Rumble strips and stripes
What's the difference?
Rumble strips are grooves or rows of indents in the pavement designed to alert inattentive drivers through noise and vibration and reduce the number of accidents.
Rumble stripes are simply rumble strips cut into the pavement where the edgeline and/or centerline are to be placed. After the rumble strips are ground in, the white or yellow line is marked right over the rumble strips. The advantage is that the edgeline or centerline is much more visible in the rain and the rumble strip provides warning to a motorist who strays from the driving lane.
Where you'll find them
- Road shoulders - Shoulder rumble strips are longitudinal rumble strips installed outside of the edgeline (the yellow or white line that separates the travel lane from the left or right shoulder). The intent of shoulder rumble strips is to notify inattentive drivers that they are leaving the roadway - with the goal of reducing run-off-the-road crashes. They are also useful during snowy conditions to help the driver keep the vehicle on the road.
- Lane edges - Edgeline rumble stripes are installed to separate the travel lane from the shoulder.
- Centerlines - Centerline rumble stripes are installed to separate opposing traffic on undivided highways. The goal of these is to reduce head-on and opposite direction side-swipe crashes.
- Middle of the lane - Transverse roadway rumble strips are placed across the traveled lane to alert drivers approaching a change of roadway condition or a hazard that requires substantial speed reduction or other maneuvering.
What are mumble strips?
Sinusoidal rumble strips are also called mumble strips. They are similar to traditional rumble strips, but mumble strips have a wave pattern ground into the pavement that lessens the external noise produced when vehicles travel across them. Traditional rumble strips do not have the wave pattern.
Common factors for lane departure crashes
Lane departure crashes can and do occur on all roads in Minnesota which is why a systematic, proactive approach is being followed; however, certain factors have been identified indicating a greater incidence of lane departure crashes and these are the characteristics that have been used to determine where MnDOT will install rumbles.
- Young drivers
- Fatigued and drowsy drivers (or “highway hypnosis”)
- Distracted driving such as texting and cell phone use
Roads and environment
- Two-lane, undivided roads
- Rural, high speed roads
- Adverse weather conditions (rain, sleet, snow, fog, etc.)
- Curvy and hilly conditions
One of the intents of the rumble is to get the driver’s attention through noise, and this can be disturbing to residences near state highways. In the past, MnDOT used edgeline rumbles, which was found to have a fair amount of nuisance hits as some drivers “drive the fog-line”. In order to reduce the amount of nuisance hits, the rumble policy encourages the use of centerline and shoulder rumbles instead.
For rumbles to be effective, there must be a vehicle interior noise increase of 6-15 dB. MnDOT rumble design results in a 15 dB increase. Exterior noise increase is variable, and depends on distance and environmental factors. One MnDOT study of rumble noise found the following noise levels near shoulder rumbles:
- 50’ away 82 dB
- 100’ away 75 dB
- 200’ away 67 dB
- 300’ away 62 dB
- 80 dB – Heavy truck traffic
- 70 dB – Business office
- 60 dB – Conversational speech