IDAHO SPRINGS, Colo. (CBS4)– Travelers heading to the mountains for spring skiing and boarding should be prepared for more construction on westbound Interstate 70 at the Twin Tunnels.

“We are back for another year,” said Twin Tunnel Project Manager Matt Hogan.

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The department is widening the westbound bore of the Twin Tunnels, located near Idaho Springs, after successfully widening the eastbound bore in a project that wrapped up late last year.

“The difference this year is that westbound will be a detour as well, that detour will use the tunnel that was constructed last year,” said Hogan.

That’s one reason the work is getting underway again so soon. The detour road that was used a year ago will be vital when CDOT needs to shift traffic to allow them to work on the westbound tunnel.

The widening project at the Twin Tunnels is complete. The expanded tunnel will reopen Dec. 13. (credit: CBS)

The widening project at the Twin Tunnels is complete. The expanded tunnel will reopen Dec. 13. (credit: CBS)

“All the work right now is prepping to put the detours in place. So you will see lane closures for another week or so and then once traffic is shifted there will be fewer lane closures than there were last year,” said Hogan.

For the next few weeks, CDOT will periodically redirect the westbound traffic into the eastbound lanes as they get ready for blasting work. During selected times, there will be lane closures and eastbound and westbound traffic will share the eastbound bore’s new three lanes.

Then in April blasting will start on a routine schedule that will widen the westbound bore. The westbound tunnel blasting and reconstruction will last for the rest of the year.

Crews work on the Twin Tunnels in April 2013. (credit: CBS)

Crews work on the Twin Tunnels in April 2013. (credit: CBS)

There will also be more rockfall mitigation completed this spring. Up to 40,000 yards of rock outside the tunnel will need to be removed.

“We have more rock work in the tunnel and outside the tunnel. The westbound tunnel is about 80 feet longer than the eastbound tunnel,” said Hogan.

Once the new wider twin tunnels are completed there will still only be two lanes heading west.

“We are looking into the feasibility of a westbound peak period shoulder lane in the future,” said CDOT Project Manager Benjamin Acimovic.

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The project is on a tight schedule.

“We will have traffic restored back to the tunnels by Dec. 20 of this year,” said Hogan.

CDOT said by completing this project now they will save about $7 million.

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The following information about this project was released by CDOT in early March.

Before crews can begin the blasting work that will widen the tunnel and remove a portion of the rock face walls above the westbound tunnel, traffic must be rerouted from the westbound bore into the eastbound bore. To accommodate this traffic shift, crews will put down temporary pavement in the center median area on both sides of the tunnel to transition westbound traffic into and out of the eastbound lanes. This center median work will take about a month to complete and requires closing the far left lane of eastbound I-70 during off-peak travel hours.

Along with these off-peak lane closures, preparatory work in the westbound tunnel bore will require putting I-70 traffic in a head-to-head configuration through the eastbound tunnel for overnight work. This will be done several nights throughout March and will involve maintaining two eastbound lanes and one westbound lane.

Other work scheduled to take place in March includes one or two small blasts outside the westbound tunnel to facilitate the extension of a drainage box beneath the highway and two or three days of rock scaling work in late March to prepare for the larger rock face blasts that will begin in April. The blasting operations in March will require stopping traffic in both directions for about 15 minutes while the rock scaling work will require stopping traffic in both directions for up to 30 minutes so crews can safely remove large boulders and rocks from the rock face above the highway.

In April, eastbound traffic will be reduced to two lanes of travel and will move back onto the detour route around the tunnel while westbound traffic slides over into the eastbound tunnel bore. Once traffic is shifted, crews will begin large-scale blasting inside the tunnel as well as rock cut blasting on both ends of the tunnel.

Blasting activities will continue through the end of summer and involve stopping I-70 traffic in both directions. Tunnel blasts require shorter duration stops of about 15 minutes while the rock cut blasts will have a greater impact on I-70 travelers. Following each rock cut blast, crews will need to scale the hillside to remove any loose rocks and debris to keep it from falling on the highway below. This scaling work requires stopping traffic for up to 30 minutes followed by about 45 minutes of free-flowing traffic to clear the queues. This alternating process of stopping and releasing traffic will continue as long as necessary to finish removing blasted materials.

Construction crews anticipate conducting one or two rock face blasts each week and tunnel blasting just about every day of the week through August.

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CDOT estimates widening the westbound tunnel now will save $5 million to $7 million because the equipment, resources and detour needed to do the work are already in place. Tunnel widening work is scheduled to be complete by the end of this year and at that time all I-70 traffic will be back in its regular alignment. Project completion is scheduled for summer 2015 when County Road 314 is restored to its original configuration with completed facia walls and an improved recreational trailhead.