Practice of Rumble Strips and Rumble Stripes (2016)

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28 survey results showed how state DOTs embraced their use as part of safety planning. All the survey participants indicated they install shoulder (edge line) rumbles, and 88% install center line rumbles. The state of the practice survey showed the variation among state DOT practices when it comes to installing, designing, and maintaining rumble strips and stripes. The variability ranges from where to install them (urban vs, rural, four-lane vs. two- lane, and undivided vs. divided roadways); their dimensions (length, width, spacing and depth); whether or not to apply sealants; and how to re-apply pavement markings in the case of a rumble stripe application. Even though rumbles have a huge safety benefit, there are issues that arise from installing them. The main issues identi- fied by the state DOTs in the survey are noise, bicycle con- cerns, and pavement deterioration. To address the noise issue, the majority of the states take traditional approaches—skipping rumbles in residential areas, adjusting their depth, or not installing rumbles at all. Very few agencies (California and Minnesota DOTs and a Pennsylvania contractor) have experimented with different pattern design (sinusoidal pattern) to reduce the noise issue. This promises to be a viable solution to the noise issue but additional research might be needed to ensure that with noise reductions, enough audible and tactile warnings are delivered to the driver to react. Related to the bicycle concern issue, the state DOTs developed policies to modify their rumble design practices to be sensitive to cyclists. Most of the DOTs deal with bicycle issues by introducing a bicycle gap (most alternate 48 feet of rumble with a 12-foot rumble-free gap); adjusting the shape of the rumble strip; and ensuring there is sufficiently wide paved shoulder or enough clearance from barriers or guard rails. More could be done in this area by communicating more with cycling groups and also explaining the importance of using such a safety countermeasure to address safety. Pavement deterioration (mostly center line joint deterio- ration) rounds off the major concerns identified by the state DOTs in the survey. Of the 18 agencies who identified pave- ment deterioration as an issue, 12 agencies (67%) also reported applying sealant over the rumble. The literature search did not produce many publications on the impact of rumbles on pave- ment performance, which is why it has been identified as Rumble strips and stripes are low-cost safety countermeasures that can be placed on highway shoulders or center line to reduce roadway/lane departure crashes. State rumble strip and stripe practices are not uniform, and there may not be one ideal design that can deliver the auditory and tactile clues required to warn drivers to correct their path. The objective of this synthesis was to identify current practices used by states installing rumble strips and stripes. The scope of this synthesis study focuses primarily on the following aspects of rumble strips and stripes: • Rumble designs–patterns, locations, pavement types and widths, etc. • Expected safety benefits such as crash modification, white-out/packed snow/fog driving, wet night driving, etc. • Tolerances for installation • Roadside noise • Impacts on bicycle community • Public outreach, including education, public involvement, department of transportation (DOT)/agency responses, etc. • Maintenance/durability issues–winter, pavement preser- vation, etc. • Other concerns identified through the survey. This list of issues was grouped into six categories, which were then used to develop a logical flow for the survey: • State DOT general rumble practices • Roadway selection criteria • Design and installation • Maintenance practices • Benefits • Issues. There were 41 responding state DOT agencies for a response rate of 82%. OVERALL FINDINGS There is overwhelming evidence that rumble strips and stripes have a positive impact on safety by reducing run-off-the-road and/or head-on crashes. The literature review showed exam- ples of how state DOTs assessed those safety benefits and the chapter five CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH

29 one of the suggestions for future research. Some agencies indicated that pavement condition is a factor in considering whether to install a rumble or not. Others also indicated that rumbles will not be installed on portland cement concrete pavements. The survey showed that very few state DOTs have created public campaigns to explain their use of rumbles to improve safety, which might minimize complaints regarding noise, bicycle issues, and others. Examples from Michigan, Minnesota, and North Carolina could be used as templates by other DOTs to start addressing the communication issues. SUGGESTIONS FOR FURTHER RESEARCH Work on this synthesis has identified several gaps in current knowledge that could be addressed by the following sug- gested research topics. • Dealing with noise (new design standards)—State DOTs could further investigate alternative rumble designs to reduce noise. As the literature showed, the sinusoidal pattern is promising, but further research is needed. As shown in the Minnesota DOT study, the reduction of the rumble length from 16 inches to 8 inches resulted in reduced audible and tactile warnings when the whole tire was not in contact with the rumble. • Specifications (audible and tactile)—Rumble strips and stripes provide feedback to the drivers by producing audible and palpable warnings. Survey responses show that only two agencies have developed specifications for these two items. Additional research could assess how powerful audible and tactile warnings need to be and how they can be measured. • Rumble stripes—When the pavement marking and the rumble strip are combined, a rumble stripe is born. The survey showed the lack of information on the impact of the rumble on the performance of the pavement marking. Another aspect of rumble stripe is the wet/night visibility advantage; as yet, very few states have measured wet retroreflectivity of rumble stripes. Additional research could provide more guidance to the state DOTs on rum- ble stripes. • Pavement deterioration—Additional research could assess the impact of the rumble on the pavement deteri- oration. A number of states said they have an electronic database with all locations of their rumbles that is tied to a location referencing system. This would allow for the integration of pavement condition data over time to determine if the rumbles have a negative impact on pavement performance, and if so, how much. • Rumble strip design (impact on safety benefits)—Results from the survey showed how the state DOT practices vary, from size to design to installation; and also how the resulting crash modification factors vary. This suggested research topic would address the potential differences in safety benefits resulting from different rumble strip and stripe designs.