CRASH MODIFICATION FACTORS CLEARINGHOUSE

Study Details

Prediction of the Expected Safety Performance of Rural Two-Lane Highways

Study ID: 25

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
		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
		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
		Cannot Be Rated (HSM)	All	All	Minor Arterial	Rural

Countermeasure: Increase vertical grade by 1%

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

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

Cannot Be Rated (HSM)

All

All

Minor Arterial

Rural

Cannot Be Rated (HSM)

All

All

Minor Arterial

Rural

Cannot Be Rated (HSM)

All

All

Minor Arterial

Rural

Cannot Be Rated (HSM)

All

All

Minor Arterial

Rural

Cannot Be Rated (HSM)

All

All

Minor Arterial

Rural

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

Category:Intersection traffic control

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

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		All	All	Not Specified	Rural

Category:Roadside

Countermeasure: Modify roadside hazard rating

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

Category:Roadway

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

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

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

Cannot Be Rated (HSM)

Head on,Run off road,Sideswipe,Single vehicle

All

Minor Arterial

Rural

Countermeasure: Provide passing lane or climbing lane

Countermeasure: Provide short four-lane section

Category:Shoulder treatments

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

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

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
		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
		Cannot Be Rated (HSM)	Head on,Run off road,Sideswipe,Single vehicle	All	Minor Arterial	Rural

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For more information, contact Sarah Weissman Pascual at sarah.pascual@dot.gov