In the United States, the minimum height of a bridge going over a road is 14 to 16 feet, or 4.3 to 4.9 meters. In general, the minimum height slightly varies depending on the type of roadway.
As of 2005, according to the Federal Highway Administration, interstate highways must be at least 16 feet high over the whole roadway width, including the shoulders. Freeways and arterial roadways have minimum height requirements that vary between 14 and 16 feet. For local and collector roadways, the minimum height is 14 feet. The intent is to create at least a 1-foot differential between the maximum-allowed vehicle height and the bridge. It is possible to apply for a design exception, although low-lying bridges create risk to the roadways that include collisions between a vehicle and the bridge, rear-end crashes from secondary vehicles due to the primary collision, roadway debris from the crash, and resulting traffic delays from accidents and debris.