Decision Support Guide for the Installation of Shoulder and Center Line Rumble Strips on Non-Freeways
While rumble strips help reduce ROR crashes and are a proven low-cost safety countermeasure, they can negatively impact bicyclist activity, generate disturbing noise, and may impact pavement quality or future maintenance activity. These special considerations are generally acknowledged in agency policies and are covered in the FHWA Rumble Strips and Rumble Stripes website.(12) The website contains implementation fact sheets targeting those involved in rumble strip design or installation and contains implementation guides targeting those making decisions on individual projects or setting standards. A brief summary follows, and the implementation guides and fact sheets can be reviewed for further details regarding bicycle accommodation, noise issues, and pavement issues.
- Bicycle accommodation: Agency systematic policies are generally based on providing an adequate clear shoulder width between the outside edge of the rumble strip and the edge of pavement. Bicyclists have a variety of basic requirements that need to be accommodated on shared roadways with vehicles. Additional factors that affect bicyclists on roadways with rumble strips are clean pavements and the ability to cross rumble strips safety. Agencies should work with the bicycle community to understand their needs, to develop policies or solutions that accommodate bicycles and increase safety, and to identify higher and lower priority corridors for bicycles. Technical specialists making decisions on individual projects or setting standards can find more information in the Rumble Strip Implementation Guide: Addressing Bicycle Issues on Two-Lane Roads.(13) Additional information can be found in the FHWA Technical Advisory on Shoulder and Edge Line Rumble Strips. (14)
- Noise issues: Most agencies address the consideration of potential noise issues in a general sense (i.e., acknowledging the possibility). Few States have specific policies regarding installation proximity to dwellings and businesses. Technical specialists making decisions on individual projects or setting standards can find more information about noise accommodation in the Rumble Strip Implementation Guide: Addressing Noise Issues on Two-Lane Roads.(15) Additional information can be found in the FHWA Technical Advisory on Shoulder and Edge Line Rumble Strips and in the FHWA Technical Advisory on Center Line Rumble Strips.(14)
- Pavement issues: Pavement considerations typically include current pavement condition, pavement depth, time to future surface overlay, and location of the rumble strip in relation to longitudinal joints. Little connection has been found between pavement condition at the time of installation and increased pavement degradation. Additionally, preventative maintenance treatments, such as chip seals, ultra-thin hot mix asphalt, and micro-surfacing have traditionally been considered to be incompatible with rumble strip installations. Recent experiences have shown that these worries may be unfounded. Technical specialists making decisions on individual projects or setting standards can find more information in the Rumble Strip Implementation Guide: Addressing Pavement Issues on Two-Lane Roads.(17) Additional information can be found in the FHWA Technical Advisory on Shoulder and Edge Line Rumble Strips and in the FHWA Technical Advisory on Center Line Rumble Strips.(14)
Agencies use several different cross-section and rumble strip designs based on these special considerations including the following:
- Different rumble strip configuration.
- Different rumble strip placement. For example, moving SRS under the pavement marking to create an edge line rumble strip. The goal is to maintain a four-foot clear space, if possible. The goal is generally five feet if curb or guardrail is present.
- Consider omitting rumble strips at locations with guardrail and/or curbing if adequate clear space cannot be maintained.
- Reduce the depth of the rumble strip to 3/8 in.
- Changing lane configurations. For example, narrowing the travel lane to accommodate a wider shoulder.
- Widening the shoulder to accommodate rumble strips and clear space for bicyclists.
- Utilizing raised rumble strips.
- Terminating rumble strips in residential areas or providing breaks near residences (as necessary).
If accommodations cannot be made, alternative safety strategies may be considered and implemented, if justified. However, alternative strategies may not focus on distracted or drowsy driving, which are targeted by rumble strips. For example, agencies may elect to enhance delineation as an alternative to rumble strips, in noise sensitive areas (e.g., curve signing, delineators, raised pavement markings [RPMs]). Potential alternatives to rumble strips include the following:
- Improving horizontal curve delineation by:
- Installing or upgrading advance warning signs.
- Installing advisory speed plaques.
- Installing Chevrons or a Large Arrow plaque.
- Installing delineators and/or raised pavement markers.
- Installing wider pavement markings.
- Applying high friction surface treatments.
Additional alternatives for horizontal curves can be found in the Low-Cost Treatments for Horizontal Curve Safety 2016.(8) The CMF Clearinghouse and the HSM Part D can be consulted to determine the potential safety effectiveness of alternative options.