The Federal Highway Administration recently revised their controlling criteria for National Highway System (NHS) design from 13, first established in 1985, to 10. The 10 criteria considered controlling for design projects on the NHS are: Design Speed, Lane Width, Shoulder Width, Horizontal Curve Radius, Superelevation Rate, Stopping Sight Distance, Maximum Grade, Cross Slope, Vertical Clearance, and Design Loading Structural Capacity.
Of the 10 criteria, the only two that apply to all NHS facility types are design loading structural capacity and design speed. Exceptions to these criteria are approved on a project basis by design and documentations of these expectations must include:
- Specific design criteria that will not be met.
- Existing roadway characteristics.
- Alternatives considered.
- Comparison of the safety and operational performance of the roadway and other impacts such as right-of-way, community, environmental, cost, and usability by all modes of transportation.
- Proposed mitigation measures.
- Compatibility with adjacent sections of roadway.