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Design > Rolled vs. Milled |
Maintenance
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 The
Best Rumble Strip–Rolled or Milled?
Every
state highway authority that has tested both the 7-inch
milled cut and the rolled-in pattern, has since abandoned
rolling.
Before
the introduction of the 7-inch milled rumble strip, contractors
would weld a series of steel pipes to rollers and press
narrow depressions into the road while the asphalt was still
hot. So that the roller could indent the asphalt, rolled
rumble strips had to be kept quite narrow -- usually less
than 2 inches wide. Nearly all the highways currently using
the 7-inch milled cut have some prior experience with rolled
rumble strips.
Rolled-in
patterns had some success in reducing drift-off accidents,
however, they have not produced results comparable with
the 7-inch milled rumble strip. Also, the rolled-in pattern
has presented critical maintenance and construction problems.
Do
your rumble strips work?
The 7-inch milled rumble strip has demonstrated a reduction
in drift-off accidents by 70% or more. Rumble strips that
do not measure up to these results may be responsible for
unnecessary injury or loss of life.
Start
saving lives this year.
Because the 7-inch milled rumble strip can be placed on
any existing shoulder, hundreds of miles of highway can
be treated in a few short months versus the 7-15 year lead
time a highway might have to wait before patterns can be
rolled-in during the next resurfacing.
Better
Performance The Virginia Department of Transportation
has determined that the 7-inch milled rumble strip generated
335% more noise, and produced 1,260% more vibration excesses
(denoted on the International Roughness Index) than rolled-in
patterns.*
The
best alarm saves the most lives. No highway using rolled-in
patterns has reported a reduction in accidents comparable
to that achieved by the 7-inch rumble strip.
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Figures
2A and 2B chart the vertical movement as a tire passes over
a narrow, rolled-in pattern (Figure 2A), and over the 7-inch
milled rumble strip. Twenty-six times more wheel movement
generates a tremendous increase in noise and vibration when
driving over the milled-in rumble strip. The difference in
performance is even more pronounced for trucks
and buses.
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| Maintenance |
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Most highway authorities have cited various maintenance
and construction problems in their decision to discontinue
rolled-in patterns in favor of the 7-inch milled cut.
Shoulder
Wear and Density Requirements
The 7-inch milled
rumble strip is constructed on existing highway shoulders,
and does not compromise asphalt density requirements.
Nearly all highway authorities using rolled-in patterns
have noted the need to sacrifice shoulder density
requirements during construction.
Consistent
Depths
Any rumble strip mill can be fitted with
control mechanisms to ensure the consistent depth
and alignment of each cut. Rolled-in patterns, however,
are typically inconsistent in depth due to the many
variables during resurfacing effecting the rate at
which the asphalt hardens (air temperature, water
on the roadway, time, asphalt density, et. al.). Shoulders
treated with rolled-in patterns typically have long
sections of washed out patterns that have little or
no effect on fatigued drivers.
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order to make these rolled-in patterns, the contractor
had to compromise shoulder density requirements.
The resulting water and air voids along the joint
triggered premature degradation of the shoulder–only
stwo years after a resurfacing. |
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*A
Study of Effectiveness of Various Rumble Strips on Highway
Safety, Virginia Department of Transportation, Chung S. Chen,
P.E., Traffic Engineering Division
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