Impact of roadway geometric features on crash severity on rural two-lane highways

• Published in: Accident analysis and prevention 2018-02, Vol.111, p.34-42
• Main Authors: Haghighi, Nima, Liu, Xiaoyue Cathy, Zhang, Guohui, Porter, Richard J.
• Format: Article
• Language: English
• Subjects: Accidents, Traffic; Automobile Driving; Crash severity; Crash type; Environment; Environment Design; Geometric feature; Hierarchical structure; Humans; Illinois; Logistic Models; Risk; Rural; Rural Population; Safety
• ISSN: 0001-4575; 1879-2057
• DOI: 10.1016/j.aap.2017.11.014

•The impact of geometric features on the crash severity were examined.•Hierarchical structure of crash data was verified using a MOL model.•Indirect impact of geometric features was captured with the setting of MOL model.•The presence of 10-ft lane and/or narrow shoulders, and lower roadside hazard rate decrease the risk of more severe crashes.•Higher driveway density, longer barrier length, and shorter barrier offset decrease the risk of more severe crashes. This study examines the impact of a wide range of roadway geometric features on the severity outcomes of crashes occurred on rural two-lane highways. We argue that crash data have a hierarchical structure which needs to be addressed in modeling procedure. Moreover, most of previous studies ignored the impact of geometric features on crash types when developing crash severity models. We hypothesis that geometric features are more likely to determine crash type, and crash type together with other occupant, environmental and vehicle characteristics determine crash severity outcome. This paper presents an application of multilevel models to successfully capture both hierarchical structure of crash data and indirect impact of geometric features on crash severity. Using data collected in Illinois from 2007 to 2009, multilevel ordered logit model is developed to quantify the impact of geometric features and environmental conditions on crash severity outcome. Analysis results revealed that there is a significant variation in severity outcomes of crashes occurred across segments which verifies the presence of hierarchical structure. Lower risk of severe crashes is found to be associated with the presence of 10-ft lane and/or narrow shoulders, lower roadside hazard rate, higher driveway density, longer barrier length, and shorter barrier offset. The developed multilevel model offers greater consistency with data generating mechanism and can be utilized to evaluate safety effects of geometric design improvement projects.