May 11, 2019 - TUOLUMNE/MARIPOSA COUNTY – The California Department of Transportation (Caltrans) has completed a project that created more than 35 miles of center and shoulder 
rumble strips on State Route 49 (SR-49) in Tuolumne and Mariposa counties.
Work was performed at the following locations:
• From the Mariposa/Madera County line to SR-140 in Mariposa County
• From West Whitlock Road to Princeton Way in Mariposa County;
• From the SR-49/SR-120 junction at Moccasin to Harvard Mine Road, one mile south of Jamestown in Tuolumne County;
• From Jack Page Road, just south of Sonora, to the Tuolumne/Calaveras County line.
Rumble strips are used to increase the safety of the roadway and reduce the likelihood of off-road collisions, head-on collisions and other incidents. Rumble strips alert motorists that they are accidentally leaving their lane or the roadway.
This $854,000 project was performed by Dreambuilder Construction Corporation of Placentia.
For the safety of workers and other motorists, please Slow For the Cone Zone.
Source: Caltrans
Rumble Strip Information
Building on knowledge gained in our quiet pavement work, Caltrans developed a rumble strip profile that lowers outside-vehicle noise levels. This new low-noise noise rumble strip is fondly referred to as a "mumble strip".
The design goal of the sinusoidal profile, or "mumble" strip, is to move some of the higher frequency excitation produced in a conventional rumble strip, with its abrupt changes in profile, to lower frequencies that can be associated with the repetition rate, or frequency, of a sine wave shape. The concept is to decrease the overall A-weighted exterior sound level while still maintaining (or increasing) noise and vibration disturbance inside the vehicle to alert the operator and occupants of lane departures.
Caltrans' typical ground-in rumble strip profile is a 5 inch cylindrical grind on 12 inch center with a 5/16 inch depth. The mumble strip profile is a sinusoidal shape with peaks on 14 inch centers and 5/16 inch depth.
For a single passenger car travelling at 60 mph, the typical reduction in passby noise is more than 6 dBA. To put this into context, a 6 dBA reduction is equivalent to doubling the distance between the noise source and the receptor.
In general, the interior disturbance levels created by the mumble strips were comparable to those generated by the conventional ground rumble strips. For light vehicles, the differences in interior noise, and seat track and steering column vibration were about 13 dB during travel on either the mumble strips or ground rumble strips compared with travel off the warning strips.
This final report (PDF) presents the development and field evaluation of the new mumble strip design.
Source: Caltrans
