Amid the sound of cars and semi-trucks whooshing down Interstate 25, officials on Thursday celebrated the start of a major widening project that many had said just a few years ago was unlikely to get done within a decade.

Construction will start Tuesday on the widening of the roughly 18-mile stretch of I-25, known as the “Gap,” between Monument and Castle Rock. About 100 people, including a slew of representatives from local and state government, gathered to kick off what Colorado Department of Transportation Executive Director Mike Lewis called “one of the biggest and most needed projects in the state.”

The project, slated for completion in late 2021 or early 2022, will add a pair of toll lanes to the highway, widening it from two to three lanes in each direction. The $350 million project is being paid for by a federal grant, state funding, and appropriations from El Paso and Douglas counties and the Pikes Peak Rural Transportation Authority.

Many residents have expressed opposition to widening the Gap by adding Express or toll lanes, saying they would benefit only those willing to pay the extra cost. They also have criticized it as double taxation because local tax dollars are helping pay for the widening.

But during the roughly one-hour event, only one speaker – state Rep. Paul Lundeen, a Monument Republican – mentioned the backlash CDOT has received on the toll lanes.

“The conversation about restricting tolling on the new managed lane is still an open conversation,” Lundeen said.

After the ceremony, CDOT Executive Director Mike Lewis confirmed that the option of not charging drivers for using toll lanes at certain times of the day is still “on the table.” He added that the tolls are set by CDOT’s High-Performance Transportation Enterprise Board, which will decide on the rates about a month before the new Express Lanes become operational.

A traffic and revenue study commissioned by the agency recommended a rate of about 15 cents per mile – around $2.25 per one-way trip. Nick Farber, head of innovative project delivery, said at the board’s Aug. 15 meeting that staff will likely be recommending that the tolls begin at a flat rate; however, as traffic on the highway increases in years to come, the board may switch to a model where the rate varies depending on the time of day and traffic on the road, Farber said.

The project will also include widening shoulders for emergency and maintenance vehicles, rehabilitating bridges and other structures, and adding four wildlife underpasses.

Other speakers – including U.S. Rep Doug Lamborn, a Colorado Springs Republican, and commissioners from El Paso and Douglas counties – emphasized that the project will make the stretch safer for drivers and also provide benefits for local economies and the tourism industry.

“This is crucially important beyond just the 18 miles. It is a template and a symbol for the progress the state has made and the progress the state continues to make,” Gov. John Hickenlooper said.

The first of the project’s three phases will widen the 5 miles from Castle Rock to Sky View Lane, according to CDOT. By next summer, the entire stretch will be experiencing active construction, the agency said in a news release.

During construction, drivers can expect two lanes to remain open in each direction during daytime peak travel hours, with lane and ramp closures restricted to nighttime off-peak travel hours.

The speed limit will also be reduced to 65 mph in construction zones, the news release states.