Carver County advances updated 'mumble‑strip' policy after noise tests and safety review

Traffic engineer Whitney Schroeder told the Carver County Board of Commissioners on April 7 that the county’s 2013 rumble‑strip policy is outdated and prevents staff from installing a low‑cost countermeasure the county’s safety plan recommends.

Schroeder said a newer sinosoidal design — referred to in the meeting as a “mumble” strip — preserves driver warning cues while reducing exterior noise. She described two pilot installations (County Roads 40 and 11) and said field decibel readings showed the new design measured roughly 10 dB lower at 100 feet compared with the older rectangular pattern, while in‑vehicle vibration/noise remained noticeable to drivers.

The presentation outlined four proposed applications: center‑line mumble stripes to reduce head‑on crashes, edgeline mumble stripes to reduce run‑off‑the‑road crashes, shoulder mumble strips offset from the fog line, and transverse mumble strips placed in advance of uncontrolled rural intersections. Schroeder also proposed design “breaks” to limit impacts near residences (a recommended 350‑foot radius) and intersections, and shortening the minimum installable length from 1,350 feet to 150 feet to increase the number of qualifying sites.

Commissioners pressed staff on tradeoffs: several recalled earlier complaints about continuous rumble strips on County Road 10, and they asked how the new design and proposed breaks would address noise for adjacent residents, bicycle/shoulder usability, snow‑plow impacts and long‑term maintenance. Schroeder said pilot sites used intermittent patterns and breaks at driveways and homes and reported no formal complaints to date. She and staff also said they will follow MnDOT guidance for many technical details and will evaluate crash history and county road safety plan priorities when choosing where to deploy strips.

Board members asked that staff run focused outreach and a resident survey in pilot areas and suggested presenting to township associations before final adoption. Schroeder said staff hope to return with a revised policy for adoption in mid‑summer, but will accommodate township feedback and can delay final action until August if needed so planned construction projects can be adjusted.

The work session closed with staff agreeing to more community outreach, a refined draft policy reflecting break distances and installation criteria, and follow‑up cost and maintenance estimates for planned highway projects.