Rumble strips create audible and tactile warnings that alert a vehicle’s driver as it crosses the center or edge line of a roadway. (When a pavement marking is applied over the rumble pattern, it is known as a rumble stripe.) Often these alerts are strong enough to get the attention of a distracted or drowsy driver, who can quickly make a corrective steering action to return to the roadway safely. Rumble strips can also alert drivers that they are on the edge of a lane in cases of low visibility conditions such as rain, fog, snow, or dust. Research has shown that installing rumble strips can reduce severe crashes. Adding center line rumble strips resulted in a 45% reduction in crashes on rural two-lane roads and a 64% reduction on urban two-lane roads. Installing shoulder rumble strips reduced crashes by 36% on rural two-lane roads and by 17% on rural freeways. Given the proven safety benefits from using rumble strips, many agencies are including them as part of their low-cost safety countermeasures. A survey of state DOTs showed that all of the 41 responding agencies install shoulder rumble strips and that 88% of those agencies also install center line rumble strips. In contrast to other standardized safety countermeasures, such as signs or pavement markings, there are no national standards of practice for rumble strips, so their lengths, widths, gaps, applicable locations, and general maintenance can vary widely among agencies. In addition, how each agency chooses to address the common issues arising from the use of rumble strips, such as noise, bicycle and alternate use safety, and pavement deterioration–identified by the state agencies as the most problematic issues–adds further variation to the state of practice. Given the wide use of rumble strips, the objective of this synthesis was to capture current practices used by states installing rumble strips and stripes and to explore variations in practice in terms of design, criteria and locations for installation, maintenance, perceived benefits, communication of benefits, and what are considered important issues. A literature search on rumble strips and stripes from national and international sources was conducted before an online survey was sent to all of the state departments of transportation (DOTs) and Canadian provinces identified in the AASHTO Highway Subcommittee on Traffic Engineering. Forty-one (41) states, 82%, responded to the survey, as well as two Canadian provinces, Nova Scotia and Saskatchewan. The analysis of survey data was based only on the state DOT responses, although the two surveys from Canada indicated those agencies had similar practices. That was followed by an in-depth analysis of how the state DOTs have addressed issues related to noise, bicycle concerns, pavement deterioration, and explaining the benefits of rumbles. The survey results document how varied state DOT practices are when it comes to designing, installing, and maintaining rumble strips and stripes. These include how agencies decide where rumbles are installed (urban vs. rural roadways, four- vs. two-lane roads, and undivided vs. divided roads); the dimensions of rumbles (length, width, spacing, and depth); whether to seal surfaces or not; and how to re-apply pavement marking in the case of a rumble stripe application. The findings from the survey, indicated here, are addressed in detail in chapter five: Conclusions and Suggestions for Further Research. To address the noise issue, two-thirds of the state agencies rely on traditional methods: skipping rumbles in residential areas, adjusting their depth, or not installing rumbles at all. The overwhelming majority of responding states, 83%, have developed policies or guidance to modify their rumble design practices to be sensitive to cyclists. Fewer than half the respondents have developed policies/guidance to address pavement deterioration; several agencies indicated that pavement condition is a factor on whether to install a rumble or not. The survey also showed that very few state DOTs have created public campaigns to explain that the use of rumbles improves safety so that complaints regarding noise, bicycle issues, and other are minimized. Based on the results from the literature search and the survey, several indicated gaps in current knowledge that could be addressed by further research are listed in chapter five. (Author/publisher)
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