Study Details

Study Title: Prediction of the Expected Safety Performance of Rural Two-Lane Highways

Authors: Harwood et al.

Publication Date: 2000

Abstract: This report presents an algorithm for predicting the safety performance of a rural two-lane highway. The accident prediction algorithm consists of base models and accident modification factors for both roadway segments and at-grade intersections on rural two-lane highways. The base models provide an estimate of the safety performance of a roadway or intersection for a set of assumed nominal or base conditions. The accident modification factors adjust the base model predictions to account for the effects on safety for roadway segments of lane width, shoulder width, shoulder type, horizontal curves, grades, driveway density, two-way left-turn lanes, passing lanes, roadside design and the effects on safety for at-grade intersections of skew angle, traffic control, exclusive left- and right-turn lanes, sight distance, and driveways. The accident prediction algorithm is intended for application by highway agencies to estimate the safety performance of an existing or proposed roadway. The algorithm can be used to compare the anticipated safety performance of two or more geometric alternatives for a proposed highway improvement. The accident prediction algorithm includes a calibration procedure that can be used to adapt the predicted results to the safety conditions encountered by any particular highway agency on rural two-lane highways. The algorithm also includes an Empirical Bayes procedure that can be applied to utilize the safety predictions provided by the algorithm together with actual site-specific accident history data.

Study Citation: Harwood, D. W., Council, F. M., Hauer, E., Hughes, W. E., and Vogt, A., "Prediction of the Expected Safety Performance of Rural Two-Lane Highways." FHWA-RD-99-207, McLean, Va., Federal Highway Administration, (2000)

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Access management

Countermeasure: Modify access point density

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Category:Alignment

Countermeasure: Improve superelevation variance (SV) where 0.01 <= SV < 0.02

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Countermeasure: Improve superelevation variance (SV) where SV > 0.02

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Countermeasure: Increase vertical grade by 1%

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.02 [°] -2 Cannot Be Rated (HSM) All All Principal Arterial Other Rural

Countermeasure: Modify horizontal curve radius and length and provide spiral transitions

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Category:Intersection geometry

Countermeasure: Change intersection skew angle

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Countermeasure: Provide a left-turn lane on one major-road approach

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.94 [°] 6 Cannot Be Rated (HSM) All K,A,B,C Minor Arterial Urban
0.65 [°] 35 Cannot Be Rated (HSM) All K,A,B,C Minor Arterial Urban

Category:Intersection traffic control

Countermeasure: Change from permissive to protected/permissive or permissive/protected phasing

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.99 [°] 1 Cannot Be Rated (HSM) All All Not specified Urban

Countermeasure: Convert minor-road stop control to all-way stop control

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.52 [B] 48 5 Stars All All Not Specified Rural

Category:Roadside

Countermeasure: Modify roadside hazard rating

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation Cannot Be Rated (HSM) All All Minor Arterial Rural

Category:Roadway

Countermeasure: Convert 12-foot lanes to 10-foot lanes

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.02 -2 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
1.3 -30 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural

Countermeasure: Convert 12-foot lanes to 11-foot lanes

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.01 -1 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Urban and suburban
1.05 -5 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Urban and suburban
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Urban and suburban

Countermeasure: Convert 12-foot lanes to 9-foot or less

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.05 -5 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
1.5 -50 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural

Countermeasure: Provide passing lane or climbing lane

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.75 [°] 25 Cannot Be Rated (HSM) All All Minor Arterial Rural

Countermeasure: Provide short four-lane section

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.65 [°] 35 Cannot Be Rated (HSM) All All Minor Arterial Rural

Category:Shoulder treatments

Countermeasure: Convert 6-foot shoulder to 0-foot shoulder

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.1 -10 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
1.5 -50 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural

Countermeasure: Convert 6-foot shoulder to 2-foot shoulder

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.07 -7 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
1.3 -30 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural

Countermeasure: Convert 6-foot shoulder to 4-foot shoulder

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.02 -2 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
1.15 -15 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural

Countermeasure: Convert 6-foot shoulder to 8-foot shoulder

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.98 2 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
0.87 13 Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural
CMF Equation Cannot Be Rated (HSM) Head on,Run off road,Sideswipe,Single vehicle All Minor Arterial Rural