Wyoming Effectiveness Report
Shoulder Rumble Strips -- Effectiveness and Current Practice
Federal Highway Administration
Wyoming Division Office
April 2, 1998
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.
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.
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.
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:
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.
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.
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.
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.
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:
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:
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.