There's a big problem with American bridges: They're getting old — and falling apart.

According to Transportation for America, there are more than 68,000 structurally deficient bridges in the U.S.

Put end to end, that's enough to connect Washington, D.C. with Denver.

To shed light on the lack of federal funds for bridge repairs and replacements, Nickolay Lamm created the photo series "The State of Our Bridges," focusing on his hometown of Pittsburgh, Penn.

The state recently put weight restrictions on several bridges in an effort to reduce wear and tear.

Lamm shared his excellent photos with us, along with commentary provided by Raymond A. Hartle, department manager of bridge management services for GAI Consultants.

We've selected 13 photos from Lamm's series (see the whole thing here), and included Hartle's explanations, along with the Federal Highway Administration's "sufficiency rating" for each bridge. A sufficiency score below 50 means the bridge is eligible for federal replacement funds. Under 80 means it's eligible for federal repair funding.