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TwoYearsLater:Safety,Operations,andEducationLessonsfrom
MinnesotasFirst
Two
Lane
Roundabout
Final City Version
June 7, 2011
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IntroductionandExecutiveSummary
AttheWoodburyCityCouncilMeetingonNovember20th,2005,theCouncilapprovedamotionto
consentto
the
design
features
which
were
to
be
included
in
the
Radio
Drive
Safety
and
Mobility
Project,
includingconditionalapprovaloftheproposedmultilaneroundaboutatBaileyRoad(CountyStateAid
Highway(CSAH)18)andRadioDrive(CSAH13).Oneoftheconditionsofthisapprovalwasthatthe
Countyconductananalysistwoyearsaftercompletiontodetermineiftheroundaboutisoperatingas
anticipatedwithrespecttodelayandsafety.Thisreportprovidesthisanalysis,andalsodetailssomeof
thevariouschangestotheroundaboutthathavebeenmadetotheroundaboutandthesurrounding
areasincetheroundaboutfirstopenedtotrafficinNovemberof2007.Thesefindingsshowthatthe
roundaboutwasconstructedatlowercostthanacomparabletrafficsignal,andthatithasout
performedacomparabletrafficsignalwithregardtovehicledelayduringPMpeakperiods,
demonstratingareductionindelayforthroughtrafficbyover50%.
Theroundaboutsrecordwithregardtosafetyhasbeenmixed.Theroundaboutoperatedforovertwo
fullyearsbeforeaverifiableinjurycrashwasreported.However,theroundabouthasalsobeenthesite
ofaninordinatelyhighfrequencyofnoninjurypropertydamagecrashes.FromJanuary2008through
Mayof2010,27propertydamagecrashesattheroundaboutwerereportedtotheMinnesota
DepartmentofPublicSafety(DPS).However,becauseonlycrashesexceeding$1000indamageorwith
injuryarerequiredtobereportedtothestate,theCountyhasalsoworkedactivelywithWoodbury
PublicSafetytokeepalistofallpolicecallsforminorcrashesattheroundabout.Accordingtothese
policerecords,80totalcrasheshaveoccurredattheroundaboutinthesameJanuary2008May2010
timeperiod,withonly27ofthemreportedtoDPS,whichsuggeststhattheremainderofthecrashes
resultedinlessthan$1000invehicledamage.Althoughmostreportedcrasheshavebeenminor,the
highrateofthesecrashesremainsahighprioritytoaddress.
Basedon
available
police
descriptions,
two
specific
crash
types
have
been
particularly
common.
The
firstisacrashresultingfromimproperlanechoice,whereavehicleattemptstoturnleftfromtheouter
lane,inviolationofinplacesignsandmarkings.Theothercrashtype,whichhasbeenthemost
common,occurswhenadriverenteringviatheouterlaneattemptstoenteralongsideavehicle
circulatingintheinsidelane,thusfailingtoyield(SeeFigure10b).Bothofthesecrashtypesstemfroma
drivermisunderstandingoftheroundaboutsconfiguration,inwhichthedriversarebehavingasthough
entryandexitisarightturnmovementratherthanathroughmovement.Underrightturnconditions,
itwouldbeacceptableforadrivertoenteralongsidecrosstrafficinthelefthandlane.Suchisthecase
atanearbytrafficcirclewhichhasexistedformanyyearsonlyafewmilesfromtheroundabout
projectsite(SeeFigures10a,10b,11a,and11b).
Toaddress
this
crash
problem,
signing,
enforcement,
and
education
efforts
must
work
to
clarify
to
approachingdriversthatentryandexitfromaroundaboutisnotarightturn.Additionalresearchis
neededinthisarea,astrafficcirclesandotherrightturnconditionsareoftensignedsimilarlyto
roundabouts.Thedifferences,mostlyrelatedtothelaneconfigurationofthecrossingtraffic,arenot
readilyapparenttoapproachingdriversundercurrenttrafficcontrolstandards.
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EducationandPublicInvolvement
Aspartoftheprojectdevelopmentprocess,WashingtonCountydevelopedanarrayofoutreach
strategiestoprovidethepublicwithinformationregardinghowaroundaboutoperates.Muchofthe
needfor
this
outreach
stemmed
from
persistent
misconceptions,
frequently
voiced
to
the
County
by
the
public,regardingroundabouts.Manyofthesemisconceptionswerebasedondriverspastexperiences
withothercircularintersectiontypeslocally,inotherregionsofthecountry,andabroad.Locally,a
persistentsourceofconfusionhasbeentheonewaycircularroadattheentrancetotheTamarack
Villageshoppingcenter,whereadualrightturnintoacircularroadiscontrolledbyyieldsigns,similarto
aroundaboutbutwithverydifferentoperatingcharacteristics(SeeFigures10and11).Manylocal
drivershadbeenexposedtohighspeedrotaryintersectionsintheNewEnglandregion,andstillmore
hadbeenexposedtobothroundaboutsandtrafficcirclesinotherstatesandcountries.
Toaddressthesemisconceptions,theCountydevelopedtheRoundaboutUoutreachprogram.This
efforthasincludedbrochuresprovidedatpublicbuildingsandevents,featuresinlocalnewspapersand
theCountys
Staying
In
Touch
newsletter,
working
with
the
City
of
Woodbury
on
afeature
for
the
citysCityUpdatenewsletter,developingeducationalhandoutsfordistributionbyWoodburypolice
officers,andworkingwiththeMinnesotaLocalRoadResearchBoard(LRRB)todevelopaMinnesota
basededucationalDVDregardingroundaboutfeatures,operation,andbenefits.TheCountyhasalso
workedwiththeMinnesotaDepartmentofPublicSafety(DPS)toimprovetheinstructionsprovidedin
theMinnesotaDriversManual,andalsoprovidedassistanceandmaterialstodriverseducation
companiesandorganizationsandtothenearbyEastRidgeHighSchoolsothatthematerialsare
availabletostudents.
Duringprojectdevelopment,theCountyalsohostedoutreacheventsatCubFoodsinWoodburyto
activelyengageresidentswhomaynototherwiseattendaprojectopenhouse.Theseeventsfeatureda
roomsizedroundaboutlayout,atoysizedroundaboutlayout,informationalpublications,andprizes
suchasballoonsandstickerstohelpattractfamiliestotheexhibit.Countystaffwerepresentatthese
eventstoanswerquestionsfromresidents,andusethedisplaystoallowresidentstoillustratevarious
scenarios.TheCountycontinuestohostthisinformationalmaterialontheCountyswebsite.
Figure 1
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Construction&OperationalCosts
Trafficsignalsandroundaboutscanbothhaveverydifferentimplicationswithregardtocostandright
ofwayimpact.Thecosttoinstallasteelpoletrafficsignalatalocationwherenoroadworkisneededis
currentlyintherangeof$250,000.However,trafficsignals,particularlyoncountyhighways,normally
requireleft
and
right
turn
lanes
to
be
present
in
order
to
operate
safely.
If
turn
lanes
are
not
yet
present,thecostofwideningtheroadwaysandinstallingatrafficsignalcanexceed$1millionevenfor
twolaneruralroadways.Whileatrafficsignalintersectiontypicallytakesuplessspacethana
roundabout,theneedforturnlanescanincreasetherightofwayimpactforaconsiderabledistance
fromtheintersection.
Roundaboutscanalsobeexpensivetreatmentstoinstall,inthattheytypicallyrequireafull
reconstructionoftheroadwayonallapproachesinordertoaccommodateaproperlydesigned
roundabout.However,inthecaseofRadioDriveatBaileyRoad,theroadwayswereinneedoffull
reconstructionandwideningevenifatrafficsignalorallwaystopwerechoseninsteadofthe
roundabout.Therefore,thecostofconstructingaroundaboutversusatraditionalintersectionasapart
ofthis
project
was
considerably
less
expensive.
Acostcomparison,calculatedduringthedesignoftheprojectwhichconsideredthecostofconstructing
eachalternative,estimatedthattheintersectionareawouldcostapproximately$677,000ifconstructed
asaroundabout,and$1,013,000ifconstructedasatrafficsignalduetotheneedforadditional
pavementforturnlanesandthetrafficsignalsystemitself.Thisestimateincludedroadwaycostsas
wellaselectricalinfrastructureandtemporaryeasementsforrightofwayimpacts.Theseestimatesdid
notincludethecostofpedestriantunnels,whichwerebeingconsideredforboththesignaland
roundaboutoptions.
Typicalmaintenanceandoperatingcostsforatrafficsignalincluderelamping,electricalcosts,repairof
damagecausedbyrodentsorlightning,repairofvehicledamageandequipmentfailure,andrepainting.
Thesecostswereassumedduringthedesignphasetobeapproximately$2000peryear.Thissame
studyconsideredtheoperatingcostsofaroundaboutandestimatedcostsof$5000peryear;however
thiscostestimatewasprimarilybasedonthemaintenanceoflandscapingincludedinthecenterisland
oftheroundabout,whichwasnotessentialtoroundaboutoperations.
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VehicularDelay
Whiletheroundaboutrequiresalltraffictoslowdowntonegotiatethecurvature,itwasprojectedto
operatewithlessoveralldelaythanatrafficsignalbymakingmoreeffectiveuseofavailablecapacity.
Becausethe
traffic
volumes
on
all
approaches
are
relatively
balanced,
atraffic
signal
would
be
expected
provideabout50%oftheavailablegreentimetoeachapproach.However,permissivephasingforleft
turns,whereleftturnsmayproceedafteryieldingtooncomingtraffic,wouldnothavebeenpermitted
underthedesignguidelinesinplaceatthetime.Therefore,thepercentageofgreentimeavailablefor
throughmovementswouldhavebeenfurtherreduced,withmostvehiclesarrivingduringaredsignal.
EvenwiththeadventofFlashingYellowArrowcontrol,throughtrafficcouldexpecttoarriveonared
signalmoreoftenthanagreensignal.
Fieldmeasurementsoftraveltimesthroughtheroundaboutwereconductedduringtheafternoonpeak
hoursinFebruaryandMarchof2011.Thecontroldelaywascalculatedbymeasuringthetimeneeded
todrivebetweentwofixedpointsonoppositesidesoftheintersectionapproximatelymileaway,and
thensubtracting
the
time
it
would
have
taken
to
travel
that
distance
at
aconstant
50
mph.
For
comparison,thesametestwasthenrepeatedattheintersectionofCSAH13(InwoodAve)andCSAH10
(10thStreetN)inLakeElmo,whichservessimilartrafficspeedsandvolumes,andiscontrolledbya
trafficsignalofidenticaldesigntowhatwouldhavelikelybeeninitiallyconstructedatRadioandBaileyif
theroundaboutoptionhadnotbeenselected.Figure2belowillustratesthelaneconfigurationand
averagedailytrafficvolumesateachintersection.
9500AADT
8200AADT
7700
AA
DT
7800AADT
6800AADT
11,000AADT
9200AADT
7500AADT
TrafficSignal
InwoodAve&10th
StreetN
(CSAH13
&
CSAH
10)
Roundabout
RadioDr&BaileyRd
(CSAH13
&
CSAH
18)
Figure 2
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Theinitialstudyconsistedofstudyingthetraveldelaytothroughmovementsonly.Eightmovements
wererecordedineachdirectionatboththeroundaboutandthecomparisonsignalizedintersection,for
atotalof32testrunsateachintersection.TheresultsofthesetraveltimesareshownbelowinFigure
3.Themeandelaytothroughtrafficattheroundaboutwasfoundtobe12.5seconds,which
incorporatestimelosttodeceleration,yielding,andacceleration.Atthetrafficsignalcomparisonsite,
theminimumdelaywaslower,sometimesallowingfreeflowpassageonagreensignal.However,the
meandelayatthetrafficsignalwas29.5seconds,morethandoublethemeasuredmeandelayattheroundabout.
Figure 3
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InAprilof2011,asimilarstudywasconductedtomeasurethedelaytoleftturnmovementsthrough
theroundaboutascomparedtothesignalizedintersectionofInwoodAveat10thStreetNorth.Aswith
thepreviousstudy,eighttestrunswereconductedfromeachapproachtotheroundabout,foratotalof
32leftturnmovements.Atthetrafficsignal,seventestrunswereconductedfromeachdirection,
ratherthaneight,inordertokeepthestudytimeperiod(4:155:15pm)consistentbetweenboth
intersections.Allmovementsatbothintersectionsincurredsomedelayduetotheneedtodecelerate
tonegotiatetheturn.TheresultsthesetraveltimesforleftturnareshowninFigure4.
Whilethetrafficsignalsometimesallowedpassagewithnodelay(greensignalandnoqueue),the
averagedelaytothroughmovementsatthetrafficsignalwas2.4timeshigherthantheaveragedelayat
theroundabout.Theseresultswereconsistentforleftturnsaswell,withthesignalizedintersection
onceagaincausing2.4timesmoredelaytoleftturnmovementsthantheroundaboutduringthepeak
hourof4:15pmto5:15pm.Additionally,theroundaboutdelaysweremoreconsistent,andtheneed
forafullstoptoyieldtoconflictingtrafficwasrare.
Figure 4
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CrashExperience
CrashesattheBailey/Radioroundabouthavebeencloselytrackedthankstocooperationfrom
WoodburyPublicSafetyofficials.Allcrashesattheroundabout,includingthosenotmeetingminimum
thresholdsfor
state
required
reporting,
have
been
forwarded
to
the
County
for
tracking
of
crash
statistics.Manyofthesecrashesareminororevenunverified,suchaswhennovehiclesarepresent
whenpolicearrive.Althoughitisdifficulttomakeatrue,objectivecomparisontoasignalized
intersection,itisclearthatthetotalnumberofcrasheshasbeenhigherattheroundaboutversus
signalizedintersectionswithinthefirsttwoyearsofoperation.
Manyofthesecrashes,particularlywithinthefirstsixmonthsofoperation,canbeattributedtothefact
thattheroundaboutwasopenedtotrafficinlateNovemberof2007,resultinginshortlivedpavement
markings.Thefreezingtemperaturesatthetimeofapplicationledtoaprematurefailureofthe
markings,thereforetheroundaboutoperatedwithoutlanestripinguntilearlysummerof2008when
finalpavingwascompleted.Thelackofstripinglikelycontributedthehighinitialcrashrate,and,more
importantly,likely
allowed
some
drivers
to
develop
or
retain
incorrect
assumptions
about
how
the
roundaboutwasintendedtooperate.
Intheabsenceofproperstriping,andevenafterpermanentstripingwasinstalled,manydriversappear
tohaveassumedthattheroundaboutwasstripedconcentrically,similartotheonewaycircleroadat
thenearbyTamarackVillageshoppingcenter(SeeFigure10aand11a).Thisincorrectassumptionleads
tothefollowingrelatedmisconceptions,allofwhicharetrueattheshoppingcenterbutfalseatthe
Radio/Baileyroundabout:
Thatenteringaroundaboutisarightturnmovement,andthatitisthereforeacceptabletoenteralongsidevehiclesalreadywithintheroundabout.
Thatitisacceptabletoenterintherighthand(outsidelane)tomakealeftturnoruturnthroughtheroundabout.
Thatvehiclesexitingfromtheinsidelaneoftheroundaboutmustyieldtovehiclesintheoutsidelane,ormakealanechangetotheoutsidelanebeforeexiting.
Publishedguidancefromstatedepartmentsoftransportationmayalsohavecontributedtothis
misconceptionbyoftenrecommendinguseofarightturnsignalwhenexitingtheroundabout,when
suchamovementisneitherarightturnnoralanechange.WashingtonCountyhasworkedwiththe
MinnesotaDepartmentofPublicSafety(DPS)DriverandVehicleServices(DVS)divisiontoclarify
guidanceintheMinnesotaDriversManualtoremovereferencestosignalingtoexitaroundabout,
howeverthisguidanceisstillwidelycirculatedfromothersources.
Failuretochoosetheproperlanefortheintendedmovementhasbeenaconcern,buthasnotbeenthe
prevailingcauseofreportedcrashes.Todate,thistypeofviolationhasbeencitedasacrashcause
approximatelyonce
every
two
months,
though
not
all
crash
reports
cite
aspecific
cause.
Despitethefactthatallapproacheshavespeedlimitsof50mphorhigher,collisionswiththecenter
islandhavebeenveryrareandhavenotresultedinverifiableinjuries.Yellowchevronsignswere
installedinthecenterisland,onthefarsideoftheapproachintersectiontomakeobvioustodriversthe
curvatureoftheroadwaythroughtheintersection,particularlyatnight.Damagehasalsooccasionally
occurredfromcollisionswiththeyieldsignsandwithcentermediandividers,butsuchcrashesdonot
appeartobemorefrequentthansimilarcrashesatstandardintersections.
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Byasignificantmargin,themostcommoncrashtypereportedattheroundaboutresultsfromafailure
ofenteringdriverstoyield.Whilemostdriversappeartounderstandthemeaningofayieldsign,itis
clearthatmanydriversfailtounderstandtowhichlanestheyarerequiredtoyield.Forexample,when
makingarightturnatayieldsign,suchasatachannelizedrightturnatatrafficsignal,driversneedonly
yieldtovehiclesintherighthandlane.However,becauseenteringaroundaboutisacrossing
movementratherthanarightturn,driversattheroundaboutmustyieldtobothlanesoftrafficfromtheleft.Whendriversyieldonlytotheouterlaneofcrossingtraffic,acrashcanresult.Supplementary
signswereaddedbelowtheyieldsignswhichreadTOALLTRAFFICINCIRCLE.However,the
installationofthesesignsdidnotresultinadropinthefrequencyofthiscrashtype.Thiswordingmay
alsoinadvertentlycontributetotherightturnmisconceptionbyreferringtotheroundaboutasacircle
roadway,asisthecasewithatrafficcirclewhereentryisalwaysarightturnmovement(SeeFigures10a
and10b).InMayof2011,thesesignswerereplacedwithplaquesreadingTOBOTHLANES.
Figure5belowshowsthenumberofcrashesreportedattheroundaboutinthreemonthintervalssince
theroundaboutopened.Failuretoyieldcrashesfrequentlymakeupmorethanhalfofthetotalcrashes,
whilecrashesfromimproperlaneuse(FailtoExit)tendtooccurmuchlessfrequently.Crashes
categorizedas
other
usually
lacked
any
description
of
the
crash
circumstances.
Figure 5
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AlthoughthetotalnumberofcrashesreportedtoWoodburyPublicSafetyhasbeenhigherthan
comparablesignalizedintersections,mostcrasheshavebeenpropertydamageonly,orwithoutany
verifiableinjuries.Allinjurycrashesandallcrasheswithpropertydamageexceeding$1000mustbe
reported,byMinnesotaStatute169.09,totheMinnesotaDepartmentofPublicSafety(DPS).The
severityofthesecrashesisassignedintothefollowingcategories:
PDPropertyDamageOnly
CPossibleInjury(Complaintsofpainorinjurywhichareunverifiableatthetimeofthereport) BNonIncapacitatingInjury(Verifiableinjury,rangingfromminorscrapestosignificantinjury)
AIncapacitatingInjury(Seriousinjurieswherethevictimisincapacitatedbythecrash)
KFatality
BasedoncrashesreportedtoDPSfromJanuary2008throughDecember2009,noverifiableinjuries
(CategoriesB,A,orK)occurredattheroundaboutduringthattime.AcomparisontootherWashington
Countysignalizedorallwaystopcontrolledintersectionswithcomparablevolumeisshownbelowin
Figure6.Althoughtheroundaboutshowsthehighestnumberoftotalcrashes,noverifiableinjuries
werereportedwithinthesefirsttwocalendaryearsofDPScrashdata.Asofthetimeofthepublication
ofthispaper,2010crashdatawasnotyetavailablefromDPS.
AllWay
Stops
Traffic
Signals
Figure 6
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TrafficControl
StripingandMarking
Asnoted
previously
in
this
report,
the
initial
striping
failed
to
properly
cure
due
to
very
low
application
temperaturesfollowingtheinitialpavingoftheroundaboutinNovemberof2007.Theroundaboutwas
stripedandopenedtotrafficonNovember30th,2007,followedseveraldayslaterbysubstantialwinter
stormwhichincluded8inchesofsnowintheareaoftheroundabout.
Thecombinedeffectsofvehicletraffic,snowandiceremoval,andunfavorableapplication
temperaturesledtoanearlyfailureofthepavementmarkings.Asaresult,theroundaboutoperated
withoutstripinguntilthespringof2008whenthefinalpavingwascompleted.Duringthistime,the
operationalconfigurationoftheroundaboutwouldnothavebeenapparenttodrivers,suchasthefact
thatlanestripingleadsoutoftheroundabout,ratherthanconcentricallyasisthecasewithatraffic
circle.Thisuncertaintyissuspectedofleadingtoahigherinitialcrashrateandalsoallowingdriversto
formmisconceptions
about
proper
roundabout
operations
even
after
permanent
striping
was
installed.
Theinitialroundaboutstripingfeaturedstandardpavementarrows,butfishhookarrowswerelater
installedinordertobeconsistentwithmarkingsbeingsimultaneouslyinstalledintheJamaicaAvenue
roundaboutsinnearbyCottageGrove.Someadjustmentshavebeenmadetothestripingsincethe
initialconstruction,includingatemporaryexperimentofusingsolidlinesratherthandashedlinesatthe
roundaboutexits,installationofwiderlineswithintheroundabouttoimprovevisibilityofthelane
configuration,andreplacementofthemarkingswithintheroundaboutwithmoredurablematerials.
Signing
Signingattheroundaboutconsistsofwarningsignstoimprovedriverawarenessoftheroundabout,regulatorysignstoassignrightofwayandlaneuse,andguidesigningtoproviderouteinformation.
Theuseofwarningsigns,specificallyyellowchevronsinthecenterislandanddiamondshapedwarning
signsontheroundaboutapproaches,havebeengenerallyeffective.Collisionswiththecenterisland
andfullspeedentrieshavenotbeenaprevailingcrashtype,whichcanbeattributedeithertothe
approachsigningortothegeometricchangestoroadwayontheroundaboutapproaches.
Theroundaboutwasinitiallysignedwiththreeregulatorylaneusesignson
eachapproach,firstasstandardlaneusearrowsandlaterupgradedtofish
hookdesignsasshowninthephotototheright(Figure7).Thesesignsare
intendedtoensurethatleftturnsareproperlypositionedintheinnerlanetopreventexitconflicts.Driverunderstandingofthismessagewas
especiallyimportant,giventhatstripingdidnotexistwithintheroundabout
formostofthefirstsixmonthsofoperation.However,italsobecame
apparentbasedoncrashreportsandconversationswithusersthat,
althoughthelaneusesignswerenecessaryforenforcement,neitherdesign
waswidelynoticednoradequatelyunderstoodbydrivers.
Figure 7
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Asaresultofconcernsoverdriverunderstandingofthelaneuseregulatorysigns,eightnewguidesigns
werecreatedcontainingdestinationinformation,andinstalledinMay2009inplaceoftwoofthethree
laneusesignsoneachapproach,asshowninthefollowingphoto(Figure8).Theintentwasto
communicatethesamemessageregardinglaneuseindifferentwaystoimproveeffectiveness.Crashes
resultingfromimproperlaneusegenerallyhavebeenminimalbothbeforeandafterthissigningchange,
soitisunknownwhetherthislowratecanbeattributedtothealteredsignageortootherfactors.
Inadditiontothelaneusesigns,otherregulatorysignsattheroundaboutincludetheYIELDsignsand
ONEWAYsignsinthecenterisland.Thegeometricdesignoftheroundaboutandtheonewaysigns
mountedinthecenterislandbothservetodeterdriversfromdrivingthewrongwayintothe
roundabout.Todate,nocrashhasbeenattributedtowrongwaymovements,norhasthecountybeen
madeawareofanyoccurrenceofwrongwaymovementsatthisroundabout.
YIELDsignsarepresentonboththeleftandrightsideofeachapproachtotheroundabout;howeverthe
prevailingcrashtypeattheroundaboutcontinuestoinvolveafailuretoyield,inwhichtrafficinthe
righthandenteringlanefailstoyieldtoavehiclewhoislawfullyexitingtheroundaboutinthelefthand
lane,asshowninFigure10b.Oncethiswasidentifiedasafrequentcrashtype,supplementaryplaques
wereaddedbelowtheyieldsignswhichreadTOALLTRAFFICINCIRCLEinordertoreinforcethe
requirementthat
entering
drivers
must
yield
to
both
lanes.
However,
the
installation
of
these
signs
did
notresultinadropinthefrequencyofthiscrashtype.Thiswordingmayalsoinadvertentlycontribute
totherightturnmisconceptionbyreferringtotheroundaboutasacircleroadway,asisthecasewith
atrafficcirclewhereentryandexitisalwaysarightturnmovement(SeeFigure10a).InMayof2011,
thesesignswerereplacedwithplaquesreadingTOBOTHLANES.Moredetailsonthistypeofcrash
canbefoundintheCrashExperiencesectionofthisreport.
Figure 8
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WorkZones
Oneuniquechallengethathasemergedattheroundaboutisthesetupoftemporarytrafficcontrols
whenmaintenanceworkisoccurringwithintheroundabout.Thestandardlayoutsfortemporarywork
zonesareoutlinedinPart6oftheMinnesotaManualonUniformTrafficControlDevices,whichshows
typicalwork
zone
configurations
for
awide
variety
of
roadway
and
intersection
scenarios.
However,
no
guidanceisgivenforthepropersetupofaworkzonewithinaroundabout.
WhenWashingtonCountyinstalledimprovedpavementmarkingswithintheroundaboutinspringof
2010,theCountysoughttodevelopaworkzonewhichkepttheroundaboutopentoallmovementsof
trafficanddidnotviolateanyoftheexistingsigningoroperationalprinciplesoftheroundabout.For
example,itwouldberelativelysimpletoclosetheleftlaneoftheapproachtotheroundaboutby
forcingalldriversintotherighthandlane.However,allowingdriverstothenproceedtomakealeft
turnfromtherighthandlanecreatedthepotentialthatdriverswouldrepeatthatbehaviorunder
normalconditionswhennoentrylaneswereclosed.
To
complete
this
work,
without
creating
a
situation
where
drivers
would
violate
any
of
the
rules
of
safe
roundaboutoperation,theCountydevelopedastagingplanfortheworkwithintheroundabout.
Becausethisstripingreplacementinvolvedworkwithinallfourquadrantsoftheroundabout,any
portionofthisstaginglayoutcouldbeusedforworkwhichrequirestheclosureofanyportionofthe
roundabout,solongasallentrancestotheroundaboutremainopen.Theselayoutsareattachedas
AppendixAtothisdocument.
TrafficEnforcement
Woodburypoliceofficershaveconductedtargetedenforcementeffortsattheroundabout,includinga
jointeffortwiththecooperationofWashingtonCountyengineeringstaffusingasharedchannelonthe
800
MHz
radio
system.
Police
reports
following
these
enforcement
efforts
reinforce
that
the
most
commontypeofviolationisfailuretoyield,andthatdriversfailuretoyieldoccursmuchmore
frequentlythanactualcrashesbecausemostdriversareabletoavoidacollisionbybraking.
Failuretoyield,bothfromfieldobservationsandfromcrashreports,mostoftenconsistsofadriver
enteringintherighthandlanefailingtoyieldtoadriverexitingfromtheinsidelaneoftheroundabout,
asillustratedinFigure10b.Policereportsfollowingcrashes,andpolicediscussionswithdriversduring
enforcementefforts,confirmthatthereisapervasivemisunderstandingamongdriversthatitis
acceptabletoenteralongsidecirculatingvehicles.Otherdriversappeartoapproachtheroundaboutat
ahigherrateofspeed,slowingenoughtonegotiatetheroundaboutbutnotslowlyenoughtostopfor
conflictingtraffic.
Theseobservations
confirm
that
the
most
important
factor
to
improving
safety
at
the
roundabout
is
to
improvepropercompliancewiththeyieldsignsandtoensurereasonableapproachspeedstotheyield
signssothatdriversareabletostopwhennecessary.Additionally,Countystaffworkedwithpublic
safetyofficerstodevelophandoutsspecifictothetwomostcommontypesofviolations,sothatofficers
canmoreclearlyexplaintodriversthetypeofviolationthattheycommittedandwhytheviolationwas
potentiallyhazardous.ThesehandoutsareattachedasAppendixBtothisdocument.
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Page|13
SpecialUserGroups
CommercialVehicles
Norecurringproblemsinvolvingtrucksorbuseshavebeenreportedattheroundabout.Therewasone
incidentwhere
an
over
height
truck
struck
an
overhead
utility
line,
though
this
was
not
directly
related
totheroundabout.Whiletrucksorbusesmaysometimesintentionallystraddlelanesontheapproach,
thisisnotconsideredhazardousasitsafelypreventsothervehiclesfromdrivingalongsidethroughout
theentireturn.Similarly,thetruckaproninthecenteroftheroundabouthasbeenableto
accommodatetrucktrailerwheelsduringleftturns,andencroachmentbyothervehiclesontothetruck
apronhasnotbeenarecurringproblem.
Pedestrians
Althoughpedestrianaccommodationshavebeenamajoritemofdiscussionforroadagencieswhen
installingmultilaneroundabouts,pedestrianissueshavenotbeenafactorattheBaileyRoad
roundaboutbecauseofthepedestrianunderpasseswhichwereprovidedaspartoftheproject.No
pedestriancrasheshavebeenreportedatorneartheroundabout,norhastherebeenanyreportofothercrimeinthetunnelsapartfromoccasionalgraffiti.Additionaltunnelsmaybeaddedduringfuture
roadwideningortrailprojectsinthearea.
EmergencyVehicles
WoodburyPublicSafety,whichoperatespolice,fire,andemergencymedicalserviceswithintheCityof
Woodbury,indicatedinearly2011thattherehadbeennoreportsofanyproblemswithoperating
emergencyvehiclesthroughtheroundabout.
PublicSupport
Publicsupportforroundaboutsremainsfairlystrong.Ina2007residentsurveyconductedbytheCityof
Woodbury,54%ofresidentssupportedconstructionofmoreroundabouts.In2009,thatpercentage
hadincreasedto68%ofthosesurveyed.ThesesurveyresultsareillustratedbelowinFigure9.
Figure 9
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Page|14
Conclusions&NextSteps
Theselectionoftheroundaboutdesign,asopposedtoatraditionaltrafficsignal,reducedinitial
constructioncosts,reducedpropertyimpacts,andhashandledheavytrafficvolumeswithminimaldelay
comparedtocomparablesignalizedintersections.Theroundabouthasalsoperformedwellin
comparisonto
similar
signalized
intersections
with
regard
to
injury
crashes.
Theroundabouthas,however,beenthesiteofanabnormallyhighrateofpropertydamagecrashes,
manyofthemattributabletoafailuretoyieldbyenteringdrivers.Mostnotably,thesecrashestendto
involveaspecificpatternofrightlaneentryvehicleswithinsidelaneexitingvehicles.Asindicatedby
driverstatementsincrashreportsandthecrashpatternitself,theproblemstemsfroma
misunderstandingoftheroundaboutratherthantheconspicuityofthesignsormarkings.Drivers
mistakenlyassumethattheroundaboutoperateslikeatrafficcircle,inwhichentriesandexitsareright
turns.Underarightturnconfiguration,itwouldbeacceptabletoenteralongsidecrosstrafficsolongas
thedestinationlaneisfreeofconflictingtraffic,asisthecaseatthenearbyTamarackVillageshopping
center.AcomparisonofthesetwolocationsisshownintheFigures10and11.
TamarackVillageShoppingCenterCircleRoad
Woodbury,MN
Entryandexitisarightturnmovement.
Leftlanecannotexitthecircle.
Entryalongsidecrosstrafficisacceptable.
RadioDr&BaileyRdRoundabout
Woodbury,MN
Entryandexitisacrossingmovement.
Leftlanemayexitandhasrightofway.
Entryalongsidecrosstrafficresultsincrash.
Figure 10a Figure 10b
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Fordrivers,therightturnmisconceptionisanunderstandablemistake,asthesigningconfigurationboth
theroundaboutandtheTamarackVillagecircleroadappearexceptionallysimilartodrivers,asshown
belowinFigures11aand11b.Althoughtherearemajordifferencesinthegeometry,striping
configuration,circlediameter,andlaneassignmentrules,thesedifferencesindesignfeaturesare
unlikelytobenoticedorunderstoodbymostdrivers.
Anysuccessfulremedytothisproblemmusttargettherightturnmisconceptionandmakecleartoall
driversapproachingtheroundaboutthatentryalongsidecrosstrafficinthefarlane,although
Figure 11a
Figure 11b
TamarackVillageShoppingCenterCircleRoad Entryalongsidecrosstrafficisacceptable.
RadioDr&BaileyRdRoundabout Entryalongsidecrosstrafficresultsincrash.
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Page|16
acceptableatatrafficcircleorrightturnlocations,isnotacceptableataroundaboutandcanresultina
crash.Toaddressthisproblem,thefollowingstepshavealreadybeentaken:
1. TheadditionofsupplementaryplaquesbelowtheYIELDsignswhichreadTOALLTRAFFICINCIRCLEinfallof2008(RemovedinMay2011Seebelow).
2. Installationofwiderlanestripeswithintheroundabout,tomakethelanearrangementclearertoenteringdriverswhoviewthesemarkingsfromtheside.
3. WorkingdirectlywiththeMinnesotaDepartmentofPublicSafetyDriverandVehicleServicesdivisiontoimprovetheinstructionprovidedintheMinnesotaDriversManualasitrelatesto
multilaneroundabouts.
4. ContinuingtoadaptWashingtonCountysRoundaboutUeducationalmaterialstofocusonexplanationofproperyielding,includingreplacingtheoriginalillustrationwithanottoscale
drawingwhichmoreclearlyemphasizesthefunctionaldifferencesbetweenaroundaboutanda
trafficcircleorotherrightturnconditions.
5. InclusionofeducationalmaterialsintheCountysStayingInTouchnewsletter,senttoallCountyresidents,andasimilareducationalpieceintheCitysresidentnewsletter.
6. WorkingwiththeWoodburyPolicetoconductandfacilitatetrafficenforcementattheroundabout,includingdevelopinghandoutsexplainingspecificviolationstodrivers.
Inadditiontotheongoingeffortslistedabove,inearly2011theCountyreplacedthesupplementary
plaquestoreadTOBOTHLANESratherthanthepreviouswordingofTOALLTRAFFICINCIRCLE,in
ordertominimizepotentialconfusionwithatrafficcirclewhereentryandexitmovementsoperateas
rightturns.Otherstepsunderconsiderationincludeinstallationofadditionalpavementarrowswithin
theroundaboutnearertotheentrypoint,theadditionofyieldlinesorotherpavementmarkings,and
workingwiththeownersoftheshoppingcentertoregardingtrafficcontrolattheircircleroadtoclarify
todriversthattheirroadwaydiffersfromaroundaboutwithregardtodriverrequirements.
Asaprofession,engineersshouldworktodefinethefunctionaldifferencesbetweenamodern
roundabout,atrafficcircle,andothercircularintersectiontypes.Signingstandardsanddriver
education
should
clearly
reflect
these
differences
to
reduce
driver
errors
resulting
from
this
confusion.
Otherrecommendationsforfuturemultilaneroundaboutprojectswouldincludethefollowing:
1. Nevercharacterizeroundaboutentriesandexitsasrightturns,eitherverballyorinprint,unlessadriverisactuallymakingarightturn,suchasenteringnorthboundanddepartingeastbound.
a. Donotuserightturnarrowsonapproachestosinglelaneroundabouts.b. Donotstripeacrosstheexitsofroundabouts.c. Donotrecommendthatdriversusearightturnsignaltoexitaroundabout.
2. Ensurethatproperstripingisavailableupontheopeningofaroundabouttotraffic.3. Beawareofothercircularshapedintersections,bothlocallyandelsewhere,thatmayshape
driverperceptionsofproperbehaviorataroundabout.
4. Avoidprovidingmorecapacitythanisneeded.Doingsomayincreasedriversentryspeedsandincrease
the
potential
for
improper
lane
use
maneuvers.
5. Workcloselywithotheragencies,drivereducators,andlocalmediatoensurethataconsistentmessageissharedwiththepublic.
WashingtonCountycontinuestoviewroundaboutsasaneffectiveandviablealternativetotraffic
signals.However,theneedtoreducethefrequencyofpropertydamagecrashesattheRadio/Bailey
roundaboutwillcontinuetobeaprimaryfocusofCountyefforts,bothtoimprovesafetyandtoimprove
publicsupportforotherprojectswhereroundaboutdesignsmightemergeasthepreferredalternative.
[End]
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Page|17
AppendixAWorkZoneLayouts
Spring2010
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19/25
NOTES:
1.
Lane
Lines:
8w
idew
ith6fts
tripe,
3ftgap
repea
ting.
One
6s
tripes
ha
llbecen
tere
d
across
the
incom
ing
lane
s,
witho
therspac
ing
measure
dfrom
tha
tpoin
t.
2.
Lanec
losuresonapproac
hess
ha
llinc
lude
advancewarn
ings
igns,i.e.
Le
ftLane
Close
d
3.
Roa
dWork
Ahea
ds
igns
ona
llapproac
hesa
t
alltimes.
4
Useo
fc
hanne
lizing
devicess
ha
llcon
form
to
Stag
e1B
A
B
A B
Stage1A
Stag
e1B
Stage1A
Type3barricade
ClosureArea
Activework
CompletedWork
A:
Type
3barr
ica
des
ha
ll
inc
lude
Roa
dClose
dw
ith
de
tourarrowpo
intingrig
ht.
B:Type
3barr
ica
des
ha
llbe
pla
ce
dinme
diana
tnex
t
me
dianopen
ingw
ithde
tour
arrowpo
inting
leftan
ds
ign
rea
ding
U-T
URNHERE
7/29/2019 Roundabout 2-Year Study - City Copy
20/25
A
B
A
B
Stag
e2B
Stage2A
Type3barricade
ClosureArea
Activework
CompletedWork
A:
Type
3barr
ica
des
ha
ll
inc
lude
Roa
dClose
dw
ith
de
tourarrowpo
intingrig
ht.
B:Type
3barr
ica
des
ha
llbe
pla
ce
dinme
diana
tnex
t
me
dianopen
ingw
ithde
tour
arrowpo
inting
leftan
ds
ign
rea
ding
U-T
URNHERE
NOTES:
1.
Lane
Lines:
8w
idew
ith6fts
tripe,
3ftgap
repea
ting.
One
6s
tripes
ha
llbecen
tere
d
across
the
incom
ing
lane
s,
witho
therspac
ing
measure
dfrom
tha
tpoin
t.
2.
Lanec
losuresonapproac
hess
ha
llinc
lude
advancewarn
ings
igns,i.e.
Le
ftLane
Close
d
3.
Roa
dWork
Ahea
ds
igns
ona
llapproac
hesa
t
alltimes.
4
Useo
fc
hanne
lizing
devicess
ha
llcon
form
to
7/29/2019 Roundabout 2-Year Study - City Copy
21/25
A
B
A
B
Stag
e3B
Stage3A
Type3barricade
ClosureArea
Activework
CompletedWork
A:
Type
3barr
ica
des
ha
ll
inc
lude
Roa
dClose
dw
ith
de
tourarrowpo
intingrig
ht.
B:Type
3barr
ica
des
ha
llbe
pla
ce
dinme
diana
tnex
t
me
dianopen
ingw
ithde
tour
arrowpo
inting
leftan
ds
ign
rea
ding
U-T
URNHERE
NOTES:
1.
Lane
Lines:
8w
idew
ith6fts
tripe,
3ftgap
repea
ting.
One
6s
tripes
ha
llbecen
tere
d
across
the
incom
ing
lane
s,
witho
therspac
ing
measure
dfrom
tha
tpoin
t.
2.
Lanec
losuresonapproac
hess
ha
llinc
lude
advancewarn
ings
igns,i.e.
Le
ftLane
Close
d
3.
Roa
dWork
Ahea
ds
igns
ona
llapproac
hesa
t
alltimes.
4
Useo
fc
hanne
lizing
devicess
ha
llcon
form
to
7/29/2019 Roundabout 2-Year Study - City Copy
22/25
A
B
A
B
Stag
e4B
Stage4A
Type3barricade
ClosureArea
Activework
CompletedWork
A:
Type
3barr
ica
des
ha
ll
inc
lude
Roa
dClose
dw
ith
de
tourarrowpo
intingrig
ht.
B:Type
3barr
ica
des
ha
llbe
pla
ce
dinme
diana
tnex
t
me
dianopen
ingw
ithde
tour
arrowpo
inting
leftan
ds
ign
rea
ding
U-T
URNHERE
NOTES:
1.
Lane
Lines:
8w
idew
ith6fts
tripe,
3ftgap
repea
ting.
One
6s
tripes
ha
llbecen
tere
d
across
the
incom
ing
lane
s,
witho
therspac
ing
measure
dfrom
tha
tpoin
t.
2.
Lanec
losuresonapproac
hess
ha
llinc
lude
advancewarn
ings
igns,i.e.
Le
ftLane
Close
d
3.
Roa
dWork
Ahea
ds
igns
ona
llapproac
hesa
t
alltimes.
4
Useo
fc
hanne
lizing
devicess
ha
llcon
form
to
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Page|18
AppendixBLawEnforcementHandouts
Summer2010
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24/25
In this type of crash,Vehicle 1 is at faultfor failing to yield. Per
the lane use signs andmarkings, the insidelane of the roundaboutis allowed to exit or toturn left and continuearound. Enteringvehicles must yield toALL traffic from theleft, not just traffic inthe outside lane.
1
2
2
1
Entering a roundabout is similar to an intersection betweentwo one-way roads, where the road from the left continuesout of the roundabout. To proceed into the roundabout,entering drivers must yield to all traffic from the left, waiting
until all traffic from the left is clear.
Unlike a traffic circle, drivers are not permitted to enteralongside vehicles circulating in the left lane, because thosecirculating vehicles are allowed to exit the roundabout.
Extra signs mountedbelow the yield signsremind drivers to yieldto both lanes. Never
enter unless all trafficfrom the left is clear.
Learn more on the webat www.co.washington.mn.us
Click on Roads & Transitand then on Roundabout U
Or contact the Washington CountyPublic Works Department at
(651)-430-4300
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In this type of crash,Vehicle 1 is at faultfor failing to obey thelane use signs andchoosing the incorrect
lane. Drivers wishingto turn leftmustbe inthe left (inside) lanebefore entering theroundabout.
As with any other intersection, the proper lane must be chosenbefore entering a roundabout. Signs in advance of the intersectionwill always indicate which lanes may be used to turn or to continueahead. As with any other intersection, keep left to turn left through
the roundabout, and keep right to turn right. Never change laneswithin an intersection, including within roundabouts.
At Radio Drive and Bailey Road, lane use signs require thatdrivers turning left must use only the left (inside) lane, preventingthe type of crash shown below.
Learn more on the webat www.co.washington.mn.us
Click on Roads & Transitand then on Roundabout U
Or contact the Washington CountyPublic Works Department at
(651)-430-4300
In this type of crash,
Vehicle 1 is at faultfor failing to yield. Perthe lane use signs andmarkings, the insidelane of the roundaboutis allowed to exit or toturn left and continuearound. Enteringvehicles must yield to
In this type of crash,
Vehicle 1 is at faultfor failing to yield. Perthe lane use signs andmarkings, the insidelane of the roundaboutis allowed to exit or toturn left and continuearound. Enteringvehicles must yield to
In this type of crash,
Vehicle 1 is at faultfor failing to yield. Perthe lane use signs andmarkings, the insidelane of the roundaboutis allowed to exit or toturn left and continuearound. Enteringvehicles must yield to
Multiple signs and
pavement markingson every approachremind drivers of theneed to choose theproper lane. Failureto use the proper lanecan result in a trafficticket or a crash.
2
1
2
1
Lane use signs requirethat drivers choose theproper lane before theyenter the intersection.Similar signs are used attraditional intersectionsas well, and preventvehicle paths from
crossing improperly.
Drivers in the outside(right) lane are notallowed to turn left, theyare required to exit the
roundabout. Drivers inthe left lane may exit orturn left.
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