Study Details

Study Title: Developing Crash Modification Factors for Interchange Influence Areas on Urban Four-Lane Freeways Using Multivariate Adaptive Regression Splines

Authors: Haleem, Gan, and Lu

Publication Date: JAN, 2012

Abstract: Crash modification factors (CMFs) are used to measure the safety impacts from 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. This paper aims at developing CMFs for interchange influence areas on urban four-lane freeways in the state of Florida. The need to model freeway interchange areas apart from their basic mainlines has been recognized by SafetyAnalyst. Different methods for developing CMFs can be found in the literature. This paper introduces a promising data mining method known as multivariate adaptive regression splines (MARS) for CMF development. MARS is characterized by its capability to accommodate the nonlinearity in crash predictors, which can be a mixture of continuous and categorical variables. In addition, MARS allows the impact of more than one geometric variable to be simultaneously considered when estimating CMFs. Separate CMFs were developed for inside and outside shoulder widths within the interchange influence areas. The results showed that MARS produced CMFs with higher confidence than those using the negative binomial model. The influential variables identified included the inside shoulder width, outside shoulder width, traffic volume, shoulder type, and speed limit. It was also found that inside shoulders less than 4 ft and 4 to 6 ft experienced safety improvement in relative to the 4-ft width.

Study Citation: 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).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Shoulder treatments

Countermeasure: Decrease inside paved shoulder width from 4ft to 2ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.728 27.2 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease inside paved shoulder width from 4ft to 2ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.668 33.2 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease inside paved shoulder width from 4ft to 2ft (outside paved shoulder width = 8ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.749 25.1 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease outside paved shoulder width from 10ft to 4ft (inside paved shoulder width = 4ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.417 58.3 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Decrease outside paved shoulder width from 10ft to 8ft (inside paved shoulder width = 4ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.819 18.1 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 10ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.665 33.5 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 10ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.977 2.3 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 10ft (outside paved shoulder width = 8ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.776 22.4 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 11ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.173 -17.3 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 11ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.294 -29.4 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 12ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.992 0.8 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 12ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.946 5.4 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 12ft (outside paved shoulder width = 8ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.043 -4.3 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 5ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.573 42.7 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 6ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.472 52.8 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 6ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.561 43.9 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 6ft (outside paved shoulder width = 8ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.757 24.3 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 8ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.78 22 3 Stars All K,A,B,C Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 8ft (outside paved shoulder width = 10ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.224 -22.4 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase inside paved shoulder width from 4ft to 8ft (outside paved shoulder width = 8ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.639 36.1 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase outside paved shoulder width from 10ft to 11ft (inside paved shoulder width = 4ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.169 -16.9 3 Stars All All Principal Arterial Other Freeways and Expressways Urban

Countermeasure: Increase outside paved shoulder width from 10ft to 12ft (inside paved shoulder width = 4ft)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.793 20.7 3 Stars All All Principal Arterial Other Freeways and Expressways Urban