Toward More Flexible Design

The standards are comprehensive, covering a broad range of design characteristics, while allowing for flexibility in their application. Since 1985, FHWA has emphasized a subset of the design criteria contained in adopted standards by designating them as the 13 controlling criteria: design speed, lane width, shoulder width, bridge width, horizontal alignment, superelevation, vertical alignment, grade, stopping sight distance, cross slope, vertical clearance, horizontal clearance, and structural capacity. In 2014, the National Cooperative Highway Research Program Report 783 Evaluation of the 13 Controlling Criteria for Geometric Design examined the safety and operational effects of the controlling criteria.\n The significant reduction in the number of controlling criteria applicable to roadways with lower speeds will give engineers the flexibility they need to design solutions that address the project goals in a way that is more compatible with the community.