The Effect of Lane and Shoulder Widths on Accident Reductions on Rural, Two-Lane Roads

The purpose of the study was to determine the effect of lane and shoulder widths on accident benefits for rural, two-lane roads and also to determine the expected cost effectiveness of widening lanes and shoulders. Information concerning geometries, accidents, and traffic volumes was obtained for over 25,000 km (15,000 miles) of roads. Run-off-road and opposite-direction accidents were the only accident types found to be associated with narrow lanes and shoulders. Wide lanes had accident rates 10 to 39 percent lower than for narrow lanes. Wide shoulders (up to 2.7 m (9 feet)) were associated with the lower accident rates. Criteria based on a cost-effectiveness approach were developed for selecting highway sections for widening.