The American Society of Civil Engineers says 42 percent of the United State's 617,000 bridges are at least 50 years old and rates 7.5 percent of them structurally deficient. It gives the U.S. a “C” grade when it comes to these vital overpasses.

CGTN examines Denver, Colorado, where the South Gap Project is the state’s longest construction zone at 29 kilometers. The four-year, $400 million-plus endeavor is widening Interstate 25 south of Denver and adding nine new bridges, five of them for trucks and cars.

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