Blasting on Red Mountain Pass began Wednesday and continue for 2½ weeks, causing delays of up to about 30 minutes.
Operations will occur mostly from 11 a.m. to 2 p.m., the Colorado Department of Transportation said in a news release Tuesday. Blasting is expected to be completed by May 27.
All summer, U.S. Highway 550 will be limited to a single lane with alternating traffic 24 hours a day, seven days a week.
The work is part of the second season of installing crib walls, which are retaining structures built below the highway for stabilization and reinforcement.
Slated to be complete by Aug. 31, crews will work near mile marker 79.5, just south of the summit of Red Mountain Pass.