A rockfall mitigation project above the Twin Tunnels is causing full closures of the westbound Interstate 70 lanes at night this week, as crews work to prepare the facility for an upcoming widening project.
Westbound traffic will be directed through the eastbound tunnel bore on one lane while the other lane is used for eastbound traffic.
The speed limit will be reduced to 35 miles per hour in the tunnels and vehicles wider than 11 feet will not be allowed through.
Westbound lanes will be closed tonight, Wednesday night and Thursday night from 7 p.m. through 7 a.m. the following morning.
During the work, crews will remove rocks at risk of falling into traffic and take measures to reduce the chances of future rockfall problems.
"They've got to knock down a few loose rocks above the tunnels themselves, but the primary purpose is to put some fencing up there to prevent any rocks from falling," Colorado Department of Transportation spokesman Bob Wilson said. "When they're working up above there, rocks could conceivably get kicked or knocked into traffic, so they can't let (cars) through there."
The project is part of the ongoing preparation for the widening of the eastbound tunnel bore, set to take place next year. Crews will be blasting out the tunnel to allow the highway to be expanded to three lanes, a measure intended to improve traffic flows along the I-70 mountain corridor.
"We're going to start blasting and that could knock things down," Wilson said. "We have to make sure the geological aspects of that (area) are all set."
Transportation officials say crews will be working to complete the rockfall project overnight this week - during a lull in the holiday traffic - to minimize impacts to drivers.
"It's a pretty quiet week," Wilson said. "Even more so because we just don't have a lot of snow. It's still pretty dry."
Crews will take a brief hiatus from preparation work in the later half of December, when holiday skier traffic peaks, resuming some time after the first of the year. Future preparation work will be scheduled outside of peak travel periods, officials say.
The widening project is set to start in full force April 1. It will cause a full closure of the eastbound I-70 lanes through October.