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.

Sen. Dylan Fernandes filed an amendment to a spending bill earlier this month that would have committed $200 million per year in state dollars toward a new “Bourne Bridge Replacement Fund,” all from a voter-approved surtax designed to fund education and transportation priorities.

The Senate quietly rejected Fernandes’s proposal, which he said was designed to “start a conversation.”

“If they go forward with the major rehabilitation, it would financially cripple our entire region. It would have massive health and public safety implications, and it would really destroy our tourism economy,” said Fernandes, a Falmouth Democrat. “That outcome just simply cannot happen.”

“We have some time to figure this out, but now is the time to start talking about it,” he added.

Both bridges were built in 1935 to cross the Cape Cod Canal, and to this day, they represent the only motor-vehicle routes connecting the tourism hotspot to the rest of Massachusetts. (Notwithstanding the whimsical permits that some people display on their cars, there is no tunnel to the Cape.)

For years, the Army Corps, which owns and operates the spans, has deemed them “functionally obsolete.”

Parties agreed in 2020 that both bridges should be replaced with modern alternatives, and the plan is to build the successors while the Bourne and Sagamore remain open to minimize the disruption. That same year, then-Gov. Charlie Baker and his team struck a deal with the Army Corps in which the state will take ownership — and therefore the not-insignificant maintenance costs — of the new bridges once complete.

Fernandes called that agreement “misguided,” pointing out that neither the Army Corps nor any other federal entity are explicitly required under the memorandum of understanding to fund the bridge replacement project.

“Essentially, with getting nothing back, the Baker administration said that we would take on ownership and the costs for centuries of maintaining and then eventually rebuilding these [successor] bridges without any funding guarantees,” he said. “It was an incredibly foolish deal to make, in my opinion.”

Officials are designing and permitting both bridges simultaneously, but the work will begin first on the Sagamore Bridge, which is funded through a combination of $1.3 billion in federal grants, $700 million in state commitments, and $350 million from the Army Corps. Last week, the state Department of Transportation hosted design and construction firms to kick-start the procurement process; project leaders expect to decide this summer which companies are eligible to bid, a timeline that could have construction begin in late 2027 or early 2028.

The timeline for the Bourne Bridge is far more nebulous, mostly because of its financial uncertainty. Last year, Massachusetts found out it did not win a combined $1.2 billion in federal grants, and officials are now waiting for the Federal Highway Administration to decide whether to approve a subsequent application for almost $1.2 billion through the Bridge Investment Program. So far, the agency has announced only a pair of winning grants, one for the Delaware River Bridge linking Pennsylvania and New Jersey and the other for bridges in Alaska.

Roughly $250 million from the Army Corps is the only funding earmarked so far for the Bourne Bridge, according to Luisa Paiewonsky, MassDOT’s executive director of megaprojects.

It’s not clear how long the Army Corps will wait before pivoting to the disruptive major rehabilitation repair program. In a 2020 report, the Army Corps wrote that the Sagamore was set to undergo major rehabilitation in 2025-2027 and the Bourne was set for the same work in 2029-2031, but those forecasts might have changed in the wake of the COVID-19 pandemic and the multiparty push to replace both bridges.

A spokesperson for the agency, which this month will launch a few weeks of shorter-term maintenance projects, did not respond to a CommonWealth Beacon inquiry Tuesday.

Paiewonsky said the Army Corps “agree[s] with us that the best course of action here is replacement.” For now, she’s optimistic about the state’s chances of securing big federal dollars, and doesn’t see the same need as Fernandes to commit more Massachusetts money.

“We’re not contemplating that kind of scenario because, again, this is a federally owned asset,” Paiewonsky said. “It has always been envisioned as a federal-state partnership, and our expectation is that they would want to contribute to their own asset.”

Niedzwiecki, the Cape Cod chamber chief, is open to pretty much any funding scheme that gets both the Bourne and Sagamore replaced, including a bigger commitment from Beacon Hill.

“Both bridges need to be replaced, whether the bulk of it comes from the federal government, whether it’s split equally, whether the state picks up more, whether we’re looking at alternative funding mechanisms,” he said. “They’ve got to be replaced. They were designed as a system almost 100 years ago to accommodate a million trips a year. They currently see 38 million trips a year, which is nearly the equivalent of the Golden Gate Bridge. So we can’t just do one.”