Crews worked tirelessly Wednesday, knocking loose boulders from the cliff above Interstate 70 in Glenwood Canyon in an effort to lessen the risk of further rock slides after a massive slide closed the interstate Monday night.

Only after officials determine that it’s safe will the highway be partially reopened, but the plan remains to try to make that happen by Thursday afternoon, Amy Ford, director of communication for the Colorado Department of Transportation, said.

It all depends on the progress of those efforts, not to mention the weather, she said during a telephone press conference Wednesday afternoon.

“Safety is our number one priority in this corridor, and we need to make sure to deal with the rockfall mitigation before we decide to open any lanes,” she said. “There is still a lot of work to be done.”

I-70 through the canyon remained closed for a second full day Wednesday after a massive huge slide involving more than a dozen car-sized boulders came crashing down onto the roadway around 9 p.m. Monday. It was the second slide of the day, after a smaller one closed the interstate for about two hours before dawn.

CDOT officials expect to have a better idea by noon Thursday whether it will be realistic to open one of the eastbound lanes and deploy a pilot car to alternate between leading eastbound and westbound traffic through the slide zone while repairs are done to the severely damaged westbound lanes, Ford said.

Rain is also forecast for Thursday afternoon and evening, which could complicate matters, she forewarned.

“I need to be real clear that we have people up on the side of the mountain pushing rocks down,” Ford said. “It’s treacherous work, and the safety of our workers is of utmost importance.”

Rock scaling operations throughout the day Wednesday involved about a half dozen workers suspended from high up on the cliffs, dislodging loose boulders and pushing them to a containment area below.

No vehicles were involved in the first slide Monday, but two semis and at least one passenger car were passing through, headed west, when the second one came down. One of the semi trailers was severely damaged, but the driver was uninjured.

A northerly detour via U.S. 40 and state Highways 13 out of Rifle and 131 at Wolcott to access Garfield County and the Roaring Fork Valley remains in effect. The detour route adds 146 miles and a couple of hours travel time between Wolcott and Rifle.

I-70 remains open to local traffic only between Wolcott and Dotsero, and on the west side of the canyon between Rifle and Glenwood Springs.

Motorists passing east through Colorado are advised to take U.S. 550 south from Grand Junction and U.S. 50 at Montrose to Gunnison over Monarch Pass, then north to U.S. 285, and vice versa from Denver.

For through traffic, either route takes about the same amount of time, Ford said.

She emphasized that motorists should ignore GPS directions and information gleaned from the Internet or by word of mouth, suggesting alternative routes via any of the area mountain passes that are closed for the winter.

Pitkin County officials reported numerous motorists and even semis being stranded in Aspen en route to Independence Pass, which is closed this time of year until at least late May. Same with Cottonwood Pass between Garfield and Eagle counties, and the Forest Service road between Eagle and the upper Frying Pan valley.

Once a single lane of I-70 reopens, traffic will be directed in alternating fashion using a pilot car for about six miles between the Grizzly Creek rest area and the east side of the Hanging Lake Tunnels before being allowed to merge back into the regular lanes.

“We anticipate that people will experience hour-plus delays, and those, too, will be dependent on the weather,” Ford said, adding the pilot car situation will likely be in effect for several days.

During the closure, CDOT’s Bustang has been terminating in Eagle and not picking up or dropping off passengers in Glenwood Springs. That could change once the pilot cars are running, although schedules may need to be adjusted to account for delays, CDOT communications manager Bob Wilson said.

Greyhound bus lines are currently taking the northern detour, Ford said.

Amtrak’s California Zephyr passenger line and freight trains are also still running through the canyon, as the railroad tracks were not impacted by the rock slide, Union Pacific Railroad spokeswoman Calli Hite said.

CDOT engineers are also still working to determine the extent of the damage from the rock slide and the cost to repair it, she said.

The slide happened in an area “just outside” where extensive rockfall mitigation was done last fall, along with nearly $10 million worth of repairs to bridge joints, decks and the asphalt road surface, as well as new guardrails. Some of that work will need to be repaired, CDOT officials said.

Colorado State Patrol officials reported that traffic was running smoothly along the U.S. 40 detour corridor without any serious incidents.

“We have see an increase in traffic, but fortunately no increase in traffic crashes,” Capt. Douglas Conrad of CSP’s Craig Troop office said. “We have had a few reports of road rage and aggressive driving, but, given the extended travel time, most people seem to be doing fairly well.”

Meanwhile, Roaring Fork Valley residents and businesses were dealing with the impacts as best they could amid uncertain travel plans and delays in delivery schedules.

Adele Melnick, director of the Growing Years Preschool in Basalt, said she and several of her teachers were waiting until today to decide whether to travel to an annual early childhood education conference in Denver this weekend.

“I know of at least 30 people going from this area,” she said. “If they do get the one lane open tomorrow afternoon, we will probably go. If not, we’re definitely debating whether we will even try.”