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Rumble and mumble strips

Edgeline rumble strips on M-32 in Otsego County.

Rumble and mumble strips

Rumble and mumble strips are a low-cost measure used to address one of the most serious types of traffic crashes: a lane departure crash. They consist of a set of either transverse or sinusoidal grooves applied on the shoulder or centerline of a roadway.

Rumble and mumble strips provide a tactile and audible warning to alert inattentive (distracted, drowsy, unfocused, etc.) drivers who may unintentionally drift out of their lane. This warning gives the driver an opportunity to correct their action or reduce speed, which may help them avoid or reduce the severity of a crash.

Rumble strips

Shoulder rumble strips have been in use all over the country for many years and their safety benefits are well-documented. They are located just outside the driving lane on both freeway and non-freeway routes.

Over the years Michigan has been leading the way for centerline rumble strips. Between 2008 and 2010, MDOT undertook the largest initiative of its kind to install 5,400 miles of centerline rumble strips (and an additional 1,700 miles of shoulder rumble strips) on high-speed rural highways across the state. This system-wide installation provided a unique opportunity to evaluate the effectiveness of non-freeway rumble strips, which was done through a two-phase research project.

Download the centerline rumble strips brochure
Centerline rumble strips on M-32 in Otsego County.
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Safety by the numbers

A before-and-after crash study performed for the 2008-2010 installation locations found significant reductions across all crash severities and lane departure crash types, including:

  • 50 percent reduction in head-on crashes,
  • 46 percent reduction in run-off-the-road crashes,
  • 51 percent reduction in fatal crashes, and
  • 41 percent reduction in incapacitating injury crashes.

Rumble strips have become a safety standard and will continue to save lives on Michigan's roads.

Mumble strips

MDOT has been searching for a way to address the roadside noise generated by rumble strips in residential areas without losing the safety benefits. At the end of 2018, MDOT installed its first trial of a new sinusoidal rumble strip design, commonly referred to as a mumble strip, in the Superior Region.

Mumble strips generate less exterior noise. They consist of a continuous sinewave pattern milled, slightly recessed into the pavement. Despite producing less noise at the roadside, the mumble strips still alert inattentive drivers through noise and vibration to keep them in their lane.

Mumble strips were made the standard for non-freeway shoulder installations in late fall 2021, and are propagating across the state as non-freeway routes with adequate shoulder width get resurfaced. Options for use include centerline, edgeline and freeway shoulder installations but the largest benefit during testing was observed for shoulder installations.

Centerline mumble strips on a rural road.