There are a lot of unanswered questions that officials will address over the next two years. Still, here’s a few things we do know:

The biggest highway project to hit Boston in a generation is going to significantly remake the western face of the city, but eight years of construction promises to disrupt traffic of all kinds. On Thursday state officials decided on a design for the $1.1 billion reconstruction of the turnpike’s Allston interchange .

So, is the Mass. Pike in Boston basically going to shut down for a decade? Will Allston be one big construction zone? Will even the commuter trains from Worcester and Framingham get through?


Um, why on earth are we doing this to ourselves?

Wasn’t one Big Dig enough? Unfortunately, the Massachusetts Turnpike in Allston has the same issue as the old I-93 in downtown Boston: the elevated section of the highway is old, expensive to maintain, and at risk of failing sometime in the future. It needs to be replaced, no matter what, and just doing that was estimated to cost more than $400 million.

So, while they’re at it, officials also plan to take a big curve out of the turnpike. Crews will essentially straighten the highway where it carves a big arc through the former rail yards. Those yards are now owned by Harvard University, meaning the change will free up 100 acres of land for new development.

The project also offers the opportunity to ease one of the more frustrating sections of roadway in Boston. For example, all-electronic tolling frees the state to relocate the highway exit ramps that currently dump all traffic into that crazy bottleneck on Cambridge Street at the Allston interchange. Instead there will new exit ramps and a bunch of new local roads within the former freight yard. That should disperse traffic over a wider area.


Why lower the turnpike?

While the state originally planned to just replace the highway viaduct with a new one, neighborhood activists didn’t love that idea, arguing that a big elevated structure essentially walls off access to the Charles River. Ideally, many wanted all the roads at ground level, and a new deck built over everything that can host new parks, bigger bike paths, and other amenities. But state officials were convinced the corridor there was just too narrow to squeeze all the roads onto one level without running into the river and violating environmental rules. A compromise emerged by elevating Soldiers Field Road.

Doesn’t that create the same problem in reverse?

Well, yes, but the Soldiers Field Road viaduct is going to be much smaller than the current one — about half the height and width — and won’t carry heavy trucks. So it shouldn’t have that same towering effect as the 30-foot elevated highway. This also frees up more room on the riverfront for park space, and provides opportunities for offshoots of the pedestrian and bike path to Commonwealth Avenue and the Boston University campus.

Where, exactly, will the new Soldiers Field Road viaduct go?

That’s still to be determined. The new viaduct will be about half the width of the turnpike, so it could go above the westbound side, which is closer to the river and paths, or further inland above the eastbound side. The latter is favored by some activists, and the city of Boston, who argue it would be less intrusive for pedestrians and cyclists and would make it easier to install barriers between the park and the highway. State officials say the ultimate course may depend on various utility lines in that area.


Sounds nice, but how horribly will this wreck my commute?

That’s one of many unknowns. Construction probably won’t start until at least 2021, which gives the state some time to devise a plan to minimize disruptions. But highway projects of this scale don’t generally get built without traffic backups, lane closures, and perhaps even some disruptions to commuter rail — though the rail interruptions are expected to be less severe in this version of the project. When the state rebuilt the nearby Commonwealth Avenue bridge, for example, the highway was reduced to about half-capacity. While this caused some big backups, the blow was somewhat softened because so many drivers heeded warnings from the state to avoid the roads altogether. Alas, the bridge project took place over a few weeks in consecutive summers, not over several years.

While it’s still not known how much of the turnpike and Soldiers Field Road will be closed off, or for how long, state officials are already anticipating that the current bike and pedestrian path along the Boston side of the Charles will probably be closed for periods during the project. The construction will also close a railroad bridge that the MBTA uses to shuttle trains needing maintenance, so that agency is going to have to get creative about a solution, too.

What else don’t we know?

For starters, just what Harvard has in store for all that now-empty land on either side of the current turnpike. The university is still devising its plans, but it probably won’t build much of anything until after the highway project is complete a decade from now.


We still don’t know when the new West Station commuter rail stop in that area will open — as late as 2040, as the state originally scheduled, or much sooner, as per activists and even Harvard and BU have requested. They argue West Station is key to ensuring the area doesn’t suffocate in traffic once Harvard starts building, and envision a big transit hub that offers rail service to both North and South stations, and buses to Cambridge and Longwood Medical Center. The state is looking into whether the station can be built sooner.

And then there’s the big one: how are we paying for all this? The state says it will hash that out as it finalizes its plans. The state is only allowed to use turnpike tolls collected near Boston — and not further west — for the project, and those tolls can only to be used for the turnpike portion of the overall project.

Officials have said they’ll also look into finding other state or federal funding sources, and may ask private parties that will benefit — like Harvard — to pony up. Harvard says it has already helped pay for the project by buying the land from the state back in 2003, converting the rail yard that once occupied it, and giving the state free rein for construction on the site.


Harvard has also already offered $58 million to help build the new rail station, which is considered part of the overall project; BU has also said it would chip in, but not yet indicated how much.

Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter @adamtvaccaro.