ISU lecture TS_04_09ter

DESIGNOFMODERNROUNDABOUTSINURBANTRAFFICSYSTEMSAntonioPratelliDepartmentofCivilEngineering“VieeTrasporti”UniversityofPisa(Italy)LecturesattheIOWASTATEUNIVERSITYApril2009IntroductionMainfeaturesTrafficsafetyissuesPublicopinionConclusionsSamplecasesOutlineFirstgeneration(TrafficCircles):-prioritytoenteringtrafficflows;-designconsidersweavingmovementsasbasicgoal;-capacityisrelatedtoeachtrackbetweensuccessivebranches.Secondgeneration(ModernRoundabouts):-priority-to-circle;-designisconceivedforloweringspeeds;-capacityisrelatedtoeachentrance.Introduction(1)1903:(NewYork)ColumbusCircleproject;1907:(Paris)Placedel’Etoilelayout(todayPlaceCharlesDeGualle)1926:roundaboutsbecametrafficmanagementtoolsforintersectionswithpriority-to-branchesrule(firstgeneration).1966:UnitedKingdomintroducesthe“priority-to-the-circle”rule:isthebirthdayofmodernroundabouts(orIIgeneration).1984:Franceintroducesthe“priority-to-the-circle”ruleandpublishestechnicalguidelines(1988);OtherEUcountriesfollow,as:Switzerland(1991);Netherland(1992);Germany(1993);Italy(1994)2000:about15.000modernroundaboutsareoperatinginFrance.Introduction(2)ColumbusCircle,NewYork,inapictureof1915Mainfeatures(1)Threecategories:-MINIroundabouts(D22mt)-COMPACTroundabouts(22D35-40mt)-LARGEroundabouts(D40mt)Mainfeatures(2)ENTRYCAPACITYhasbeeninvestigatedusingtwoapproaches:a)the“gap-acceptance”theory;b)theempiricalregressionmethod.Mostdesignguidelinesusestatisticallyderivedlinearformulas,suchas:Ce=f(geometry,Qc,Qu)Trafficsafetyissues(1)Basicaspects:1)Loweredcirculatingspeeds,thisisachievedbyentrypathdeflection(expeciallyinwell-designedroundabouts).2)Reducednumberofconflictpoints.Influenceoftheaveragespeedvariationsonaccidents.(EuropeanProject“Master”,FinalReport,1998)-60-40-200204060-10-50510Changeinaccidents(%)FatalSevereinjuryAllAveragespeedvariation(km/h)Withoutpathdeflectionenteringtrafficaimstotherightofthecentralislandandproceedsstraightaheadatspeed,then:•causesseriousaccidents,expeciallyifappliedonfastroads;•theyieldingprocessisdefeatedbyfastentries.Toavoid!VehiclepathdeflectionrequirementsfromItalianstandardguidelines.Afour-leggedroundaboutshows8instead32conflictpointsofafour-wayintersection.Atleasta7.4%averageannualreductionisneededtohalveroaddeathsbetween2001and2010Roughly43.000peoplearestilldyingeveryyearonEurope'sroads.EU:•Althoughtherehasbeena20%dropoffatalaccidentsinsevenyears,theEUstatisticisstillsomewayofffromits50%target.Italy:•In2007,5313peoplediedontheItalianroads;25%lessthanin2001.•Italyneedstodofurthereffortstoprogressinthewayofimprovingraodsafety.Trafficsafetyissues(2)0123456123CrashTypeAveragecrashesperyearSenzarotatoria(prima)Conrotatoria(dopo)CrashType:1)Totalcrashes2)Injuries3)Moped/Bicycleinjuries(basedonaB&AstudyintheNetherlands,1992)Trafficsafetyissues(3)0.691.541.581.813.84.401234530m30-50m50-70m70-90m90mOvaliSizeofInscribedDiameterAverageAnnualCrashesAnnualCrashFrequenciesandSizeofInscribedDiameter(Statisticsfor83roundaboutsinFrance,1986)PublicOpinionPercentofrespondentsinfavourof/opposedtoaroundaboutconstruction(B&AsurveysinUSA,2000-2002).051015202530354045MoltoAbbastanzaPocoAffattoNonsodrivers%primadopoStronglyF.SomewhatF.SomewhatO.StronglyO.Don’tknowBeforeAfter“PonteaEma”projectexample:BEFORE4-armssignalizedintersectionAFTERCompactroundabout(a=30,7m;b=26,6m;b/a=0,87)12341B&AentryaveragedelaysduringAMpeakcalculatedfor“PonteaEma”roundaboutproject,Florence(It.)entrytwsignaltwroundabout(secs)%1)SR222(Fi)26,79,6-17,1-64%2)PonteaEma55,811,7-44,1-79%3)SR222(Grass.)13,99,6-4,3-31%4)ZonaArt.68,98,7-60,2-87%“PonteaEma”projectexample:0510152025303540450102030405060708090Velocitàmedia(km/h)Tassodiemissionedegliinquinanti(g/km)0500100015002000250030003500TassodiemissionedellaCO2(g/km)COVOCNOXPMCO2Pollutantemissionfunctionsforbuseswithhotengine(J.Hickmanet.al.,“Methodologyforcalculatingemissionsandenergyconsumption”MEETProjectFinalReportfortheEuropeanCommissionDGVIIbyTransportResearchLaboratory,1999).Modernroundaboutsareoneofthemostimportanttrafficengineeringdevelopment,bothonthesideofroadsafetyandoperations.Abriefoverviewofmodernroundaboutsdesignandpracticeismade.WewishconcludeshowingsomesamplecasesofroundaboutsinItaly(allmyownprojects).ConclusionsExamplen.1Double-miniroundabout.ViaTonfano,MarinadiPietrasanta,Lucca,(It.)2003Examplen.1–Satelliteviewofthepreviousstate.Examplen.1–Layout(D1=20m;D2=19m;X=7m)12XExamplen.1–Westboundaerialviewofthe“minitwins”.Examplen.1–Eastboundroadwayview.Examplen.1–Westboundroadwayviewwithbus.Examplen.2Double-largeroundabout.Loc.“Battifollo”,Sarzana,LaSpezia(It.)2005Examplen.2–SatelliteviewofthepreviousstateExamplen.2–Layout(D1=50m;D2=35m;X=50m)12XExamplen.2–Nightlightingdesignsimulation.Examplen.2–AerialSouthboundviewduringtheconstructionstage.Examplen.2–Northboundroadwayview.Examplen.2–Satelliteviewoftheactualstate.Examplen.3Ellipticalcompactroundabout.VialeCarducci-VialeEuropa,Lucca,(It.)2006Examplen.3–AerialWestboundviewofthepreviousexperimentalroundabout(dangerousduetoitspoorgeometry).Examplen.3–Layoutwithwe