Study Details

Study Title: Safety Effects of Shoulder Paving for Rural and Urban Interstate, Mulitlane, and Two-Lane Highways

Authors: Li et al.

Publication Date:OCT, 2013

Abstract: This paper introduces an Empirical Bayesian (EB) before-after analysis method for assessing the effects of highway shoulder paving on safety performance. In the first step, multi-year data on field-observed crash frequencies for highway segments with pavement resurfacing and shoulder paving (Type I treatment) and highway segments with pavement resurfacing only (Type II treatment), as well as untreated highway segments, on the Illinois state-maintained rural and urban interstate, multilane, and two-lane highways are collected. Next, data on untreated highway segments are used to calibrate safety performance functions (SPFs) and to predict crash frequencies for Type I and II treated highway segments, in the cases where respective treatments not been implemented. After computing the EB-adjusted crash frequency as a weighted sum of field-observed and SPF-predicted crash frequencies, the EB crash frequency for the after-treatment period is established by adjusting the EB crash frequency for the before-treatment period according to changes in traffic volumes and segment lengths between before- and after-treatment periods. The safety effects of shoulder paving are determined as the difference in the EB-adjusted Type I and II crash frequencies for the after-treatment period. It is revealed that reductions in shoulder-related fatal, injury, and property damage only (PDO) crashes from shoulder paving varies greatly by highway functional classification; and adding a new paved shoulder tends to be more effective in terms of crash reductions than paving the same width of the existing paved shoulder that has deteriorated over time or widening the paved shoulder.

Study Citation: Li, Z., K. Kepaptsoglou, Y. Lee, H. Patel, Y. Liu, and H.G. Kim. "Safety Effects of Shoulder Paving for Rural and Urban Interstate, Multilane, and Two-Lane Highways". Journal of Transportation Engineering, Vol. 139, (2013) pp 1010-1019.

Related Citations: Bamzai, R., Y. Lee, and Z. Li. "Safety Impacts of Highway Shoulder Attributes in Illinois." Report No. FHWA-ICT-11-078, Illinois Department of Transportation, Springfield, IL, (April 2011).


CMFs Associated With This Study

Category: Shoulder treatments

Countermeasure: Pave deteriorated shoulder (2 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9374 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.81194 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9914 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9734 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9284 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.89114 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.85154 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.9284 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.73274 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
0.9194 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Pave deteriorated shoulder (4 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9464 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.81194 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9914 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9914 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.9374 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9824 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.8204 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.8204 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.9104 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.73274 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
0.9104 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9464 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Pave deteriorated shoulder (6 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9554 StarsHead on,Left turn,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.8204 StarsHead on,Left turn,Run off road,SideswipeKNot specifiedRural
0.9914 StarsHead on,Left turn,Run off road,SideswipeKNot specifiedRural
0.9824 StarsHead on,Left turn,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.88124 StarsHead on,Left turn,Run off road,SideswipeKNot specifiedUrban
0.9824 StarsHead on,Left turn,Run off road,SideswipeKNot specifiedUrban
0.9824 StarsHead on,Left turn,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
0.9914 StarsHead on,Left turn,Run off road,SideswipeA,B,CNot specifiedRural
0.9464 StarsHead on,Left turn,Run off road,SideswipeA,B,CNot specifiedRural
0.9554 StarsHead on,Left turn,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
0.9644 StarsHead on,Left turn,Run off road,SideswipeA,B,CNot specifiedUrban
0.9554 StarsHead on,Left turn,Run off road,SideswipeA,B,CNot specifiedUrban
0.73274 StarsHead on,Left turn,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.81194 StarsHead on,Left turn,Run off road,SideswipeONot specifiedRural
0.79214 StarsHead on,Left turn,Run off road,SideswipeONot specifiedRural
0.72284 StarsHead on,Left turn,Run off road,SideswipeOPrincipal Arterial InterstateUrban
0.9284 StarsHead on,Left turn,Run off road,SideswipeONot specifiedUrban
0.9194 StarsHead on,Left turn,Run off road,SideswipeONot specifiedUrban

Countermeasure: Pave deteriorated shoulder (8 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9734 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.78224 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.85154 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9914 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9464 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
104 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9284 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
0.9914 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.88124 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.64364 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.82184 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.7304 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.84164 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9104 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Pave deteriorated shoulder (>8 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.19-194 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
1.21-214 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.1-104 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
1.03-34 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.02-24 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.08-84 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
1.44-444 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9464 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
1.02-24 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
1.16-164 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.72284 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9554 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
1.35-354 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
1.07-74 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
1.06-64 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
1.14-144 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.89114 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen paved shoulder from 4 ft to 6 ft

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.03-34 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.03-34 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9914 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.9104 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.02-24 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.05-54 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
1.03-34 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
1.01-14 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.87134 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
1.02-24 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.77234 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
1.04-44 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9194 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen paved shoulder from 4 ft to 8 ft

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.06-64 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.07-74 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.84164 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.04-44 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
1.06-64 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9374 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
1.07-74 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.65354 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.67334 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
1.05-54 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.59414 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
1.23-234 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
1.09-94 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.87134 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen paved shoulder from 6 ft to 8 ft

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.03-34 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.04-44 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
104 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.9374 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.02-24 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
0.9284 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
1.02-24 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
1.01-14 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
1.06-64 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.69314 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.81194 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
1.04-44 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.82184 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
1.25-254 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
1.05-54 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9734 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen shoulder (paved) (from 0 to 4 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.86144 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.05-54 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.9374 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.07-74 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.1-104 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9914 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.7304 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.77234 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.54464 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
0.9734 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.9104 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen shoulder (paved) (from 0 to 6 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.89114 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.08-84 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9734 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.83174 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.09-94 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.15-154 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
0.9824 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9554 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
104 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.9374 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.57434 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.79214 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.75254 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.52484 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
104 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.8204 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban

Countermeasure: Widen shoulder (paved) (from 0 to 8 ft)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9284 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateRural
0.9284 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
1.11-114 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeKPrincipal Arterial InterstateUrban
0.77234 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.11-114 StarsFixed object,Head on,Run off road,SideswipeKNot specifiedUrban
1.07-74 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateRural
104 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9284 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedRural
0.9644 StarsFixed object,Head on,Run off road,SideswipeA,B,CPrincipal Arterial InterstateUrban
1.06-64 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.63374 StarsFixed object,Head on,Run off road,SideswipeA,B,CNot specifiedUrban
0.38624 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateRural
0.82184 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.57434 StarsFixed object,Head on,Run off road,SideswipeONot specifiedRural
0.77234 StarsFixed object,Head on,Run off road,SideswipeOPrincipal Arterial InterstateUrban
1.06-64 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban
0.77234 StarsFixed object,Head on,Run off road,SideswipeONot specifiedUrban