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ITD says Highway 55 rockslides not their fault

The Long Valley Advocate of Cascade, Idaho

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CASCADE - Idaho Transportation Department officials say work on the hillsides along Highway 55 in the Payette River canyon didn't cause the rockslides and mudslides which closed the road this spring.

There is a misconception among the public the efforts caused instability.

"In fact, the location of the slides is not even where our crews - nor the contractor - were working last fall and this spring," Transportation spokesman Reed Hollinshead said.

The landslides that closed Idaho 55 in mid-January and again last week occurred at about milepost 82.7, just north of the location where the ITD contractor was working on a rockfall mitigation project, he said.

When such a slide occurs, the public questions whether work to permanently prevent such slides actually triggered them.

The rockslide occurred about 3.5 miles north of Banks, closing the road between Banks and Smith's Ferry from about 1 p.m. on Sunday, April 3, until 5:30 p.m.

the following day. A rock and mudslide in this same area closed the highway for two days back in January.

"This (second) landslide was immediately north of an area worked by our contractor - the slope had not been touched by us. Intense rainfall and rapid snowmelt triggered the landslide and debris flow," Hollinshead said.

When possible, ITD maintenance crews provide lighting and flagging to keep the highway passable. When it was deemed too great a risk to allow travel through the area, the department closed the section, but continually monitored it for a safe opportunity to reopen.

"This was based on conditions observed on the ground and our ability to maintain safety, which is our number one priority," he said. "When peoples' physical welfare and personal property (their vehicle) is at stake, and we tend to err on the side of safety whenever possible," he said.

"Our apologies that this has created an inconvenience, but we just wanted to be clear that it is a situation neither caused by the actions of ITD nor the contractor," he said.

Transportation officials say the slope at the last slide became saturated with water

from the rains. A slide the size of a football field came down the mountain and covered the roadway.

In 1997, the slope on the east side of the Payette River at Lower Banks gave way.

Transportation plans a number of improvement projects on the road.

A "thin-lift overlay" pavement project will be done from Cascade's northern city limits to Donnelly, from milepost 115 to 131. About two inches of new asphalt will be applied to the existing surface.

A pavement preservation project involving 14.5 miles of roadway from the Payette River Bridge just north of Horseshoe Bend is slated. About 1.8 inches of a new thin-lift overlay and plant-mix paving will be placed. It could occur in spring or summer.

The South Fork Payette River Bridge at Banks also will be improved. The preservation project will do a silica fume treatment to prevent corrosion and penetration by water and salts. Cracking and splitting will be repaired on the bridge rail, which will also be repainted.

Construction on the North Fork Payette River Bridge at milepost 114 on the south end of Cascade is expected. The existing

bridge will be replaced with a three-lane, 392-foot long, three-span bridge and the adjacent roadway approaches reconstructed.

A two-mile pavement rehabilitation also is in the works. It will extend from milepost 114 to 116 in downtown Cascade.



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Original Publication Date: April 13, 2011



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