Rumble strips for Highway 1 north of Santa Cruz

Caltrans plans to install rumble strips into the centerline and along the shoulders of California Route 1 from Santa Cruz north to Davenport.

Update: Santa Cruz Cycling Club caught this in the planning stages and are working with Caltrans for alternative treatments that address Caltrans crash concerns.

Caltrans District 5 — the state transportation agency responsible for Santa Barbara, San Luis Obispo, Monterey, San Benito and Santa Cruz Counties — performed a safety analysis on Highway 1 north of the city of Santa Cruz and discovered over a third of traffic collisions are “roadway departure” collisions. The driver either cross the centerline and hits another vehicle head on, or the driver goes over the right shoulder flies off into the ocean (for southbound traffic) or crashes into a large cliff (for northbound traffic).

Rumble strips are a proven method of reducing roadway departures. Caltrans plans to add rumble strips into the centerline and along the shoulders from near Shaffer Road on the west side of Santa Cruz north to Swanton Road near Davenport, CA.

View Planned rumble strips Santa Cruz County Highway 1 in a larger map

Cyclists in Santa Cruz and elsewhere are beginning to protest the installation of rumble strips on Highway 1. Although rumble strips can potentially save cyclist lives by keeping drivers out of the road shoulder, many cyclists often oppose rumble strips because they themselves create a hazard. Cyclists may need to leave the shoulder for any number of reasons — road debris, obstructions, or to make a turn — but continuous rumble strips keep the cyclist from leaving the shoulder. Along the Coast Highway north of Santa Cruz, common obstructions include slower cyclists; surfers, mountain bikers, and hang gliders unloading their gear from the side of the road; day trip tourists pulled over to enjoy the view; encroaching sand dunes on the southbound side and fallen boulders on the northbound lanes; and the occasional hitchhiker.

Highway 1 Hitchhiker

Rumble strips are often milled in the portion of the shoulder favored by cyclists — the part adjacent to the fog line, because that’s the portion of the shoulder swept clean by passing traffic. The further right you move into the shoulder, the more debris and junk you’ll encounter.

Why are rumble strips a problem?

Modern, milled in rumble strips are horizontal divots along the sides of the road to startle an inattentive driver awake through noise and vibration when a tire hits the strip. While car handling is not affected by rumble strips, rumble strips are uncomfortable for cyclists to ride on, and deeper rumble strips can cause wheel damage and crashes for cyclists. (Disclosure: I caught a wheel in a rumble strip on Highway 66 east of Lyons, CO and went down hard. I moved left to avoid piles of sand in the road — some of this sand had covered up the divots so I didn’t see them and pow! down I went.)

cyclists often oppose centerline rumble strips because they discourage people from crossing the centerline while they’re passing cyclists, especially on narrow mountain roads with no shoulders. (Bicycle Colorado convinced CoDOT to change their mountain road centerline rumble strip policy, which now prohibits rumble strips on roads with narrow shoulders.) There are segments of Highway 1 with narrow shoulders where this concern would apply.


California rumble strip standards alleviate some of the concerns we as cyclists have: for wide shoulder roads, maximum depth of milled rumble strips is 8.5 mm. For narrow shoulder roads, Caltrans design manual indicates the use of “inverted profile thermoplastic,” a corrugated application of fog line paint that looks like this:


Still, it’s up to cyclists to ensure traffic engineers adhere to the design standards. If Caltrans uses milled rumble strips, the only real way to remove them after the fact is to repave the shoulder.

Bicycle friendly rumble strips?

Ways to improve the bicycle friendliness of rumble strips include:

  • Bicycle Gaps: The latest US Federal Highway Administration Technical Advisory on rumble strips recommends “bicycle gaps” of 10 to 12 feet in between milled segments of 40 to 60 feet long.
  • Decreased Depth: California’s design standard says “ground in rumble strip treatments greater than 8.5 mm shall not be installed on shoulders where bicyclists are allowed.” Still, I’ve seen recent installations that exceed this 8.5 mm depth, so it’s good to point out the importance of the depth.
  • Lateral location: Placing rumble strips as close to the roadway as possible (versus, for example, 10 inches into the shoulder where cyclists want to ride) reduces the amount of room taken from the shoulder for cyclist use. Making the milled out portion a little less wide also helps. The Federal technical advisory, for example, advises a width of 16 inches for milled rumble strips.

Local bicycle guru Jim Langley asks cyclists to write letters regarding this project to local transportation officials. District 5 Caltrans Director Richard Krumholz can be contacted at Rich_Krumholz at The Santa Cruz County Regional Transportation Commission can be contacted at info at Neal Coonerty, the Santa Cruz County supervisor who represents the district encompassing this area, can be contacted at bds031 at In your letter, remind these officials to accommodate cyclists in the design and placement of these rumble strips.

With a nod to:

  • Carlton, who joins Apple in placing Santa Cruz along Big Sur coast, though he does know better. A portion of the Tour of California 2012 will travel along a portion of Highway 1 proposed for rumble strip treatment from Davenport to Bonny Doon Road.
  • The people of the California Association of Bicycle Organizations for their invaluable technical feedback.


  1. Wouldn’t it be a lot simpler to make lanes narrower so motorists slow down and pay attention to what is going on?

  2. A possible solution might be to install one wide, dark-colored rumble strip in the middle of the lane between the tire tracks, as opposed to two of them on either side. If a car drifts into the sholder, its left tires catch the strip, and vice versa. 

  3. No I have not seen this tried anywhere, but maybe.  Just came out of my head inspired by your article. One big concern, though, is that motorcyclists wouldn’t like this, and it can indeed be a safety hazard for them.

  4. That was brought up once at the California Bicycle Advisory Committee, but from what I hear, it ended up being pushed aside without much consideration. It could be an issue for motorcyclists, though they tend to favor one tire track or the other and not the center of the lane.

  5. Having dealt with these  leaving Yellowstone, I hope they don’t do it. They often get them way to close to teh road edge, and therer is NO room for cyclists. And they are really jarring. I can easily see losing them in sand or junk, and going down as you did.

  6. problem i see is that you instinctively turn away from the noise of the rumble strip. one in the middle would create the noise on the wrong side of the car.

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