CDOT Twin Tunnels Expansion Program
Idaho Springs, Colo.
Region Mountain States
Highway/Bridge

Project Team
Owner Colorado Dept. of Transportation
Lead Design Firm Atkins Global
Designers WSP | Parsons Brinckerhoff, Yeh & Associates Inc., THK Associates Inc.
Prime Contractor Kraemer-Obayashi JV
Major Subs APC Construction Co. LLC, Harrison Western Construction and Horn Construction Corp.

On the first major construction job in decades along a busy stretch of Interstate 70, the project team expanded two highway tunnels, added an eastbound freeway lane and provided for future westbound capacity. The narrow freeway corridor, west of Denver, carries heavy ski traffic in the winter and a high volume of tourist traffic in the summer. Also, the highway is bordered by unstable rock faces and sensitive streamside habitats.

“This was, by far, the most complex project I’ve ever been involved in,” says Matt Hogan, project manager for the Kraemer-Obayashi joint-venture contractor. “That’s because we completed so many activities in such a small space.” The eastbound project encompassed 1.5 miles, while the westbound portion was only 2,000 ft long, he says.

During the first year, the contracting team finished the eastbound tunnel, widened the highway, built a new bridge and placed nearly 4,500 linear ft of cast-in-place concrete wall to support a future lane. That segment finished ahead of schedule and $3.5 million under the final budget. Then, the same team expanded the westbound tunnel and performed extensive surface-rock blasting, followed by stream restoration and storm drainage improvements.

To minimize traffic delays, the Colorado Dept. of Transportation developed an aggressive schedule that, April through December, restricted I-70 detours. “We delivered a hugely complex project with as minimal traffic disturbance as possible,” says Bob Smith, CDOT’s construction project engineer. It was also one of the agency’s first ventures into construction manager-general contractor project delivery.

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