The condition of bridges nationwide has improved markedly since the early 1990s. Of the 591,877 roadway bridges in 2002, the Federal Highway Administration found that 14 percent were structurally deficient and 14 percent were functionally obsolete. About 35 percent of all bridges in 1992 were either structurally deficient or functionally obsolete .
Structurally deficient bridges are those that are restricted to light vehicles, require immediate rehabilitation to remain open, or are closed. Functionally obsolete bridges are those with deck geometry (e.g., lane width), load carrying capacity, clearance, or approach roadway alignment that no longer meet the criteria for the system of which the bridge is a part.1 In the 1990s, while the number of structurally deficient bridges steadily declined, the number of functionally obsolete bridges remained constant (figure 11-5).
In general, bridges in rural areas suffer more from structural deficiencies than functional obsolescence (particularly on local roads), whereas the reverse is true for bridges on roads in urban areas (figure 11-6 and figure 11-7). A large number of problem bridges nationwide are those supporting local rural roads: 44,156 of the 163,000 deficient and obsolete bridges in 2002 (27 percent) were rural local bridges. Problems are much less prevalent on other parts of the highway network. Nevertheless, in 2002, 26 percent of urban Interstate bridges and 16 percent of rural Interstate bridges were deficient or obsolete.
1. U.S. Department of Transportation, Federal Highway Administration, Office of Engineering, Bridge Division, National Bridge Inventory database, available at http://www.fhwa.dot.gov/bridge/britab.htm/, as of January 2004.
1 Structurally deficient bridges are counted separately from functionally obsolete bridges even though most structurally deficient bridges are, by definition, functionally obsolete.