Colorado’s next major highway undertaking kicks off this week as crews begin work on the $700 million reconstruction of Interstate 70 in the mountains — a project aimed at eliminating the Floyd Hill bottleneck and improving safety through a notorious eight-mile stretch.

Much of the most intensive work over the next five years or so will occur off the highway. But the Colorado Department of Transporation says drivers traveling I-70 between the top of Floyd Hill and Idaho Springs still can expect lower speed limits, narrowed lanes and traffic shifts, along with some daytime traffic holds and overnight closures.

The project technically broke ground last fall with the start of several associated off-highway projects, including the first of two wildlife crossings outside the project zone and new roundabouts on a frontage road.

But now comes the main event. Soon CDOT’s contractors will begin rock blasting to make more room, and in coming years they’ll construct a 7,000-foot-long bridge to carry westbound traffic into Clear Creek Canyon at the bottom of Floyd Hill.

“The mountain corridor is a challenging environment,” said Kurt Kionka, CDOT’s project director, at a stop midway down Floyd Hill during a project corridor media tour in June. “In order to construct this, we need to build up above the current alignment, and then we also need to cut into the mountainside.”

Here is a look at the project, the construction schedule and the expected impact — both while it’s underway and once it’s all done in late 2028.

The plan: A soaring bridge and more traffic capacity

The project’s main capacity expansion will come with the addition of a westbound tolled express lane. It will begin where the highway currently narrows to two lanes, near the top of Floyd Hill, and to the west it will tie into an existing peak-period express lane at the Veterans Memorial Tunnels, near Idaho Springs. The three-lane eastbound side won’t get any additional through lanes.

Crews also will straighten several sharp curves through Clear Creek Canyon, rebuild old bridges and construct the new, more-than-a-mile-long bridge for westbound traffic. On the eastbound side going up Floyd Hill, they will add an extended on-ramp from U.S. 6 to serve as a climbing lane for slow-moving semitrailer trucks and other heavy vehicles.

Off the highway, the project includes the construction of a missing two-mile stretch of frontage road in the canyon for local and emergency traffic, along with improvements to the Clear Creek Greenway trail.

The project’s most notable features

Some designs are still being finalized by CDOT’s construction manager, Kraemer North America, and lead designer Atkins. But the major components are set, drawing on creative solutions to ease the flow of traffic in sometimes-harrowing circumstances — particularly on Floyd Hill, where drivers descend nearly 700 feet in just over two miles and then must make a sharp left turn into the canyon.

While the eastbound side will stay mostly on the ground when the project’s done, westbound traffic will leave the existing I-70 footprint near the bottom of the hill, soaring 100 feet in the air on that long new bridge as it banks more gently into the canyon.

Part of that smoother curve will be accomplished by crossing westbound traffic over the eastbound lanes — resulting in a reverse traffic configuration for a short stretch, until the westbound lanes cross back over and return to the ground.

Kionka says the tight curve at the bottom of Floyd Hill, now rated for 45 mph, will be upgraded to 55 mph by the end of the project, reducing backups caused now by drivers hitting the brakes as they approach the curve on the downhill.

How construction will play out

CDOT and its contractors have divided the project corridor into three sections with overlapping construction timelines:

• East section: Work between County Road 65 (Exit 348, Beaver Brook) and the bottom of Floyd Hill includes rock-blasting and outside widening on both sides of I-70 to make room for the westbound express lane and the eastbound climbing lane. Timeline: Starts this month, with completion set in 2026.
• Central section: The most intensive section, accounting for roughly two-thirds of the project’s cost, runs from the midpoint of Floyd Hill to the Hidden Valley interchange (Exit 243) partway through the canyon; it overlaps slightly with the east section. Crews first will build the 7,000-foot-long westbound bridge on piers off the current highway, then use the room freed up by the removal of the old westbound lanes to reconstruct the eastbound side at ground level. At a tight curve at Sawmill Gulch, both directions of traffic will cross Clear Creek into a short “tiered cut” built into the mountainside on the south side of the canyon, before crossing back to the north side of the creek. The new frontage road link will be added in this section. Timeline: Starts in 2024, with completion expected in fall 2028.
• West section: Work between Hidden Valley and Exit 241 (Idaho Springs) includes widening and significant blasting of rock, mostly at one curve east of the Veterans tunnels where the rock cut will reach 200 feet high, according to CDOT project manager Jeff Hampton. Timeline: Starts this fall, with completion expected in fall 2027.

How will construction affect traffic?

The construction zone will come with lower speed limits and other constraints that unavoidably affect traffic. But CDOT officials expect to keep all existing lanes open during peak travel hours, with lane closures restricted to overnight hours.

There’s a big exception: Rock blasting that starts in the east section in late July or August will require 20-minute traffic holds during daytime hours that could back up traffic for more than twice as long, CDOT says. Those are expected to happen once or twice a week, but additional blasting in other project sections will make the holds a recurring feature through 2025, affecting not only highway traffic but rafting companies that run trips on Clear Creek.

Later in the project, full overnight closures of I-70 in the central section will come with detours of traffic onto U.S. 6 and U.S. 40.

Drivers can stay on top of expected holds and lane closures by checking the project website, at codot.gov/projects/i70floydhill, keeping tabs on CDOT’s COtrip website or app, or signing up for text alerts (text “floydhill” to 21000).

Will the project improve I-70 traffic?

Project officials are careful to say the project is as much about improving safety along one of the most difficult mountain corridors as it is about addressing congestion.

But Kionka, the project director, says the project’s changes, including the new westbound express lane, at least should improve traffic flow. Unlike the existing mountain express lanes to the west, which were built on the road shoulders and are open only during peak periods, the new express lane will be built at full width and will always be open.

“When we are complete here, we will certainly see alleviating the bottleneck” at Floyd Hill, Kionka said. “With flattening the curves, improving the sight distance, it will be much safer to travel through here, and I think you’ll see traffic move much better.”

CDOT aims to reduce environmental impact

There’s no doubt that this is a highway-widening project, one launched in an era in which CDOT faces new greenhouse gas emission reduction targets that could make such projects less common.

But the Floyd Hill project was the impetus for CDOT’s launch last year of Pegasus, a van-based transit service aimed at providing an alternative to driving on the corridor. Now running daily between Denver’s Union Station and Avon, with several stops in towns along the way, the service has grown from hundreds of riders a month to 3,300 in March, according to the latest figures available.

Two wildlife crossings are among the side projects begun last year. One underpass being built on I-70 near Genesee will accommodate an elk herd, officials say, while a land bridge planned to the west — over U.S. 40 between I-70 and Empire — is intended for bighorn sheep that frequent the area.

Project designs at one point included significant rerouting of Clear Creek through the canyon, but that’s no longer planned, Kionka said — a move that saves money but also will avoid further disturbance to the environment. The highway will be routed farther from the river in the middle of the canyon, potentially allowing for limited riparian restoration.

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