On its website, a group called Citizens for North South Rail Project says the disconnected system as it stands today is a "hodgepodge of 19th-century rail lines" that has created what is essentially two separate commuter rail systems on the north and south sides of the city. "They are disconnected from each other, and neither connects fully to our subway system," the group says. "The result is a fragmented region in which workers and employers cannot access each other efficiently, where highway congestion is severe, and economic opportunity is very unequally distributed.

"These disconnections squander the potential of our existing transportation infrastructure and hobble our regional economy, particularly impacting areas to the north and west of the city."

Awarded to Arup on June 30 by MassDOT's Office of Transportation Planning, the North-South Rail Link Feasibility Reassessment "will update a prior study on a proposed rail tunnel connecting North Station and South Station and determine whether further technical and financial analysis is warranted," says Joe Pesaturo, director of communications at the Massachusetts Bay Transportation Authority. 

According to a report in the Boston Business Journal, the goal of the study will be to estimate the projects cost. Pesaturo says the study is to be completed by Spring 2018. A 1995 draft environmental-impact report on the project was shelved in 2003 during Gov. Mitt Romney's administration. 

In a statement, Arup Project Director Jeff Tubbs, saus, “We are excited to apply Arup’s global expertise to this project. Through our effective delivery of the Green Line Extension, we understand the priorities and policies of MassDOT and the MBTA, as well as the concerns of the communities in the Boston metro area. We look forward to combining this with our deep planning and engineering experience in the assessment of effective solutions for the North-South Rail Link.” 

Anthony Bruzzone, who will serve as Arup’s project manager, says in the statement, “The knowledge gained from our work on the Green Line Extension in Boston and our recent planning and tunnel experience in San Francisco and Los Angeles gives us great insight into this very similar project. While significant challenges exist to implementation, understanding these challenges, as well as the project's costs and benefits, are essential to inform MassDOT's decisions on next steps.” 

The firm's rail work includes the Second Avenue Subway in New York City, the Transbay Transit Center in San Francisco and the Thameslink and Crossrail projects in London. 

This story was updated with new information on July 25