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Rumbles will greet U.S. 12 drivers who cross the line

Rumble strips, which have proven effective in reducing automobile crashes by alerting drivers when their vehicle drifts out of the traffic lane, will begin appearing next week in an unfamiliar place – on the centerline of U.S. 12 curves between Lewiston and Kamiah.

Although centerline rumble strips have been tried in other parts of the Pacific Northwest, this is the first centerline application on a two-lane highway in Idaho, according to Dave Couch of the Lewiston ITD office. It is part of a federally funded 3E (Engineering, Education and Enforcement) safety project.

'The rumble strips literally are a wake-up call for motorists. The noise and vibration caused by driving over rumble strips alert drivers that they have strayed outside the lines.'
– Dave Couch, District 2 Traffic

“The rumble strips literally are a wake-up call for motorists,” Couch explains. “The noise and vibration caused by driving over rumble strips alert drivers that they have strayed outside the lines.”

Rumble strips are created by grinding a series of parallel grooves in the asphalt that are about 12 inches wide and one-half to five-eights of an inch deep.

Traditionally, they are used on the outside edges of highways to keep motorists from driving onto soft shoulders where they often over-correct and lose control of their vehicle. Their new use on the centerline of U.S. 12 “no-passing” curves is designed to reduce head-on and side-swipe crashes.

A three-year safety study (1997-1999) showed there were 213 vehicle crashes on the segment of highway; 71 percent of those crashes involved single vehicles, said Mark Strait, of Idaho’s Office of Highway Safety. Centerline rumble strips might have prevented more than 14 percent of the 213 crashes had they been in place, he said.

The study also showed that 21 percent of the 62 multiple-vehicle crashes were “side-swipes” involving vehicles traveling opposite directions; contact usually resulted when one of the vehicles crossed the centerline.

“The intent of this 3-E project is to provide safer driving conditions by removing some of the factors that contribute to crashes – drowsy, inattentive and aggressive driving,” Strait said. “We anticipate increased traffic along this route because of the Lewis & Clark Bicentennial celebration. The centerline rumble strips and new pavement markings will improve safety for those travelers.”

Heavily used U.S. 12 winds along the Clearwater River and in many places is confined by steep slopes on one side and by the river on the other side, leaving little or no room to add shoulder rumble strips. A unique alternative is to add the strips to the centerline on curves, beginning at the Arrow Bridge about 15 miles east of Lewiston and continuing to Kamiah – a distance of about 50 miles.

In addition to the rumble strips on double-yellow-lined curves, crews will grind shallow strips of the centerline and install durable pavement markings – inlaid plastic striping material – that are much more durable than normal painted lines, Couch said. The pavement markings are about four inches wide and are imbedded in grooves about one-eighth of an inch deep. They are flush with the road surface to resist snowplow damage, withstand harsh winters and de-icing chemicals. They are expected to last five to six times longer than paint.

“This is one of our higher wear areas where current (painted) markings usually don’t make it through the winter,” Couch explained. “We hope to get about five years of wear out of the durable pavement markings.”

They have been used successfully in northern Idaho where winters are similarly harsh.

Funding for the $892,000 3-E project was secured as part of a federal program that allocated incentives to states enacting .08 blood alcohol content as the legal threshold for intoxication.

The project also includes installation of new variable message signs on both ends of the U.S. 12 segment and increased law enforcement. Education and law enforcement will receive $34,000 of the project funds.

The centerline rumble strip/pavement marking safety project should take about three weeks to complete, depending on weather. The contractor, Apply-A-Line out of Pacific, Wash., anticipates working weekends. Pilot cars will lead motorists through the work areas, but delays should be minimal.

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