Governor Maura Healey’s administration said Thursday that it reached a new agreement with federal officials for its plans to replace the aging Cape Cod bridges, under which the state and US Army Corps of Engineers will commit a combined $1.3 billion toward the multibillion-dollar project.
The memorandum of understanding between the Healey administration and Army Corps of Engineers effectively replaces one the state signed in 2020 when it embarked on replacing the 89-year-old Bourne and Sagamore bridges, the only roads on and off the peninsula.
Similar to that deal, the state will take over ownership of and operate the two new spans over the Cape Cod Canal once they are built.
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But it includes several new details to reflect the $4.5 billion project’s changing scope, officials said. The Army Corps of Engineers — which owns and maintains the current bridges — will commit $600 million, subject to Congress appropriating the money, according to state transportation officials. That comes on top of $700 million Healey has already pledged in state money.
When state and federal officials first signed an agreement four years ago under governor Charlie Baker’s administration, they estimated the project would cost more than $1 billion.
The agreement also reflects a major shift in the state’s approach to building the new spans. Healey administration officials have pursued funding to first replace the Sagamore Bridge, which officials say alone will cost more than $2.1 billion.
They then intend to seek funding to replace the Bourne Bridge at some point later in what they’ve called a “phased process.” State officials said they chose the Sagamore Bridge first because it carries nearly 17,000 more cars on average each day than the Bourne.
In a statement, Healey called the deal an “important step forward,” while others said it underscored the state’s commitment to seeing the project through.
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“Today, we renew our vows to replace the Cape Cod Bridges, in sickness and in health, for richer or poorer,” US Senator Edward Markey said in a statement.
Healey administration officials on Thursday did not immediately respond to requests for a copy of the agreement itself.
State officials are still piecing together the funding for the first bridge. In December, they won $372 million in federal grant money in what officials at the time called a “breakthrough,” before scoring another $350 million in a separate federal appropriations bill.
The Healey administration is also seeking more than $1 billion in grant funding through the federal Bridge Investment Program.
The project is a complex one. The bridges are owned by the federal government and are considered functionally obsolete. Officials have said pursuing long, costly fixes in lieu of replacement could be catastrophic to crossings that carry tens of millions of cars each year. They’ve also warned that without replacing or fixing each bridge, they’ll be forced to permanently close a lane in each direction by 2032 on the Bourne Bridge and 2036 on the Sagamore Bridge.
State transportation officials said Thursday that the first new span will be built “fully offset” from the current Sagamore Bridge, so that traffic can continue to flow over it during construction.
The Healey administration has estimated that for the Sagamore Bridge alone, construction on a new bridge would begin in late calendar year 2028 and would last until late 2035 or early 2036.
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Yet, how the state has structured its pitches to federal officials for funding is not totally clear. Healey’s transportation department has repeatedly denied Globe requests for the federal grant applications it has submitted so far, which would provide details of the state’s financing plan and construction timeline.
Matt Stout can be reached at matt.stout@globe.com. Follow him @mattpstout.