Everyone with a stake in the Cape Cod bridges megaproject agrees the two 91-year-old spans are so far past their useful lives that they ought to be replaced with modern successors. But what happens if federal funding falls short?

That’s a scenario that has Cape Cod business officials and the region’s lawmakers worried. A significant delay in securing money for bridge replacement could set in motion a costly repair project as a short-term stopgap measure, something local leaders say would not only squander limited resources but also create a months-long, maybe years-long traffic bottleneck that would strangle the Cape economy.

The first half of the massive infrastructure effort, focused on the Sagamore Bridge, is fully funded through a mix of state dollars, federal grants, and investments from the US Army Corps of Engineers. But that’s not the case for the Bourne Bridge, the sister span constructed at the same time as the Sagamore about three miles away.

After missing out on a pair of grants last year, Massachusetts leaders are waiting to find out if the state’s latest application for nearly $1.2 billion in federal money toward the Bourne Bridge replacement is successful. If the Trump administration passes over the Bay State, it would leave the Bourne with only a fraction of the money committed toward the roughly $2.3 billion cost — and, concerned locals think, less time in a closing window to figure out a plan.

That’s because the bridges are also due for an extensive repair blitz known as a “major rehabilitation.” The Army Corps deems that treatment necessary about every 45 years, and both spans last underwent such a program in the early 1980s. And to complete such a project, the Bourne Bridge — which the Army Corps once estimated carries an average of more than 45,000 vehicles per day — would need to close entirely for about six months, plus undergo some 16 months of partial lane closures.

Locals are not shy about casting that outcome in dire terms. With that much disruption to the Bourne Bridge, the Cape would “basically lose a third of our economy,” according to Cape Cod Chamber of Commerce CEO Paul Niedzwiecki.

“A [major] rehabilitation of the Bourne Bridge would cause an economic dislocation on Cape Cod that would probably take a generation to recover from,” he said. “We don’t really see that as a workable option.”

Worried about running out of time to avert that worst-case scenario, the region’s senator floated an eye-catching idea: maybe the state should start putting some money aside now to keep construction from being delayed too long.