The Twin Tunnels Expansion widened the eastbound and westbound tunnels on Interstate 70 through an active mountain corridor. This was the first major construction in decades along the busy stretch of highway. The project added an eastbound lane and provides for future westbound capacity and mobility improvements. The narrow freeway corridor has seasonal peak demands, and both directions are bordered by unstable rock faces and sensitive streamside habitats.

During eastbound widening, crews stabilized the tunnel and mitigated rockfall, along with wall construction and detour preparations. During the first year of work, the Kraemer-Obayashi joint venture team completed the tunnel, three miles of highway widening, a new bridge and nearly 4,500 linear ft of cast-in-place concrete wall to support the future lane. The job finished on schedule and $3.5 million under the final contract budget. The same team also constructed the westbound tunnel and performed significant surface rock-blasting operations east and west of both tunnels, followed by stream restoration. Later work included trailhead and county-road restoration after the detour alignments were removed.

To minimize traffic impacts, the Colorado Dept. of Transportation developed an aggressive schedule that restricted the I-70 detour to the months of April through December.
 

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