Safe passage on Highway 3

Motorists should find the full length of Colorado Highway 3 open to two-way traffic Saturday, four months to the day after the south end was closed to accommodate a safety project.

Scaling rock from a 0.7-mile section of shale and sandstone cliffs that border the highway was a precautionary move.

Highway 3, only 2.2 miles long, carries 8,700 vehicles a day. In the past decade, falling rocks have caused five accidents. In one incident, a boulder crashed onto the top of a woman’s pickup. She was hospitalized in fair condition. Her 8-year-old son, who was in the back seat, was not injured.

Fissures in the cliffs are vulnerable to freeze/thaw cycles that loosen rocks of all sizes, which then tumble onto the highway and can bounce to the Animas River below.

In the latest mitigation project, TK Construction, a Grand Junction contractor, removed more than 5,000 cubic yards of rock from the craggy cliffs.

Workers then drilled 743 metal bolts 25 feet long into the hillside to hold the land mass together.

Steel rods 6 to 12 feet long were installed at different angles to anchor 48,000 square feet of protective steel netting. The work began Aug. 21.

The netting hangs away from the cliff face to guide falling rock to a catch area at highway level. The curtain, 1,600 feet long and 30 feet high, consists of 8-inch squares of half-inch steel.

In contrast, netting on a slide area on Red Mountain Pass lies on the mountainside to prevent rock movement.

“This was the most extensive rockfall mitigation done in this area, not only on Highway 3,” said Nancy Shanks, communications manager for the Colorado Department of Transportation in Durango. “Typically, a project of this magnitude requires single-lane travel and stopping traffic for up to 30 minutes.”

In this case, those measures weren’t necessary.

Highway 3 was closed completely between Sawmill Road and its junction with South Camino del Rio. But it carried two-way traffic to serve businesses, a hospital, medical practices and condominium residents to the north. Access was from Santa Rita Drive and East Eighth Avenue.

Except for a few bad-weather days that kept crews off the cliffs, the project moved along well, Shanks said.

Scaling was done by workers suspended on ropes using pry bars. They also used small explosive charges, air bags and grout under pressure to break apart chunks of the rock.

The lower portion of the cliffs is Lewis shale, topped by pictured-cliffs sandstone. A Fruitland coal deposit lies immediately beyond the ridge.

The $1.56 million project also includes rock mitigation on Colorado Highway 145 south of Telluride. That work will begin in 2015.

TK Construction hoped to complete the work in November, but foul weather and an unfinished project elsewhere left the company short of workers for a while.

daler@durangoherald.com