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.
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.
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.
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.
In 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.
*A Study of Effectiveness of Various Rumble Strips on Highway Safety, Virginia Department of Transportation, Chung S. Chen, P.E., Traffic Engineering Division