Study Details

Study Title: Using multivariate adaptive regression splines (MARS) to develop crash modification factors for urban freeway interchange influence areas

Authors: Haleem et al.

Publication Date: JUN, 2013

Abstract: Crash modification factors (CMFs) are used to measure the safety impacts of changes in specific geometric characteristics. Their development has gained much interest following the adoption of CMFs by the recently released Highway Safety Manual (HSM) and SafetyAnalyst tool in the United States. This paper describes a study to develop CMFs for interchange influence areas on urban freeways in the state of Florida. Despite the very different traffic and geometric conditions that exist in interchange influence areas, most previous studies have not separated them from the rest of the freeway system in their analyses. In this study, a promising data mining method known as multivariate adaptive regression splines (MARS) was applied to develop CMFs for median width and inside and outside shoulder widths for "total" and "fatal and injury" (FI) crashes. In addition, CMFs were also developed for the two most frequent crash types, i.e., rear-end and sideswipe. MARS is characterized by its ability to accommodate the nonlinearity in crash predictors and to allow the impact of more than one geometric variable to be simultaneously considered. The methodology further implements crash predictions from the model to identify changes in geometric design features. Four years of crashes from 2007 to 2010 were used in the analysis and the results showed that MARS's prediction capability and goodness-of-fit statistics outperformed those of the negative binomial model. The influential variables identified included the outside and inside shoulder widths, median width, lane width, traffic volume, and shoulder type. It was deduced that a 2-ft increase in the outside and inside shoulders (from 10 ft to 12 ft) reduces FI crashes by 10% and 33%, respectively. Further, a 42-ft reduction in the median width (from 64 ft to 22 ft) increases the rear-end, total, and FI crashes by 473%, 263%, and 223%, respectively.

Study Citation: Haleem, K, A. Gan, and J. Lu. "Using multivariate adaptive regression splines (MARS) to develop crash modification factors for urban freeway interchange influence areas". Accident Analysis and Prevention, Vol. 55, (2013) pp. 12-21.

Related Citations: Haleem, K., A. Gan, and J. Lu, "Developing Crash Modification Factors for Interchange Influence Areas on Urban Four-Lane Freeways Using Multivariate Adaptive Regression Splines." TRB 91st Annual Meeting Compendium of Papers, Washington, D.C, (2012).


CMFs Associated With This Study

Category: Access management

Countermeasure: Decrease median width from 64ft to 22ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
3.629 -262.9 3 Stars All All Principal Arterial Other Freeways and Expressways Urban
3.227 -222.7 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban
5.732 -473.2 3 Stars Rear end All Principal Arterial Other Freeways and Expressways Urban
4.184 -318.4 3 Stars Sideswipe All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease median width from 64ft to 40ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.071 -7.1 3 Stars All All Principal Arterial Other Freeways and Expressways Urban
1.073 -7.3 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban
1.43 -43 3 Stars Rear end All Principal Arterial Other Freeways and Expressways Urban
1.151 -15.1 3 Stars Sideswipe All Principal Arterial Other Freeways and Expressways Urban

Category:Shoulder treatments

Countermeasure: Decrease inside shoulder width from 10ft to 4ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.446 55.4 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease paved outside shoulder width from 10ft to 8ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.081 -8.1 3 Stars All All Principal Arterial Other Freeways and Expressways Urban
1.172 -17.2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban
1.111 -11.1 3 Stars Rear end All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside shoulder width from 10ft to 11ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.98 2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside shoulder width from 10ft to 12ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.669 33.1 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase paved outside shoulder width from 10ft to 12ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.774 22.6 3 Stars All All Principal Arterial Other Freeways and Expressways Urban
0.9 10 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban
0.816 18.4 3 Stars Rear end All Principal Arterial Other Freeways and Expressways Urban