This is the Greenfield Bridge in Pittsburgh.

Looks normal, right?

Nope. Take a closer look.

It's ... a bridge. Under a bridge.

"Why on Earth would anyone build a bridge under a bridge?" You may ask.

They built it because the Greenfield Bridge is crumbling.

And they need it to catch falling concrete, so that cars driving under the bridge aren't smashed apart. Meanwhile, thousands of commuters drive across the Greenfield Bridge everyday, possibly unaware that it's actually breaking apart underneath them.

And the scariest part? It's not alone. Not even close.

There are at least 70,000 other bridges in America just like it.

A bridge you drive on every day could be one of them.

Take a look.

CORRECTION: We previously misidentified the bridge in the photo at the top as the Liberty Bridge. It is, in fact, the Greenfield Bridge. We made the change and super regret the mistake (and apologize to the city of Pittsburgh). Thanks so much to Facebook commenters Lynn Settelmaier Nikolas and Cece Peterson for pointing out our error!