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Vehicles travel on Highway 99 between Vancouver and Whistler April 6, 2015. After a series of accidents and with fissures opening in the road surface, the B.C. Ministry of Transportation and Infrastructure has decided to spend $60-million to make a section of Highway 99 safer.Jeff Vinnick/The Globe and Mail

By the time it is stabilized and repaired, a short stretch of highway that has slowly been sliding down a mountainside near Lillooet will be the most expensive kilometre of road in British Columbia.

After a series of harrowing accidents and with fissures opening in the road surface, the B.C. Ministry of Transportation and Infrastructure has decided to spend $60-million to make a section of Highway 99 safer.

"This site is one of the most technically complex and challenging locations to maintain in the entire province. At cost per kilometre, the Highway 99 / Ten Mile Slide project will be the most expensive rehabilitation project undertaken by the ministry," government spokesperson Sonia Lowe said in an e-mail Thursday.

The highway, which links Lillooet and two nearby native communities to Highway 1 near Cache Creek, runs through steep terrain along the Fraser River, passing through an ancient earthflow known as the Ten Mile or Fountain Slide.The ground has been shifting at the site for decades, but after years of trying quick fixes to the road, the government has decided tackle the mountain itself. "We're dedicated to improving this section of Highway 99 for the Xaxli'p, the St'at'imc [First Nations] and all the residents and businesses of Lillooet," Jackie Tegart, Liberal MLA for the region said in announcing the project.

Transportation Minister Todd Stone said the highway is vital to the economy of the area.

"For so many, this highway is a lifeline to employment and means of financial support, which is why it is crucial we get going on a long-term fix to get people – and goods – moving again," he said.

The highway was closed for several weeks in the fall and has been restricted to one lane of traffic through the slide zone since October, after fissures appeared in the road surface and nearby ground moved so much that hydro lines began to tighten as poles drifted apart.

Jack Crompton, chair of the Squamish-Lillooet Regional District, said the community is "ecstatic" about the government decision.

"This is a massive investment which will make a big difference to the economic success of our region," he said.

The slide is only about 300 metres wide where it reaches the highway, but to stop the earthflow engineers say they will have to sink 400 "soil anchors." A shear-resistant wall will also be built below the highway and about one kilometre of Highway 99 will be repaved.

Movement of the earthflow was first noted in 1985 when shear cracks appeared in the pavement. The highway was realigned in 1989 and again in 1995. For years the short section through the slide zone has had a gravel surface only, to make it easier for crews to fill the frequent cracks.

Provincial officials have long been monitoring the "slow creep" of the earthflow. In a paper prepared for a 2012 science symposium, Sarah Gaib, an engineer with the Ministry of Transportation, reported there had been "extensive slide movement at the highway" and that the slope above the road had moved more than four metres in three years.

She said cracks up to three metres wide and 10 metres deep had appeared on the slope.

Although the slide was moving extremely slowly, some consultants did warn it could accelerate and reach "sudden failure" in the future.

Two traffic accidents on the highway last year heightened public concerns about the road and led to an online petition that soon had 1,700 signatures urging government to act.

Deanne Zeidler, a Lillooet resident who started the petition after a mother and her seven-year-old son died in a crash in January, 2015, said she hopes the project succeeds because the community desperately needs "a route that is safe and reliable."

Phora Horton, who survived a crash over a roadside cliff in July, 2015, after her car lost control on gravel in the slide zone, said Thursday she isn't convinced the soil anchors will do the trick.

"To me it would be like nailing mud to mud. However, if they are attaching it to the solid mountain like a bridge that might work," she said in an e-mail.

In her paper Ms. Gaib said soil anchors were tried in a test section in the slide zone and they slowed down and in some places stopped movement.

"Completion of the trial section has shown that such work on an active sliding area is possible but not without its challenges," she stated.

Work on the project is expected to start next summer.

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