Study Details

Study Title: Assessment of safety effects for widening urban roadways in developing crash modification functions using nonlinearizing link functions

Authors: Park et al.

Publication Date: MAR, 2015

Abstract: Since a crash modification factor (CMF) represents the overall safety performance of specific treatments in a single fixed value, there is a need to explore the variation of CMFs with different roadway characteristics among treated sites over time. Therefore, in this study, we (1) evaluate the safety performance of a sample of urban four-lane roadway segments that have been widened with one through lane in each direction and (2) determine the relationship between the safety effects and different roadway characteristics over time. Observational before-after analysis with the empirical Bayes (EB) method was assessed in this study to evaluate the safety effects of widening urban four-lane roadways to six-lanes. Moreover, the nonlinearizing link functions were utilized to achieve better performance of crash modification functions (CMFunctions). The CMFunctions were developed using a Bayesian regression method including the estimated nonlinearizing link function to incorporate the changes in safety effects of the treatment over time. Data was collected for urban arterials in Florida, and the Florida-specific full SPFs were developed and used for EB estimation. The results indicated that the conversion of four-lane roadways to six-lane roadways resulted in a crash reduction of 15 percent for total crashes, and 24 percent for injury crashes on urban roadways. The results show that the safety effects vary across the sites with different roadway characteristics. In particular, LOS changes, time changes, and shoulder widths are significant parameters that affect the variation of CMFs. Moreover, it was found that narrowing shoulder and median widths to make space for an extra through lane shows a negative safety impact. It was also found that including the nonlinearizing link functions in developing CMFunctions shows more reliable estimates, if the variation of CMFs with specific parameters has a nonlinear relationship. The findings provide insights into the selection of roadway sites for adding through lanes.

Study Citation: Park, J., M. Abdel-Aty, J. Wang, and C. Lee. "Assessment of safety effects for widening urban roadways in developing crash modification functions using nonlinearizing link functions". Accident Analysis and Prevention, Vol. 79, (2015) pp. 80-87.


CMFs Associated With This Study

Category: Roadway

Countermeasure: Increase from 4 lanes to 6 lanes

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.85 15 4 Stars All All Not specified Urban
0.901 9.9 3 Stars All All Not specified Urban
0.847 15.3 4 Stars All All Not specified Urban
0.798 20.2 4 Stars All All Not specified Urban
0.802 19.8 4 Stars All All Not specified Urban
0.761 23.9 4 Stars All K,A,B,C Not specified Urban
0.841 15.9 3 Stars All K,A,B,C Not specified Urban
0.755 24.5 4 Stars All K,A,B,C Not specified Urban
0.696 30.4 4 Stars All K,A,B,C Not specified Urban
0.702 29.8 4 Stars All K,A,B,C Not specified Urban
0.809 19.1 4 Stars All All Not specified Urban
0.853 14.7 3 Stars All All Not specified Urban
0.918 8.2 3 Stars All All Not specified Urban
0.657 34.3 4 Stars All K,A,B,C Not specified Urban
0.742 25.8 3 Stars All K,A,B,C Not specified Urban
0.868 13.2 3 Stars All K,A,B,C Not specified Urban
0.916 8.4 3 Stars All All Not specified Urban
0.807 19.3 3 Stars All K,A,B,C Not specified Urban
0.737 26.3 4 Stars All All Not specified Urban
0.702 29.8 4 Stars All K,A,B,C Not specified Urban