American Society of Civil Engineers

Evaluating the Relationship between Traffic Safety and Traffic Flow States

by Cheng-cheng Xu, (Graduate Research Assistant, School of Transportation, Southeast University, Sipailou#2, Nanjing, China, 210096. E-mail:, Pan Liu, (Professor, School of Transportation, Southeast University, Si Pai Lou #2, Nanjing, China, 210096. E-mail:, Wei Wang, (Professor, School of Transportation, Southeast University, Sipailou #2, Nanjing, China, 210096. E-mail:, and Zhi-bin Li, (Graduate Research Assistant, School of Transportation, Southeast University Sipailou #2, Nanjing, China, 210096. E-mail:
Section: Traffic Safety and Emergency Management, pp. 2402-2411, (doi:

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Document type: Conference Proceeding Paper
Part of: ICCTP 2011: Towards Sustainable Transportation Systems
Abstract: Along with the rapid development of highways in China, traffic safety problems are becoming more and more serious. Hence, there is a growing concern focusing on freeway crash studies. The main objective of this paper is to study the relationship between traffic safety and traffic flow state and to discover dangerous traffic flow states that lead to crash occurrences. The traffic flow data and crash data collected from a 15 kilometer section of the I-880 freeway in the state of California, United States are applied in this paper. To extract the characteristics of dangerous traffic flow state leading to crash occurrences, K-means clustering analysis combined with odds ratios statistics are used to classify traffic flow into 5 different traffic flow states. The results show that two of these five traffic flow states have significant relationships with crash occurrences. And the odds ratio value 3.945 and 3.102 of these two states quantify the impact on crash occurrences of these two states. In other words, when traffic is exposure to these two traffic flow states, the risk of a crash occurring is increased by 2.945 and 2.102 times respectively.

ASCE Subject Headings:
Traffic safety
Traffic flow