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What are some regulations regarding bridge clearance?

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Bridge clearance regulations include the requirement that rural and urban interstate freeway bridges must provide a minimum vertical clearance of 14 to 16 feet over the entire road width, including the usable shoulder, and a 17-foot clearance for sign trusses and pedestrian overpasses, according to U.S. Federal Highway Administration regulations. All collector and local road bridges must have a minimum clearance of 14 feet. Clearances provide a minimum 1-foot differential between the roadway and the maximum legal vehicle height.

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National defense requirements drive the bridge clearance standards of the U.S. interstate highway system and any design exceptions require coordination with the Department of Defense, explains the U.S. Federal Highway Administration.

While the clearance guidelines for bridges spanning navigable U.S. waterways are non-regulatory they may impact bridge permitting, explains the U.S. Coast Guard, Department of Homeland Security. Guidelines exist for all navigable waterways in the United States. For example, the clearance guidelines for the Colorado River in California, Arizona and Nevada are a 25-foot clearance for fixed bridges and a 17-foot clearance for removable spans.

The Manual on Uniform Traffic Control Devices provides guidance on bridge clearance signage, including placement, size and type of warning signs and signals, to reduce damage due to low vertical clearances. It also advises marked detours, where possible, and the prohibition of large vehicles on certain non-interstate routes where no alternative exists, according to Mitigation Strategies for Design Exceptions, a 2007 publication of the Federal Highway Administration.

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