Experts shoveling suggestions for North-South Rail Link, other T improvement ideas

The idea of building a tunnel under a tunnel through downtown Boston might give people flashbacks of the horrors and hassells of the Big Dig.

But experts say that tunneling under Boston to link the two major rail hubs in the North-South Station Rail Link would not disrupt life on the surface or in the Central Artery Tunnels at all.

“The original plan for the Big Dig included this rail connector,” Wentworth Institute of Technology Civil Engineering Professor James Lambrecht said. “It died out because of the cost overruns, but the tunnel was built with this link in mind.”

Lambrecht said the connector link should be much lower on the list of priorities.

“I would rather see them extend the Blue Line down to Riverside through Back Bay, and getting rid of the D Line on the Green Line,” Lambrecht said. “I refuse to punish myself by riding the Green Line, and if they bring in an estimated 30,000 more people once the Medford extension is complete, we’re talking about taking an overcrowded line and making it much worse.”

Lambrecht said that by creating a Blue Line track through Back Bay and to Riverside, a passenger could ride from Hynes to Airport station in just 12 minutes on just one train.

However, proponents of the North-South Station link project met behind closed doors on Monday to look over the benefits and costs of the project. At present, there are 140 state representatives and senators signed onto a 2012 letter of support for the 1.5-mile connector line.

Former governors Mike Dukakis and Bill Weld met with Governor Charlie Baker earlier this month to sell him on the $2-$4 billion link idea.

“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.”

Tunnel boring machines would tear 35- to 40-foot in diameter circular holes under the city and lay concrete in its wake at a rate of 50 to 100 feet each day, but there would be no blasting or surface digging to disrupt traffic at all.

The connector rail line would run about 130-feet below the city surface, which Lambrecht said would be a problem because trains don’t like running on steep grades. The track would have to start a mile away, Widett Circle for the South Station line and Mystic River/Sullivan Station for the North Station line, and would have to ease their way to the ultimate depth.

The tunnel itself would only take about a year, Lambrecht estimated. The stations might take four or five.

Lambrecht said the low-ball $2 billion price tag is too low and the $8 billion estimate from the Romney administration is far too high, making the current estimate of somewhere are $4 billion possible.

“There have been some high estimations from prior administrations, which is why we need a more comprehensive study,” Rep. Sean Garballey and MBTA Caucus co-chair said. “We owe it to the taxpayers to have a more comprehensive study, and we owe it to the commuters to being our transit system up to 21st-century standards.”