KENNEBUNK – A bridge that passes over railroad tracks used by Amtrak’s Downeaster was found to be beyond repair after buckling and will have to be replaced with a temporary span.

A prefabricated, military-style bridge should be in place within two weeks, restoring traffic on Route 35, Maine Department of Transportation spokesman Greg Nadeau said Wednesday.

Nadeau could offer neither a timeline nor a projected budget for the bridge replacement. It is also uncertain whether the bill for fixing the bridge will belong to the state or the railroad’s owner.

The span, which has carried residents and tourists between Kennebunk and Kennebunkport for more than 70 years, is an important corridor.

State engineers thought it might be possible to repair the bridge until they learned that excavation on the train tracks below the overpass caused one end of the roadway to buckle.

Workers labored to stabilize the bridge’s abutments by digging around the granite-block structures and replacing clay with solid fill before they discovered their work was adding to the instability of the bridge’s supports.

“They could actually hear motion,” said Bruce Van Note, deputy commission of the transportation department. “You saw these cracks getting a little wider.”

The transportation department has inspected the bridge over the years, but railroad overpasses traditionally belong to railroads, Nadeau said.

Before its slump earlier this week, the 72-year-old bridge had given state inspectors no cause for concern, said project director Paul Pottle. The bridge was last inspected in January, when its supports received a good rating.

The inspection did not find that the bridge posed any structural risk, but Nadeau said it would have been in better condition had the state owned it.

Business owners on the section of Route 35 south of the bridge said they were feeling the effects of the closure Wednesday.

“We’re dead in the water,” said John Daamen, owner of Mainely Quilts and the Waldo Emerson Inn. He said people with reservations were still making their way to the inn, but he had not seen a customer in the quilt shop in the last two days.

Trained as an engineer himself, Daamen said he was intrigued by what had happened to the bridge.

“As an engineer, it’s an interesting problem,” he said. “As a businessman, I’m in trouble.”