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(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural

Category:Alignment

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural

Countermeasure: Increase vertical grade by 1%

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.02[#chr(176)#]-2text textAllAllPrincipal Arterial OtherRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural

Category:Intersection geometry

Countermeasure: Change intersection skew angle

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural
CMF Equationtext textAllAllMinor ArterialRural
CMF Equationtext textAllAllMinor ArterialRural
CMF Equationtext textAllAllMinor ArterialRural
CMF Equationtext textAllAllMinor ArterialRural
CMF Equationtext textAllAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.94[#chr(176)#]6text textAllK,A,B,CMinor ArterialUrban
0.65[#chr(176)#]35text textAllK,A,B,CMinor ArterialUrban

Category:Intersection traffic control

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.99[#chr(176)#]1text textAllAllNot specifiedUrban

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.52[B]482 StarsAllAllNot SpecifiedRural

Category:Roadside

Countermeasure: Modify roadside hazard rating

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textAllAllMinor ArterialRural

Category:Roadway

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.02-2text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.3-30text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.01-1text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialUrban and suburban
1.05-5text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialUrban and suburban
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialUrban and suburban

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.5-50text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.05-5text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural

Countermeasure: Provide passing lane or climbing lane

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.75[#chr(176)#]25text textAllAllMinor ArterialRural

Countermeasure: Provide short four-lane section

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.65[#chr(176)#]35text textAllAllMinor ArterialRural

Category:Shoulder treatments

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.1-10text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.5-50text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.07-7text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.3-30text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.15-15text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
1.02-2text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
CMF Equationtext textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
0.8713text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural
0.982text textHead on,Run off road,Sideswipe,Single vehicleAllMinor ArterialRural