Beckie Curtis, director of the Bureau of Bridges and Structures at the Michigan Department of Transportation (MDOT), explains the stark reality.

Bridges must maintain a minimum condition to keep the transportation system open.
Bridges are expensive investments in the highway network.
Bridges are long-lived assets, and many bridges on the trunkline system were built in a short window of time as part of the interstate and other freeway systems.
Because of these factors, combined with historic underfunding, widespread bridge closures can be expected in the next 10-20 years unless funding is increased.