Analysis of safety factors for urban expressways considering the effect of congestion in Shanghai,China |
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| Affiliation: | 1. Department of Traffic Engineering and Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, No. 4800, Cao’an Road, Shanghai 201804, China;2. Jiangsu Province Collaborative Innovation Center of Modern Urban Traffic Technologies, SiPaiLou #2, Nanjing 210096, China;3. Key Laboratory of Road Structure & Material Research, Institute of Highway, Ministry of Transport, No. 8 Xitucheng Road, Haidian District, Beijing 100088, China;1. Griffith School of Engineering, Griffith University, Gold Coast, 4222 QLD, Australia;2. Department of Civil and Environmental Engineering, National University of Singapore, Singapore 117576, Singapore;1. Department of Civil, Environmental and Construction Engineering, University of Central Florida, Engineering II-215, Orlando, FL 32816, United States;2. School of Transportation Engineering, Tongji University, 4800 Cao’an Road, 201804 Shanghai, China;1. School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China;2. Tianjin Key Laboratory for Fabrication Building and Intelligent Construction, Tianjin 300401, China;1. Green Transport and Logistics Institute, Korea Railroad Research Institute, Uiwang, Republic of Korea;2. Department of Civil and Environmental Engineering, Seoul National University, Seoul, Republic of Korea;1. School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510641, PR China;2. Jiangsu Province Collaborative Innovation Center of Modern Urban Traffic Technologies, Southeast University Road #2, Nanjing 211189, PR China;3. Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, PR China;4. Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, PR China |
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| Abstract: | Urban expressways are the key components of the urban traffic network. The traffic safety situation on expressways directly influences the efficiency of the whole network. A total of 48,325 crashes were recorded by Shanghai Expressway Surveillance System in a three-year period. Considering the different crash mechanisms under different congestion levels, models for the total crashes, non-congested-flow crashes and congested-flow crashes were respectively formulated based on the real-time traffic condition corresponding to each crash. Moreover, considering the potential spatial correlation among segments, the adjacent-correlated spatial and distance-correlated spatial models were formulated and compared to the traditional non-spatial-correlated model. A Bayesian approach was employed to estimate the parameters. The results showed that the congestion index, merging ratio, ramp density, and average daily traffic significantly affect the crash frequency. The safety factors in non-congested flow and congested flow are different; diverging behavior is more risky in non-congested flow, more lanes tend to increase the risk of crashes in congested flow, and horizontal curves tend to decrease the crash risk in congested flow but cause high risk in non-congested flow. In addition, the distance-correlated spatial model is found to be the best-fitting model. The results of this study suggested that dedicated safety countermeasures can be designed for different traffic situations on urban expressways. |
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| Keywords: | Urban expressway Safety Traffic situation Congestion index Bayesian approach Spatial correlation |
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