Study Details

Study Title: Collision Models for Multilane Highway Segments to Examine the Safety of Curbs

Authors: Baek and Hummer

Publication Date:JAN, 2008

Abstract: The objective of this study was to develop valid statistical collision models for multilane highway segments to examine the safety of curbs. For this, road geometric traffic, and collision data for 2001 to 2003 were collected. The data included 2,274 collisions and 885 injury collisions that occurred on 191.85 miles of 199 directional segments in North Carolina. The authors applied a new modeling method of introducing variables into the model one by one in a multiplicative form. A nonlinear optimizing algorithm for estimating parameters using a negative binomial log likelihood function was adopted for the modeling. The authors determined the functional form of the variable to be introduced based on the relationship between the recorded number of collisions and the number of collisions predicted by the current model without the variable. The integrate-differentiate method was applied to find candidate functional forms for each variable. Model selections were based on the -2 log likelihood and BIC statistics. The authors adopted the cumulative residuals (CURE) plot method to check the goodness of fit of the models. As a result of the modeling efforts, the annual average daily traffic, access point density, shoulder width, and shoulder type (including curb presence) variables were introduced to the final model for total collisions. The same variables except the shoulder type variable were introduced to the injury collision model. Overall, then, it appears that curbs mean fewer total collisions and no change in injury collisions as compared to no curbs on the sampled road segments.

Study Citation: Baek,J. and J.E. Hummer (2008). Collision Models for Multilane Highway Segments to Examine the Safety of Curbs. 87th Annual Meeting of the Transportation Research Board, TRB 2008 Annual Meeting CD-ROM.


CMFs Associated With This Study

Category: Shoulder treatments

Countermeasure: Install curb and gutter

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.89114 StarsAllAllNot SpecifiedSuburban