North and South Station are almost a mile and a half apart as the crow flies.

But commuters who travel from one major transit hub to the other know timing that the Red Line at South Station to Downtown Crossing, then switching to the Green or Orange Line and arriving at North Station to catch a rush hour Commuter Rail train to or from work is a daily acrobatic feat.

Given that both stations have seen enough of an uptick in congestion that large-scale expansion has been proposed, two former governors are pushing Governor Baker to connect the two stations via a new rail line. At a press conference held on Wednesday, Baker said that the estimates of the project center between $2 billion and $4 billion, but he wants to review those estimates and other details of the proposals.

"This is a lot of money, taxpayer money, and a lot of people call me skeptical when I get into these conversations,” Baker said. “I'm not being skeptical. I'm being cautious. There's a difference.”

This current plan, which differs from other proposals going far back into Bay State history, calls for a tunneling under downtown wide enough for two tracks to unite the station which points north to Maine and south to New York and Washington D.C. respectively.

Former Governor and 1988 presidential candidate Mike Dukakis came out strongly in favor of the connector. He said that the expansion of the respective stations would ultimately be a fool’s errand which will fill to capacity in a few years time.

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"What do you need South Station expansion for if you connect two stations? You'll have unlimited capacity," Dukakis said. "You won't have unlimited capacity with another seven tracks, folks. They'll fill up in four, five, six years and you'll have the same problem all over again. It makes no sense at all."

Dukakis said that cities around the world, including Philadelphia and Los Angeles, have either finished or are constructing similar rail tunnels to link stations, Dukakis said the plan calls for a more modern version of the tunneling technology used in the Red Line extension to Alewife.

"This is not the Big Dig, folks," Dukakis said. "This is very different."

Baker has entertained the idea of a separate project to expand South Station that would first require annexing the Post Office building next door to the Commuter Rail and Amtrak hub, but he and his administration have not leapt at the idea. He has spoken enthusiastically about opening up Dorchester Avenue and to create development opportunities along the waterfront.

Baker acknowledged that mere months after the T shut down during the winter of 2015, combined with the news that the current Green Line extension into Somerville and Medford is almost $1 billion over budget, selling this proposal to the Bay State residents will be a difficult task.

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“My main focus on this issue has been to fix the T,” Baker said. “I do believe that fixing the T is my largest priority. But obviously, in this context of economic development and regional planning, not just for Boston but for the rest of the Commonwealth, this is certainly something worth considering as part of that.”

MBTA Spokesman Joe Pesaturo said that all planning and design work was stopped in 2003, and there are no plans to change that at this time.