Study Details

Study Title: A Simultaneous Equations Model of Crash Frequency By Collision Type for Rural Intersections

Authors: Ye et al.

Publication Date: JAN, 2008

Abstract: 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. Estimation of crash frequencies at intersections is paramount for effective intersection design, for identifying sites with promise, and for supporting proactive safety planning. 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 a data set of crash frequencies by collision type 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. The multivariate count data modeling methodology developed and presented in this paper is a significant methodological contribution to the field, and is only beginning to be applied in the field to intersection safety analysis.

Study Citation: Ye, X., R.M. Pendyala, S.P. Washington, K. Konduri, and J. Oh (2008). A Simultaneous Equations Model of Crash Frequency By Collision Type for Rural Intersections, 87th Annual Meeting of the Transportation Research Board, TRB 2008 Annual Meeting CD-ROM.


CMFs Associated With This Study

Category: Highway lighting

Countermeasure: Provide intersection illumination

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.67 32.6 4 Stars Angle All Not Specified Rural
0.56 43.8 3 Stars Vehicle/pedestrian All Not Specified Rural

Category:Intersection geometry

Countermeasure: Increase the number of left-turn lanes on the major road from X to Y

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars Sideswipe All Not Specified Rural

Countermeasure: Increase the number of left-turn lanes on the minor road from X to Y

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 4 Stars Angle All Not Specified Rural

Countermeasure: Increase the number of right-turn lanes on the major road from X to Y

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars Rear end All Not Specified Rural
CMF Equation CRF Equation 3 Stars Sideswipe All Not Specified Rural

Category:Shoulder treatments

Countermeasure: Widen paved shoulder from X to Y ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 4 Stars Angle All Not Specified Rural
CMF Equation CRF Equation 3 Stars Sideswipe All Not Specified Rural
CMF Equation CRF Equation 3 Stars Vehicle/pedestrian All Not Specified Rural