After 15 years of study and debate, one of Denver’s largest ever construction projects begins.

After 15 years of study and debate, one of Denver’s largest ever construction projects is underway: the rebuilding of Interstate 70.

Even as debate over the project rages, demolition crews have torn down dozens of homes while new construction workers are training on heavy equipment near the aging highway in north Denver.

The project will rework close to 10 miles of the highway over four years of construction, from Interstate 25 to Interstate 225, bringing significant disruption to interstate drivers and especially to those who live alongside the project.

“We want to be really honest with commuters and help them get prepared …. We’re going to do everything we can to reduce the impacts — but it’s still going to be an active construction zone for four years,” said Colorado Department of Transportation spokesperson Rebecca White.

“I want people to know there will be an impact — but it’s not going to be a huge one.”

Here’s where it’s going to hurt:

Construction beneath and around the I-70 viaduct starts this year and runs from 2018 to 2022 . That’s from Brighton to Colorado boulevards. It will result in a hectic driving experience, and the residents of Elyria-Swansea and nearby neighborhoods are expecting a lot of frustration.

. That’s from Brighton to Colorado boulevards. It will result in a hectic driving experience, and the residents of Elyria-Swansea and nearby neighborhoods are expecting a lot of frustration. Crews will be working between Colorado and I-225 from 2018 to 2020. Overall, drivers on the highway will see slowdowns and traffic shifts, but there will not be major highway detours.

What do you do with a highway on a bridge?

Construction crews will start rebuilding large stretches of the highway this year — but CDOT plans to keep highway traffic flowing along the same route.

It’s going to be tricky.

Right now, the interstate runs on an elevated viaduct for about 1.8 miles through north Denver, an imposing structure that has loomed over residential neighborhoods since the mid-1960s. CDOT will demolish the viaduct, instead digging a huge trench and lowering the highway below the surface grade.

“The viaduct stays up for the first two years of construction,” White said. “I think that’s the most difficult part for people to wrap their heads around.”

First, crews will dig part of the trench along the north side of the viaduct. Prep work on the streets beneath I-70 begins this year, and the digging starts in 2019.

They’ll build a section of new, lowered highway that will be just wide enough to fit six lanes of traffic — same as the current highway. Around 2020, traffic will be rerouted off the viaduct and into the baby trench.

“That’ll be wide enough to move all the traffic down from the viaduct. It’s going to be in a tight condition,” White said.

At that point, the viaduct can be demolished and the second half of the trench will be dug in its place. (CDOT calls it the “lowered” section, but, whatever.)

This strategy should keep the same number of lanes flowing at all times, but the shifting lanes and traffic cones will jam up traffic.

“I think the commuters will have a pretty consistent experience. There’ll be limited major traffic shifts and it will operate very similar to how it is today,” said Brenda Tierney, a spokesperson for CDOT.

The work does extend far east of the viaduct. In 2018 and 2019, crews will work on the eastern section of the project, beyond Quebec Street. In 2019 and 2020, work will begin on the project’s central section, which includes a full rebuilding of the highway from Colorado to Quebec.

Overall, it may feel to drivers something like the T-REX work that rebuilt and added rail lines to parts of I-225 and I-25 in the 2000s.

“It’s very similar in the scale of it — the enormity of building miles and miles of new highway in an urban landscape, neighbors on both sides, with a lowered section and cross-streets,” Tierney said.

The project will introduce a new toll lane in each direction across its length. It also includes a “cap” that will cover 1,000 feet of the highway with a recreational area.

The project will cost CDOT about $2.2 billion over 30 years, some of which will be paid by tolls, as the Denver Post’s Jon Murray reported.

Construction will be worse for the neighborhoods.

Right now, the viaduct crosses over 10 streets that connect the neighborhood of Elyria-Swansea to the rest of Denver. And the road that many of the area’s residents use to get around — East 46th Avenue — runs beneath the viaduct.

“How are folks going to get in and out … when it compromises your north-south and east-west connectivity?” said Councilwoman At-large Debbie Ortega.

That particular pain begins in 2018 and continues into 2020. Crews will be replacing the north-south roads under the viaduct, such as Clayton Street, with structures that eventually will be bridges over the trench.

“They will actually build those on the ground and dig out from underneath them,” White said. CDOT will try to keep north-south connectivity by limiting the number of simultaneous closures in any one area.

Still, it’s a lot of construction in one neighborhood. Next year in particular could bring a lot of frustration, according to Tierney.

“It’s going to be horrible. They’ve already been talking with the employers in the neighborhoods about having (central) parking places and shuttles,” said Nola Miguel, a member of the Globeville Elyria-Swansea Coalition.

That’s true: CDOT is working to make bicycles and other alternative transportation available available. “To the extent we can keep folks using the interstate, carpooling, or switching over to the rail, that’s going to minimize impacts on the neighbors,” White said.

To reduce noise and other disruptions, the builders won’t be allowed to set up staging zones — where heavy equipment is kept — “anywhere near the homes and the elementary school,” White said. They’ll also have to keep driveways open for businesses at all times.

And it’s not just I-70.

While all this is happening, the city of Denver is rebuilding Brighton Boulevard and preparing for a similar project on Washington Street, both on the west side of the viaduct.

Meanwhile, development of the $765 million National Western Center project is just getting underway, and private developers are in overdrive.

“I don’t think there’s any place in the city like what’s going on in this area,” Ortega said. “The need to coordinate that is so critical.”

She’s particularly concerned that trucks will leave traffic jams on I-70 and cut through the neighborhoods, and that idling vehicles will worsen air pollution. (In fact, the last major challenge to the project was a lawsuit that argued the presence of the highway itself has caused higher rates of asthma and heart disease for people living nearby.)

Now, the mammoth project is nearly here — and the scope of change is so great that many people are still missing basic details. In response, Ortega’s urging her constituents to get educated, and asking that the city ramp up its efforts to coordinate construction work throughout north Denver.

“People haven’t looked at the details of what this project will entail,” Ortega said, “or how it will create different traffic patterns.”

The city’s Public Works department plans to dedicate a team of about five people to coordinate lane closures and keep traffic flowing in north Denver, and the North Denver Cornerstone Collaborative also will be working on the challenge, according to spokeswoman Nancy Kuhn.

This post was updated to include official CDOT distance measurements and a comment from Denver Public Works.