A recently completed study shows that rumble strips are proving to be an effective and low-cost way to reduce crashes on Michigan's state highways.
The Michigan Department of Transportation (MDOT) started a major rumble strip program for two-lane high-speed rural highways in 2008. Centerline and shoulder rumble strips were installed on all MDOT rural, non-freeway highways with posted speed limits of 55 mph and appropriate paved lane and shoulder widths. To date, MDOT has placed 5,700 miles of centerline rumble strips and 1,700 miles of shoulder rumble strips.
The study, conducted by the Wayne State University (WSU) Transportation Research Group, found significant reductions in several targeted categories of crashes, including head-on, sideswipe and run-off-the-road crashes. In the categories examined, the study showed a 47 percent reduction in total crashes and a 51 percent reduction in fatal crashes.
"This study is one of the largest and most comprehensive investigations of effectiveness of any safety countermeasure that has ever been performed at a state level," said Tapan Datta, a WSU civil engineering professor and principal investigator of this research project. "Analyzing all of MDOT's two-lane high-speed highways with rumble strip treatments targeted to alleviate lane departure-related traffic crashes makes the results real and reliable. They can be used by other states to establish their own rumble strip programs."
Datta said future research should focus on use of rumble strips on two-lane county roads and multi-lane non-freeway high speed roads.
''Rumble strips are a proven and cost-effective countermeasure to lane departure crashes brought on by driver drowsiness, distraction, and/or inattention,'' the report said. ''We can project … this initiative in Michigan will result in an annual reduction of 337 crashes, saving 16 lives, and 62 serious injuries each year.''
These safety gains aren't coming at great cost to taxpayers. The report's economic analysis of the rumble strip program showed a high benefit-to-cost ratio. Depending on how the cost was spread out over time, the ratio was between 58:1 and 18:1. Researchers estimated a total safety benefit of more than $79 million over three years.
In another facet of the study, researchers surveyed road users to gain insight into the public's perception of rumble strips. The survey indicated strong public support for the use of centerline rumble strips. And the experts agreed: a survey of MDOT pavement design and maintenance personnel showed the majority of staff strongly agree that the installation of centerline rumble strips improves safety.
A previous rumble strip study, completed in 2012, found that the presence of centerline rumble strips improves driver performance in most conditions. Drivers position themselves more centrally in lanes, leading to fewer encroachments over centerlines and shoulders, thus increasing safety. And while drivers generally tended to ride onto or across the centerline when passing bicyclists, they did so less frequently when centerline rumble strips were present. They also found that centerline rumble strips did not contribute to short-term cracking in asphalt pavements. Further, rumble strips typically produced no more noise than that made by tractor-trailer trucks traveling on normal highways.
The full rumble strip report is available online athttp://www.michigan.gov/documents/mdot/RC1627_489159_7.pdf.