A simultaneous equations model of crash frequency by collision type for rural intersections

Xin Ye, Ram Pendyala, Simon P. Washington, Karthik Konduri, Jutaek Oh

Research output: Contribution to journalArticlepeer-review

134 Scopus citations


Safety at roadway intersections is of significant interest to transportation professionals due to the large number of intersections in transportation networks, the complexity of traffic movements at these locations that leads to large numbers of conflicts, and the wide variety of geometric and operational features that define them. A variety of collision types including head-on, sideswipe, rear-end, and angle crashes occur at intersections. While intersection crash totals may not reveal a site deficiency, over exposure of a specific crash type may reveal otherwise undetected deficiencies. Thus, there is a need to be able to model the expected frequency of crashes by collision type at intersections to enable the detection of problems and the implementation of effective design strategies and countermeasures. Statistically, it is important to consider modeling collision type frequencies simultaneously to account for the possibility of common unobserved factors affecting crash frequencies across crash types. In this paper, a simultaneous equations model of crash frequencies by collision type is developed and presented using crash data for rural intersections in Georgia. The model estimation results support the notion of the presence of significant common unobserved factors across crash types, although the impact of these factors on parameter estimates is found to be rather modest.

Original languageEnglish (US)
Pages (from-to)443-452
Number of pages10
JournalSafety Science
Issue number3
StatePublished - Mar 2009


  • Collision type
  • Crash frequency
  • Intersection safety
  • Multivariate Poisson regression
  • Simultaneous equations model
  • Unobserved heterogeneity

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Safety Research
  • Public Health, Environmental and Occupational Health


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