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ALTERNATIVEINTERSECTIONDESIGNSTRATEGIES

HowGeorgiaandtheU.S.areChangingOutdatedTransportationDesignTechniques

MarcusH.AshdownMCRP2015

GeorgiaInstituteofTechnologySchoolofCityandRegionalPlanningGraduateAdvisor:MichaelDobbins

ALTERNATIVEINTERSECTIONDESIGNSTRATEGIES:

HowGeorgiaandtheU.S.AreChangingOutdatedTransportationDesignTechniques by

MarcusH.Ashdown

Anoptionpapersubmittedtothefacultyofthe

SchoolofCityandRegionalPlanning

inpartialfulfillmentoftherequirementsforthedegreeof

MasterinCityandRegionalPlanning

SchoolofCityandRegionalPlanning

GeorgiaInstituteofTechnology

April2015

ABSTRACT

ALTERNATIVEINTERSECTIONDESIGNSTRATEGIES:

HowGeorgiaandtheU.S.AreChangingOutdatedTransportationTechniques

MarcusH.Ashdown

MasterofCityandRegionalPlanning

GeorgiaInstituteofTechnology:SchoolofCityandRegionalPlanning

Themostdeadlylocationsonourroadsaretheintersections.A2008studyfound

thatstop‐controlledintersectionswereresponsiblefor70%ofthedeathsonUnitedStates

roadwaysthatyear.Thealarmingsignificanceofoneparticularaspectofthetransportation

systemhavingsuchanegativeeffectonhumansafetyyearafteryearhaspropelled

reconsiderationintothedesignstrategiesofourroadwayintersectionsandhavefueledthe

needforoptionsindesignasopposedtoonescriptedmethod.Localandnationalexamples

ofalternativedesignstrategiesareoccurringatafasterrate,furtherdemonstratingthat

thestrengthsandweaknessesassociatedwitheachstrategyarelargelydependentonsite‐

specificcircumstances.Thispaperpresentsamyriadofcasestudiesthatoutlinethe

successfulimplementationofalternativedesignstrategiesinadditiontothelocal

circumstancesthatmadethemsuccessful.Itisthepurposeofthisstudytodemonstratethe

newstandardofalternativedesignconsiderationsalongwithdevelopedexamplesofthose

stillless‐commonintersectiontypes.Thesedeliberationsareconductedinaneffortto

combatinvestmentfearsandpromoteamoresuccessfulandappropriatedesignofour

transportationsystem.

ACKNOWLEDGMENTS

Myday‐by‐dayabilitytoaccomplishnotonlythispaperbutmygraduatedegreeasawholeisalmostentirelyduetotheconsistenteffortandsacrificeofmydearwifeChelsea.Yoursupportpairedwiththeunwaveringloveofourtwobeautifulgirlsmadethisachievementpossible.Awayfromthehomefront,myadvisorMichaelDobbinsprovidedthereal‐worldperspectiveintomyresearchwithconsistentinsightfromtheamazingcareerthathehasled.Lastly,mywonderfulparents,whomareresponsibleforeverygooddecisionateachstepoflifethathasgotmetowhereIamtoday,thankyou.

TABLEOFCONTENTS LISTOFTABLES……………………………………………...……………………….………………………………………………..i

LISTOFFIGURES................................................................................................................................................................ii

1 INTRODUCTION.........................................................................................................................................................1

1.1 ProblemStatement.........................................................................................................................................1

1.2 Objective.............................................................................................................................................................4

1.3 Background........................................................................................................................................................6

2. LITERATUREREVIEW...........................................................................................................................................7

2.1 IntersectionSafetyImplementationPlanning.....................................................................................8

2.2 IntersectionDesignGuidelines................................................................................................................10

2.3 ProvenSafetyCountermeasuresandSafetyStrategies.................................................................10

2.4 Accuracyvs.Precision.................................................................................................................................12

3. NON‐MOTORISTCONSIDERATION...............................................................................................................12

3.1 Site‐SpecificConsideration........................................................................................................................13

3.2 TheCompleteStreetsMovement............................................................................................................14

3.3 PedestrianSignals.........................................................................................................................................15

4. TRAFFICCALMINGSTRATEGIES...................................................................................................................16

4.1 CurbExtensions.............................................................................................................................................16

4.2 WoonerfDesign..............................................................................................................................................17

4.3 Road“Wiggle”orChicanes........................................................................................................................20

4.4 IntersectionRetrofit/RoadDiet.............................................................................................................21

5 ALTERNATIVEDESIGNSTRATEGIES...........................................................................................................25

5.1 TrafficCircles..................................................................................................................................................26

5.2 Ovalabout..........................................................................................................................................................27

5.3 AccessManagementTechniques............................................................................................................28

5.4 ReducedConflictIntersections................................................................................................................31

5.5 ContinuousFlowIntersections................................................................................................................33

6 TRAFFICOPERATIONSSTRATEGIES...........................................................................................................35

6.1 TrafficSignalCoordination........................................................................................................................35

6.2 TheBarnesDance..........................................................................................................................................37

6.3 FlashingYellowArrow................................................................................................................................38

7 POLICYSTRATEGIES.............................................................................................................................................39

7.1 SpeedLimitReduction................................................................................................................................40

7.2 DesignGuidelineImplementation..........................................................................................................42

8 LOCALCASESTUDIES...........................................................................................................................................43

8.1 MidtownTrafficOperationsProgram...................................................................................................43

8.2 AshfordDunwoodyDivergingDiamondInterchange....................................................................47

8.3 PleasantHillDivergingDiamondInterchange..................................................................................47

8.4 ContinuousFlowInterchangeinDawsonville...................................................................................52

9 NATIONALCASESTUDIES..................................................................................................................................55

9.1 RoundaboutImplementationinMaryland.........................................................................................55

9.2 NewYorkCity.................................................................................................................................................56

10 CONCLUSION........................................................................................................................................................60

REFERENCES......................................................................................................................................................................62

i

LISTOFTABLESTable1.ConflictPointandCrashRateRelationship.................................................................................................4

Table2.Mid‐blockandIntersectionCrashRatesbyMedianType...................................................................30

Table3.TravelTimeRunResults‐SpringSt.............................................................................................................45

Table4.AirPollutantImpact‐SpringSt......................................................................................................................46

Table5.LevelofServiceAnalysisforDawsonvilleCFI..........................................................................................54

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LISTOFFIGURES Figure1.Vehicle‐to‐VehicleConflictPointLocationsat4‐WayandCircleIntersections........................2

Figure2.Vehicle‐to‐PedestrianConflictPointLocationsat4‐wayandCircleIntersections...................2

Figure3.Vehicle‐to‐VehicleConflictPointLocationsatTandCircleIntersections....................................3

Figure4.Vehicle‐to‐PedestrianConflictPointLocations.......................................................................................3

Figure5.IntersectionSafetyImplementationPlanProcess..................................................................................9

Figure6.ExampleofCompleteStreetproject..........................................................................................................15

Figure7.CrossingwithPedestrianBeaconinMidtown,Atlanta......................................................................16

Figure8.ExampleofChannelizedCurbExtensionforDrainage.......................................................................17

Figure9.WesternexitofAppletonStWoonerf,Boston........................................................................................18

Figure10.EasternEntranceofAppletonStWoonerf,Bost.................................................................................19

Figure11.RoadWigglewithChicaneonMemorialDr..........................................................................................20

Figure12.AtMemorialDr,CottageGroveand4thSt............................................................................................21

Figure13.OverviewofareaaroundMemorialDr.andCottageGroveintersection.................................22

Figure14.CottageGroveRetrofitProposalonMemorialDr..............................................................................22

Figure15.EastLakeBlvdandMemorialDr...............................................................................................................23

Figure16.EastLakeBlvdRetrofitProposalonMemorialDr.............................................................................24

Figure17.MemorialDrbetweenGreenandOakridgeAvewithaccesspointsmarked..........................25

Figure18.RoundaboutConflictPointLocations......................................................................................................26

Figure19.RoundaboutVehicle‐to‐PedestrianConflictPointLocations......................................................26

Figure20.OvalaboutConceptDesignatMemorialDr.andWhitefoord........................................................27

Figure21.ReducedConflictIntersectionDiagram..................................................................................................32

Figure22.ContinuousFlowIntersectionDiagram..................................................................................................33

Figure23.4‐PhaseSignalCycleTimes………………………………………….....………………………………………….32

Figure24.ConflictPointLocationsatCommonCFI................................................................................................34

Figure25.Traditionalvs.CFIConflictPointLocations..........................................................................................35

Figure26.Time‐SpaceDiagramfromTrafficModelingSoftware.....................................................................36

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Figure27.TimeSpaceDiagramofSpeedingVehicleHittingSuccessiveLights..........................................37

Figure28.PedScrambleinDenver................................................................................................................................38

Figure29.Pedestrian’sChanceofDeathifHitbyaMotorVehicle...................................................................41

Figure30.MTOPProjectAreaandCoordinatedSignals.......................................................................................44

Figure31.DDIOperationsDiagram...............................................................................................................................48

Figure32.ExampleofSPUIformfromI‐40inDurham,NC.................................................................................49

Figure33.OverviewofcompletedPleasantHillDDI..............................................................................................50

Figure34.DDIEffectivenessMeasurements.............................................................................................................51

Figure35.DawsonvilleCFIVISSIMmodelwithturningmovementsadded................................................53

Figure36.BenefitCostAnalysisforDawsonvilleCFI.............................................................................................54

Figure37.BeforeandaftercomparisonofWestHoustonStreet......................................................................59

(PageIntentionallyLeftBlank)

1

1 INTRODUCTION

Wehaveprobablyallhadtheexperiencewhereweareinourcar,stoppedatared

light,watchingthenextsignaloneblockawayholdagreenlightwithnoonegoingthrough

theintersection,onlyforthesignaltoturnredassoonasyoureachit.Likewiseithas

probablybeenapastdrivingdecisiontocircumnavigateaparticularintersectionor

interchangebecauseoffrequentcongestionatthelocation.Althoughdesigncannotsolve

allproblemswefaceontheroad,ithasbeenproven,aswillbepresentedwithmanycases

inthispaper,thattheconfigurationofaroadwayorintersectioncanhaveasignificant

impactondriverdecision‐makingaswellasoverallabilitytomeettheobjectivesthatwere

hopefullyenvisionedwhenthesitewasdeveloped.

Thispaperisprimarilyacasestudyanalysisofthemethodsleadingthewayin

impactingtheweaknessesintheconventionalfour‐waystopsignalizedintersection.Some

methodsareasoldorolderinconceptthanthefour‐waystopbuthavejustbeguntogain

tractioninthepastdecadeortwoastheresearchandexperienceinthestrengthsand

opportunitiesofsomeofthesealternativemethodscontinuestogrow.Althoughlocal

exampleshereinGeorgiaaretheprimaryfocusofthispaper,somenationalexamplesof

alternativeintersectiondesignareincludedwithadditionalstrategiesthoseeffortsbringto

thesubject.

1.1 Problem Statement

AccordingtotheNationalHighwayTrafficSafetyAdministration,70%ofallfatalcar

crashesthatoccurredintheUnitedStatesin2008occurredatastop‐controlled

intersection(NHTSA2008);furthermore,ithasbeenfoundthat35%ofallvehicle

collisionsoccurataroadwayintersection(GreenandAgent2003).Intersectionsprovide

forthesuccessofourroadwaynetworkastheyenhanceaccessandfacilitateahigherlevel

ofefficiencyintravelwithmoreconnectionstoalternativenetworklinks.Itistherefore

ironicthatakeyandnecessaryfeatureofacomprehensivetransportationnetworkisalso

themostdeadlyaspectofthatsystem.

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Thereare32vehicletovehicleconflictpointsand16vehicle‐to‐pedestrianpoints(4

ateachapproachfromrightturnandthroughmovementsgoingeachdirection)inthe

conventional4‐wayintersection.Thereasonwhythereismorethanonevehicle‐to‐

pedestrianconflictpointforeachapproachandexitisbecausethedesignofthe

intersectionlendsfortheright‐turnmovementtopresentapointofconflictthatisslightly

differentthanthethroughandleft‐turnmovements,whichmergeontothesamevehicle

pathbeforereachingthepedestriancrosswalk.Additionally,giventhatconventional4‐way

intersectionsgenerallypermitarightturnonaredlight,theconflictpointispresented

continuouslyandnotwithcertainphasesofacycle.

Figure1.Vehicle‐to‐VehicleConflictPointLocationsat4‐WayandCircleIntersections.Source:Monroe,2001

Figure2.Vehicle‐to‐PedestrianConflictPointLocationsat4‐wayandCircleIntersections.

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Thepreviousfigureshowsthestarkreductionofconflictpointsbetweena

conventional4‐wayintersectionandatrafficcircle.Intotal,thereare75%fewervehicleto

vehicleconflictpointsatatrafficcircleand50%fewervehicletopedestrianconflictpoints.

Thenumberofconflictpointsinathree‐wayor“T”intersectionarealsosignificantlylower

thanafour‐wayintersectionwith9vehicle‐to‐vehiclepoints,70%fewerthan4‐way,and

10vehicle‐to‐pedestrianpoints,40%fewer.Likewise,asdepictedbelow,athreewaytraffic

circlehasfewerconflictpointsthanathree‐way,stop‐controlledintersection.

Figure3.Vehicle‐to‐VehicleConflictPointLocationsatTandCircleIntersections.Source:Monroe,2001

Figure4.Vehicle‐to‐PedestrianConflictPointLocations

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Thenumberofconflictpointsatanintersectionhasameasurableimpactonthe

numberofcollisionsthatcanbeexpectedtooccuratanintersection.Thefollowingcrash

ratesaredeterminedbythenumberofcollisionspermillionvehiclesenteringthe

intersectionandwerecalculatedbyCalTransandMNDOT.Theresultsdemonstratethe

relationshipbetweenthenumberofconflictpointspresentatanintersectionandthe

amountof“realizedrisk”(crashes)thatoccuratthatintersection(Monroe,2001).

Table1.ConflictPointandCrashRateRelationship(permillionvehiclesenteringintersection)

4‐Way Stop‐controlled

3‐Way Stop‐controlled

4‐wayTrafficCircle

Numberof ConflictPoints

32vehicle 16ped

9vehicle 10ped

8vehicle 8ped

CrashRate 0.77 0.47 .25 Source:Monroe,2001

Astheperformanceofanyintersectionorroadwaysegmentisjudgedbyitslocal

useandhowwellitservesthecommunitiesthatittiestogether,theprioritiesand

objectivesofintersectiondesignwilldifferfromlocationtolocation.Thisisthefirstreason

whytheone‐size‐fits‐allapproachwiththe4‐waystopthathasbeenusedforthegreater

partofthelastcenturyisnotappropriateateverylocationandcanresultinalow

performanceforanytravelexperience.

1.2 Objective

Becausetransportationprojectscommonlyhavenotonlyahighpricetagbutinduce

socialandfurtherdevelopmentimplicationsforyearsandevendecades,thereisacommon

fearofinvestmentintocreativesolutionstoeverydayproblems.Althoughthisfearis

understandable,itisincreasinglyunfoundedasmunicipalities,communities,planning

boards,privateinvestorsandmorecontinuallybreakthemoldonhowweimpactthe

usabilityofourtransportationnetworkinmorewaysthanjustvehicleoperations.The

overarchingobjectiveofthispaperistomeasuredeveloped”alternative”strategiesintheir

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abilitiestomeetlocaldemandandsolvemobilityconcerns.Theamountofobservedand

testedexamplesincludedinthisargumentdemonstratethatthese“creativesolutions”are

notonlybeingincreasinglyimplementedandstudiedinlocationsacrossthecountrybut

becomingthenewstandardinsomelocations,givenqualifyingfeasibilityfortheparticular

strategy.Nomorearethedayswhereafearoftheunknowndictatedthedismissalofanon‐

standardsolutionatthereplacementofa4‐waystop‐controlledintersectionthatfits

poorlyandcreatesadditionalinefficienciesandhazardsonourroadways.

Therearefourgeneralmeasurestothefunctionofanintersectionthatcaneitherbe

aprioritystrengthorsupportingfactortotheperformanceofanintersection.Asthe

differentdesignstrategiesarepresentedinthisanalysis,thesemeasureswillbeusedto

weighthedifferingmethodsemployedtoengagewithlocalneedsandfuturedemand.Itis

theobjectivethatallstrategies,includingtheconventional4‐waystop,willbeshownto

haveacriterionofstrengthsandweaknessesthatmustbeconsideredupon

implementation.Thefourjudgmentcriteriaare:

● Safety

● Efficiency

● SenseofPlace

● Accessibility

Safetyisaprimaryconcerngiventhesheeramountofrisks,damage,injuriesand

deathsthatoccuralongourroadways,especiallyatroadwayintersections.The

considerationofsafetyisnotastrategypersebutofcoursemustbeaconsiderationinany

development.Thereasonwhythisfactorisincludedinthisanalysisisbecausediffering

designscanofferslightmodificationsonexactlyhowauserissafebyalteringthelocations

ofpotentialrisk.Thereforethestrategyinsafetyisnotwhethertoincludeitornotbuthow

toimplementitinawaythataddresseslocalneedsandprevailingcircumstances.

Theefficiencyofanintersectionisjudgedbyitsabilitytohandletheneedsthatitis

beingdesignedfor.Itisimportanttonotethatthroughput(automobilelevelofservice)and

efficiencyarenotsynonymousasthroughputisonlyonepieceofwhatmakesan

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intersectionefficientornot.Forexample,anefficientintersectionmayconstrict

throughputifthedesignisplannedtodothis.

Intersectionshavingasenseof“place”soundsfluffybutistheprimaryreason

“places”havebeendevelopedthroughoutrecordedhumanhistory.Intersectionsofrivers,

landandsea,traderoutes(includingmodernhighways),andnationalbordersdefinethe

locationofalmosteverymajorandmostminorhumanestablishmentsaroundtheworld.

Eventhisplace,Atlanta,wastheresultofintersectingrailroadsandsub‐continental

divides.Intersectionsprovideavitalopportunitynotonlyforthesuccessofthe

transportationnetworkbutforthelandusessurroundingit,giventheadvanced

accessibility.Toooftenhoweverintersectionsaredevelopedasaconventionalexpanseof

pavementwithtrafficsignalsoverheadandpaintedcrosswalksoneachside(maybe),

leavingnoindividualimpactontheuserwhetherinacarorontheirbikeorfeet.Giventhe

levelofimpacttheselocationscanhaveonthesurroundingarea,theconventionalsystem

leavesalotofopportunityuntapped.Morerecentlyhowever,anincreasingnumberof

strategiestosupportintersectionfunctionsinadditiontodistinguishingthelocationasa

memorableplacehavebeenimplementedalongwiththepavementandcrosswalks.

Finallyaccessibility,astrategythatcanbeasefficientwhenitispromotedasitcan

bewhenitisrestricted.Aswillbefurtherdemonstratedlater,althoughacertainamountof

accessibilityisrequiredtomakethetransportationnetworkwork,toomanyaccesspoints

inacertainarea,howmanydependingonwhattheareais,canactuallydetractfrom

efficiencyandcreatesafetyrisks.

1.3 Background The21stcenturyhasbenefitedcivilizedsocietywithamyriadoftechnological

advancesthatbothadvancehowweinteractwithsocietyandtheenvironmentaroundus

aswellasourabilitytoreactwithinformedreasontothechallengesthatgrowthandsocial

progressdevelop.Withtheadventoftheaffordablepersonalautomobileandtheeconomic

boomofthepost‐WorldWarIIconditionoftheUnitedStates,theAmericanpopulation

begananunprecedentedrelocationmovementfartherandfartherfromtraditionalurban

cores.

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Theroadwaynetworkexplodedinsizeandcapacityoverthesecondhalfofthe20th

centuryalongwiththeadditionoftheworld’smostcomprehensivehighwaysystemin

humanhistory.WiththesprawlingeffectthismovementhadonAmericancities,vehicle

accessbecametheprimaryconsiderationovermuchofthecountryandthenumberof

roadwayintersectionsmultipliedwiththecontinuingdevelopmentofthemodern

Americancity.Forallofthisgrowthaneedwasdevelopedwherebytheincreasingly

dominanttransportationmodeoftheautomobilecouldefficientlyaccessallfunctionsof

theurbansettingwiththehighestamountofconvenienceorLevelofService(LOS)

possible.Throughputwastheresultinggoalofroadwaydesigninthe20thcentury.

Althoughefficiency,placeandaccessibilityarevitalmeasuresofthesuccessina

roadway,theprimaryconcernofanyroadwaydesignstrategymustbesafety.Thisisthe

casenotonlybecauseitshouldalwaysbethedesignofanydevelopmenttoimprovethe

humanconditionandnotkillit,butalsobecauseofthefactthatourroadwaysclaimso

manyliveseachyearalready.Asstatedpreviously,theNationalHighwayTrafficSafety

Administrationreportedthat70%ofallfatalcarcrashesthatoccurredintheUnitedStates

in2008tookplaceatastop‐controlledintersection(NHTSA2008),meaningthatover

26,000peoplewerekilledthatyearatintersectionsthatweredesignedtoenhancehuman

life.Bearinmindthatnotallofthesedeathsoccurredinsideofanautomobile,thatyear

5,320ofthe37,423deathsonAmericanroads,orover14%,weredeathsofnon‐motorist

suchaspedestriansandcyclist(FARS2015).

2. LITERATURE REVIEW

Duetothehighlevelofriskthathasbeenpresentonourroadsfordecades,a

significantamountofdatahasbeencollectedandanalyzedonroadwayfunctions.Areview

hasbeenperformedonanalysesdoneinconsiderationofalternativeintersectiondesign

andispresentedgenerallyhereafter.Althoughacompletereportonallstudiesintothe

subjectwouldbeimpracticaltothepurposesofthispaper,acomprehensiveoverviewon

thetypesanddepthofthosestudiesisincluded.

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2.1 Intersection Safety Implementation Planning

CreatedasaresourceforeachStates’StrategicHighwaySafetyPlan(SHSP),the

“IntersectionSafetyImplementationPlanProcess”isaFederalHighwayAdministration

(FHWA)reportthatoutlinesthestepsforcreatingacomprehensiveprocessondesigninga

modernintersection.Detailedinthetitleoftheplan,thisprocessincludestheusageof

historicallessonsinunjustifiablesafetyrisks(Bryer2009).Thisprocessisinitiatedbythe

settingofa“CrashReductionGoal”,wherebytheplanning,analysis,developmentand

implementationoftheplanasawholerevolvesaroundthebenchmarkgoalofenhanced

safety.

FHWA’sprocessofdevelopinganintersectionorroadway,presentedinFigure5,

ensuresthatthereismoredepthandconsiderationinthedesignprocessthatrevolves

aroundapredetermined,measurable“crashreductiongoal”.Furthermore,theinclusionof

identifyingcountermeasuresinthethirdstepoftheprocesspromotestheuseof

alternativestrategiesdetailedfurtheronandimplorestheprojectstakeholderstostray

fromconventionaldesigninordertocapitalizeonthenewestdesignstrategiesthatimpact

travelfunctionindifferentways.

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Figure5.IntersectionSafetyImplementationPlanProcess.Source:Bryer2009

Thisstep‐by‐stepprocesswouldbeappropriateasafocusontheaspectofvehicle

operationsaspartofamuchlargerprocessthatincludestheotheressentialelementsofa

successfulintersection.TheFederalHighwayAdministration’s(FHWA)processislimited

toconsiderationofsafetyimplementationinregardstovehicletravelwithno

considerationtopedestrian,bicycleortransitmodes.Althoughitcanbeassumedthata

strategysuccessfullyimplementedinordertoreducevehiclecrasheswouldhaveapositive

impactonreducingpedestrianandtransitcollisionsaswell,thelackofinclusive

considerationmayfailtooptimizetheoverallsafetyofthelocationordesign.Havinga

narrowedfocusonenhancingonlyvehicularoperationscouldimplicatehazardsforother

modesattheexpenseofamorethoroughconsiderationofautomobiletraffic.

Asecondaryconcernwiththisprocessisthatitslinearnaturecouldhaverestrictive

effectsonthecreationprocessandthereforelimittherangeofsolutionsthatcouldbe

employedtorespondtosite‐specificintersectionneeds.

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2.2 Intersection Design Guidelines TheInstituteofTransportationEngineersisaprofessionalgroupmadeupofmuch

ofthepersonnelprimarilyresponsibleforhowandwhatgetsdevelopedintheworldof

transportationacrossthecountry.Intandemwithothertransportationprofessional

groupsandagenciessuchastheTransportationResearchBoard(TRB),FederalHighway

Administration(FHWA),NationalAssociationofCityTransportationOfficials(NACTO),and

TexasTransportationInstitute(TTI),allofwhichwillbewell‐representedinthispaper,

theseorganizationsarepartoftheleadingefforttoimpactourtransportationstrategiesby

meansofanalysis,designstandardsandpolicyrecommendations.

Designmanualsareanaspectofthehistoryoftransportationthatdidalmostas

muchhurtastheydidgoodtothepublicrealm.Withthedynamicnatureofthesepublic

spaces,settingfixeddesignguidelinesgenerallyrestrictsalocalofficial’sabilitytorespond

tosite‐specifictransportationneeds.

AlthoughtheITEpublishesIntersectionDesignGuidelines,theyareresearchedand

provenrecommendationsasopposedtostandardmethodsandpredeterminedform.In

additiontothedynamicnatureofthisparticularmanual,therecommendationsare

updatedfrequentlyasfurtherdevelopmentsinresearchbyITEorotheragenciesadvance

thefieldofpossibilities.Thispublicationaswellasseveralsimilarworkspublishedbythe

othermentionedagenciesandmorewillbeheavilyreliedupontoestablishtheargument

ofthispaper.

2.3 Proven Safety Countermeasures and Safety Strategies

Althoughsafetycountermeasurescanvarygreatlydependingonlocalissuesorsite‐

specificintersectionconsiderationsthereareasetof“ProvenSafetyCountermeasures”put

forthbytheFHWAOfficeofSafety(FHWA2012).Theseareninetacticsthatatanational

levelcanbeappropriateforanyintersectionconflictreductionstrategyintheUnitedStates

(andglobally).The“provencountermeasures”fornationalconsideration,manyofwhich

areincludedinthispaperlater,are:

11

● Roundabouts

● CorridorAccessManagement

● BackplatesonTrafficSignalswithRetroreflectiveBorders

● LongitudinalRumbleStrips

● EnhancedDelineationandFrictionforHorizontalCurves

● SafetyEdge

● MediansandPedestrianCrossingIslandsinUrbanandSuburbanAreas

● PedestrianHybridBeacon

● RoadDiet

Meanwhile,theNationalHighwayCooperativeResearchProgram(NCHRP),a

researchprogramadministeredbytheTRB,publishedtheirownsetof“safetystrategies”

thatincludephysicalelementssuchastheonesfoundinFHWA’slistbutalsoincorporate

tacticalelementsofintersectiondesign.Surveyingplanningagenciesandpublicworks

officesaroundthecountry,thislistrepresentsacollectionofthemostsoughtafterchanges

inintersectiondesignwiththeperspectiveofutilizingdevelopingtacticsofmaking

signalizedintersectionssafer.Theshortenedlist,innoorderofpriorityandwithout

considerationforpedestrianorbicyclesafety,includedthefollowingstrategies(Srinivasan

etal,2011):

● Splitphasing

● Addingprotectedleft‐turnphasing

● Modifyingthechangeinterval

● Restrictingoreliminatingturnsattheintersection

● Removeunwarrantedsignals

● Addingleft‐turnlanes

● Lengtheningleft‐turnlanes

● Improvingright‐turnchannelization

● Modifyintersectionskew

● Improvesightdistance

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● AdvanceWarningSignsforRedSignal

● Improvementsinsignalvisibilityandconspicuity

2.4 Accuracy vs. Precision Thefinalinsertintothisliteraturereviewpertainstothenatureinwhichthe

analysisofthevaryingstrategiespresentedinthispaperaswellasinotherlikesourceson

thesubjectisconductedandperceived.Inhiscomparisonofutilizingeitheraccuracyor

precisioninmeasuringtransportationefficiencymeasures,ToddLitmanoftheVictoria

TransportPolicyInstitutesaysthat“...vehicletrafficvolumesandspeedsarerelatively

easytomeasureandsoareoftenusedtoevaluatetransportsystemquality.Butothermore

difficultfactorsmaybeequallyimportant,suchaswalkingconditions,thedistributionof

commondestinations,andtheeasewithwhichnon‐driverscanperformactivitiessuchas

commutingandshopping.Anaccurateassessmentoftransportsystemqualityrequires

thatthesefactorsbeconsideredeveniftheirmeasurementislessprecisethanthose

measuringtraffic.”(Litman2003)

Furthermore,inconsiderationofthestrategiesincludedhereafter,resultsofsafety,

efficiencyandaccessibilitymeasureswillbepresentedwithintheframeofbeingan

accuraterepresentationofthedesign’sabilitytoimpacttransportationfunctionsrather

thansimplyaveryprecisemeasurementofacertaintrafficphenomenon.

3. NON‐MOTORISTCONSIDERATION

Inthecommontransportationdialogue,pedestrianconsiderationisspecialized

dependingontheissueathandatthetime;thesetopicscouldbe“pedestriansafety”or

“pedestrianaccessibility”,orothersalongthatline.Pedestrianconsiderationhowever

shouldbematchedateverystepofadesignprocesswiththatofthevehicleconsideration.

Becauseoflanddevelopmentpatternsoverthepastcenturynationwide,theroadnetwork

isalmostalwaystheonlymeansoftravelingfromanypointtoanotherwithacertainlevel

13

ofefficiency.Bythatreason,travelingpersonsoutsideofavehiclehavethesamenecessity

ofaroadwayintersectionasthosewhoareinsideavehicle.

Considerforexample,thesafetycountermeasuresandstrategiespublishedbythe

FHWAandNCHRPinthepreviouschapterofthispaper.AlthoughtheFHWAincludessome

considerationtopedestrianinvolvementatroadwayintersectionsintheir“proven

countermeasures”suchaspedestrianhybridbeaconsandcrosswalks,nosuch

considerationisgivenintheNCHRPsafetystrategies.Althoughsomeofthemeasurescould

haveapositiveimpactonnon‐motoristsafetyatintersections,suchasimprovingsight

distance,itisclearthatthecreatorsofthislistwereonlydirectlyconsideringvehiclesafety

ontheroads.Thisisacommonmistakethatcouldgiveunbalancedattentiontoonetypeof

usersoftheroad,eventhoughtheyaretheprimaryusersinmostcases,atthepossible

expenseoftheminoritymodesthatusethesamefacilities.

3.1 Site‐SpecificConsideration

Thereisanunderstandableexceptionwithruralintersectionsthatmayseea

pedestrianonceeveryotheryear;urbanandsuburbanintersectionshowever,evenifnot

populartopedestriantraffic,musthaveequivalentattentiontopedestriansafety,

efficiency,senseofplaceandaccessibilitywiththatofthecar.Althoughthesurrounding

landusepatternswilllargelydeterminetheoveralldemandofpedestriantraveland

whetherasenseofplacecanbeachievable,abuiltintersectionshouldretainaneffective

standardofthesequalitiesregardless,muchlikethetreatmentofavehicleatarural

intersectionwouldallowforsafeandefficienttravelregardlessofanyimmediate

developmentatthatlocation.

Genericguidelinesfordesignmaybearisktosite‐specificconsiderationbutcertain

considerationsarebasicenoughthatholdingthemasaminimumstandardshouldnot

imposeoneithercreativeabilitiesorlocalfunctions.Infrastructureforalternativemodes

thatshouldbeheldstandardatanylocationincludesidewalks,workingdetectionand

markedvehiclestoplocationsforstop‐controlledintersections.Furthermore,enhanced

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pedestrianvisibilityshouldbeaconsiderationinanydesignbecauseoftherisknotonly

inherentwithvehicleinteraction,butalsopresentedwiththeaforementionedconflict

pointscreatedatanintersection.

3.2 The Complete Streets Movement

Althoughthemovementtodevelopintersectionsthatmoreadequatelyadhereto

theneedsofmultipletransportationmodeshasbeenanongoingbattle,thebrandingofthis

movementofredevelopmentinto“completestreets”wasinitiatedbySmartGrowth

America(SGA)in2004astheNationalCompleteStreetsCoalition(NCSC)(SGA2015).

Commonlytiedwithanotherredevelopmentstrategyofroaddietingthatwillbe

expoundedonlater,thecompletestreetsmovementisnotasingularlistofstrategiesbuta

comprehensiveprocessofturninganautomobile‐orienteddesignthatisunfriendlyand

dangeroustoallothermodes,inadditiontoautomobilesthemselves,intoaplacethat

interactswithandaccommodatesmultiplemodesandnecessitiesoftheindividuallocation.

Individualconsiderationisanessentialapproachtothecompletestreetscoalition.

Thegoalofthecompletestreetsmovementisnotsimplytomakepedestrianoperations

dominantattheexpenseofautomobileoperations,assomewouldargueitcanonlydo,but

toengageinanexhaustiveprocessofoptimizingroadwayefficiency,asdeemed

appropriatebysurroundinglandusesandconsideringalltransportationmodesthat

requirethefacility.CitedfromtheNCSC’sfundamentalobjectives:“A“complete”streetina

ruralareawilllookquitedifferentfroma“complete”streetinahighlyurbanarea,butboth

aredesignedtobalancesafetyandconvenienceforeveryoneusingtheroad”(SGA2015)

Initsdecade‐longexistence,CompleteStreetpolicyrecommendations,design

guidelines,andeducationeffortsinprofessionalandcommunityforumshaveresultedin

over700“agenciesatthelocal,regional,andstatelevels”adoptingCompleteStreetpolicies

(SGA2015)

15

Figure6.ExampleofCompleteStreetproject.Source:BestCompleteStreetsPoliciesof2014

3.3 PedestrianSignals

MentionedasoneofthenineprovensafetycountermeasuresbytheFHWA,

pedestriansignalshaveasignificantimpactonpedestriansafetyontheroadway.Typically

locatedbetweenandatvehicleintersections,severaldifferentstylesofpedestriansignals

havebeenevaluatedandfoundthat“motoristyieldingtopedestriansincreasedfrom31to

93percent.”(Fitzpatricketal.2005)

Theimplementationofapedestriansignalproducesanopportunitysignalthatin

mostsystemsisactivity‐activated,wherevehicletrafficoperatesnormallyunlessasensor

istriggeredbyapedestrianandwarninglightsbegintoflash.Althoughthismethodis

optimalaccordingtoNACTO,othermethodscouldrequirevirtuallynomaintenanceand

thereforemaymoreeasilybeimplementedinmorelocations(NACTO2015).These

methodscouldbeassimpleasapaintedcrosswalkandwarningsignsalertingvehiclesto

thepossibleoccurrenceofpedestriantraffic.Figure7includesapedestriansignal

opportunityintersectionlocatedinMidtown,Atlanta.

16

Figure7.CrossingwithPedestrianBeaconinMidtown,Atlanta.Source:NACTOUrbanStreetDesignGuide

4. TRAFFICCALMINGSTRATEGIES

Inanefforttoimpacthigh‐speedtrafficflowasanalternativetoapolicy‐ledspeed

limitchange,certaindesigntacticscanbeimplementedthatenhancedriverperception.

Theviewofthedriver,especiallyonetravellingfasterthanthedesignspeedoftheroad,is

criticaltosafetyalongtheroadwayandevenmoresowhenapproachinganintersectionas

vehiclesandpedestrianscrossthedirectpathofthevehicle.

Thesestrategiesarenotsolelyengineeredtomakeeverystreetaresidential‐style

roadwithcarssloweddowntoacrawl,althoughtheycoulddefinitelybeusedtoachieve

thatresult,butthesestrategiesareeffectiveinmakingthespeedofvehiclesappropriateto

theactivitiestowhichtheroadgivesaccess.

4.1 CurbExtensions

Trafficcalmingstrategiescanworktonotonlyslowthespeedofpassingvehicles

butforcedriverstopaymoreattentiontotheirsurroundingsthanthehistoricalstraight‐

shot,linearvehiclepathwithminimalimpedimentsdoes.Curbextensionsareonewayto

narrowtheroadwayataspecificlocation,whicheffectivelybringsapproachingvehicle

17

speedsdownanddriver’sattentionupaswellasshorteningthedistancethatapedestrian

mustwalktocrossovereachapproach(Figure8).

PromotedinTexasTransportationInstitute’s“UrbanIntersectionDesignGuide”,

curbextensionsalso“Improvethevisibilityofpedestriansbyplacingthemwheredrivers

canseethemandwhereparkedvehiclesdonotobscuretheirpresence”(Fitzpatricketal.,

2005).Somedisadvantagesofthisoptionarerelatedtomaintenanceissueswherebyit

createsdifficultiesforsweepersandsnowplowstoadequatelyremovetrashanddebris

fromtheroadway.Stormwaterdrainagewasanissueinthepastbuthasbeenobservedto

beremediedbymakingthecurbextensionanislandwithasmallcanalinbetweenthe

extensionandthecurbas

opposedtoonesolidpiece.This

smallcanalallowsstormwater

todrainpasttheextensionand

notcreateanunsafebuild‐upat

theintersection.

Figure8.ExampleofChannelizedCurbExtensionforPedestrianSafetymitigatedforStormwaterFlow.Source:NACTO

4.2 WoonerfDesign

Insomelocationswherehigh‐speedvehiclesdiminishoreveneliminatethesenseof

placeandcommunityfromanareacravingforacommunityspace,thewoonerfconcepthas

beenabletocreateaplacefromtheroadwaybyreducingvehicularspeedanddesigningfor

aplaceofcommunityinteraction,notjustcartravel.Thisconceptdealsmorewithroadway

betweenintersectionsbuthasanimpactonintersectiondesigninthatoneoftheprimary

principlesofthewoonerfconceptisadistinctentranceintothesharedspace.The

guidelinesofawoonerfareoutlinedin“TheWoonerfConcept”(Collarte2012).

18

● Haveaclearanddistinctentrance.

● Eliminatethecontinuouscurb‐Pedestrianandautomobileonsamelevel.

● Implementationoftrafficcalmingmeasures‐slowspeedsneededforsharedspace

● Onstreetparking‐Ameasureoftrafficcalmingaswellassafety

● Incorporateoutdoorfurnishingsandlandscape‐turningtheroadwayintoaplace.

CollarteincludesanexampleofAppletonStreetinBoston,aone‐waystreetthatwas

previouslyusedasashortcutbydriverswishingtogettoanadjacentarterialquicker.The

resultingwoonerfdesignisdepictedbelow:

Figure9.WesternexitofAppletonStWoonerf,Boston.Source:Google

Thewesternexitoftheblock.TheAppletonStwoonerfcanbeseenontheright.The

pavementchangesfromasphalttobrick,thestreetlevelisraisedsothereisadeclineto

exitthewoonerf(inclinetoenterontheothersideoftheblock).

19

Figure10.EasternEntranceofAppletonStWoonerf,Boston.Source:Google

AlookdowntheAppletonSt.woonerfdemonstrateson‐streetparking,bollards,

distinctpavement,landscaping,lighting,andchicanesworkingtoproduceanenvironment

wherecarsarecompelledtosharethespacewithneighbors.

Thewoonerfconceptisonethatemphasizessafety,placeandisefficientincalming

trafficspeedsincomparisontoothernon‐woonerfsegmentsofthesamestreet,allatthe

expenseofacertainlevelofmobility.Choosingtomaketheroadanunattractivealternative

tothecollectorroadthatitrunsparallelwith,theraisedentrance,chicanes(shownin

Figure10andexpoundeduponinnextsection),onstreetparkinganddifferentpaving

effectivelyworktorestrictmid‐to‐highlevelsofmobilityandthereforepromoteonly

residentialuseofvehiclesandameasurablysaferenvironmentforothermodes.

20

4.3 Road“Wiggle”orChicanes

Chicanesarephysicalimpedimentsthatintrudeintothestraightpathofthe

roadwayandforcevehiclestoperformans‐curvetypemovementthatcanonlybesafely

conductedatloweredspeeds.Studiedasastandardtrafficcalmingmeasure,theCityof

Seattlehasobservedchicaneimplementationtoreducecarspeedsfrom18to35%

(Burlington2007).

Similarly,“wiggling”theroadremovesthestraight‐linefunctionofcommonstreets

andreplacesitwithaserpentinecurvaturethatisuncomfortabletodriversathighspeeds.

ProposedforspecificsegmentsofMemorialDr.inAtlanta,introducinghorizontalcurvature

intotheroadwayhasbeenobservedtobeaneffectivetoolinimpactingvehicularspeeds

withroadwaydesign.Thedegreeofhowvehiclespeedsareimpacteddependsonthe

degreeofhorizontalcurvaturethatisimplemented.Asanexample,thisconceptof

“wiggling”theroadasdepictedinFigure11,canbeaccomplishedondeveloped

streetscapesbyremovingonelanefromtheexistingroadwayandthereforegaining10‐12’

ofroadwidthinordertorestripetheroadtoincludethecurvaturedepictedinthemodel

below.Themodelalsodepictsthedevelopedopportunityforon‐streetparkingand

widenedsidewalks,butbikepaths,landscapingandotherusescouldbehelpfuladditions

totheroadway.

Figure11.RoadWigglewithChicaneonMemorialDr.Source:MarcusAshdownandCharlesJiang

21

4.4 IntersectionRetrofit/RoadDiet

Communitieschangeovertimeandoftenintersectionsaredesignedwhiletheland

usesarounditarestillunderdeveloped.Featuredinthefigurebelow,theintersectionof

MemorialDr,CottageGroveand4thStwasonethatincorporatedaT‐intersectionthatis

unceremoniouslyjoinedbyCottageGroveatanangle,resultinginanintersectionwith

blindcorners,irregularphasing,on‐streetparking(withintheareaoftheintersectionas

vehiclesareparkedinfrontofthestopbarinFigure12)andaccesspointscomingfrom

everydirection.Clearlythispresentsanunsafesituationforanyusernomatterthemode.

Thissafetyhazardwasobservedwhileonlocationwhenamotorcyclistenteredtheroad

fromthecardealership(white‐roofedbuildingonleftsideofimage)andwasinstantlyhit

inthesidebyacarwhichhadjustturnedontotheroadfrom4thSt,whichistheroadthat

isstraightupanddowninthefigure.Becauseoftheblindspotcreatedbythedealership,

thecarhadalready

gainedtoomuchspeed

bythetimethe

motorcyclewasinview.

Figure12.AtMemorialDr,CottageGroveand4thSt.Source:Google

Afterananalysisoftrafficdemand,itwasfoundthattheamountofvehicles

travelingonCottageGrove,theslantedroad,wasverylightevenatpeakperiods.

Furthermore,justtotheleftoftheintersection,3rdSttravelsstraightsouthfromCottage

GrovetolinkwithMemorialDr.,lessthan150metersfromthisintersection.Sincetheonly

accesspointtoCottageGrovebetween3rdStandthisintersectionwasaschooldriveway,

itwasproposedthatCottageGrovebeclosedafter3rdStandthedrivewayredirectedto

enterstraightonto4thStasopposedtoattheintersectionasCottageGrovepresentlydoes.

22

Figure13.OverviewofareaaroundMemorialDr.andCottageGroveintersection.Source:Google

ClosingCottageGroveat3rdStallowedfortheretrofittingofthisintersectionintoa

smaller,moreconventionalT‐intersectionandalsoresultedinanexpanseoflandthat

couldberepurposed.Aftermodelingseveralalternativeusesfortheacquiredland,public

opinionexpressedpreferenceforabuspull‐outandplazatobelocatedatthesite.Thebus

pulloutwouldreplaceacurrentbusstop50feetawayandprovidespaceforthebusto

stopwithoutholdingtrafficduringthetimeofdaywherethereisonlyonewestbound

travellane.

Theplazawasapositiveadditiontothesurroundingcommunitiesthathasnosuch

amenitiesintheimmediatearea.Thelocationofthecoffeeshopinthisbuildingcould

encourageoutdoorseating,smallparkfunctionsandmostofall,adashofpublicspacein

anareathatisinneedofsuchplaces.Therefore,thisconceptnotonlysolvestheissuesand

hazardsofaroadwayintersectionbutdoessoinawaythatiscongruenttothesurrounding

landuses.

Figure14.CottageGroveRetrofitProposalonMemorialDr.Source:MarcusAshdownandCharlesJiang

23

Thisretrofitproposalwasaimedattakinganexistingintersectionwhichfailedat

adequatelyprovidinganefficientlevelofusetosurroundingcommunitiesandnotonly

relievingthelocationoftherisksthathadbeendevelopedtherebutprovidingapublic

placewhereanelementaryschool,coffeeshop,salonandbusstopcouldbenotonly

accessedbutenjoyedsafely.Theefficiencyoftheintersectionconsideringallmodesis

greatergivendrivercomprehensionandpedestriancrossingwidthsandvisibility.

Asanotherexample,lessthanamiledowntheroadonMemorialDr.isthe

intersectionofEastLakeBlvdwheresurroundinglandusesincluderesidentialhousing,a

YMCAcenterandacharterschool.Ayounggirlwashitwhilecrossingthisintersectionless

thansixmonthspriortothisproposalandresultedinsomeredevelopmentincludingmore

timegivetothecrosswalkandlightingupgradeshowevernochangesinthedesignofthe

intersectionwereimplemented.

Thefigurebelowdepictsthestreetviewofthepaththatpedestrianscomingfrom

theKirkwoodneighborhood(totheright)use,whichisadirtpaththatturnstoconcreteon

MemorialDr.butiselevatednotmorethanthreeinches.Inadditiontothispracticallyat‐

gradesidewalk,thereisawallthatincreaseswithheightthatrestrictsthesidewalktobe

lessthantheneededwidthtobeadequatefortwopeoplewalkingsidebyside,forexample

amotherandchildwalkingtotheYMCAorelementaryschoollocatedontheothersideof

MemorialDr.Withvehiclestravelingabove40mphonaverage,theriskforinjuryordeath

issignificant.

Figure15.EastLakeBlvdandMemorialDr.Source:Google

24

Figure16.EastLakeBlvdRetrofitProposalonMemorialDr.Source:MarcusAshdownandCharlesJiang

Thereforeitwasproposedthatalanebetaken(MemorialDristhreelanereversible

atbothendsofthesegmentthisintersectionislocatedin)inordertonotonlyreduce

vehiclespeedsclosertotheposted35mphlimit,butgainopportunities,forwider

sidewalkswithfencingandlandscapingandmidblockcrosswalksinorderforpedestrians

toaccesstheelementaryschoolbetter.

Thissegmentofthearterialhighwaymayhavebeendevelopedwhenthe

surroundinglandwaseitherundevelopedorunderdevelopedbutisnowalmostcompletely

builtoutwithsingle‐familyhousing,acharterschoolandaYMCAfacility.Thisnewuse

structurethatinvolvesnotonlyarterialvehiclesbutcommunitymembersaccessingthe

intersectiontogotoschoolorplayrequiresareconsiderationonthedesignofthat

intersectionandworthyretrofittingtobeimplemented.Speakingofroadwayintersections

thataredesignedwithoutcompleteconsiderationtosurroundinglanduses,JamesKunstler

contendedinhisbookTheGeographyofNowherethat:

“Anybodyknowsthatachildofeightwalkinghomefromschoolat

threeo’clockintheafternoonusesastreetdifferentlythanaforty‐

six‐year‐oldcarpetcleanerinapaneltruck”(Kunstler1994)

Besidesareducedvehiclespeed,whichwasplannedalreadyandtechnically

requiredbylaw,noaccessibilitywastakenordelayaddedtovehiclesonthearterialroad,

whichwasoperatingwellwithincapacityatfourlanes.Instead,furtherdevelopmentinthe

safety,accessibilityandplaceandthereforeoverallefficiencywasmodeledforallusersof

theintersection.

25

5 ALTERNATIVEDESIGNSTRATEGIES

Thestrengthoftheclassicfour‐waystopisitsalmostuniversalcompatibility.

Developedduringatimewhenassemblylinesandinterchangeablepartswere

revolutionizingtheworldover,thefour‐wayapproachwithtimedsignalswasastandard

conceptthatwasfunctionalinalmostanyintersectionscenario.Thedisadvantagesofthis

stylehoweverincludethedriver’sobediencetosignaling,attentivenesstosignage,and

knowledgeofright‐of‐way.Theseconceptshavebeenfoundtocausemoredeathsat

intersectionsthaninanyotherlocationonAmericanroads(NHTSA,2008).

Additionaldisadvantagesincludebreakingupthenaturalflowoftrafficinan

attempttogatherandcontrolusageoftheintersection.Thefallacyinthisgoalarethe

manyaccesspointsinbetweensignalizedintersectionsthatworkagainstthe“platooning”

ofvehicletrafficbyintroducingmergingvehiclesrandomly,aswellascreatingnumerous

conflictpointsthatheightensafetyrisks.Forexample,betweenEastLakeDr.andCandler

Rd,twosignalizedintersectionsalongSR‐154/MemorialDr.aboutahalfmileapartfrom

eachother,therearemorethan70accessandpotentialconflictpointsontoSR‐154.

Figure17.MemorialDrbetweenGreenandOakridgeAvewithaccesspointsmarked.

Therehavealwaysbeenalternativeintersectiondesignstrategiestothatofthefour‐

waystop.SomehavebeenmorepopularoutsideoftheUnitedStateswhileothersareonly

appropriateinspecificcircumstancesandthereforeremainuncommon,eitherwaythese

optionsjoinemergingideasthathavebeendevelopedtocombattherisksandfailuresin

theclassicalmodel.

26

5.1 TrafficCircles

Forurbanarterialstreets,roundaboutsmaybeaneffectivealternativedesignto

signalizedintersectionsundercertaincircumstancesastheypromotecontinuousflowas

opposedtosegmentedphasesandcycles.AccordingtoaNationalCooperativeHighway

ResearchProgramreport,therewasa35%overalldecreaseincrashesand81%decrease

infatalcrashesat55intersectionsnationwideafterroundaboutswereimplemented

(FHWA2006).

Theadvantagestotheroundabouthavebeenproventobeverysuccessfulinmany

locationsaroundthecountryandhaveevenbeensetasoneofFHWA’sprovensafety

countermeasuresasindicatedbefore.Withthecontinuousflownatureoftheroundabout,

losttimewaitingforaccesstotheintersectioniskeptataminimumwhereonlyheavy

trafficflowbecomesanimpediment(anissue

withanyintersection).Additionallythe

roundaboutisdesignedwithaconsolidated

vehiclepathsothenumberofconflictpointsis

significantlyreducedtoonly4vehicletovehicle

conflictpointsand8vehicletopedestrianpoints.

Figure18.RoundaboutConflictPointLocations.Source:ITEIntersectionDesignStandards,Ch.10

Figure19.RoundaboutVehicle‐to‐PedestrianConflictPointLocations.

Theperceiveddisadvantageofa

roundaboutintersectionisthatitisdriver‐

controlled,acharacteristicthatAmerican

highwayengineersinthepasthaveavoided.Itis

alsomaintainedbyAmericantrafficstudiesthat

onlycertaintrafficdemandpatternswouldbe

appropriateforroundaboutimplementation,one

27

guidelinebeingthatthemajorroadoftheintersectionshouldnotholdmorethan80%of

thetrafficthatentersthatintersection(Raff,2014).

5.2 Ovalabout

AnotherconceptdevelopedintheImagineMemorialDr.proposalprocesswasthat

ofthe"ovalabout",whichbuildsonthecontinuousefficiencyoftheroundaboutwitha

focusonmitigatingdangerousoffsetsignalizedintersectionssuchasMemorialDr.and

Whitefoord.Thedesignfeatureofanovalaboutisthatofanellipse‐shapedmedianlocated

atthecenteroftheoffset.Theconceptualillustrationofanovalaboutincluded

demonstratesthedesign'sminimalneedforadditionalrightofwaybeyondthatofa

standardintersection.

Thisdesignwasappropriateforthelocationbecauseitislocatedatamostly

residentialportionofMemorialDr.andthereforerarelyrequireslargetruckstoturnonto

thesidestreets.However,thesidewalksandelongatedmedianaredesignedwithgradient

curbingthatcanbeeasilyrolled‐overgiventheinfrequentcircumstancewherealarge

truckwouldneedtoaccesstheneighborhoodroadsateitherendoftheoffsetintersection.

Figure20.OvalaboutConceptDesignatMemorialDr.and

Whitefoord.Source:MarcusAshdownand

CharlesJiang

28

ProsoftheOvalaboutdesign:

●Continuous lowdesign

●Zerohead‐to‐headcollisionpoints

●Enhancedpedestriansafety

●Trafficcalmingresults

ConsoftheOvalaboutdesign

●Elongatedleftturnmovementoffofprimaryroute

●Difficultturningradiusforlargetrucks(withoututilizingtherollovercurb)

5.3 AccessManagementTechniques

Althoughaccessibilityhasbeenreferenceduptothispointasanaspectof

intersectiondesignthatshouldbefurtherdeveloped,thereisapointinwhichtherecould

betoomuchaccesstothetransportationnetworkattheexpenseofotherneeds.This

oversupplyofaccessismostcommonlyfoundtobeanissuewithautomobilesandatoo‐

frequentoccurrenceofcurbcutsoraccesspointstotheroad.Althoughtoofewaccess

pointsdiminishtheeffectivenessofaserviceroad,toomanymayalsohaveanegative

effectontheroadscapacityandevensafety.

Imagineyouwereonanurbaninterstatehighwaythathadconsistentback‐to‐back

onandofframps,notonlywouldthehighwaylackanypriorityandwouldhavedrivers

usingthehighwayforshort‐distanceroutesmanageableonsurfacestreets,buttheamount

oflaneweavingandentriesandexitswouldresultinacongestedandunsafedriving

experience.Likewise,arterialandcollectorfunctioningroadscanreachapointwhere

accessopportunitiesareinoverabundanceanddetractfromthefunctionofallmodes.

Whenaccessisnotproperlymanageditcanfalltoeithersideofbeingtoolimitedor

tooabundantandalthoughitismoreoftenunderdeveloped,therearesituationswhere

accessreachesanineffectiveandunsafepointandmustbemitigated.Thetechniquesto

reigninaccessareplentifulandalmostalwaysgreatlydislikedbyadjacentproperty

29

owners,especiallythoseowningbusinesses,astheyhavebeenaccustomedtohaving

individualaccesstotheirindividualparcel.

Asconvergingpathsandresultingconflictpointsarewhatmakeintersectionsarisk

tothoseinteractingwithit,sodosubsequentconflictpointsaroundorafterthe

intersection.Thepreviousexampleofthemotorcyclistbeinghitbyaturningvehicle

occurredduetothebikeraccessingthearterialtooproximatetotheintersectionthatasafe

sight‐distancewasunattainableforthevehicledriver.Itisnotunusualtofindcorner‐lot

propertieswithdrivewayslessthan100feetfromanintersection.

Intersectionsaredesignedwithspecificmeasurementsthattakeintoaccountthe

stoppingsightdistanceforavehicletoadequatelyreacttothefunctionsofanintersection

withinamanageabledistance.Furthermore,pedestriancrossingsarenormallynot

protectedonlybutsharetimewiththeleftturnmovementinapermissiveleftphasing

sequenceandifvehiclesareaccessingtheroadfarwithinthatsightdistanceand

acceleratingquicklyinordertomakethelight,fromadesignperspective,thedriverwill

nothaveadequatetimeorspacetoavoidacollisionwiththepedestrian.

Althoughminimumdistancerequirementsaroundanintersectionshouldbe

commonplace,aquantitativemeasureonwhenthenumberofaccesspointswithina

sectionofroadwaybecome“toomany”isdifficulttosetasageneralrule.Unfortunately,

withsafetyitisoftenconcerns,andregrettableexperiences,withsafetythatrevealan

excessiveamountofaccesspoints.Howtheyaredealtwithcanrangefromconsolidating

curbcutstoinstallingaraisedmedian.

Installingaraisedmedianisonetacticofaccessmanagementthathasbeen

observedtosucceedinaddressingsafetyconcernsinparticular.Thetwo‐wayleftturnlane,

or“suicidelane”asitisoftenreferredtoas,hasbeenusedasameanstoallowvehicles

makingaleftturntoexitthegeneraltrafficflowandwaitforagapintheopposingtrafficto

maketheirturn.Theconcernswiththisdesignisthatnotonlyisthelanetwo‐wayand

thereforeraisesright‐of‐waybattles,butitintroducesallofthe32vehicletovehicle

conflictpointsfoundinastandardintersectionhoweverwithnopresenceofatrafficlight

regulatingthedifferentmovements.Itcanbeassumedthatthisscenarioobviously

providesforanunsafetravelingscenariowhereanaccidentiswaitingtohappen.

30

AstudywaspresentedintheThirdAnnualAccessManagementConferenceheldin

1998onMemorialDrive,wheretheseexactconcernswerehadandresultedintheTwo

WayLeftTurnLane(TWLTL)beingreplacedbyaraisedmedian4.34mileslong,with

breaksonlyatsignalizedintersections.Inabeforeandaftercomparisonconductedbya

GeorgiaTechprofessorandtwoGDOTofficials,itwasfoundthattherewasa37%decrease

inthecollisionrate(permillionVMT)anda48%dropintheinjuryratealongthat

particularstretchofMemorialDr.Additionally,“whereasinthe11.6yearsprecedingthe

projecttherewas15fatalities,includingsixpedestriandeaths”therewasnofatalitiesof

anykindpost‐constructionuptothelastpointitwasmeasuredandreported,8yearsafter

themedianhadbeenimplemented(Parsonsonetal.1998).

Meanwhile,astudyintocrashratesasaffectedbyroadwaytypewasconducted

usingUtahDepartmentofTransportationdatatoassesstheimpactonpedestriansafety

thatdifferingaccessmanagementtechniquescanproduce.Forfurtherobservation,the

crashratesweredividedbymid‐blockcollisionsandintersectioncollisionswith

pedestriansinordertocomparetheimpactthesetechniqueshaveinbothlocations.Itis

significanttonotethatinalltypes,pedestriancrashratesatintersectionswerebetterthan

mid‐blockcrashrates,furtheringtheargumentforadequatepedestrianconsiderationat

vehicleintersectionsinadditiontomid‐blockconsideration.

Table2.Mid‐blockandIntersectionCrashRatesbyMedianType.(Lewis2006)

Accessmanagementcontrolstrategiessuchasaraisedmedianarenecessaryin

someareasbecauseofthedevelopeddisconnectbetweenlanduseregulationand

transportationinfrastructure.“Curb‐cutting”onanarterialstreetinordertocreatean

31

accesspointtoaprivately‐ownedlocalbusinesscreatesconflictpointsonaroadwith

typicallyhighlevelsofactivity.Compoundingthisissuewithsuccessiveindependentcurb‐

cutsupanddownthestreetcreateadangerousscenarioforpedestrians,cyclist,and

vehiclepassengersusingthepublicspace.Communicationbetweenregulation

departmentssuchastransportation,publicworks,communitydevelopmentorplanning,

andvariousgoverningcouncilsisessentialtomitigatingthecreationofthishazardous,yet

common,scenario.

Breakingthecompartmentalizingofdevelopmentplansandstrategiescouldhave

manymorebenefitsthanjustoptimizingtransportation.Forexample,landusezoning

regulationsthatcoordinatemoreeffectivelywiththetransportationnetworkcanenhance

morewalkabledevelopmentopportunitiesgiventhatprivateandprioritybusinessaccess

canbeonamoreversatilelocalroadneighboredbyothercommercial,office,and

residentialuses.Thatscenariocontrastsgreatlytotheprivatedrivewayonanarterial

highwayscenariointhecaseofMemorialDriveinAtlantaandcountlessothersuch‐cases.

5.4 ReducedConflictIntersections

CurrentlytheStateofMinnesotahaseightReducedConflictIntersectionsinplace

withfivemoreplannedinthenearfuture(MNDOT2015).Theseintersectionsaredesigned

tobecontinuousinnatureandaremosteffectiveatintersectionsofaruralroadwitha

dividedhighway.Asthroughtrafficisnotallowedfortheruralroad,nosignalizationis

requiredandtheflowofthehighwaycanremainconstant.Driversontheruralroad

wishingtoeithermakealeftturnmovementorcontinuethroughthehighwayjointhe

establishedflowoftrafficonthehighwayandthencontinuetoadesignedpointwhereaU‐

turncanbemanagedandthosemovementsachieved.

32

Figure21.ReducedConflictIntersectionDiagram.Source:MNDOT

Thistypeofintersectiondependsongapsintheflowoftrafficonthehighwaytobe

successfulandhasnopedestrianconsideration,botheffectsofitsrequiredrurallocation.

SafetyisthemainobjectiveofanRCIandhasbeenobservedtobeeffectivein

accomplishingit.MNDOTreportsthatinabeforeandafterstudyontheRCIs,therewasan

observed49%decreaseinthetotalnumberofcrashesatthelocationswitha70%

reductioninthenumberoffatalcrashesand42%lessinjurycrashes.

Becauseofthelackofabridgeorsignalequipmentandmaintenance,MNDOThas

alsoreportedthatthecostofanRCIisnoticeablylowerthanatypicalintersectionwould

be.CostsarealsolowerinthatconstructingaCFItypicallytakesnomorethanayear

whereasatypicalhighwayinterchangewouldtake3‐5yearstoconstruct.

33

5.5 ContinuousFlowIntersections

CloselyrelatedtotheRCIconceptistheContinuousFlowIntersection(CFI).CFIs

includethesimilardesignswithmedianaccesspointsbutemploycoordinatedtraffic

signalsandallturningmovementcapabilities,allowingforamoreadequatefitintomore

urbanlocations.AsdepictedbyCompass,aplanningfirmoutofIdaho,aCFIseparatesthe

movementsatanintersectionspatiallyandthereforeallowsforcarefullycoordinated

signaltimingtoincreasethevehiclecapacityineachsignalphase.

Figure22.ContinuousFlowIntersection

Diagram.Source:Compass

ThepurposeofaCFIistoseparatethemultiplefunctionsrequiredatatraditional

four‐wayintersection.Ifanintersectionhasanadequateamountofdemandforleftturn

service,protectedtimeisgivenwhereonlytheleftrunmovementisallowedtoaccessthe

intersection.Thedrawbacktothisfunctionisthatwitheachadditionalphaseofan

intersection,additionaltimeisrequiredforyellowandallredtimebetweenphases.Itis

alsocommonthatdespiteasignificantdemandforleftturnservice,thethroughmovement

stillcarriesthemajorityoftheroad’sactivity.

34

Asdepictedinthispiechart

developedbyCompass(Figure23),only

62%oftheoverallsignaltimegoestothe

throughmovementswhenaprotectedleft

turnphaseisincludedinthephasingcycle.

Sinceitiscommonthat75‐80%ofthe

vehiclesapproachinganintersectionare

notturningbutgoingstraightthrough,there Figure23.4‐PhaseSignalCycleTimes.Compass

isanimbalancecreatedanddrivertimeand

intersectionservicecapacityarelost(Compass).

AlthoughaCFIcontains

allturningandthrough

movementsthatarepresentin

astandardinterchange,by

displacingtheleftturn

movementthenumberof

conflictpointsisreducedto28

insteadof32.Ashasbeen

previouslyargued,thenumber

ofconflictpointscanbea

reliable,althoughgeneral,measure Figure24.ConflictPointLocationsatCommonCFI

inpredictingtheoverallsafetySource:Hughes,etal,2010

opportunityofanintersection.

Thelocationoftheconflictpointshoweverisdifferentthanastandardintersection

asalthoughtherearealmostasmanyconflictpointsintotal,theyaredispersedthroughout

asignificantlygreaterareathanatraditionalintersectionthatholdsallconflictpoints

together.Itcanbethereforearguedthatthenumberoftotalconflictpointsisless

significantataCFIduetothereducedamountofinteractionbetweenalltheintersecting

paths.Thiscanbeonereasonwhyithasbeenobservedthatconvertingatraditional

interchangeintoaCFIsawa24%reductioninthenumberofcrashes,despiteonly

35

removingfourtotalconflictpoints.Thispointcanbeseenillustratedbelowinasidebyside

comparison.

Figure25.Traditionalvs.CFIConflictPointLocations

TherearecurrentlythirtyCFIsindifferentvariationsacrosstheU.S.,Georgiahas

planneditsfirstCFIinDawsonvilleandwillbeassessedfurtherlateron.Dependingon

specificsitecharacteristicsandlocaltraffic,thecurrentlyoperatingCFIshavehadan

observedimpactonvehicledelaydecreasewithinarangeof20‐90%.Thisbenefitisin

additiontoa15‐30%increaseinavailablecapacity(CFI2015).

6 TRAFFICOPERATIONSSTRATEGIES

Referencedheavilyinthe“SafetyStrategies”listpublishedbyNCHRP,certain

techniquesintheactualoperationofvehiclesandpedestriansatanintersectionare

changingpartlyinresponsetoefficiencyandsafetypressuresbutalsolargelyasaproduct

oftheaddedcapabilitieswithmoderntrafficcontroltechnologies.

6.1 TrafficSignalCoordination

Thepaperwasintroducedbydescribingacommonscenariowhenagroupof

vehiclessittingaredlightwatchthedownstreamsignalgofromgreentoyellowtored

beforetheyevengetthere,thereforecausingthevehiclestostopatsuccessivesignals.

36

AccordingtoTrafficEngineering,afterbeingreleasedfromatrafficsignal,vehiclesremain

inagroupforwellover1000feet.Itiscommonconsiderationintrafficengineeringthat

signalslocatedwithinamileofeachotherbecoordinated(Roessetal.2004).

Signalcoordinationismodeledusingtimespacediagramsandutilizesequivalent

cyclelengthsandvehiclespeedstotimedownstreamlightstoturngreenasvehicle

platoonsapproach.Successivedownstreamsignalsaredelayedfortheamountoftimethat

ittakesavehicletoreachthatintersectionafterbeingreleasedfromtheupstreamsignal,a

measurementoftimereferredtoasanoffset.Theresultisawaveofgreenlightsthat

progressatthecalculatedspeedofthevehicles,allowingforcorridorefficiencyintraffic

flow(Roessetal.2004).

Figure26.Time‐SpaceDiagramfromTrafficModelingSoftware.Source:MTOP2015

Bycoordinatingdownstreamsignals,aspeedregulatoryeffectisalsorealizedasvehicles

whoacceleratequicklytospeedshigherthanthecorridordesignspeedswillcontinueoutrunning

thegreenwaveandrunningintoeachsuccessiveredlight.Theconclusiveresultisthatsignal

37

coordinationcanplatoonvehicleflowandthereforecreatemorecrossingopportunitiesforbikes

andpedestriansinadditiontopunishingspeedingvehicleswithsuccessivestopsastheytraverse

thecorridor.

Locally,theCityofAtlantaannouncesinthefirstpartof2015thatplansofcompletesystem

signaloptimizationwereinprogresswithbudgetapproval.Althoughcertainsegmentsofroadway

havebeencoordinatedandroutinelyoptimizedunderothertrafficoperationsprograms,asystem‐

widecoordinationprojecthas

notbeenundertakenintheCity

ofAtlantaforoverthreedecades

(Blau2015).

Figure27.TimeSpaceDiagramofSpeedingVehicleHittingSuccessiveLights.Source:Roessetal.2004.Pg689

6.2 TheBarnesDance

KnownastheBarnesDance,namedaftertheDenverTrafficEngineerHenryBarnes

whopioneeredtheconcept,diagonalcrosswalksatselectintersectionspairedwitha

pedestrian‐onlyphasereducedpedestrian‐vehiclecollisionsby40%inOakland.

Converselyintersectionssawnon‐compliancetotrafficsignalsincreaseby25%dueto

longerredlightsforvehicles(Reimink2012).

38

Theeffectivenessofthistechniquemorecommonlyreferredtoasa“pedscramble”

reliesonahighdemandofpedestriantrafficonmultiplesidesofanintersection.Because

theoperationrequiresapedestrian‐onlyphaseinthesignalcycle,allvehiclesarerestricted

fromanyprotectedorpermissivemovementsandconsequentlyreducetheriskforvehicle‐

to‐pedestriancollisions.Thereisonlyonepedestrianscramblecurrentlyimplementedin

Atlanta,locatedontheGeorgiaStateUniversity’surbancampusindowntown.Thereis

howeverconsiderationintoimplementingapedscrambleattheintersectionofSpringSt

and5thStinMidtownonGeorgiaTechcampus(MTOP2015).

Figure28.PedScrambleinDenver.Source:DenverPost,2011

6.3 FlashingYellowArrow

Flashingyellowarrow(FYA)signalingisthenewestfrontinProtected‐Permissive

LeftTurn(PPLT)phasingwherevehiclesmakingaleftturnhaveaprotectedphasein

additiontobeingpermittedtomakealeftturnbetweengapsofvehiclesinoncoming

traffic.PPLTphasinghasa30to50%reductioninvehicledelaywhencomparedto

39

protected‐onlyphasing.PPLTphasinghasalsobeenobservedtoreducestandardly‐

measuredemissionsby12%perday(Brehmeretal.2003).

AccordingtotheNCHRPreportontheFYAoperation,thebenefitsofFYAas

opposedtothecommonsolidgreencircleforthroughtrafficare:

● Statisticallysignificanthigherdrivercomprehension

● Operationalplusinabilitytolead‐lagleftturnswithoutdevelopinga“yellow

trap”

● “Displayswiththecirculargreenpermissiveindicationwereassociatedwith

significantlymorefailcriticalresponsesthandisplayswitheithertheflashing

yellowarroworcirculargreen/flashingyellowarrowpermissive

indications.”(Brehmeretal.2003)

Simulationandstatictestsalsorevealedthatsignalcomprehensionandopposing

vehiclemovementscombinedmaketheturningdecision;therefore,havingayellowtrap

scenarioisextremelydangerousandsignalcomprehensionshouldbemaximized.

Therearecurrently30locationsstatewidehavealreadybeenimplementedwith

FYAstatewidewiththeconfigurationbecomingthenewstandardforallfuturePPLTtraffic

signals(GDOT2015).

● Reducesleftturncrashesby35%(citedFHWA)

● Operationalefficiencywithasafelead‐lagphasingsequencepossible

● Reducesvehicleidlingandairpollution.

7 POLICYSTRATEGIES

Theuseofpolicytoregulatebuiltformandtransportationactivitiesshouldbea

carefulconsiderationasunlikesite‐specificdesign,enactedpolicytendstocovera

collectionoflocationsandsituations.Althoughuniformitycreatedbypolicyguidelineshas

benefitsinmoregeneralcomprehensionandminimumstandardstoprotectusersafety

andproductquality,italsorestrictstheamountofspecificconsiderationthatisrequiredto

40

makealocationorregion,dependingonthesignificanceoftheproject,effectivetotheuses

thatitisbeingdesignedtoaccomplish.

Anexampleofthiscouldbemanyhistoricalengineeringguidelinesthatrestricted

trafficflowfrombeingleft‐side‐orientedforevenaportionofaroadwaysegmentdueto

thefearofconfusionthatthedriverwouldnotunderstandthedifferenttreatmentand

injuriouscollisionswouldoccur.Iftheseguidelineswerestillprevailingtoday,alternative

intersectionformssuchasthedivergingdiamondwouldbepoliticallyimpossible

renderingtheobservedbenefitsofthisdesign,whichwillbedepictedindetaillater,

unattainable.

Furthermore,highly‐generalizedminimumparkingrequirementswhichwereset

forthinengineeringmanualsandfollowedreligiouslyfordecadesrequired,bylaw,an

oftenoversupplyofindividualparkingtreatmentsforeachlandusedevelopment.The

implementationoftheseparkinglotsgreatlydiminisheddensitiesneededforconnected

socialactivityinadditiontocreatingtheargumentfortheneedforincreasinglymore

accesspointsalongourroadways.Aspreviouslypresented,thecontinuingdevelopmentof

theseaccesspointsmultipliestheexistenceofconflictpointsalongtheroadwayandcan

notonlydetractfromtheeffectivenessofanintersectionbutcanalsopresentapotentially

fatalrisktousersoftheroadway.

Itisfortheconcernsofdesign‐restriction,over‐generalizationandthepossible

productionofexternalrisksinsafetyandtransportationefficiency,thatcautionisadded

whenconsideringpolicyimplementationasameansofimpactingintersectionand

roadwaydevelopment.Thatbeingsaid,therearemanypositiveexamplesofpoliciesand

guidelinemanualsthatdelineatecomprehensiveconsiderationofqualityandeffectiveness

withoutcompromisingindividualisticdesigninknownsignificantways.Suchaguideline

shouldallowforthedynamicnaturethatempowersefficientdevelopment.

7.1 Speed Limit Reduction

Unlikepreviousstrategiesthatimpactprevailingvehiclespeedsbydesign

implements,policyenactmentsthatreducespeedlimitsrequireindividualwillingnessto

obeyandenforcementtoencourageobedience.Speedlimitalterations,whetherupor

41

down,havebeencommonmeanstofurtherclassifytheroadtypeavehicleisdrivingon.

TherecenthikingofTexashighwaysspeedsincertainlocationsto85mphencourages

swifttravelanddoessowiththeargumentofnoconsiderabledevelopmentofsafetyrisks

withthehigherspeeds.

Atintersectionshowever,automobilesaresharingspacewithpedestrians,cyclist

andotherautomobilestravelinginconflictingdirections.Thereforeatmoreurban

locationswhereintersectionsaremoreclustered,lowerspeedsmayprovetonotonly

increasetrafficefficiencybyavoidingcongestion,butalsosavethelifeofoneoftheusersof

theroad,nomattertheirmodeoftravel.

Themainargumentbehindloweringurbanspeedsiscommonlyforthesafetyof

pedestrians,althoughobviouslyaddingreactiontime,stoppingdistance,andreducing

collisionforcewillhaveasignificantimpactonvehicletovehiclecollisionsaswell.The

localAtlantianvoiceforpedestriansafetyismostoftenthePedestriansEducatingDrivers

onSafety(PEDS)initiative.Leadingprogramstoeducatedriversandpedestrianson

currentlawsaboutpedestrianinteractionontheroadwayinadditiontopromotingand

supportingnewpoliciesonthesubject,PEDSisaconsistentforceinAtlantaonanalyzing

pedestriansafetyandpushingdesigntomakeconsiderationchangesinfacilitatingnon‐

vehicularmodesoftravel.Includedinthisanalysiswasthechanceavehicletopedestrian

collisionwouldresultinafatalitygivenvaryingspeedsoftheautomobile.

Figure29.Pedestrian’sChanceofDeathifHitbyaMotorVehicle.Source:PEDS2015

Althoughpedestrianfatalitiesarealmostguaranteedattravelingspeedsabove40mph,

thesespeedsarenotcommonlyfoundatintersectionlocations.Thetwootherfindingsdepictedin

thefigurehoweverillustratethechanceofpedestriandeathat30and20mphat50%and10%

respectively.Thereforealthoughthespeedofthevehicleisonlyreducedby10mph,thechancea

42

pedestriansurvivesifstruckbyacarisalmosteliminated.“Alittlespeedisalotmoredeadly.”

(PEDS2015)

Althoughtheactualspeedofavehicleisimportant,themainfactorinvolvedinpedestrian

safetyisnotthespeedofvehiclesdirectlybutthestoppingdistance,whichgrowslongerwith

increasingspeeds.Ithasbeenobservedthatanaveragedriver,travelling40mph,whoseesand

reactstoapedestrianintheroad100feetahead,willstillbetraveling38mphatthepointof

impact.Conversely,giventhesamesituationandthevehicleisdrivingonly25mph,thereisenough

distanceforthedrivertocometoacompletestopbeforethepedestrianishit(McLeanetal.1997).

AforeignexampleoftheseresultstookplaceinZurichwhenthespeedlimitwasloweredto

31mph(a6mphreduction)forenvironmentalpurposesandinresultloweredpedestrian

collisionsby16%andpedestrianfatalitiesby25%(McLeanetal.1994).Inareasofpedestrian

activity,notjustfrequentpedestrianactivity,loweringlegalvehiclespeedsto20‐30mph

significantlyincreasesthechanceofavoidingpedestrianfatalitiesmorecommonlylocatedaturban

intersections(onesthecanoftenbeavoided).

7.2 Design Guideline Implementation

Usuallyanextensionoflocalland‐usezoningcodes,designguidelinescanbealocal

assetinensuringthequalityandconsiderationofhowdevelopmentsareplannedandbuilt.

Primarily,municipalitieswilldevelopasetofdesignguidelinesforaparticulardistrictor

regionwithintheareathatiseitherplannedtoholdahigherlevelofurbanqualityoris

alreadydevelopedtoastandardthatiswantedtobeupheld,asituationusuallyinvolving

historicallanduses.

Fewmunicipalitiescreatecity‐widedesignregulation.NewYorkCity;however,will

bedetailedfurtheronasanexceptionandmayserveasamodel.Theamountofconception

thatneedstobetakenunderconsiderationwithmanydifferentland‐usetypesandspecific

scenarioscanbedifficultforlocalgovernments.

43

8 LOCALCASESTUDIES

Therehavebeenlocalimplementationmentionsinthestrategiesdetailedabove;

howeveradetailedlookintolocalexamplesofthesealternativestrategiesisincludedto

considertheimpactsthesetechniquescanhavehereintheAtlantaarea.

8.1 MidtownTrafficOperationsProgram

TheMidtownTrafficOperationsProgram(MTOP)isaprojectthathassoughtto

optimizetrafficfunctionswithinacertainarea,inthiscase,theMidtownareaoftheCityof

Atlanta.TheprojectisfundedthroughGDOT'sRegionalTrafficOperationsProgram(RTOP)

andisathree‐yearprojectwiththepurposeofenhancing"travelandsafetybymaximizing

theefficiencyofallmodesoftravel(includingpassengervehicles,buses,pedestriansand

bicycles)throughproactivelymanagingtrafficsignalswithinthestudyarea."(MTOP2013)

TheMTOP"studyarea"includes100signalizedintersectionsthatareeachvisitedat

leasttwiceamonthtocheckthatsignalcoordinationisprecise(tothesecond),vehicleand

pedestriandetectionisfunctioningproperlyandageneralinventoryofequipmentand

overallintersectionoperationsisperformed.

Althoughsignalcoordinationisnotanewtechniqueinimpactingintersection

efficiency,itisanevolvingone.Withupgradesinmoreprecisecommunicationwiththe

intersectioncontrollerthroughdevicessuchasfiberconnectionstosurrounding

intersectionsandthelocaltrafficcontrolcenter,GPSclocksfortimingprecision,Ethernet

modems,fieldswitchesandaplethoraofothertechniquesthatallownear‐instantaneous

managementofanyintersection.

44

Figure30.MTOP

ProjectAreaand

CoordinatedSignals.

Source:MTOP

AssessmentReport,

2013

Aftercollectingtrafficdemanddataandextensivemodeling,newtimingplanswere

downloadedthroughoutthe100‐signalsysteminlate2014.Thesenewsignaltimeswere

modeledtoenhancetravelefficiencythroughreductionofdelayandthenumberofstops.

Onaverage,theeast‐westcorridors(14thStreet,10thStreet,PonceDeLeonAvenue,and

NorthAvenue)wereimprovedbytheupgradedsignalcoordinationbya41%reductionin

traveltimes,a57%reductionindelay,anda35%reductionintheaveragenumberofstops

avehicleneedstomaketraversingthecorridor(MTOP2014).Belowaretheobserved

resultsalongoneofthemainNorth‐Southcorridors,SpringSt.

45

Table3.TravelTimeRunResults‐SpringSt.Source:MTOP2015

AMPeak Midday PMPeak

TravelTime

(sec)

Before 592 445 671

After 348 368 501

%Improved 41% 17% 25%

AverageSpeed

(mph)

Before 12.3 16.4 10.9

After 20.7 19.5 13.9

%Improved 68% 19% 28%

NumberofStops

Before 8.7 7.2 11.4

After 2.3 4.3 5.6

%Improved 74% 40% 51%

Throughthereductionoftraveltimeinefficiencies,thenumberandamountoftime

andonevehiclespendstravelingthroughMidtownisreduced.Furthermore,thereduction

inthenumberofstopsandamountofdelaypervehiclereducesthenumberofidlingcarsin

thearea,allfactorsofreducingairpollutioninMidtown.Themeasuredeffectonairquality

canbemeasuredwiththetraveltimerundatacollectedbeforeandafterthenewsignal

timingwasimplemented.Table3belowpresentsanexampleoftheimpactefficientsignal

coordinationcanhaveonairpollutantproductioninaregion.VolatileOxygenCompounds,

CarbonMonoxideandNitrogenOxidesareallpollutantsthatarefederallyregulatedaspart

oftheCleanAirActbytheEnvironmentalProtectionAgency.

46

Table4.AirPollutantImpact‐SpringSt.Source:MTOP2015

AMPeak Midday PMPeak

VolatileOxygen Compounds (g/veh)

Before 18.869 16.022 19.920

After 12.623 13.993 15.730

%Improved 33% 13% 21%

CarbonMonoxide

(g/veh)

Before 153.318 129.121 157.603

After 121.461 124.470 134.595

%Improved 21% 4% 15%

OxidesofNitrogen (g/veh)

Before 10.183 9.816 10.061

After 7.301 8.648 8.213

%Improved 28% 12% 18%

TheMTOPportionofGDOT'sRTOPprogramissignificantasalthoughitisfinanced

bytheRTOPprogram,ithasanadditionalstakeholderinMidtownAlliance,theCIDforthe

Midtownarea(MTOP2013).ThisuniquerelationshipdifferentiatesMTOPfromthe

maintenance‐onlyorientedRTOPprogramandincludes"specialstudies"alongwiththe

maintenanceobjective.Oneofthese"specialstudies"hasalreadybeenmentionedinthat

MTOPiscurrentlyunderconsiderationofimplementingapedestrianscrambleatSpringSt

and5th,oneoftheprimaryintersectionsusedinaccessingGeorgiaTechcampusfrom

Midtown.Otherspecialstudiesthathavebeenincludedintheprogramare:

● CorridorSpeedStudywherebeforeandafterLiDARobservationsweretaken

alongmajorcorridorsinMidtown.Theresultsconcludedthatthenumberof

high‐speedvehicles,traveling50mphandabove,wasreducedby55%

duringthePMpeakperiodafterthenewsignalcoordinationtimingswere

implemented.(MTOPSpeedStudy2015)

● 10thSt.I‐85on‐rampwasre‐designedinordertoaccommodatehigher

trafficflowwithfewerconflictpoints.

47

● SouthMidtownPedestrianandCirculationImprovementProject

● LeadPedestrianIntervals(LPI)implementationonPeachtreeSt.tobetter

accommodatethehigherpedestriantrafficalongthesegmentofthecorridor.

● 15thSt.extensiontoWilliamsStinordertoimproveconnectivityandbreak

upaverticalblockthatiscurrentlyover1000feetlong.

8.2 AshfordDunwoodyDivergingDiamondInterchange

Thedivergingdiamondinterchange(DDI)formisanexcitingexampleofdesignthat

makesdriversslightlylesssecureandeffectivelyresultsinallusersofthefacilitybeing

safer.SeveraloftheseformshavebeenrecentlyimplementedintheAtlantaareaandare

currentlyatdifferentstagesofdevelopment.TheAshfordDunwoodyinterchangewasthe

StateofGeorgia’sfirstDDIandwasopenedtothepublicinJuneof2012andimmediately

sawareductioninthenumberofcrashesby30%(Fox,2012).

8.3 PleasantHillDivergingDiamondInterchange

ThedivergingdiamondatPleasantHillRdfollowedtheAshfordDunwoodyDDIas

thesecondsuchinterchangeintheStateofGeorgiaandwasopenedtotrafficonJune9,

2013.TheconstructionoftheDDIatPleasantHillwaspartofacongestionreliefinitiative

conductedbytheGwinnettPlaceCommunityImprovementDistrict(GPCID)inGwinnett

CountyGA.ProvidingaccesstoI‐85,themostcongestedinterstateservingtheAtlanta

metro,thegrowthinactivityintheregionoverthepastfewdecadeshaveincreasingly

cloggedthearterialsoftheareawithvehiclespushingtoaccesstheinterstateinthevery

highwayandinterstate‐dependentAtlanta‐fashion.Becauseofthehighvolumeofvehicles

accessingtheinterchangeinordertoutilizetherampsincomparisontodrivingstraight

through,adivergingdiamonddesignwasappropriateforthelocation.

48

Figure31.DDIOperationsDiagram.DDIgraphiccourtesyofNicolePuckett/GwinnettDailyPost Amodificationfeasibilitystudywasconductedinordertodetermineifanalternate

interchangeformwouldbemoreefficientthanthetightdiamondformthatwascurrently

atthebridge.TheresultsofthestudydeterminedthataSinglePointUrbanInterchange

(SPUI)wouldhavethegreatestoperationalimpactatthelocation.GDOThowever

encouragedGPCIDtolookintotheDDIformanduponcontractingURS,theengineering

firmthateventuallydesignedandconstructedtheDDI,itwasfoundthattheSPUIwas

projectedtohavea35%improvementonoperationsandtheDDIwasmodeledtohavean

impactintherangeof30‐35%improvement.Giventhecomparableoperationability,the

pricemadethisdecisionasaSPUIwasprojectedtocost$49millionwithbridgewidening

enhancementswhereastheDDIwasonlyprojectedtocost$7milliontoimplement(Fry,

2015).

49

Figure32.ExampleofSPUIformfrom

I‐40inDurham,NC

Source:Esawey&Sayed2012

Thegoalsofthisprojectincludedkeepingallthreethroughlanesgoingacrossthe

bridge,whereastherewasareductiondowntotwoatthebridgebefore.Thislossofalane

ineachdirectionforcedmoreweavingbetweenlanesasvehiclesfoundthemselvesinthe

droplaneandcausedunnecessarycongestionandtrafficcollisions.

TheothergoalsoftheprojectaccordingtoErickFry,thecontractor’sproject

manager,werebasedonwalkabilityandplacemakingasGPCIDwishedtohavethis

improvedinterchangebeabeacontothehundredsofregionalvisitorspassingbeneaththe

bridgeonI‐85everyday.Theprojectcalledfortheremovalofacommoninterchange

treatmentinGeorgiawhereaddlanesareincludedsothatvehiclescomingoffthe

interstatecan“KeepMovingRight”fromtheexitrampontothearterialroad.This

treatmentcreatesarisktopedestriansandcyclistasvehiclesarelessfocusedonslowing

downandlookingfornon‐vehiculartraffic.

Pedestrianmobilityacrossthebridgewasimprovedfromthetightdiamond

interchangeformthatwastherebeforeandtheaestheticsattheinterchangeweregreatly

improvedtoenhancevisualimpactsattheveryautomobile‐heavylocation.

50

Figure33.OverviewofcompletedPleasantHillDDI.Source:GPCID2015

EffectiveimplementationoftheDDIincludedprecisesignaltimingofthe

intersectionssurroundingtheDDIinadditiontothetrafficsignalsthatoperatethe

differentmovementsoftheinterchangeitself.Inatrafficstudyconductedafterward,and

detailedlaterinthisreport,trafficflowimprovementsattheinterchangewereobservedas

a51%decreaseintheaveragenumberofstopsanda43%decreaseintotaldelayof

vehiclestravelingalongPleasantHillRoad(GPCID2015).

Ahigherlevelofpedestrianprotectionwasconsideredasinsteadofhaving

pedestrianandcyclisttaketotheoutsidesofthebridgeasiscommonatstandard

interchanges,an8footprotectedwalkwaywasconstructedbetweentrafficwithbarrier

wallspreventinganyconflictpointsalongtheroute.Thistreatmentalsogivespedestrians

longercyclelengthstomaketheircrossingastheysharethetimeofopposingmovement

thatislongeratahighwayinterchangethanataregularfour‐wayintersection.

TomeasuretheeffectivenessoftheDDIimplementationonPleasantHillRd,a

beforeandaftereffectivenessstudywasconductedbythecontractorthatmanagesthe

51

trafficsignalsforGwinnettPlaceCID,WolvertonandAssociates.Thestudyincluded

analysisattheinterchangebeforeandafterDDIimplementationontypicalweekdays

duringtheAMandPMpeakperiodsandamiddayperiod.Amongthefactorsincludedin

thestudyarefederallyregulatedvehicleemissions,traveltimes,totaldelayatthe

interchangeandtheaveragenumberofstopsavehiclemakesduringthecourseof

accessingtheDDI.

AstheimplementationoftheDDIinterchangewasprimarilyfocusedonrelieving

theoverly‐congestedinterchangeatI‐85andPleasantHillRd,theprimarydeterminantsof

theeffectivenessoftheDDIimplementationaretheobservedimprovementstotrafficflow

inresultofthealternativeinterchangedesign.Travelstudiesmeasuredtheaveragetimea

vehicletakestotravelthroughtheinterchangealongwiththeaveragenumberofstopsthe

vehiclemakesandtheresultingdelaythatthosestopsincur.Theresultsofthistravelstudy

areincludedinthefigurebelow.

Figure34.DDIEffectivenessMeasurementsSource:Wolverton2013 Byreducingcongestionataninterchange,vehicle‐producedemissionsarereduced

aswell.Atacongestedintersection,vehiclesidlemorefrequentlyandburnfuelandtime

whilestalled.Byimprovingtrafficflowandthelevelofserviceanintersectionprovides,not

onlywilltraveltimesbeimprovedashasbeenrepresentedalready,butthenumberof

stoppedandidlingvehicleswillbereducedandthereforehavepositiveenvironmental

impacts.Threeemissionsthatarefederallyregulatedarecarbonmonoxide(CO),oxidesof

nitrogen(NOX)andvolatileoxygen(VOC).Theresultsbelowshowthebeforeandafter

emissionreductionsatthePleasantHillDDIinunitsofkilogramsemittedperhourbythe

vehiclesaccessingtheinterchange(Wolverton2013).

52

COEmissions(kg/hr):19%reduction

NOXEmissions(kg/hr):17%reduction

VOCEmissions(kg/hr):26%Reduction

Inadditiontothesetrafficimprovements,WolvertonandAssociates,thecontractor

conductingthestudy,includedacostbenefitanalysisduetotheobservedimprovementsto

PleasantHillRoad.ThefollowinghasbeenextractedfromtheEffectivenessStudyasthe

explanationofthecostbenefitsaftertheDDIandsignalretimingimplementationprojects:

“Motoristsusingthesignalsystemduringthethree(3)peakperiodswillsave

15,600hoursand9,360gallonsofgasolineeachyearbecauseofimproved

trafficflowduetothenewtimingplans.Conservativelyassumingavehicle

occupancyrateof1.2,$12.00perhourforthevalueofmotorist’stimeand

$3.50pergallonforgasoline,annualsavingstomotoristsinthesignalsystem

willbe$224,640intheformofreduceddelayand$32,760duetoreduced

fuelconsumption,foratotalannualsavingsof$257,400.”

8.4 ContinuousFlowInterchangeinDawsonville

AContinuousFlowInterchange(CFI)isplannedtobeimplementedinDawsonville,45

milesnorthoftheCityofAtlanta,attheintersectionofSR400andSR53.GDOThasinitiatedthe

projectinanefforttoreduceprojectcostfromaconventionalbridge‐and‐ramphighway

interchange.ThefirmcontractedbyGDOTfortheproject,GreshamSmithandPartners,createdthe

modelfortheplannedinterchangeandreportedthatsimilarCFIimplementationresultedin10‐

20%ofthetotalcostofagrade‐separatedinterchangewiththecapacityofapproximately75%

(Gresham2011).Therefore,althoughagrade‐separatedinterchangewouldprovideadditional

vehiclecapacity,GDOTandthemunicipalityaresaving80‐90%ofwhattheycouldbepayingwith

buildingabridge.

53

Figure35.DawsonvilleCFIVISSIMmodelwithturningmovementsadded.Source:GS&P

Themaindifferenceinagrade‐separatedconventionalbridgeinterchangeandaCFI

isnotonlytheoperationaldesignbuttheamountofspaceaCFIrequires.Inresponsetoa

YouTubevideooftheCFImodelinDawsonville,localresidentsexpressedconcernsonthe

lackofaccessibilitymostlybycarasthisisamoreruralareaandmostlyunwalkable.“IfI’m

travelingweston53…howdoIgettothegasstation.”(Gresham2011)Asmentionedin

theoverviewoftheCFItechniquethesetypesofintersectionsrelymostlyonthedivision

islandsforpedestrianaccess.Evenfromavehicle,iftheCFIisimplementedinalocation

thatisofaverageurbandevelopment,withdevelopedlandonallsidesoftheinterchange,

accessibilitymaytakeanegativeimpactdueprimarilytothesheeramountoflandthatis

requiredtoperformCFIoperations.Itwasreportedthat32parcelsoflandneededtobe

purchasedbyGDOTinordertoplanfortheinterchange,includingonecommercial

relocation(Hester2014).

Althoughitisyettobedeveloped,theDawsonvilleCFIwillgainadetailedreviewin

drivercomprehension,trafficimpactsandsafetyconsiderationsasitwillbeGeorgia’sfirst

CFItypeinterchange.WithsimilarCFIdevelopmentselsewhereintheU.Sandmodeled

trafficvolumes,GDOTprojectsthattrafficcongestionwillbereducedbyasmuchas85%

(Hester2014)

54

Table5.LevelofServiceAnalysisforDawsonvilleCFI.Source:GDOT2011

Figure36.BenefitCostAnalysisforDawsonvilleCFI.Source:GDOT2011

55

DetailedintheCost/Benefitbreakdown,theimpactsonvehicletrafficcongestion

willresultina$38millionsavingsinreduceddelayandtimespentaccessingthe

interchangeviacarfromconstructiontotheyear2035.Itshouldbeapriorityforlocal

officialsandtransportationadministratorstodedicateasignificantamountofthosemonies

tomitigatingthebrokenpedestrianconnectivitythatresultsfromhighervehicle

movementthroughtheinterchange.

AnadditionalCFIunderconsiderationinGeorgia,althoughnotofficiallyplanned

yet,wouldbelocatedattheintersectionofJimmyCarterandBufordHighway,alocation

muchmoreurbanthaneventheDawsonvilleinterchangeconsistingoftwoofmetro

Atlanta’smoreformidablearterialhighways(GVCID2014).

9 NATIONALCASESTUDIES

Thereareexemplarydevelopmentsandcasestudiesthathaveoccurredon

AmericanroadsoutsideoftheAtlantaareathatdemonstratenotonlytheopportunityfor

thesealternativestrategiesbutalsospeaktothegeneraltrendofimpactthatcanbe

expectedatsimilarlocations.

9.1 RoundaboutImplementationinMaryland

Fiveintersectionswereselectedtobeconvertedfromasignal‐controlled

configurationtoaroundabout.Thestudywasalsoabefore‐and‐afterobservationofa

minimumof15yearsateachofthefiveintersections.Theintersectionswereselectedfrom

alistoflocationsthathadahistoryofsafetyconcernsandcouldthereforepossiblybenefit

greatlyfromaroundabout.Theresultingchangesamongstthefiveroundabout

intersectionswerea100%reductioninfatalcrashesperyear,an88%reductionininjury

crashes,anda69.1%reductionintotalcrashesperyear(FHWA2010).

56

A2007NCHRPbefore‐and‐afterstudyconsidering55Americanintersections

reportedthatroundaboutimplementationresultedinthefollowingreductionsinsafety

considerations:

● 35%overalldecreaseincrashes

● 76%decreaseininjurycrashes

● 81%decreaseinfatal/incapacitatingcrashesforsinglelaneurbanroundabouts

● 71%decreaseinfatal/incapacitatingcrashesforsinglelaneruralroundabouts

Source:(FHWA2010)

9.2 New York City

NewYorkCity(NYC)isaninternationalstandardofmodernurbanismandhasheld

acaptivatingholdonlocalsandvisitorsalikeforcenturies.Unfortunatelythe“modern”

aspectofthisgreatmetropolisreliesheavilyontheheavyuseofcommercialtrucksand

personalautomobiles,eveninthedensestplacesofthecity.Thishighvolumeof

automobiletrafficpairedwithanabnormal,byAmericanstandards,volumeofpedestrian

andcyclisttraffichasmadeforahistoricallynegativerelationship.

NYCreportsthatthereareonaverage4,000peopleseriouslyinjuredand250killed

inNYCastheresultofvehiclecrashesperyear.Thismeansthatonaverage,someoneis

eitherseriouslyinjuredorkilledonNYCstreetseverytwohours.Furthermore,beinghitby

avehicleistheleadingcauseof“injuryrelateddeath”forchildrenyoungerthan14years

oldandthesecondhighestcauseofdeathforseniors(VisionZero2015).

Thesestaggeringstatisticshavesupportedchangesinstreetdesignguidelinesinthe

NewYorkCityStreetDesignManual,“majorengineeringchanges”andacoordinated

permanenttaskforceintheMayor’sOfficeofOperationsonthesubjecttitledVisionZero.

TheVisionZerocampaignreportedthatdefinitivechangesarebeingobservedastraffic

fatalitiesinNYChavefallen“from701in1990,to381in2000,toanall‐timelowof249in

2011”(VisionZero2015).The“majorengineeringchanges”thatwerepartoftheNYDOT’s

commitmenttotheinitiativehavebeenreportedatreducingtrafficfatalitiesby35%,a

57

valuethatistwicetherateofimprovementthansimilarlocationsoftheworld’smosturban

cities(VisionZero2015).

TheinitiativesincludedinVisionZeroincluderesponsibilitiesfortheCityHall,

PoliceDepartment,DepartmentofTransportation,Taxi&LimousineCommission,

DepartmentofCitywideAdministrativeServices,andDepartmentofHealthandMental

Hygiene.Eachitemonthelistforeachagencythenhasanindicatorthatdepictsthelevelof

completenessofeachtask.TheDOTlistonlyhasthreetasksthatarecompletedinmajority

withtheonlyitemnotatleaststartedbeing“Additionalstreetreconstructionsafety

project”(VisionZero2015).ThelistofresponsibilitiesfortheDOTare:

● Conductintensivestreet‐leveloutreachandenforcementonsafetyproblemsandtrafficlaws,focusedinareaswithknowncrashhistories

● ConvenemonthlymeetingsoftheDOTTrafficDivisionandtheNYPDTransportationBureautoreviewtrafficsafetyperformanceandsetstrategyfor

improvement

● Developdata‐drivencitywideenforcementstrategy

● Developborough‐widesafetyplansinclosecoordinationwithcommunityboards,communityorganizations,andtheMayor'sCommunityAffairsUnit

● Conducttargetedoutreachin500schoolseachyear,educatingstudentsaboutprotectingthemselvesassafepedestriansandworkingwiththeirfamiliesforsafer

schoolzones

● Complete50streetimprovementprojectsthatenhancedsafetybyreengineeringintersectionsandcorridors

● Create25newarterialslowzones

● Implement8newneighborhoodslowzones

● Installspeedcamerasat20newauthorizedlocations

● Install250speedbumps,includinginneighborhoodslowzones

● Enhancestreetlightingat1,000intersections

● Enhancemaintenanceofstreetmarkings

● Installtrafficsignalswhereneeded

● Additionalstreetreconstructionsafetyprojects

● Surveynationalandinternationalbestpracticestoexpandpotentialstrategies

● Holdworkshopsformajorstreetdesignprojects

● Undertakeahigh‐qualityadcampaignaimedatreducingspeeding,failure‐to‐yieldandotherformsofrecklessdriving

58

● Increaseextentof"Choices"anti‐DWIcampaign

● Doublenumberofprogrammablespeedboardsforintensiveeducation/enforcementinitiative

● Makeeffective,age‐appropriatesafetycurriculumavailabletoschoolsthroughout

thecity

● Partnerwithseniorcenterstoincreasecommunicationandgetspecificfeedback

fromagingNewYorkersaboutstreetsafetyimprovements

● Increasethenumberandvisibilityofhands‐onsafetydemonstrations

● AddsafetyflyersandmessaginginDOTmailingssuchasAlternateSideParkingregulationsandconstructionpermits

SupplementarytotheVisionZerotaskforce,NewYorkCity’sStreetDesignManual

supplementsfederalengineeringandenvironmentalstandardswhilepromotingand

providingforapprovedchoicesofintersectionandroadwaytreatmentsthattakeallmodes

needingaccesstothefacilityunderconsideration.Statedinthemanual’s“Purpose”:“The

StreetDesignManualleavesampleroomforchoice,andalldesignsremainsubjecttocase‐

by‐caseDOTapprovalbasedonestablishedengineeringstandardsandprofessional

judgment,withthesafetyofallstreetusersbeingofparamountimportance.”(NYCDOT

2013)

Consistingof26.6%oftheoveralllandinNYC,streetsmakeupasignificantportion

oftheoveralldesignofthecity.Furthermore,this26.6%providesanindispensablerolein

howthelocalandvisitingpopulationofthecityaccesstheother74.4%ofNYCmadeupof

housing,parks,cemeteries,employmentcenters,storesetc.Thegoalsandprinciples

behindthepoliciesinthemanualarestatedas:

● DesignforSafety

● DesigntoBalanceAccessandMobility

● DesignforContext

● DesignStreetsasPublicSpaces

● DesignforSustainability

● DesignforCost‐Effectiveness

59

OneofthemanyexamplesofTheStreetDesignManual’ssuccessinimpactingroad

designprojectsisonWestHoustonStreet.Previouslyconfiguredmuchlikemosturban

multiple‐lanestreetsare,withwidethoroughfarescomplicatingpedestrianandvehicular

movement,thecapitalprojecttooktheopportunitytoenrichtravelefficiencyfor

pedestriansandcarsinadditiontomakingabetterplace.Theredesigncreatedmore

usableraisedmediansthatcamewithlandscapingandtreesforshadingandprotectionbut

evenhadseatingavailablewhenappropriateasthecompletelengthofthecrosswalkwas

stillalmost100feetinlength.

Intotaltherewere74treesplantedintheprojectarea,anewpark,extensive

implementationofbenchesandlandscaping,enhancedlightingandpaving,androadway

improvements.Observationsaftertheproject’scompletionsawthatcrasheswithinjuries

werereducedby24%and“motorvehicletraveltimesinwestboundlanesdropped

dramaticallyduringweekdayafternoonpeak”(NYCDOT2013).Thiscasestudyisan

exampleofhowwell‐structurespolicycanimpactintersectiondesignchoicesinawaythat

benefittheoperationsandtheaesthetics,themobilityandtheaccessibility,thecarsand

thepeople.

Figure37.BeforeandaftercomparisonofWestHoustonStreetSource:NYCDOT2013

60

10 CONCLUSION

Thisanalysisofintersectionstrategiesisinnowayexhaustiveofthemanycreative

solutionsthatareimpactingmodernroadwaydesignandoperationsefforts.Rather,these

casestudiesandmethodsrepresentmuchlargermovementofthinkingthatnotonly

breakstheconventionalmoldofone‐size‐fits‐allbutalsocorrectspastinadequaciesthat

furtheredautomobileoperabilityattheexpenseofpedestrian,cyclistandtransitaccess.

Howmuchtimehasbeenlostbecauseofcollision‐prone4‐wayintersections,the

formthatholdsthehighestnumberofconflictpointsandthegreatestlevelofriskthanany

otherstrategyconsideredinthisanalysis?.Howmuchmoneyhasbeenlostbecauseoftime

wastedincongestion?Howmanycommunitieshavebeendilutedanddegradedby

separatedlandusesdesignedaroundtheautomobilebecausethemaingoalatroadway

intersectionsfordecadeswasalmostexclusivelyvehiclethroughput.Howmanyliveshave

beenlostorinjuredbecauseanintersectionwasdesignedtobelegallyprotectedwith

manualsandagency‐backedguidelines,insteadofsociallyprotectedwithconsiderationsof

locallandusesandtraveldemandsofmultiplemodes?

Theengineeringdependencyonthesemanualsmustbebrokenandreturnedtoa

placeintheprocesswheretheyarebutoneresourceindesigninganintersectionandnot

THEresourceoreventheprimaryresource.Theamountofinformationandcollected

traveldatathatisavailablefromagenciessuchastheTTI,FHWA,USDOT,NCHRP,ITE,

AASHTO,SGAandNACTOinadditiontocountlessstate,localandprivatesourcesisnot

onlymorethanadequatetodaybutcontinuestogroweveryyear.Thesesourcesprovide

scientificallymeasuredprocessesforevaluatingthefeasibilityofanalternativeintersection

design,designingthesite‐specificfacilitywithacomprehensivereviewoflocalneedsand

goals,andimplementingthedevelopmentinsuchawayastooptimizethefunctionalityof

thatplace.

Giventheamountofdatathathasbeencollectedandpresentedinthispaperonthe

fallaciesofthe“conventional”4‐wayintersection,suchaformshouldbeconsideredthe

alternativedesignforallfutureintersectiondevelopments.Althoughthe4‐waystop

controlledintersectionhasbenefitsthatareuniquejustasanyotherform,itsriskshave

61

beenobservedtobefartoogreat,fartoodeadlytoholdprimaryconsiderationforany

futureintersectiondesignconsideration.

Fortunately,therehavebeenpioneersofalternativedesignstrategiesbothdomestic

andinternationallywhomhaveshownthroughtheirexamplesthesignificantimpactthese

designscanhaveonnotonlythesafetyandusabilityoftheintersectionitself,butitsability

tointeractwiththelandusesarounditandcreateatrueintersectionofplacesthatconnect

andengagesocialforces,eveniftheydoitoutoftheircar.

62

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