investigated. It is turned out that the main reason for capacity decrease at peak period is fluctuations induced by competition between main road and ramp. However, on-ramp and off-ramp are different in the way for triggering a capacity drop. Based on empirical investigation, mathematical descriptions for congestion evolution process are developed for further modelling. |
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Keywords:traffic flow; transportation system; empirical investigation; urban freeway |
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