Frequently Asked Questions
Q. What does bridge sufficiency rating mean?
A. The sufficiency rating formula is a method of evaluating factors that indicate a bridge’s sufficiency to remain in service. The result of the formula is a percentage in which 100 percent represents an entirely sufficient bridge and zero percent represents an entirely insufficient or deficient bridge. The sufficiency rating is never less than 0 or more than 100.
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Q. What is the age and condition of interstate bridges?
A. The Interstate System has 55,315 bridges. Of that number, 17.4 percent were constructed during the 1950s, 44 percent in the 1960s, and 20 percent in the 1970s.
While bridge conditions have improved over the past decade, some 8,841 interstate bridges are rated as structurally deficient. Exhibit 11-9 shows that approximately 15.9 percent of all rural interstate bridges were deficient in 2004, including 1,163 that were structurally deficient (about 4.2 percent of the total number) and 3,224 that were functionally obsolete (11.7 percent of the total number).
The National Highway System (NHS) comprises only 4.1 percent of the nation's total road mileage, but carries 44.8 percent of vehicle traffic. There are 115,104 bridges on the NHS, which includes the interstate bridges. Of these, 5.6 percent are considered structurally deficient, down from 7.9 percent in 1995.
In 2004, 19.4 percent of all U.S. bridges were located on the NHS, but these bridges had 49.5 percent of the total deck area of all bridges and carried 71.1 percent of the traffic on all bridges. Approximately 20.5 percent of NHS bridges were considered structurally deficient in 2004, including 5.6 percent classified as structurally deficient and 14.9 percent classified as functionally obsolete.
In 2004, all levels of government spent a combined $34.6 billion for capital improvements to the NHS, which was 49.2 percent of total capital expenditures on all roads.
Q. Which bridges are included in the National Bridge Inventory (NBI) system?
A. NBI structures are bridges or culverts that are open to the public, carry vehicular traffic and have an opening longer than 20 feet, measured along the center of the roadway.
Q. What bridges are not considered part of the Nation Bridge Inventory (NBI) system?
A. Non-NBI structures include bridges or culverts that carry vehicular traffic and are equal to or less than 20 feet at the center of the bridge.
Q. What is a "structurally deficient"bridge?
A. Structurally deficient means there are elements of the bridge that need to be monitored and/or repaired. The fact that a bridge is "structurally deficient" does not imply that it is likely to collapse or that it is unsafe. It means the bridge must be monitored, inspected and
repaired/replaced at an appropriate time to maintain its structural integrity.
Federal Highway Administration's 2006 Conditions and Performance Report