Elevated Massachusetts Turnpike between BU and Charles River with Soldiers Field Road at grade. The bend in the Turnpike at the top of the picture would be straightened if the broader project I-90 Allston interchange project is pursued. Massachusetts Department of Transportation.

THE I-90 ALLSTON interchange has always been a challenge to design, particularly squeezing the Massachusetts Turnpike, Soldiers Field Road, and four railroad tracks at ground level into in the narrow area called the throat between Boston University and the Charles River.

But as the state seeks federal funding for the nearly $2 billion project, the staging plan for construction is starting to come together – and may be an even bigger challenge.

Jonathan Gulliver, the state’s highway administrator, says the elevated section of the Turnpike that runs through the throat area was built in such a way that it can’t just be torn down and rebuilt at ground level. Since the idea is to keep traffic flowing while the new highway is built at ground level, the rebuild has to be done in what amounts to a series of chess moves.

First off, the elevated section of the existing Turnpike needs to be shored up so it will last through the seven years of construction.  The state currently spends $1 million a year to keep the crumbling elevated highway upright, but now a “major rehabilitation” is planned. The price tag for the rehabilitation had been $75 million, but the cost rose to $90 million in the state’s application for federal funding.

The biggest surprise in the funding application is that the state is also planning to build a new, temporary elevated roadway capable of carrying half the Turnpike traffic while the old, rehabilitated elevated Turnpike is torn down in stages. 

You read that right. The state does a major rehabilitation of the existing elevated Turnpike and then builds a new elevated roadway to carry traffic while the old rehabbed Turnpike is torn down in stages and rebuilt at ground level. The new temporary roadway would be a lot like a temporary bridge, used for awhile and then discarded.

“This is a one of the things we’re trying to eliminate,” Gulliver said. “The last thing you want to do is add more infrastructure, even on a temporary basis. It’s costly and it’s time consuming.” 

Gulliver said the construction approach is necessary to keep traffic moving during construction and make enough room in the throat to build out the project. But he’s hopeful the engineers can find a way to dispense with the temporary elevated highway, which is referred to as a viaduct.

“There are a lot of needs that force us to look at the project this way. This particular phase, with the temporary viaduct, our hope and our goal is to eliminate the need for it all together,” he said. “My gut tells me there is a way to do that.”

Bruce Mohl oversees the production of content and edits reports, along with carrying out his own reporting with a particular focus on transportation, energy, and climate issues. He previously worked...