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
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
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 Idahos
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 dont 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.