THE MOST POPULAR configuration for the I-90 Allston interchange is facing yet another hurdle, as the Federal Highway Administration sent state officials a terse letter saying the current design is not viable because it violates federal flood plain regulations.
In a letter dated June 22, Jeffrey McEwen, a division administrator for the federal agency, said he had warned state officials repeatedly about the flood plain problem since 2018. “This requirement cannot be waived nor are there any means of exception or mitigation,” he said.
Still, McEwen said, he was “confident” the problem could be remedied with the right design solutions. His letter did not mention possible solutions.
State Highway Administrator Jonathan Gulliver, who is overseeing the I-90 Allston project, released the letter and outlined the problem to a stakeholder group Thursday evening. In an interview, Gulliver said he continues to believe the state’s assessment of the flood plain situation is correct. As for coming up with a design solution, he said it was too early to tell how difficult that would be.
“It throws a huge wrench in the project,” he said of McEwen’s letter.
The state is looking to replace the crumbling, elevated Turnpike that runs through a narrow stretch of land between Boston University and the Charles River and straighten the roadway as it runs west to make room for a new neighborhood being developed by Harvard University. The challenge has been how to make all the transportation infrastructure – eight lanes of Turnpike, four lanes of Soldiers Field Road, and four railroad tracks – fit in that narrow corridor.
State officials have come up with three options – replace everything pretty much the way it is now, with the Turnpike elevated; elevate Soldiers Field Road and leave everything else at grade; and put all of the elements at ground level. The all-at-grade approach is heavily favored because it means the Turnpike would no longer act like a wall between the areas to the south and north of the highway.
The focus to date has been on finding enough room to squeeze everything in, which has beern a battle of inches and feet. But the Federal Highway letter adds a new wrinkle. State officials have taken the position that the bank of the Charles River acts much like a dam, holding back the water and preventing it from flooding the roadway. The river itself is also dammed, so water levels in the river can be controlled to curb flooding.
Federal officials, however, are taking the position that the current at-grade design is not in compliance because the Turnpike runs below flood plain elevation even though the roadway would be set back from the river.
Rick Dimino, the president and CEO of the business group A Better City and one of the chief proponents of the all-at grade design, said he thinks the state’s interpretation of the flood plain regulation is the correct one. He said he hopes the Federal Highway Administration comes around.
Gulliver also feels the current at-grade design doesn’t violate the federal flood plain regulation, but he indicated it might be difficult to change the agency’s mind. “It’s their regulation. We have to be in compliance with it,” he said.
If the agency doesn’t change its position, the state does have some options. It could add fill to raise the level of the Turnpike above the flood plain, but that creates another hurdle, as the current design calls for the roadway to go underneath an elevated railroad track making its way over to the BU Bridge where it crosses into Cambridge. If the roadway is raised too high, it could come too close to the rail track and make it difficult for trucks to pass underneath.
Possible solutions to that problem include reducing the depth of the rail bridge to expand the amount of room underneath it. Another approach could leave the rail track at ground level and design the Turnpike so it rises up and over the track.
