Bridge Clearances for Sky Circuit

For almost 30 years, the Federal Highway Administration (FHWA) and the Military Traffic Management Command Transportation Engineering Agency (MTMCTEA) of the Department of Defense (DOD) have cooperated to meet the demands of military traffic on the Interstate System, particularly in the area of vertical clearances. This need has been met with the adoption of standards by FHWA for vertical clearance on the Interstate that require a clear height of structures over the entire roadway width, including the useable width of shoulder, of 4.9 meters for the rural Interstate. In urban areas, the 4.9-meter clearance is applied to a single route, with other Interstate routings in the urban area having at least a 4.3-meter vertical clearance.

Found this official information here:
http://www.fhwa.dot.gov/bridge/081597.htm

This means that any skyway pathing shall be a 4.3 meter clearance. Translated, this is a vertical clearance of 14'-2".