Most bridges collapse not because of an engineering failure, but because the structures can’t withstand natural forces such as unusually high winds or earthquakes. In America, specifically, concerns over aging infrastructure have sparked more recent conversations around the stability and reliability of bridges.

The American Society of Civil Engineers have given the more than 614,300 American bridges a C+ rating, saying that one in nine are considered structurally deficient. Most of that has to do with weaknesses that arise because of age, and a total update of the system is estimated to cost about $123 billion. The average age of a bridge in the US is about 42 years. On average, Americans make 188 million trips across structurally deficient bridges every day.

The incident in Florida had nothing to do with age. While the project was still unfinished, authorities will be investigating what engineering failure might have contributed to the collapse.

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