(AP) — Thousands of bridges around the U.S. may be one freak accident or mistake away from collapse, even if the spans are deemed structurally sound.

The consequence of that risk was evident Thursday on Interstate 5 over the Skagit River, where a large section of the bridge collapsed into the water after officials say an oversized truck load clipped the steel truss.

Public officials have focused in recent years on the desperate need for money to repair thousands of bridges deemed structurally deficient.

But the bridge that collapsed was not in that category, highlighting major problem with the nation’s infrastructure: Although it’s rare, some bridges deemed to be fine structurally can still be crippled if they’re struck hard enough in the wrong spot.