title: Assessing the risk of secondary crashes on highways.
abstract: BACKGROUND
  The occurrence of "secondary crashes" is one of the critical yet understudied highway safety issues. Induced by the primary crashes, the occurrence of secondary crashes does not only increase traffic delays but also the risk of inducing additional incidents. Many highway agencies are highly interested in the implementation of safety countermeasures to reduce this type of crashes. However, due to the limited understanding of the key contributing factors, they face a great challenge for determining the most appropriate countermeasures.
  
  
  METHODS
  To bridge this gap, this study makes important contributions to the existing literature of secondary incidents by developing a novel methodology to assess the risk of having secondary crashes on highways. The proposed methodology consists of two major components, namely: (a) accurate identification of secondary crashes and (b) statistically robust assessment of causal effects of contributing factors. The first component is concerned with the development of an improved identification approach for secondary accidents that relies on the rich traffic information obtained from traffic sensors. The second component of the proposed methodology is aimed at understanding the key mechanisms that are hypothesized to cause secondary crashes through the use of a modified logistic regression model that can efficiently deal with relatively rare events such as secondary incidents. The feasibility and improved performance of using the proposed methodology are tested using real-world crash and traffic flow data.
  
  
  RESULTS
  The risk of inducing secondary crashes after the occurrence of individual primary crashes under different circumstances is studied by employing the estimated regression model. Marginal effect of each factor on the risk of secondary crashes is also quantified and important contributing factors are highlighted and discussed.
  
  
  CONCLUSIONS
  Massive sensor data can be used to support the identification of secondary crashes. The occurrence mechanism of these secondary crashes can be investigate by the proposed model. Understanding the mechanism helps deploy appropriate countermeasures to mitigate or prevent the secondary crashes.
authors.affiliation: Department of Civil and Urban Engineering, Center for Urban Science and Progress (CUSP), New York University (NYU), One MetroTech Center, 19th Floor, Office 1919Q, Brooklyn, NY 11201, USA. Electronic address: hong.yang@nyu.edu.
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Civil and Urban Engineering, Center for Urban Science and Progress (CUSP), New York University (NYU), One MetroTech Center, 19th Floor, Brooklyn, NY 11201, USA. Electronic address: kaan.ozbay@nyu.edu.
authors.forename: Kaan
authors.initials: K
authors.lastname: Ozbay
authors.affiliation: Department of Civil and Urban Engineering, New York University (NYU), One MetroTech Center, 19th Floor, Office 1919N, Brooklyn, NY 11201, USA. Electronic address: kun.xie@nyu.edu.
authors.forename: Kun
authors.initials: K
authors.lastname: Xie
mesh_terms: D000063:Accidents, Traffic / Q000517:prevention & control; D006801:Humans; D016015:Logistic Models; D008962:Models, Theoretical; D018570:Risk Assessment / Q000379:methods*; D012449:Safety
keywords: Crash risk; Highway; Rare event logistic regression; Secondary crash; Traffic safety