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Analysis of Traffic Flow Characteristics on Ring Road Expressways in Beijing

The primary objective of this paper is to analyze traffic flow characteristics on ring road expressways in Beijing on the basis of floating car data (FCD) and remote traffic microwave sensors (RTMS) data. Traffic flow characteristics are studied in relation to lane use, the relationship between occupancy and density, relationship of flow–speed–density, and the relationship between FCD speed and RTMS speed. It is demonstrated that lane use characteristics on the basic sections of ring road expressways are similar to those of freeways, in which the average vehicle lengths in the median, center, and shoulder lanes are found to be approximately 5.78 m, 6.03 m, and 6.33 m, respectively. Further, the four essential parameters used to characterize the Van Aerde flow–speed–density relationship are calibrated and compared for the second, third, and fourth ring road expressways. Results indicate that the fourth ring road, which has the highest free-flow speed, speed-at-capacity, and capacity, has characteristics similar to those of typical freeways. Traffic flow characteristics observed on the second and third ring roads are roughly consistent with the Greenshields model. It is observed that the second ring road has the worst traffic conditions, followed by the third ring road, and that the basic sections of ring road expressways have better traffic conditions than the areas around the ramp junctions. Finally, a regression analysis is done to develop the relationship between FCD speed and RTMS speed. It is found that RTMS speed is slightly higher than FCD speed, with a difference of less than 6%.