Designing Safer Roads

TRB Special Report 214: Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation examines the cost-effectiveness of safety-related geometric design elements such as lane and shoulder widths, crest vertical curves, stopping sight distances, and intersections.

Safety is a central design consideration for modern highways. For roads receiving federal aid, safety is incorporated through the design policies established by the American Association of State Highway and Transportation Officials (AASHTO), adherence to which is required by the Federal Highway Administration for roads funded with federal aid. Many older and rural roads, however, were built before AASHTO’s modern guidelines had been established. When federal aid is used to improve these roads—when they are resurfaced, for example—safety advocates have urged that they be upgraded to incorporate modern design standards, which might include wider lanes, improved provision for driver sight distance, and other enhancements. State and local officials, by contrast, often contend that raising these roads to the current standards would greatly reduce the number of miles of road that could be resurfaced or upgraded, which would itself be detrimental to safety.

Unfortunately, the safety benefits of such design features have not been well established. Moreover, the variability in local conditions, the amount of daily traffic, and other considerations undermine the usefulness of specific standards. Nonetheless, the committee that produced this report recommended a number of safety-conscious design practices and improvements, including minimum lane and shoulder widths for two-lane roads and bridge widths. The committee also recommended analytical approaches that could be used by state and local officials to determine when safety improvements should be considered, and outlined an approach for assessing the safety cost-effectiveness of doing so. The report produced by the committee has become a standard reference for engineers designing improvements to rural roads.