Roundabout 2-Year Study - City Copy

7/29/2019 Roundabout 2-Year Study - City Copy

1/25

TwoYearsLater:Safety,Operations,andEducationLessonsfrom

MinnesotasFirst

Two

Lane

Roundabout

Final City Version

June 7, 2011


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Page|1

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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Page|5

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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Page|8

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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Page|9

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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Page|10

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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Page|11

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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Page|12

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.


14/25

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


15/25

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


16/25

Page|15

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.


17/25

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


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


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


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


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


23/25

Page|18

AppendixBLawEnforcementHandouts

Summer2010


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


25/25

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





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.

Roundabout 2-Year Study - City Copy

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Transcript of Roundabout 2-Year Study - City Copy