ALTERNATIVE INTERSECTION DESIGN STRATEGIES
Transcript of ALTERNATIVE INTERSECTION DESIGN STRATEGIES
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
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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
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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:
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● 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
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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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