More than a half million bridges carry cars and trucks across rivers in the U.S. every day. The U.S. Department of Transportation estimates one in four of these bridges is structurally deficient or functionally obsolete. This is not surprising given that the majority of U.S. bridges are 50 to 60 years old, having been built during the 1950s and 1960s after President Eisenhower signed the Federal-Aid Highway Act.
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