Bridges, Condition of

National Bridge Inspection Standards

The National Bridge Inspection Standards were developed as a result of the Federal Aid Highway Act of 1968. The standards went into effect for all public bridges on federal highways in 1972, and thereafter routine inspections were mandated at least once every two years. In 1978, the inventory was extended to include all public bridges greater than 20 feet. The standards were adopted by all state transportation departments.

Inspectors categorize bridges that rank as less than 5 on a 9-point scale as structurally deficient, functionally obsolete, or fracture critical. The deck (riding surface), the superstructure (main supporting element of the deck, usually beams, girders, trusses, etc.), and the substructure (supports to hold up the superstructure and deck, usually abutments and piers) are rated on a scale from zero (closed to traffic) to 9 (excellent condition). A bridge receives a structurally deficient rating if any one of its main elements is rated 4 (meets minimum tolerable limits to be left in place as is) or less. States are quick to assure the public that structurally deficient bridges are not unsafe. The label structurally deficient is intended to sound an early warning that making repairs or building a replacement should become a priority. Speed or weight restrictions may be placed on the functionally deficient bridge.

Functionally obsolete bridges are those built to earlier standards that fail to meet current minimum federal requirements. These bridges are not automatically rated as structurally deficient, nor are they inherently unsafe. Functionally obsolete bridges include those that have substandard features, such as narrow lanes, narrow shoulders, poor approach alignment, or inadequate vertical under clearance. The Chesapeake Bay Bridge in Annapolis, Maryland, built in 1951, received one 5 (fair) and two 6s (satisfactory) in its 2011 inspection, but it is considered functionally obsolete.

...