In response to a provision of the Surface Transportation Assistance Act of 1982, the Secretary of Transportation, acting through the Federal Highway Administration, requested the National Academy of Sciences to study the safety cost-effectiveness of geometric design standards and recommend minimum standards for resurfacing, restoration, and rehabilitation (RRR) projects on existing federal-aid highways, except freeways. RRR projects can extend the service life of existing highways through pavement and other repairs and at the same time improve highway safety by making selective improvements to highway geometry and other roadside features. Striking a balance between preservation and safety improvements on RRR projects has proved controversial, however. The controversy has centered on which minimum geometric design standards should be applied to RRR projects to qualify for federal aid. This report presents the findings of a study committee which conducted case studies of current RRR design practices, reviewed current knowledge about relationships between geometric design and safety, and analyzed the cost and safety trade-offs of geometric improvements to existing highways. The report concludes with the study committee recommendations concerning a variety of practices that will increase the safety cost-effectiveness of RRR projects.