Caltrans will begin to install mumble strips—whose shallower, wave-like indentations are spaced further apart than rumble strips—down the center of Highway 1 from Valley Ford Road to Mill Valley next week, with the aim of keeping drivers from drifting outside their lanes.
About a third of accidents between 2008 and 2011 on the coastal highway were attributed to “cross-centerline movements,” Caltrans reports. Of those, 11 were head-on collisions and over 30 caused injuries.
The agency originally proposed rumble strips but altered the project during the permitting process. “Mumble strips are not rumble strips—they’re quieter,” Robert Haus, a spokesman for the agency, said.
In response to residents’ concerns about noise, strips will be limited or eliminated in town centers and near commercial driveways or other sites with maneuvering traffic. Around isolated homes in areas of low traffic, Caltrans might leave gaps in the strips or install low noise barriers such as concrete or landscaped berms.
Inverness resident Bob Johnston, a former professor at the University of California, Davis, who taught land use and transportation planning, submitted numerous letters to Caltrans to protest the strips.
“The strips are loud and they are going to be obnoxious. And they aren’t necessary,” he said.
According to him, agencies across the country as a standard don’t use strips on roads that are winding and have speeds below 45 mph.
“Caltrans says it will make the roads safer, but I doubt that,” he added. “People are going to swerve to the right when they hit the strips and bicyclists are going to be in danger.”
To address concerns brought by the Marin County Bicycle Coalition, Caltrans is widening shoulders at nearly 30 locations as part of the project. The agency will largely avoid removing vegetation to widen shoulders, instead using existing areas like gravel pullouts.
At one section of highway, around a fifth of a mile in Stinson Beach, Caltrans will fill in 700 square feet of wetlands. Since that work is considered a public service with no feasible alternative, the agency was granted an exemption from strict rules against filling wetlands. Caltrans agreed to a number of mitigation measures, including minimizing impact to birds and red-legged frogs and stricter documentation requirements for impacts to that area.
Mr. Haus said drivers can expect single-lane closures during the shoulder work and moving closures with flaggers for the mumble strips. Construction is slated to finish by October.
An interactive map of the project is posted at dot.ca.gov/d4/marin1mumblestrips/.