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In order to clarify the relationship of lane location and saturation on speed of ring expressway, a cameral traffic survey was carried out on the basic section of ring expressway in Xi'an, and considering lane location and saturation, the speed data were divided into 12 groups. The distribution type, centralized trend parameter and discrete trend parameter were selected to describe the distribution characteristics of vehicle speed. Combined with the frequency distribution curve of vehicle speed and P-P diagram, the optimal distribution type of vehicle speed in different groups was determined. The variation characteristics of the 15th percentile speed, the 85th percentile speed, the standard deviation of speed and the average speed difference in different groups were analyzed. The results show that lane location and saturation have great influence on the speed distribution characteristics of ring expressway. The more freely the vehicle operates and the simpler the vehicle composition of different lanes is, the more suitable vehicle speed data are fitted by normal distribution, on the contrary, the more suitable the vehicle speed data is to be fitted with lognormal distribution. From the inside to the outside of the lane, the 15% speed and the 85% speed gradually decrease, and the standard deviation of speed and average speed difference gradually increase. From the first level to the fourth level, the 15% speed, the 85% speed and the average speed difference gradually decrease, while the standard deviation of speed first increases and then decreases when the saturation reaches the third level.
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