National Bridge Inventory - Structural Evaluation Scale

Structural Evaluation Scale

The National Bridge Inventory includes a structural evaluation of deck, superstructure, and substructure, on a 0-9 scale:

• 9 Superior to present desirable criteria
• 8 Equal to present desirable criteria
• 7 Better than present minimum criteria
• 6 Equal to present minimum criteria
• 5 Somewhat better than minimum adequacy to tolerate being left in place as is
• 4 Meets minimum tolerable limits to be left in place as is
• 3 Basically intolerable requiring high priority of corrective action
• 2 Basically intolerable requiring high priority of replacement
• 1 This value of rating code not used
• 0 Bridge closed

It also classifies bridges as either "structurally deficient" or "functionally obsolete". Neither necessarily implies lack of safety, though that could be a concern as well. "Structurally deficient" means that the condition of the bridge includes a significant defect, which often means that speed or weight limits must be put on the bridge to ensure safety; a structural evaluation of 4 or lower qualifies a bridge as "structurally deficient". The designation can also apply if the approaches flood regularly. "Functionally obsolete" means that the design of a bridge is not suitable for its current use, such as lack of safety shoulders or the inability to handle current traffic volume, speed, size, or weight.

In December 2008, 72,868 bridges in the United States (12.1%) were categorized as "structurally deficient", representing an estimated $48 billion in repairs, and 89,024 (12.2%) were rated "functionally obsolete", representing an estimated $91 billion in replacement costs.