The big squeeze at Big Dig 2

THE MASSACHUSETTS TURNPIKE PROJECT that some are starting to call Big Dig 2 is struggling to squeeze 12 lanes, four railroad tracks, park land, a pedestrian path, and two bike lanes into a narrow 210-foot section of land between Boston University and the Charles River.

Like a jigsaw puzzle, state officials keep moving the pieces around to see if they fit and also provide enough room for construction staging areas. It’s no easy task, particularly with stakeholders who all have different priorities. Many of the options rely on creating more space in the area by either adding permanent or temporary structures out in the Charles River. The latest twist is a proposal to build a two-track rail tunnel underneath the Charles, freeing up room onshore.

The impetus for the I-90 Allston interchange project is a crumbling viaduct that carries the Turnpike between Boston University and the Charles River. There is also a need to straighten out the Turnpike in the Allston area to make room for a new neighborhood being built by Harvard University.

The state’s initial plan was to just rebuild the viaduct as is, but that status quo approach didn’t sit well with the public, so it was scrapped. State transportation officials then looked at building all the roadways and rail tracks at grade, but decided that wouldn’t work because it would require altering or filling in a significant portion of the Charles River to make all the elements fit.

What Transportation Secretary Stephanie Pollack ultimately settled on last January was a plan that put the Turnpike, two rail lines, and bike and pedestrian paths at ground level and Soldiers Field Road elevated above. “It is very complicated to build and it will take longer and be disruptive to travelers,” Pollack said before adding that it was the best overall design.

But as planning for that design has moved forward, state officials have decided they don’t have enough room to do the work and keep traffic moving during the estimated 10-year construction period. During construction, they are already planning to reduce the number of Turnpike lanes from 8 to 6; periodically shut down one of the two tracks on the Worcester commuter rail line; and close the Grand Junction line, a little-used freight line that runs over the Charles under the BU Bridge into Kendall Square and ultimately North Station.

State planners say they will also need to build a temporary Soldiers Field Road and a pedestrian and bike path on a bridge out over the Charles River.

In recently filed public comments on the state’s current plan, stakeholders are raising a host of concerns. “What everyone is saying – based on what we know now, not what we were told before – is we need to look at other options,” said Harry Mattison, an Allston resident who follows the deliberations closely.

Lawmakers from west of Boston are concerned that their constituents will be stuck in traffic for the 10-year construction period. “The current level of congestion for both drivers and riders on commuter rail is prohibitive and the undertaking of this massive construction project, with already forecast multi-year losses of driving lanes and rail tracks, will have an enormous and unacceptable impact without swift and decisive investments to mitigate these detrimental conditions,” said a letter signed by Senate President Karen Spilka and 44 other lawmakers.

Environmental advocates are alarmed at the decision to plunk a temporary highway in the Charles River for 10 years. They are recommending other ways to free up space, either by shutting Soldiers Field Road down during construction or eliminating some lanes on the Turnpike and Soldiers Field Road in the final design.

The business group A Better City is urging state officials to go back and revisit the idea of putting all the transportation elements at grade level. The group said the state went with its current approach (elevating Soldiers Field Road) largely because it didn’t want to disturb the Charles River either permanently or temporarily. Given that the state’s current plan now calls for a temporary bridge in the Charles for 10 years, A Better City says a better approach would be to run two lanes of Soldiers Field Road and the pedestrian/bike path on a 40-foot extension of the river bank.

The right-leaning Pioneer Institute recommends building a permanent bike/pedestrian path over the Charles River to free up land onshore for an at-grade construction plan. The institute downplays the impact on the river. “The ‘natural beauty’ of the Charles is not so natural,” the institute says. “It’s a product of many carefully engineered and designed initiatives to allow the public to enjoy the experience of the river.”

Pioneer also opposes any reduction in travel lanes and raises the sticky question of who will pay for the Turnpike project by suggesting that toll revenues may be used. “Ironically, those most adversely impacted by the project may also be paying for a large portion of it,” the institute says.

Fred Salvucci, the MIT professor and former secretary of transportation, appears to favor building a bike and pedestrian path and Soldiers Field Road out over the Charles. But he also includes a comment letter from Antonio Di Mambro, an architect and planner, who wants to see a much quicker embrace of  the Grand Junction railroad for commuter rail service to Kendall Square and North Station. He favors building a two-track tunnel descending from the site of a proposed West Station in Allston, then going under the Charles before surfacing again on the Cambridge side.

Di Mambro’s approach would allow Grand Junction to operate throughout the construction period, allow more parkland along the Charles, and free up space for construction of everything else. It comes out of left field late in the process, but Salvucci says it should be thoroughly studied.

“When he has given me advice, which I felt was too radical, I have lived to regret not embracing Antonio’s vision,” Salvucci said in his letter to state transportation officials.