The American Society of Civil Engineers’ 2013 Report Card for Washington’s Infrastructure provides definitions for this bridge-condition jargon:
Structurally Deficient (SD) bridges are in structurally deteriorated conditions and do not adequately carry their designed traffic loads. These bridges require significant maintenance, rehabilitation, or replacement. Of the 7,743 bridges in our state, 391 are classified as SD.
Functionally Obsolete (FO) bridges do not have adequate approach alignment, geometry, clearance, structural adequacy, or waterway adequacy to meet the current traffic needs or standards. In other words, they are effectively over the hill.
Examples are narrow lanes or low load-carrying capacity. FO bridges often tend to bottleneck traffic or lack many safety features. The Skagit River Bridge was built in 1955; it is one of the 1,548 Washington bridges classified as FO.
The Sufficiency Rating is a qualitative value that measures the bridge’s relative capability to serve its intended purpose. The value is generated from a formula that combines inspection data regarding structural adequacy and safety, serviceability, and functional obsolescence essential for public use and special conditions.
A sufficiency rating varies from 0 to 100. The Bridge Replacement Program requires a sufficiency rating of 80 or less to qualify for repair, and a sufficiency rating of 50 or less to qualify for replacement.
This Department of Transportation page has more information on bridge conditions and ratings. The National Bridge Inventory Database has just about everything you ever wanted to know about every bridge in the nation.
Check out their data sheet for the 1-5 Skagit River Bridge.