The purpose of the study was to determine the cost-effectiveness of widening lanes and shoulders on rural, two-lane roads. Information concerning geometries, accidents, and traffic volumes was obtained for over 15,000 miles (25,000 km) of roads. Reductions in accident rates occurred as lane and shoulder widths increased. Run-off-road and opposite direction accidents were the primary accident types associated with narrow lanes and shoulders. Reductions in accidents ranged from 10 to 39 percent for lane widening and 6 to 21 percent for shoulder widening. Priority listings were prepared for 531 projects based on critical rate factor. Priority listings were also prepared for tbe top 120 lane widening projects and the top 36 shoulder-widening projects based on benefit-cost ratios.

Report Date


Report Number

No. 524

Digital Object Identifier



The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein, The contents do not necessarily reflect the official views or policies of the Bureau of Highways, This report does not constitute a standard, specification, or regulation.