Design

Vertical Clearance on the Interstate System

1. It must be emphasized that the integrity of the Interstate System for national defense purposes be maintained to meet AASHTO Policy as stated in A Policy on Design Standards - Interstate System, incorporated by reference in 23 CFR 625. On Interstate sections in rural areas, the clear height of structures shall be not less than 4.9 meters (16 feet) over the entire roadway width, including the usable width of shoulder. On Interstate sections in urban areas, the 4.9-meter (16-foot) clearance shall apply to a single routing. On other Interstate urban routes, the clear height of structures shall be not less than 4.3 meters (14 feet). Design exceptions must be approved whenever these criteria are not met.
2. The FHWA has agreed that all exceptions to the 4.9-meter (16-foot) vertical clearance standard for the rural Interstate and the single routing in urban areas will be coordinated with the Surface Deployment and Distribution Command Transportation Engineering Agency (SDDCTEA) of the Department of Defense. This agreement applies whether it is a new construction project, a project that does not provide for correction of an existing substandard condition, or a project which creates a substandard condition at an existing structure. Furthermore, it applies to the full roadway width including shoulders for the through lanes, and to ramps and collector-distributor roadways in Interstate-to-Interstate interchanges.
3. A number of toll roads have been incorporated into the Interstate System under the former provisions of Section 129(b) of Title 23, United States Code. While the FHWA does not have any particular "leverage" on the toll authorities to comply with Federal standards on non-federally funded projects, it is expected that the SHA's have established appropriate procedures to assure that proposed changes or alterations of the toll road will meet applicable policies established for the Interstate System. The working relationship should ensure the needs of the military are considered and that necessary coordination occurs.
4. The approval action for Interstate design exceptions has been delegated to FHWA field offices and, in some cases, to the SHA. Whoever has responsibility for approving the design exception also is responsible for coordination with SDDCTEA. A request for coordination may be forwarded directly to the SDDCTEA at any time during project development but in all cases prior to taking any action on the design exception. It should include a time period of 10 working days (after receipt) for action on the request. The office initiating a request for coordination to the SDDCTEA can verify receipt of the request by telephone or fax. If the SDDCTEA does not respond within the time frame, it can be concluded that the SDDCTEA does not have any concerns with the proposed exception. If comments are forthcoming, the FHWA and/or SHA will consider mitigation to the extent feasible. A request for coordination should be addressed to:

Director, Surface Deployment and Distribution Command Transportation Engineering Agency (SDDCTEA)
ATTN: SDTE-SA
709 Ward Drive, Building 1990
Scott AFB, IL 62225
Telephone: 618-220-5229; Fax 618-220-5152