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Urban expressway speed spatial inconsistency and its effect on safety

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Chuan Xu,Xuesong Wang,Xiaohong Chen

Abstract:Crashes on urban expressways lead to large external costs due to its process effects of congestion and to reduce its influence is a main objective for traffic management. The speed difference between the adjacent positions along the road, called speed spatial inconsistency, is a potential risk factor which is less studied because of data limitation. It may be one of the substantial reasons of crash on urban expressway. Thanks to the floating car data (FCD) generated by the globe positioning system (GPS), which are installed on taxies, we can acquire detailed speed data along a road by viewing taxies as probe vehicles instead of isolated loop-detectors. The objective of this study is to explore the relationship between crash frequency and speed spatial inconsistency on urban expressway while controlling for other relevant factors. To accomplish this objective, we chose 174 segments belonged to the four main urban expressways of Shanghai where trucks are prohibited in the analysis time. Meanwhile, more than 45,000 taxies’ FCD with 10 seconds fixed time interval were obtained, and a series of indicators to speed spatial inconsistency were developed. Also, the relevant crash data, traffic data and road characteristics data were collected. After that, Bayesian Poisson-gamma models were established for the frequencies of total crash, rear-end, and sideswipe. The results suggest that larger speed spatial inconsistency for a road segment lead to more crashes and each factor has the same positive or negative effects on the three kinds of frequencies.

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