This report describes the impact of the controlling roadway design criteria on safety and operations for urban and rural roads. In 1985, the FHWA designated 13 specific design elements as controlling criteria for roadway design. The 13 controlling criteria are (1) design speed, (2) lane width, (3) shoulder width, (4) bridge width, (5) structural capacity, (6) horizontal alignment, (7) vertical alignment, (8) grade, (9) stopping sight distance, (10) cross slope, (11) superelevation, (12) vertical clearance, and (13) horizontal clearance. Federally assisted highway construction and reconstruction projects must meet the established design criteria for these elements, or a formal design exception must be prepared and approved. Different procedures apply to rehabilitation projects, but these design elements are still key considerations in design. Since their designation, the 13 controlling criteria and their application have not been reconsidered as new knowledge has been gained about the relationships between geometric design elements and safety and operations.

In this research project, the research team investigated what is known about the safety and operational effects of the 13 controlling and other important geometric design criteria. Several small studies were done to augment the information found in the literature. This information was used to assess the sensitivity of safety and operations to design decisions for these criteria for different types of roads. The research also addressed how to reduce confusion related to the definitions of the controlling criteria. The use of the controlling criteria in design exception processes was also explored, including through interviews with state department of transportation (DOT) personnel. This report will be useful to geometric designers and those responsible for reviewing designs, particularly in agencies that are transitioning away from “standards-based design.”