Transportation officials have approved an $806 million project to add an express lane to I-270 after years of studying proposed solutions to congestion and deterioration of the interstate.

The Federal Highway Administration and Colorado Department of Transportation have been weighing options since November to add either a general-use lane or an express lane to the 6.5-mile stretch of I-270 from the U.S. 36 interchange to I-70 in north Denver.

A final Environmental Impact Statement and Record of Decision were published Tuesday, giving officials the green light to move forward with construction. The project will include reconstructing the entire 6.5-mile stretch of interstate and adding the new lane.

Construction is expected to begin this fall.

The project will also replace 12 bridges, rebuild the Vasquez Boulevard interchange, add a new pedestrian overpass bridge and improve the on and off-ramps at I-76.

Other plans were considered throughout the process, but the chosen plan “most effectively improves travel time and reliability, corridor safety, and freight operations,” the Record of Decision states.

Adams County Commissioner Julie Duran Mullica said county officials are “grateful” to the state transportation department and the federal agency for deciding to improve I-270.

“This is an important next step toward needed improvements to the I-270 Corridor that will make a real difference for the people who live, work and travel along this corridor,” Mullica said. “We’re excited to see this project move into its next phase and, ultimately, to see these long-needed improvements come to fruition for our residents, businesses and the entire region.”

The I-270 corridor improvements project team will host a telephone town hall at 6 p.m. on Oct. 6 for 133,000 residents who live along the corridor to share more information about the final design and construction phasing.

Funding will come from a combination of state and federal sources, including the Colorado Transportation Investment Office, state legislative funds and federal grants.

Phase I of the project, to fix critical bridges along the corridor, will cost $307 million. Phase II, reconstructing and redesigning the roadway, will cost $402 million. Phase III, which includes designing and reconstructing final bridges and pedestrian overpasses, will cost $97 million.

The decision ends a six-year environmental review of the corridor, which included “extensive” public comment and coordination with local government and agencies, according to a news release.

I-270 started construction in the late 1960s, according to CDOT. The highway was meant to help connect metro area residents to Stapleton International Airport, which opened in 1929 and was replaced by Denver International Airport in 1995.

The highway corridor now handles more than 100,000 vehicles every day, with up to 17% of those vehicles being freight trucks.

The state transportation agency began looking into options in 2020 to fix a variety of challenges on I-270, which, officials acknowledged, carries “far more traffic than it was designed for.”

In 2023, the state agency determined that the project was complex enough that it warranted a detailed environmental assessment. The process of creating an Environmental Impact Statement (EIS) started in August 2024.

In November, the agency released an EIS outlining issues and proposed solutions. Officials recommended adding a toll lane to the two-lane highway and finalized that decision in Tuesday’s published report.

The I-270 currently averages about 42 crashes per mile per year, about 40% more than other similar freeways in Colorado, a state report said.

Between 2014 and 2022, more than 3,000 crashes were reported on I-270, with almost 1,000 reported injuries and 14 reported deaths.

At its posted speed limit, it should take up to eight minutes to drive from end-to-end. It typically takes more than twice that long in the morning and up to 25 minutes in the afternoon, according to data cited by the state report.

Without improvements, peak-hour travel times on I-270 are projected to more than double by 2050.

Other issues along the corridor include deteriorating pavement, tight interchange ramps, narrow shoulders and short merge areas.

Not everyone agrees with the newly finalized plan.

Several environmental groups, including Earthjustice and GreenLatinos, argue that adding lanes does not solve traffic problems and the interstate project will impact certain communities more than others.

The two organizations proposed another plan for the interstate that involved expanding transit, creating “green” buffers and building safer connections for people walking and biking.

Their concerns were ignored, Earthjustice wrote in a statement Wednesday.

“CDOT is choosing to widen a highway when it could be investing in solutions that actually move people while protecting the health of the communities along I-270,” GreenLatinos project manager Carlos Matutes said. “The choice is not between congestion and highway expansion. We can reduce congestion without asking communities that have already carried the burden of pollution to carry even more.”

The full Environmental Impact Statement and more information on the project are available on the state transportation agency’s website.