WASHINGTON — A routine trip to run errands almost cost Katherine Dean her life. In February, just as Ms. Dean, of suburban Maryland, drove underneath a bridge on the Capital Beltway, a large chunk of concrete fell from the structure, crushing the hood of her car and smashing the windshield.

She was unharmed, but the incident left her shaken. After the news media picked up her story, the state apologized to her, and state officials ordered an immediate inspection of other aging bridges along the suburban route encircling Washington, also known as Interstate 495.

“My biggest fear is that once this is no longer in the headlines it will fall by the wayside,” said Stephen M. Gensemer, a Maryland lawyer who represented Ms. Dean in a financial settlement with the state. “It concerns me that we have this focus on our aging infrastructure only when you have pieces of concrete falling on a motorist.”

It is a concern shared by many Americans. From coast to coast, the country’s once-envied collection of bridges, dams, pipelines, sewage treatment plants and levees is crumbling. Studies have shown that a lack of investment in public infrastructure costs billions of dollars a year in lost productivity, as people sit in traffic or wait for delayed shipments.