Study Details

Study Title: Safety Effectiveness of Lane and Shoulder Width Combinations on Rural, Two-Lane, Undivided Roads

Authors: Gross et al.

Publication Date: JUN, 2009

Abstract: There is a need to evaluate low-cost safety strategies that States may implement as part of their Strategic Highway Safety Plan. The Federal Highway Administration organized a Pooled Fund Study of 26 States to evaluate several low-cost safety strategies; reallocation of total paved width was one strategy selected. This study identifies whether it is "safer" to increase lane width or increase shoulder width given a fixed total width. Geometric, traffic, and crash data were obtained for more than 52,000 miles of roadway segments in Pennsylvania and Washington. A case-control approach was applied to evaluate the safety effectiveness of lane-shoulder configurations for fixed total paved widths. There was a general reduction in the odds ratio as total paved width, lane width, and shoulder width increase individually; this is consistent with previous research and validates the modeling approach. However, the primary research objective was to estimate the safety effectiveness of reallocating a fixed total paved width. Individual State results did not indicate a clear trade-off between lane and shoulder width for a fixed total width. In some cases, adding lane width is favorable where in other cases, adding shoulder width is favorable. Supplementing the results of this study with previous research, crash modification factors (CMFs) are provided for several lane-shoulder combinations. The selected values present a more apparent trade-off, indicating a slight benefit to increasing lane width for a fixed total width. Importantly, the results differ from other studies that developed CMFs without considering the interaction between lane and shoulder width, including those studies currently referenced in the Highway Safety Manual. This raises the question of whether CMFs should reflect the interaction between lane and shoulder width.

Study Citation: Gross, F., P.P. Jovanis, K. Eccles, and K. Chen. "Safety Effectiveness of Lane and Shoulder Width Combinations on Rural, Two-Lane, Undivided Roads." Federal Highway Administration, Report FHWA-HRT-09-031. (June 2009).

Related Citations: Gross, F., P.P. Jovanis, and K. Eccles, "Safety Effectiveness of Lane and Shoulder Width Combinations on Rural, Two-Lane, Undivided Roads." TRB 88th Annual Meeting Compendium of Papers CD-ROM. Washington, D.C., (2009).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Roadway

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 10-ft lanes and 3-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.13 -13 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 10-ft lanes and 4-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.2 -20 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 2-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.12 -12 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 3-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.19 -19 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 4-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.14 -14 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 5-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.06 -6 2 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 6-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.84 16 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 11-ft lanes and 7-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1 0 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 12-ft lanes and 2-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.16 -16 3 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 12-ft lanes and 3-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.11 -11 2 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 12-ft lanes and 4-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.04 -4 2 Stars Run off road All Not Specified Rural

Countermeasure: Convert 12-ft lanes and 6-ft shoulders to 12-ft lanes and 5-ft shoulders

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.87 13 3 Stars Run off road All Not Specified All