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6. Staff Report PW Supporting Mumble Strip Summary
DSPU–SummaryDocument:MumbleStrips September2015 Page|1 Topic:MumbleStrips WhatareMumbleStrips? Theintendedpurposeofarumblestripistoprovidedrivers withbothanaudibleandatactilewarningthattheyare approachingapotentiallyhazardouscondition–theroad edge,opposingtrafficetc.Traditionalrumblestrips accomplishthistaskbutalsoprovideanundesirableside effectforadjacentlandowners–increasedtrafficnoise levels.Unlikethetraditionalrumblestrips,“mumble”stripsproducelowerexteriornoiselevelswhen vehiclespassoverthem.Dependingonthedesign,mumblestripscouldalsoreduceinteriornoiselevels. However,reducedinteriornoiselevel,toacertaindegree,isundesirablesincethenoisecreatedis supposedtowarnthedriversoferrors.Themostsignificantdifferencebetweenatraditionalrumblestrip designandamumblestripdesignisthesinusoidalpattern.Thisrelativelynewpatternofpavement groovinghasnotbeenwidelydeployedaroundthecountryduetotheminimalresearchavailable.MnDOT andtheLocalRoadResearchBoard(LRRB)haverecentlycompletedastudythatcomparedthreedifferent rumblestripdesignsneartheCityofCrookstonMinnesotaonarural2ͲlanesectionofCSAH11inPolk County.Thisstudyutilizedthreevehicletypes(passengercar,smalltruckandsemiͲtractortrailer)topass overthedifferentdesignsatlow(30mph),medium(45mph)andhigh(60mph)speeds. WhatisthedifferencebetweenMumbleandRumbleStrips? Tocreateamumblestripinsteadofa traditionalrumblestrip,adifferent patterniscutintothepavement.Figure1 showsthegeneralshapeofrumblestrip designsinCalifornia,Minnesotaand Pennsylvania.Thethreedesignswere analyzedintheRumbleStripNoise EvaluationstudypublishedbytheLRRB. Traditionalrumblestripdesigns,similarto Minnesota’s,arerectangularinshapeand aretypicallycutintothepavementonce thesurfacehashardened.Thestudy comparedthenoiselevelsbyrecording theAͲweighteddecibel(dBA)readingsbothinsideandoutsideofthedifferentvehiclesanddifferent designs.Additionally,anAͲweighteddecibelreadingwasrecordedforvehiclespassingoverthepavement absentrumblestrips.Therectangularpatternproducedthehighestnoiselevelsinandoutsideofthe vehiclewhereasthePennsylvaniadesign,whichmostcloselyrepresentsasinewave,wasthequietest overall.Thereisconcernconsideringthatlowerlevelsofinteriornoisemaynotbeenoughtowarndrivers ofthelanedeparture. KeyPoints x Maintainsinteriornoiseand vibration x Reducedexteriornoisetranslatingto satisfiednearbyresidents x Potentiallyaseffectiveinalerting driversofpotentialconflictsas traditionalrumblestrips DSPU–SummaryDocument:MumbleStrips September2015 Page|2 HowdoMumbleStripsoperate? Mumblestripsoperatethesamewaythattraditionalrumblestripsoperate.Theystillprovideanaudible andtactilesensationthatalertsdriverswhentheyaredepartingthetraveledway.However,quieter exteriornoiseproducedbypassingvehiclesbenefitsresidentswhoarenearthemandthemumblestrips couldpotentiallyprovideequivalentsafetybenefits. WhereisthebestplaceforMumbleStrips? Mumblestripswouldideallyreplacetraditionalrumblestripsinruralareaswithadjacentresidential developmentorinurbanenvironmentswhereaddressinglanedeparturecrasheshasbeenidentifiedasa priority.Anotherlocationwheremumblestripsmightbeappropriateareonhighwaysthatpassthrough ornearsmallerruraltowns.Oneoftheintendedoutcomesofthisnewdesignistoreducetheamountof noiseproducedbyvehiclespassingoverthem.Residentswholivenearpatchesofrumblestripscould activelyhearthenoiseproducedbyvehiclesstrikingthemfromoveroneͲhalfmileaway.Tomanyatthis distance,thelevelofnoisecouldbeconsideredambientnoiseandwouldnotbeconsideredanuisance. HowexpensiveareTransverseRumbleStrips? Sincetherehasnotbeenwideuseofsinusoidalrumblestrips,thecostassociatedwiththemis undetermined.Theoverallcostofmumblestripswouldbecomparabletotraditionalrumblestripsbut perhapswithaslightincreaseduetotheuniqueshapecarvedintothepavementaswelltheproprietary machinerythatmaynotbereadilyavailabletocontractors. Whataresomedesigndifferences? Thetypeofsinewavecutintopavementsisanimportantfactorwhendesigningreducednoiserumble strips.ThedepthandcenterͲonͲcenterspacingoftherumblestripsareasignificantfactorwhenproducing theappropriateinteriornoiseleveltoalertdrivers,butalsoreducingtheexteriornoisewheninstalled nearresidents.Additionally,designvariationscouldtaketheformofincreasedwidthofthemumblestrip toaddressheavycommercialtirebridgingwiththe8Ͳinchstrips,andalsoconsideringcenterlinemumble stripstudiesaswell. OtherConsiderations Otheragencieshavetriedreducingroadsidenoiseinpopulatedareaswithalternativetechniques.One optionthatisusedinareaswithlowsnowfallisthermoplasticprofilepavementmarkingsorraised pavementmarkings.Eventhoughthisalternativehasbeenproventoreduceroadsidenoiselevels,it wouldnotbeaviableoptioninMinnesotaduetosnowplowingduringwinterweather. References MnDOT.RumbleStripNoiseEvaluation.February2015.MN/RC2015Ͳ07 [http://www.dot.state.mn.us/research/TS/2015/201507.pdf] Caltrans.TrafficNoiseGeneratedbyRumbleStrips.March2012. [http://www.dot.ca.gov/newtech/researchreports/preliminary_investigations/docs/rumble_strip_noise _preliminary_investigation_3Ͳ5Ͳ12.pdf]