Design Policy - Roadside Safety Design - Rumble Strips

WSDOT began installing rumble strips on undivided highways in 1999 as a countermeasure for roadway departure crashes. Installations on the shoulders were intended to reduce run-off-the-road crashes, while centerline rumble strips targeted reductions in cross-centerline crashes.

What are rumble strips?
Rumble strips are milled grooves or rows of raised pavement markers placed perpendicular to the direction of travel, or a continuous sinusoidal pattern milled longitudinal to the direction of travel, intended to alert inattentive drivers to a potential lane departure. A sinusoidal pattern can be used when a low noise design is desired.

Rumble strips are grooves in the roadway or rows of raised pavement markers placed on the roadway in such a manner that, as the tires of a vehicle contact them, they produce sound (noise) and vibration. The noise and vibration produced by rumble strips is intended to alert inattentive drivers that they have departed from their lane, or to give advance notice of a change in the roadway ahead.

Where and how does WSDOT use rumble strips?
The Washington State Department of Transportation (WSDOT) currently uses shoulder rumble strips (SRS), centerline rumble strips (CLRS), and roadway rumble strips (RRS) as a matter of policy. In Washington, rumble strips are most commonly a pattern of grooves milled into the pavement surface.

Shoulder rumble strips and rumble stripes are installed on the shoulder to alert a driver that they are leaving the travel way. Rumble strips are installed inside the painted edge line, rumble stripes are installed under the painted edge line.


Shoulder Rumble Strips

Centerline rumble strips are placed on the centerline of undivided highways to warn drivers that they are leaving their intended lane of travel. 

Centerline Rumble Strips

Roadway rumble strips are placed across the traveled way to alert drivers who are approaching a change of roadway condition or an object that requires substantial speed reduction or other maneuvering. 

Roadway Rumble Strips

Why does WSDOT use rumble strips?
WSDOT’s Strategic Highway Safety Plan (SHSP) – also referred to as Target Zero – provides a comprehensive framework of specific goals, objectives, and strategies for reducing traffic fatalities and serious injuries. The overall goal of the SHSP is a safe and efficient surface transportation system, with no deaths or serious injuries on state highways by 2030.

Rumble strips are an effective and efficient countermeasure for reducing run-off-the-road and cross centerline crashes.

Shoulder Rumble Strips
Shoulder rumble strips are well documented regarding their effectiveness, primarily in reducing the frequency of vehicles departing the roadway to the right on undivided highways and to both the left and right on divided highways.

Centerline Rumble Strips
Centerline rumble strips are well documented as an effective countermeasure for crossover collisions, which are those where a vehicle strays out of the lane to the left and collides with an oncoming vehicle or object off the roadway. WSDOT began experimenting with CLRS in 1995 and, once effectiveness was verified, began a systematic program of installation throughout the state.

Roadway Rumble Strips
The effectiveness of roadway rumble strips is not as well established as shoulder rumble strips or centerline rumble strips. They are usually deployed to warn drivers of changing conditions in the roadway ahead. 

Design Considerations

The pavement receiving rumble strips needs to be in good condition and thick enough to support the rumble strips. Certain pavement types, such as open graded pavements, are not suitable for rumble strip installation. Grinding rumble strips into inadequate pavement will lead to premature deterioration of the surrounding pavement. Areas where the pavement is inadequate for rumble strip installation require removal and replacement of the existing pavement at and adjacent to the location of the rumble strip. Consult with the Region Materials Engineer to determine whether the existing pavement is adequate for rumble strip installation. The Region Materials Engineer will provide a pavement design for removing and replacing the existing pavement near the rumble strip if needed. When installing both rumble strips and recessed lane markers, follow the Standard Plan to avoid overlapping the grindings.

Installing rumble strips in bituminous surface treatment (or BST) or other thin surface treatments can expose pavement structure and lead to delamination. In new rumble strip locations where BST will be applied on an Hot Mix Asphalt (HMA) pavement, install the rumble strips in the HMA pavement before placing the BST. In existing rumble strip locations, note that a single application of BST on top of an existing rumble strip installation typically results in satisfactory rumble strip depth. Where rumble strips currently exist and an additional BST application is contemplated, evaluate whether the depth of the grooves following paving will provide their continuing function to alert drivers. If not, or in the case of an HMA overlay, it may be necessary to remove existing rumble strips and install new ones.

Provide an offset to the longitudinal paving joint so that rumble strips are not ground into the joint where practicable. For additional guidance on surface preparation and pavement stability, refer to the WSDOT Pavement Policy.

The noise created when vehicle tires contact a rumble strip may adversely impact nearby residences and other land uses. Left-turning or passing vehicles, frequent passing maneuvers on two lane highways, and off-tracking of vehicles or trailers in tight radius curves, are examples of situations where incidental contact can happen. Noise impacts may be anticipated, and a low noise rumble strip design may be warranted (sinusoidal installations are low noise albeit with a higher cost to install), when installing rumble strips in urban growth areas, and/or within 600 feet of a residence, school, church, or campground. In situations where a low noise rumble strip is desired but is not feasible, measures can still be taken to reduce incidental contact, including discontinuing the rumble strip through frequently used road approaches, through passing zones, and in tight radius curves. Contact HQ Design for more information about low noise rumble strip designs, noise mitigation strategies, and the criteria for employing them.

Shoulder Rumble Strips and Stripes
Shoulder rumble strips are placed parallel to the traveled way just beyond the edge line to warn drivers they are entering a part of the roadway not intended for routine traffic use. Shoulder rumble stripes are rumble strips placed immediately under the shoulder delineation paint, with any excess width milled or placed outward towards the shoulder. Shoulder rumble stripes are only installed where there is insufficient space to install shoulder rumble strips per one of the standard configurations.

When shoulder rumble strips and shoulder rumble stripes are used, discontinue them where no edge stripe is present, such as at intersections and where curb and gutter are present. Discontinue shoulder rumble strips and rumble stripes where shoulder driving is allowed.

Shoulder rumble strip and rumble stripe patterns vary depending on whether bicyclists are expected to use the highway shoulder, and whether they are placed on divided or undivided highways. Rumble strip patterns for undivided highways are shallower and may be narrower than patterns used on divided highways. Rumble strips and rumble stripes installed on undivided highways also provide gaps in the pattern, providing opportunities for bicycles to move across the pattern without having to ride across the grooves. There are four shoulder rumble strip and four shoulder rumble stripe patterns. Consult the Standard Plans (rumble strips) or Plan Sheet Library (rumble stripes) for patterns and construction details.

When selecting a rumble strip or rumble stripe design, consult the Standard Plans and Plan Sheet Library for the patterns and construction details, and apply the following criteria:

  • Consider using a low noise pattern, or employ measures to reduce incidental contact, in areas where noise impacts are anticipated.
  • Consider using a rumble stripe pattern where usable shoulder width is less than 4 feet (5 feet where barrier is present).
  • The Shoulder Rumble Strip Type 2 or Type 3 pattern is used on highways with minimal bicycle traffic. Use the Shoulder Rumble Strip Type 4 pattern where the bicycle traffic level on the shoulder is determined to be high. Consult the region and Headquarters Bicycle and Pedestrian Coordinators to determine the bicycle traffic level, and engage them in decision-making processes related to the use of rumble strips or rumble stripes on bike touring routes, and/or on other routes where bicycle events are regularly held.

Centerline Rumble Strips
Centerline rumble strips are installed on the centerline of undivided highways to alert drivers that they are entering the opposing lane. They are installed with no differentiation between passing permitted and no passing areas. Refresh pavement markings when removed by centerline rumble strips.

Centerline rumble strips are typically installed on rural highways where the posted speed is 45 mph or higher. They may also be installed on urban routes with posted speeds as low as 35 mph.  

  • Field verify lane and shoulder widths. See Chapter 1230 of the Design Manual for guidance on lane and shoulder widths. Centerline rumble strips are only installed where the combined lane and shoulder width in either direction is greater than 12 feet.
  • In locations where the combined lane and shoulder width in either direction is 14 feet or less, consider the level of bicyclist and pedestrian use along the route before installing centerline rumble strips. When drivers shift their lane position away from centerline to avoid the rumble strips, they are moving closer to pedestrians and bicyclists on the shoulder.
  • Consider using a low noise rumble strip design in locations where noise is an issue, or employ measures for reducing incidental contact where a low noise design is not feasible.
  • In urban areas, do not consider installing rumble strips where the need to interrupt the rumble strip pattern to accommodate left-turning vehicles is very frequent, or where the posted speed is 35 mph and below.
  • Do not use centerline rumble strips where two way left-turn lanes exist.

Document the decision to omit centerline rumble strips in a Design Analysis, when that decision is outside of the policy provided in this section (see Chapter 300 of the Design Manual.) 

Coordinate with WSDOT's Bicycle & Pedestrian Coordinator
Determine whether your project is along a rural bicycle touring route or accommodates regularly scheduled bicycle touring events. Also, ask if the route is developing into a bicycle route.

The Headquarters Bicycle and Pedestrian Coordinator is a good resource for evaluating the use of shoulder rumble strips. Request information that quantifies the number of riders using the segment and what their associated peak volume and duration is. 

Links to other information sources on rumble strips

Share your thoughts on rumble strips with WSDOT
We are presenting this information to aid in the knowledge and discussion of the use of rumble strips in Washington State.

If you have any comments or questions, please send an e-mail or give us a call:
John Donahue
Ph: 360-705-7952
Fax: 360-705-6815