Road Services - High-Risk Rural Road Program frequently-asked questions
What is the High Risk Rural Road Program (HRRRP) and what is its relationship to the Run-Off-Road Safety Project?
The HRRRP is a Federal Highway Administration grant program intended to reduce the frequency and severity of collisions on rural roads. In Washington, the grant is administered by the Washington State Department of Transportation (WSDOT). The call for grant applications for this project emphasized low-cost, wide-spread solutions (as opposed to spot improvements) and listed rumble strips as an example of such an improvement.
The King County Department of Transportation (KCDOT) Run-Off-Road Safety Project is the first of two KCDOT projects funded by HRRRP grants. This project received $500,000 in federal grant money. No local matching funds are required. The project is currently in the construction phase.
How were projects selected for the HRRRP?
The six rural county roads with the highest number of run-off-road/crossing centerline collisions were selected for this project. These roads are SE Petrovitsky Road, Vashon Highway SW, SE May Valley Road, SE North Bend Way, Preston Fall City Road SE, and SE 400th Street.
What are rumble strips?
Rumble strips are grooves in the roadway or rows of raised pavement markers placed on the roadway. When the tires of a vehicle contact them, they produce noise and vibration. The sound is intended to alert drivers that they are veering off the road or out of the lane, or to give advance notice of a change in the roadway ahead. In Washington, rumble strips are most commonly a pattern of grooves milled into the pavement surface.
Three types of rumble strips are commonly used in Washington state: shoulder rumble strips, centerline rumble strips, and roadway rumble strips.
Shoulder rumble strips are placed on the shoulders just beyond the lane edge. Centerline rumble strips are placed on the centerline of undivided highways. Roadway rumble strips are placed across the roadway to alert drivers who are approaching a change of roadway condition.
The HRRRP project includes all three types of rumble strips.
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Are safety features other than rumble strips part of the program, and how did KCDOT decide which features to install?
The project also includes signs, delineators (guide posts), minor shoulder widening, and removal of fixed objects near the roadway.
The call for grant applications emphasized the following criteria, which were used by KCDOT in selecting safety improvements:
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Low cost
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Proven effectiveness (as opposed to experimental treatments)
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Rural roadways
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Improvements over long distances as opposed to spot treatments at high accident locations
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Rumble strips were specifically mentioned as a possible improvement
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Guardrail was specifically excluded because of its somewhat higher cost
The following safety features were proposed in the grant application:
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Rumble strips or profiled thermoplastic
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Guideposts at locations with roadside hazards
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Reflectors (aka “butterflies”) on existing guardrail
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Warning signs such as chevrons and object markers
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Mowing, clearing and related sight distance improvements
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Removal of hazards in the clear zone
KCDOT eliminated profiled thermoplastic during the design process due to concerns about how it would affect bicycling and about its vulnerability to damage from plowing. Guideposts were installed on guardrail instead of butterfly reflectors on some of the roadways. Shoulder widening was planned at some locations to provide adequate shoulder width for rumble strip installation; these locations were limited due to the cost of widening.
The design process included a thorough review of all six roadways to identify safety improvements that were applicable to the intent of the grant. The review included field visits and gathering of information such a traffic volumes and collision history. Standard references were used to assess improvements. These included the King County Road Design and Construction Standards, WSDOT Design Manual, Standard Plans and Specifications, Manual on Uniform Traffic Control Devices, AASHTO Policy on Geometric Design of Highways and Streets, the Highway Safety Manual, and the Guidance for Implementation of the AASHTO Strategic Highway Safety Plan.
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Are data available showing that rumble strips are effective in reducing run-off-road and crossing-centerline collisions?
Nationwide, approximately 40 percent of non-intersection-related fatal crashes were run-off-road collisions and 20 percent were two-vehicle head-on collisions. The percentages for Washington state are nearly identical to national statistics. In unincorporated King County, approximately one percent of the total collisions each year are head-on collisions and 30 percent are run-off-road crashes.
Numerous studies document the effectiveness of rumble strips. A recent WSDOT study found that centerline rumble strips reduced injury and fatal head-on collisions by nearly 50 percent. WSDOT is completing a study on shoulder rumble strips; WSDOT currently recommends assuming that they result in a 30 percent reduction in run-off-road collisions.
What transportation design guidelines exist for rumble strips? What is the basis for those guidelines?
The Federal Highway Administration has posted guidelines on its website, and a number of state transportation agencies, including WSDOT, also have guidelines.
Generally, transportation guidelines balance competing demands, including the needs of different road users (e.g. private vehicles, transit, cyclists, and pedestrians), maintenance considerations, safety, ease of mobility, and economic considerations. In practice, trade-offs and compromises are involved in balancing these factors.
WSDOT’s rumble strip design guidelines are based on the work of a committee that included design professionals, the WSDOT Bicycle and Pedestrian Coordinator, the Bicycle Alliance of Washington, and other local cyclist groups. One result of this work was the “Shoulder Rumble Strip Type 4” design used in this program. This design includes narrower rumble strips and gaps to accommodate cyclists.
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What are KCDOT's design practices for rumble strips?
First, the difference between standards and guidelines should be clarified. The term “standards” generally refers to practices that are legally required, while “guidelines” are practices that are recommended by the issuing agency. The WSDOT rumble strip documents are guidelines.
Local transportation agencies (cities and counties) typically develop their own standards and guidelines based on what they have determined to be appropriate for the roadways they manage. State guidelines are applied to state roads, which are significantly different from many of the roads in local jurisdictions.
KCDOT developed the following design practices, which are based on WSDOT guidelines:
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Rumble strips should be installed only on rural roads that have a minimum of 0.6 run-off-road crashes per mile per year or 34 crashes per hundred million vehicle miles. In addition to evaluating the entire roadway, these criteria will be applied to sub-corridors within each roadway. Sub-corridors will be defined based on obvious breaks such as major intersections with changes in traffic volumes or roadway characteristics.
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They should not be installed in dense commercial/residential areas
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They can be installed where posted speeds are 35 MPH and higher
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There should be a minimum of 4 feet between the edge of shoulder rumble strips and the pavement edge
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There should be a minimum of 5 feet between the edge of shoulder rumble strips and the pavement edge where guardrail is present
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Shoulder rumble strips should not be installed on downgrades exceeding four percent for more than 500 feet. They can be placed on the uphill side.
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The following additional practices apply to roadways with frequent bicycle usage, defined as at least 15 cyclists per hour during any measured period:
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Warning signs will be installed at the start and end of shoulder rumble strip sections.
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Transverse thermoplastic markings will be used to delineate rumble strips at 200-foot intervals.
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Discontinuing centerline rumble strips will be considered at locations with less than 14 feet between the centerline and edge of pavement.
Two specific practices addressed in both the WSDOT and KCDOT guidelines should be clarified:
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The WSDOT Design Manual indicates that shoulder rumble strips should not be installed where downhill grades exceed 4 percent for more than 500 feet. According to the WSDOT design office, the purpose of this guideline is to avoid situations where cyclists travel downhill at a high rate of speed beside shoulder rumble strips. According to WSDOT, shoulder rumble strips can be present on the right side of a road heading uphill.
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The WSDOT standard plans also indicate that shoulder rumble strips should be terminated 40 feet prior to the right turn radius or at the beginning of the taper when approaching an intersection. This applies to intersections with public roads and other locations where the channelization (striping) is broken at the intersecting street. It does not apply to private roads or driveways where the edge line extends through the intersection, although the county has terminated rumble strips at some of the more frequently used driveways and private roads in this project.
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Are any data available on the frequency of cycling collisions associated with rumble strips?
Neither KCDOT nor WSDOT have found data about bicyclist crashes associated with rumble strips.
Are there any issues with pedestrians and rumble strips?
Neither KCDOT nor WSDOT have any documented evidence of issues with pedestrians and rumble strips. A potential issue is that pedestrians would compete with bicyclists for the same portion of the roadway shoulder. However, because of the small number of pedestrians in rural areas, substantial conflicts with bicycle users are unlikely.
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What are KCDOT’s plans for keeping the road shoulder clear of debris?
The Road Services Division plans to sweep the roads more frequently, and welcomes community input on when and how frequently to sweep.
Can anything be done to make rumble strips more visible both in daylight and at night?
On roadways with frequent bicycle usage, defined as at least 15 cyclists per hour during any measured period, the following treatments will be used to improve the visibility of rumble strips:
Information from the Road Services Division's website is available to people with disabilities in alternate formats upon request by calling 206-263-6482 or 711 for the TTY relay service.
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