Wyoming Effectiveness Report

U.S. DOT LogoShoulder Rumble Strips -- Effectiveness and Current Practice

Federal Highway Administration

Wyoming Division Office

April 2, 1998



Introduction

Shoulder rumble strips have proven to be an effective roadside treatment in preventing run-off-the-road crashes on rural highways. Based upon the proven effectiveness, most States now require the incorporation of rumble strips during the reconstruction, rehabilitation, or resurfacing of rural highways. Retrofitting rural highways with shoulder rumble strips is also gaining increased use.

Based upon nationwide use and proven effectiveness, the purpose of this report is to promote the required use of shoulder rumble strips on Wyoming rural highways as a necessary treatment to reduce the frequency of single vehicle run-off-the-road crashes.

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Problem Identification

Run-off-the-road crashes represent a significant percentage of fatal and injury crashes in Wyoming. This is supported by a five-year review of Wyoming's Comprehensive Report on Traffic Crashes, 1992 through 1996. These publications provide crash type comparisons and for this report, overturn crashes were used to best represent a single vehicle run-off-the-road incident. Selected crash comparisons are presented for: Rural fatal crashes as a percentage of total fatal crashes; fatal overturn crashes as a percentage of total fatal crashes; and injury overturn crashes as a percentage of total injury crashes.

Year Rural -
% Fatal
Overturn Crashes -
% Fatal
Overturn Crashes -
% Injury
1996 81.0 38.8 21.1
1995 84.8 45.7 20.4
1994 82.3 41.5 20.3
1993 74.0 35.0 21.9
1992 85.4 37.4 22.1

For the presented five years, the percent of fatal and injury crashes due to single vehicle overturns has remained relatively constant and are a significant percent of fatal and injury crashes in Wyoming. This conclusion warrants the consideration and incorporation of roadway design features including rumble strips which, through national use, have proven effective in reducing this type of crash.

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Shoulder Rumble Strip -- National Use

NCHRP Synthesis 191 published in 1993 reports 18 to 21 States, depending on pavement type, incorporating shoulder rumble strips on their rural highways.

The Wyoming Division surveyed a total of 13 States and found that 11 of those States require the use of shoulder rumble strips and two States recommend their use. A summary of the Divisions' survey follows:

State Standard
(Std) Plan
Written Policy/
Considerations
Design
Considerations
Bicycle
Arizona Policy Yes Yes
Illinois Policy Yes Yes
Maryland Recommended No No
Massachusetts Policy Yes* No
Minnesota Policy Yes* Yes
Montana Policy Yes* Yes
Nebraska Recommended Yes No
Nevada Std Plan Yes No
New York Policy Yes No
Pennsylvania Policy Yes* No
Virginia Policy Yes* No
Washington Policy Yes* Yes
Wisconsin Policy Yes No
* Require milled shoulder rumble strips

These particular States were selected to give a national cross-section of State policies and practices. The current policies from each of the above States are available from the Wyoming Division Office.

Further review of design considerations contained in these policies indicates that half of the States are now requiring the use of milled rather than rolled shoulder rumble strips, based upon their determination that milled rumble strips are more effective in producing long-term audible and vibrational warnings.

FHWA, through Notice N7560.9, dated April 28, 1986 recommends shoulder rumble strips on long tangents or monotonous sections of rural highways with high rates of run-off-the-road crashes. Most recently, in a December 29, 1997 memorandum, FHWA has indicated that 85 percent of States use shoulder rumble strips.

Based upon our survey, we would conclude that the required use of shoulder rumble strips has gained national acceptance and that a milled rumble strip is the more effective design.

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Shoulder Rumble Strip -- National Effectiveness

Numerous studies have been completed to determine the effectiveness of shoulder rumble strips in reducing single vehicle run-off-the-road crashes. This office has obtained copies of those studies, or summaries, and their results are summarized below.

State/Date Highway Type % Crash Reduction
Pennsylvania/1994 Thruway - Rural 70
New Jersey/1995* Turnpike - Rural 34
New York/1994 Thruway - Rural 72
Massachusetts/1997* Turnpike - Rural 42
Washington/1991* Six Locations 18
California/1985 Interstate - Rural 49
Kansas/1991* Turnpike - Rural 34
FHWA/1985 Interstate - Rural (Five States) 20
* Summaries

The FHWA study included rural Interstate locations in California, Arizona, Mississippi, Nevada, and North Carolina. The California locations were the same as used in the California study and if the California locations are omitted, the remaining four States showed a 6 percent reduction.

These studies produce a wide variation in the percent crash reduction attributable to shoulder rumble strips. NCHRP Synthesis 191 concludes that a 20 percent system-wide reduction in run-of-the-road crashes can be expected with the incorporation of shoulder rumble strips, with reduction rates up to 70 percent reserved to isolated, long, monotonous stretches of rural highways.

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Shoulder Rumble Strip -- Cost Considerations

The cost of shoulder rumble strips-milled taken from the WYDOT 1997 Weighted Average Bid Prices is $0.194 per linear foot on a contract quantity of 2.95 million linear feet. The State of Virginia which extensively uses shoulder rumble strips recently received a contract unit price of $0.125 per linear foot on an overall quantity of 2.5 million linear feet. These unit prices are taken from the full contract bid and includes other items such as mobilization and traffic control. As with any product, the unit cost of shoulder rumble strips will decrease over time as contractors gain experience and as Statewide contract quantities increase.

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Shoulder Rumble Strip -- Design Practices

As a result of national use and studies of effectiveness, certain design practices have evolved which enhance shoulder rumble strip performance in providing both audible and vibrational warnings and promote public acceptance. The following practices are taken from previously noted State policies:

General:

  • Incorporate on all rural divided highways, both inside and outside shoulders.
  • Incorporate on all rural undivided highways with shoulder widths 1.8 m (6 ft) or greater.
  • Incorporate on all rural undivided highways with shoulder widths 1.2 m (4 ft) to 1.8 m if evaluation of run-off-the-road crashes versus bicycle use supports use of rumble strips and public acceptance is evident.
  • Incorporate on any rural highway with a history of run-off-the-road crashes.
  • Do not incorporate on shoulders in urban areas, on curb/gutter sections, on bridge structures, or through intersections, driveway entrances, and ramp entrances/exits.
  • Continuous rumble strips are preferred over intermittent.

Asphalt Shoulders:

  • Milled rumble strips are the preferred method for new or existing (retrofit) shoulders. Rolled rumble strips, while still in use, are not as effective as milled for new or existing shoulders.
  • The WYDOT Standard Plan 401.02A provides acceptable design features.

Concrete Shoulders:

  • Formed-in rumble strips are the preferred method for new concrete shoulders, milled rumble strips are acceptable for existing shoulders.
  • The WYDOT Standard Plan 414-01B provides acceptable design features.

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Shoulder Rumble Strip -- Bicycle Considerations

A system-wide effort to incorporate shoulder rumble strips must include considerations to gain public acceptance. The most vocal opposition to shoulder rumble strips comes from the bicycle community. Bicyclists consider shoulder rumble strips as a hazard which prevents them from entering and exiting the shoulder area safely, with the remaining shoulder widths too narrow and often covered with sand, rock or other debris.

According to the December 29, 1997, FHWA survey, 68 percent of those States with a policy requiring the use of shoulder rumble strips also use a design that accommodates bicycle use. The following recommended practices are taken from various State policies and bicyclist concerns:

  • Bicycle travel corridors should be identified based upon usage (minimum 25 ADT for peak three months).
  • For identified bicycle travel corridors, the existing shoulders should provide a minimum 0.9 m (3 ft) clear and smooth shoulder width for bicycle use. (Should not be designated or signed as a bike route unless full AASHTO bicycle standards are met).
  • For identified bicycle travel corridors, a minimum 1.8 m (6 ft) shoulder width should be adopted for reconstruction or rehabilitation projects to accommodate rumble strips and bicyclists on highway shoulders. (Should not be designated or signed as a bike route unless full AASHTO bicycle standards are met).
  • Any rural highway corridor, also identified as a bicycle travel corridor, with a history of run- off-the-road crashes should be improved with a minimum 1.8 m shoulder to accommodate both shoulder rumble strips and bicycle use. Without available funding for shoulder width improvements, the environmental document and public involvement process should be used to evaluate the ‘best use' of public dollars--shoulder rumble strips or clear and smooth shoulder widths for bicycle use.
  • Consistently implement a system-wide effort.
  • For identified bicycle travel corridors, a minimum 0.9 m shoulder width should be maintained clear and smooth for bicycle use.

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Conclusion

Shoulder rumble strips have proven to be an effective roadside treatment in reducing run-off-the-road crashes on rural highways. Currently, 85 percent of State Transportation Agencies incorporate the use of shoulder rumble strips in their highway improvement programs. Many of these same State Transportation Agencies have appropriately included program considerations to accommodate bicycle use of these same shoulders, and are also realizing lower unit costs in contracting for the construction of shoulder rumble strips.

Wyoming has historically experienced a significant percentage of fatal and injury run-off-the-road (overturn) crashes and this historical record warrants the incorporation of effective roadway design features to reduce this type of crash. Shoulder rumble strips provide this effective roadway design feature.

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Program Contact

Cathy Satterfield

708-283-3552

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