This investigation was undertaken to develop revised roadway width guidelines based on accident analyses, cost estimates, and operational considerations. The primary data source selected was a data base of approximately 3,862 km (2,400 mi) of two-lane road from seven States and supplemented with data from approximately 2,736 km (1,700 mi) of paved and unpaved two-lane roadway (mostly local and collector roads) from two Highway Safety Information System (HSIS) States (Utah and Michigan) and North Carolina. A detailed statistical analysis was conducted on the primary data base, and accident rates were determined for various lane and shoulder widths. As a result of the data analyses, revised American Association of State Highway and Transportation Officials (AASHTO) roadway width criteria were developed and recommended to replace the guidelines in the current AASHTO "Green Book." The goal is that these revised design guidelines would be likely to reduce the costs of reconstructing two-lane rural highways, and would result in more cost-effective use of limited highway funding.