The MBTA Fiscal Management and Control Board will a South Coast Rail update Monday and could decide whether to continue discussions of the Middleboro proposal, along with discussions of the long-planned Stoughton route, at public meetings this fall.

DARTMOUTH — Like cars pouring into a newly opened lane after hours stuck in traffic, support is building across the region for discussion, if not adoption, of the newly possible Middleboro route for South Coast Rail.

The key driver is timeliness — in other words, a perceived opportunity to get a rail connection completed, after decades of stops and starts for frustrated commuters idling in Boston gridlock.

“There’s nothing more important for my city of Fall River, for changing its social and economic conditions,” than the realization of commuter rail to Boston, said state Sen. Michael Rodrigues, a Westport Democrat whose district also includes Fall River, Swansea, Freetown and Rochester.

“This is our No. 1 issue in the partnership … there is nothing bigger,” said David Slutz, former CEO of Precix and current co-chair of the SouthCoast Development Partnership’s executive board.

“We want something as quickly as possible, period,” Slutz added.

Their comments came at a Friday meeting of the Development Partnership. Business and community leaders from the Greater New Bedford, Fall River and Taunton areas gathered at the UMass School of Law in Dartmouth, with about 10 state legislators, to discuss South Coast Rail developments.

The meeting came ahead of a potential turning point for the project.

The MBTA Fiscal Management and Control Board is scheduled to hear a South Coast Rail update Monday in Boston, and could decide whether to continue discussions of the Middleboro proposal, along with discussions of the long-planned Stoughton route, at public meetings this fall.

The Development Partnership confirmed its support for Middleboro discussions, citing a potential opportunity for a diesel rail connection that would turn east in Taunton, to Middleboro and Lakeville. Backers say a Middleboro route could be built sooner and for less money than electric trains on the Stoughton route, which would head directly north from Taunton.

“On Monday, we plan to go and ask that they expedite the review of (a Middleboro route),” said Hugh Dunn, the Development Partnership’s executive director. “We’d like to know by the end of the year whether this is technically, legally and fiscally feasible.”

MassDOT introduced the Middleboro option — and projected that costs for the Stoughton route have climbed from $2.2 billion to about $3.4 billion — in a June 27 presentation to the MBTA control board.

The Stoughton route is 15-percent designed, though, and continues to have ardent supporters, including state Sen. Marc Pacheco, D-Taunton. Pacheco has noted that the state’s Middleboro proposal doesn’t yet include costs for a potential new rail station in that town — to accommodate the increased traffic — or for a related widening of the I-93 section known as the Southeast Expressway. That project could include tunneling and underground tracks.

Mark Hess, a vice president with real estate company HallKeen Management, noted the larger implications of the Middleboro route at Friday’s meeting.

“You’re hitching your cart to a huge infrastructure project in this whole corridor,” Hess told the crowded conference room, referring to the potential I-93 work in the Savin Hill area, and elsewhere.

Hess added that a 15-minute difference in travel time could have significant implications for future passenger numbers. Stoughton is acknowledged as the faster route, but estimates of how much faster have ranged from 12 to 30 minutes. Hess said just a few minutes could matter to riders.

“There are huge break points in people’s decision-making,” he said.

Pacheco did not attend Friday’s meeting. Taunton was represented, though, by Kerrie Babin, president of the Taunton Area Chamber of Commerce; and Kevin Shea, Taunton’s economic and community development director. Neither expressed positions on the issue.

“This is kind of the first time we’ve worked with Taunton — but it’s a project that impacts all three communities, so I think we should all be at the table,” Dunn said, referring to Fall River and New Bedford, as well.

Jean Fox, South Coast Rail project manager for MassDOT, said her office had gone through “10-12 drafts” of Monday’s update in recent days.

“We’ll be tweaking (the update) until Monday morning, I promise you,” she said.

Follow Mike Lawrence on Twitter @MikeLawrenceSCT