Slippery Slope: ITD studies slope stability to prevent rock slides

The Idaho Transportation Department is studying the stability of several rock slopes along U.S. 26 east of Swan Valley. The study has several purposes behind it, but one is to help understand better to alleviate an ever-occurring problem: rock falls that create hazards for drivers.

“Every year we see probably three to four cars that get to the point, right here, and can’t go any further, because they’ve hit their oil pan or their transmission,” said Randy Husky, the owner of the Chevron station in nearby Irwin. “Probably the worst one was a lady came in just really shaken. About 9 o’clock at night, a rock large enough to go through and dent it down on her hood about… 18 inches.”

ITD says clearing and removing rocks has become an almost daily chore along some stretches of U.S. 26. Occasionally the rocks are large enough that the road becomes a bit of an obstacle course for motorists.

That’s why ITD is investing in studying the mountainside. “Basically the point of the study is to identify the content of the material of the slope,” said Bruce King, public information specialist for ITD.

King says the hope is to understand in detail the kinds of rocks, soils, and patterns they’re dealing with in the mountainside. “That enables us to identify its stability,” said King

The study has another purpose for ITD: how to dig into the mountainside if the agency decides to expand the highway in the future. “If we decide to dig into it to widen the road, we’ll know how well it will hold up.”

ITD says researchers spent dozens of man hours looking into the current geotechnical conditions of the slopes. The state agency hopes to have the final results from the study in the coming months.