IDAHO SPRINGS, Colo. (CBS4) – If you have traveled on Interstate 70 near Idaho Springs lately it’s likely you’ve noticed an impressive looking 30 foot tall structure.

It’s called a tunnel form, and installing it will be a key step in the $106 million Twin Tunnels project. The project, which will be completed by the end of the year, will add another lane to the highway at the tunnel and ease traffic at what the Colorado Department of Transportation calls the main pinch point for I-70 in the mountains.

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The tunnel form weighs 250,000 pounds and will create the necessary lining between the rock and vehicles traveling through the tunnel.

“This tunnel lining now is the permanent support that will give it a 75 to 100 year life span,” said Twin Tunnels Project Manager Matt Hogan.

The tunnel form is sitting on a railing and it will slowly be brought hauled into the west end of the tunnel after some more blasting work is completed. After that another tunnel form will be installed in the east end.

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The tunnel form is shaped like an upside down U.

“That shape you see today will be the final lining of the tunnel when it’s said and done,” Hogan said. “On average the design thickness is two feet. Because the rock doesn’t break consistently, because that’s the way rock is, it will be anywhere from two feet to four-and-a-half feet where the rock broke.”

The tunnel is currently about 60 feet wide thanks to 75 blasts taking out nearly 20,000 pounds of rock.

Once the tunnel forms are in place, it will still be about six to eight more weeks before the lanes are actually put in.

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LINK: I-70 Twin Tunnels Project Website