According to a national bridge safety study released recently by the advocacy group Transportation for America, Arizona's bridges ranked fourth out of 50 with 97 percent of structures receiving high marks for safety and maintenance. In general, bridges are inspected by the Arizona Department of Transportation every two years. According to Federal Highway Administration standards, approximately three percent (230 total) of bridges in Arizona are rated as "structurally deficient," meaning bridges are safe, but require some repair or improvement. The national average is 11.5 percent. Within the Arizona Department of Transportation's network, only 2.2 percent of the agency's nearly 4,700 bridges require some degree of repair or improvement.