Chapter 1-4 - Intersection Design - VHB.com

Intersection Design 1.4‐1

SECTION 1, CHAPTER 4

Intersection Design

4.1 Introduction

Anintersectionistheareawheretwoormorestreetsjoinorcrossat‐grade.Theintersectionincludestheareasneededforallmodesoftravel:pedestrian,bicycle,motorvehicle,andtransit.Thus,theintersectionincludesnotonlythepavementarea,buttypicallytheadjacentsidewalksandpedestriancurbcutramps.Theintersectionisdefinedasencompassingallalterations(forexample,turninglanes)totheotherwisetypicalcross‐sectionsoftheintersectingstreets.Intersectionsareakeyfeatureofstreetdesigninfourrespects:

Focusofactivity‐Thelandnearintersectionsoftencontainsaconcentrationoftraveldestinations.

Conflictingmovements‐Pedestriancrossingsandmotorvehicleandbicycleturningandcrossingmovementsaretypicallyconcentratedatintersections.

Trafficcontrol‐Atintersections,movementofusersisassignedbytrafficcontroldevicessuchasyieldsigns,stopsigns,andtrafficsignals.Trafficcontroloftenresultsindelaytouserstravelingalongtheintersectingroadways,buthelpstoorganizetrafficanddecreasethepotentialforconflict.

Capacity‐Inmanycases,trafficcontrolatintersectionslimitsthecapacityoftheintersectingroadways,definedasthenumberofusersthatcanbeaccommodatedwithinagiventimeperiod.

Thischapterdescribestheconsiderationsanddesignparametersforintersections.Thechapterbeginsbyoutliningdefinitionsandkeyelements,andthendescribesthecharacteristicsofintersectionusers,intersectiontypesandconfigurations,capacityandqualityofserviceconsiderations,geometricdesignelements,andotherconsiderations.

1.4‐2 Intersection Design DRAFT

4.1.1 Intersection Users

Allroadwayusersareaffectedbyintersectiondesignasdescribedbelow:

Pedestrians.Keyelementsaffectingintersectionperformanceforpedestriansare:(1)amountofright‐of‐wayprovidedforthepedestrianincludingbothsidewalkandcrosswalkwidth,accuracyofslopesandcrossslopesoncurbcutrampsandwalkways,audibleand/ortactilecuesforpeoplewithlimitedsight,andabsenceofobstaclesinaccessiblepath;(2)crossingdistanceandresultingdurationofexposuretoconflictswithmotorvehicleandbicycletraffic;(3)volumeofconflictingtraffic;and(4)speedandvisibilityofapproachingtraffic.

Bicyclists.Keyelementsaffectingintersectionperformanceforbicyclesare:(1)degreetowhichpavementissharedorusedexclusivelybybicycles;(2)relationshipbetweenturningandthroughmovementsformotorvehiclesandbicycles;(3)trafficcontrolforbicycles;(4)differentialinspeedbetweenmotorvehicleandbicycletraffic;and(5)visibilityofthebicyclist.

Motorvehicles.Keyelementsaffectingintersectionperformanceformotorvehiclesare:(1)typeoftrafficcontrol;(2)vehicularcapacityoftheintersection,determinedprimarilyfromthenumberoflanesandtrafficcontrol(althoughthereareotherfactors);(3)abilitytomaketurningmovements;(4)visibilityofapproachingandcrossingpedestriansandbicycles;and(5)speedandvisibilityofapproachingandcrossingmotorvehicles.

Transit.Whentransitoperationsinvolvebuses,theysharethesamekeycharacteristicsasvehicles.Inaddition,transitoperationsmayinvolveatransitstopatanintersectionarea,andinfluencepedestrian,bicycle,andmotorvehicleflowandsafety.

Ownersandusersofadjacentlandoftenhaveadirectinterestinintersectiondesign,particularlywheretheintersectionissurroundedbyretail,commercial,historicorinstitutionallanduses.Primaryconcernsincludemaintenanceofvehicularaccesstoprivateproperty,turnrestrictions,consumptionofprivatepropertyforright‐of‐way,andprovisionofsafe,convenientpedestrianaccess.

4.1.2 Intersection Design Process

Theneedforintersectionimprovementisidentifiedandvariousoptionsforaddressingthisneedareconsideredandanalyzed.Thespecificdesignelementsofintersectionsmayimpactanyorallpotentialusers.Sections4.2through4.6definekeytermsanddiscussintersectionusers,configurations,trafficcontrol,capacity,andqualityofservice.Section4.7describestherangesofphysicaldimensionsandtheoperationalcharacteristicsofeachintersectiondesignelement.

Section 1 – Chapter 4


4.2 Definitions and Key Elements

Themajorstreetistypicallytheintersectingstreetwithgreatertrafficvolume,largercross‐section,andhigherfunctionalclass.Theminorstreetistheintersectingstreetlikelytohavelesstrafficvolume,smallercross‐sectionandlowerfunctionalclassificationthanthemajorstreet.Thetermintersectionencompassesnotonlytheareaofpavementjointlyusedbytheintersectingstreets,butalsothosesegmentsoftheintersectingstreetsaffectedbythedesign.Thus,thosesegmentsofstreetsadjacenttotheintersectionforwhichthecross‐sectionorgradehasbeenmodifiedfromitstypicaldesignareconsideredpartoftheintersection.Exhibit4‐1summarizestheextentandterminologyusedtodefineanintersection.

Exhibit 4‐1 Intersection Terminology

Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2004.


Twogeometricfeaturesarecommontoallintersections.Theangleofintersectionisformedbytheintersectingstreets’centerlines.Wheretheangleofintersectiondepartssignificantly(morethanapproximately20degrees)fromrightangles,theintersectionisreferredtoasaskewedintersection.Intersectionlegsarethosesegmentsofroadwayconnectingtotheintersection.Thelegusedbytrafficapproachingtheintersectionistheapproachleg,andthatusedbytrafficleavingisthedepartureleg.Sidewalks,crosswalksandpedestriancurbcutrampsareconsideredtobewithintheintersection.Thepavementedgecorneristhecurveconnectingtheedgesofpavementoftheintersectingstreets.Inadditiontothebasicgeometricdesignfeatures,optionsmaybeaddedtoimproveserviceforvarioususers.Auxiliarylanesarelanesaddedattheintersection,usuallytoaccommodateturningmotorvehicles.Theymayalsobeusedtoaddthroughlanesthroughanintersection.Channelizinganddivisionalislandsmaybeaddedtoanintersectiontohelpdelineatetheareainwhichvehiclescanoperate,andtoseparateconflictingmovements.Islandscanalsoprovideforpedestrianrefuge.Aturningroadwayisashortsegmentofroadwayforarightturn,delineatedbychannelizingislands.Turningroadwaysareusedwhereright‐turnvolumesareveryhigh,orwhereskewedintersectionswouldotherwisecreateaverylargepavementarea.Trafficcontroldevicesassignrightofway,tobothmotorizedandnon‐motorizedtrafficandincludetrafficsignals,pavementmarkings,STOPsigns,YIELDsigns,pedestriansignalheadsandotherdevices(suchasraisedpavementmarkings,flashingbeacons,andelectronicblank‐outsigns).

4.3 User Characteristics

Thefollowingsectionsdescribecharacteristicsofintersectionusers.Pedestriansandbicyclistsarepresentedfirst,followedbymotorvehicleandpublictransitusers.Thisorderofpresentationreinforcestheneedtoconsiderthesemodesthroughouttheintersectiondesignprocess.

4.3.1 Pedestrians

Pedestrianrequirementsmustbefullyconsideredinthedesignofintersections.Thereareseveralimportantfeaturestoconsiderincluding:

CrossingsandPedestrianCurbCutRampLocations—Locationsshouldcorrespondtotheplacementofsidewalksalongapproachingstreets,andlikely



crossinglocations.Pedestriancurbcutrampsneedtoensureaccessibilitytocrossinglocations.

WalkingSpeed—Undernormalconditions,pedestrianwalkingspeedsonsidewalksandcrosswalksrangefrom2.5feetpersecondto6feetpersecond.Elderlypedestriansandyoungchildrenwillgenerallybeintheslowerportionofthisrange.Awalkingspeedof3.5to4feetpersecondforcrosswalksignaltimingiswidelyacceptedasaguidelineforwalkingspeedincrosswalks.Thedesignershouldnotethatthecurrentreviseddraftversion(2005)oftheADAAccessibilityGuidelinesforPublicRight‐of‐wayandthecurrent(2009)ManualonUniformTrafficControlDevices(MUTCD)(bothnotadoptedatthetimeofthisGuidebook)requireamaximumwalkspeedof3.5feetpersecondovertheentirelengthofcrosswalk.

PedestrianFlowCapacity—Thenumberofpedestriansperhourthatcanbeaccommodatedbythefacilityundernormalconditions.

TrafficControl,YieldingandDelay—Inadditiontopedestrianflowcapacity,pedestriansaresignificantlyaffectedbythetypeoftrafficcontrolinstalledatanintersection,thespecificparametersofthecontrol,andtheresultingmotorvehicleoperations.AtSTOPcontrolled,YIELDcontrolled,anduncontrolledintersections,pedestrians’abilitytocrossthestreetandthedelayexperiencedisinfluencedbytheyieldingbehaviorofmotorvehicles.Atsignalizedintersections,thelengthandfrequencyoftimeprovidedforpedestriancrossings,theclarityofinformationprovided,conflictingturningmovements,andmotorvehicleyieldingarekeyinfluencesonpedestrians’abilitytocrossthestreet,andondelay.

4.3.2 Bicyclists

Bicyclists’needsmustbeintegratedintothedesignofintersections.Whentravelingwithmotorvehicles,bicyclistsaresubjecttomotorvehicletrafficlaws.Importantconsiderationsforbicycleaccommodationinclude:

Cross‐section—Bicyclistspositionthemselvesfortheirintendeddestinationregardlessofthepresenceofbikelanesorshoulders.Ifbicyclelanesarepresent,thedesignneedstoinsurethatbicyclistscanmergetotheproperlocationbasedonthebicyclist’sintendeddestination.

OperatingSpeed—Atunsignalizedintersections,anaveragebicyclespeedof15milesperhourcanbeassumedonthemajorstreet.Ontheminorstreet,bicyclistsusuallystoporslow,andtravelthroughtheintersectionatspeedswellbelow15milesperhour.Atsignalizedintersections,bicyclistsreceivingthegreensignalproceedthroughtheintersectionatanaveragespeedof15milesperhour.Bicyclistswhohavestoppedforasignalproceedthroughtheintersectionatspeedswellbelow15milesperhour.


BicycleCapacity—Thenumberofbicyclesperhourthatcanbeaccommodatedbythefacilityundernormalconditions.

TrafficControl—Bicyclistsarerequiredbylawtoobeycontroldevicesatintersections.Therefore,trafficcontroldevicesneedtoaccountforbicycleactivity.Trafficsignalswhichoperateusingdetectionsystems(suchasloopdetection,videocamera,andmicrowave)mustbedesignedandfieldtestedtobesensitivetobicycles.Manyoftheaspectsoftrafficcontroldescribedformotorvehicles(below)alsoapplytobicyclists.

4.3.3 Motor Vehicles

Thefollowingimportantcharacteristicsofmotorvehiclesareconsideredinintersectiondesign:

DesignVehicle—Thelargesttypeofmotorvehiclethatisnormallyexpectedtobeaccommodatedthroughtheintersection.

DesignSpeed—Themotorvehiclespeedselectedonadjoiningsegmentsofroadway.

MotorVehicleCapacity—Thenumberofmotorvehiclesthatcanbemovedthroughanintersectionundernormalconditions.

TrafficControl‐Muchlikeotherusers,motorvehiclesareinfluencedbythetypeandtimingoftrafficcontrolinstalledatanintersection,andnumberofotherusers.Atroundabouts,STOPcontrolled,YIELDcontrolled,anduncontrolledintersections,motorvehiclecapacityanddelayareinfluencedbyconflictingtrafficstreams.Atsignalizedintersections,thetimeprovidedforeachmovement,conflictingturningmovements,andthevolumeandmixofotherusersarekeyinfluencesonbothmotorvehiclecapacityanddelay.

4.3.3.1 Design Vehicle

Thedesignmotorvehicleisthelargesttypeofvehicletypicallyexpectedtobeaccommodatedonthestreet.Atintersections,themostimportantattributeofdesignvehiclesistheirturningradius,whichinturninfluencesthepavementcornerradiusandthereforethesizeoftheintersection.Lanewidth,anotherfeaturerelatedtothedesignvehicle,hassomeimpactonintersectiondesign,butlessthanturningradius.Thedesignvehiclemayalsoaffectthechoiceoftrafficcontroldeviceandtheneedforauxiliarylanes.Thedesignvehicleforintersectionsisthelargerofthedesignvehiclesselectedfortheintersectingstreets.Forexample,attheintersectionofaminorarterialandalocalstreet,theappropriatedesignvehiclefortheintersectionisthatrequiredbytheminorarterial(i.e.,“larger”street).Exhibit4‐2,TypicalDesignVehiclesatIntersections,providesgeneralguidanceforselectingdesignvehiclesappropriateforintersectiondesignunderconditionsofnormaltrafficcomposition.Atlocationswherecollectorsintersectwith



arterialsexperiencinghightruckvolumes,theappropriatetruckdesignvehicleshouldbeselected.SampleturningtemplatesforthesemotorvehiclesareprovidedinExhibit4‐3.

Exhibit 4‐2 Typical Design Motor Vehicles at Intersections

Functional Class of Major Road Design Motor Vehicle (AASHTO Category)

Typical for Intersection

Major Arterial Tractor-trailer Truck (WB-65)

Minor Arterial Tractor-trailer Truck (WB-50)

Major Collector Single-unit Truck

Minor Collector Passenger Car (P)

Local Roads and Street Passenger Car (P)

Notes: Design vehicles from AASHTO A Policy on Geometric Design of Highways and Streets, 2011 Passenger Car (P) applies to Light Trucks and SUV’s SU category can also be used for school and transit buses

4.3.4 Transit

Thedesignvehicleappropriateformosttypesoftransitserviceisthe“City‐Bus”asdefinedbyAASHTO.Thisvehicleis40feetlong,8feetwide,andhasouterandinnerturningwheelpathsof42.0feetand24.5feet,respectively.The“mid‐size”bus,typicallyaccommodating22to28passengers,isalsousedinscheduledtransitservice.Theturningpathforthemid‐sizebuscanbeaccommodatedwithinthesingle‐unit(SU)truckturningpathdiagram.Transitstopsareoftenlocatedatintersectionseitherasanear‐sidestopontheapproachtotheintersectionorasafar‐sidestoponthedeparturelegoftheintersection.Locationnearintersectionsisparticularlyadvantageouswheretransitroutescross,minimizingthewalkingdistanceneededforpassengerstransferringbetweenbuses.Abusstop,whethernear‐sideorfar‐side,requires50to70feetofcurbspaceunencumberedbyparking.Onstreetswithoutparkinglanesorbusbays,busesmuststopinamovingtrafficlanetoservicepassengers.Passengerstypicallyrequire4to6secondsperpersontoboardabus,and3to5secondstodisembark.Thetotalamountoftimeatransitvehiclewillblocktrafficmovementscanthenbeestimatedusingthenumberofboardingsandalightingsexpectedatastop.


Exhibit 4‐3 Sample Vehicle Turning Template

Passenger Car (P) Single Unit Truck (SU-12 [SU-40])

Intermediate Semi-Trailer (WB-12 [WB-40]) Transit Bus (CITY BUS)


Note: Not to scale



4.4 Intersection Types and Configurations

Intersectionscanbecategorizedintofourmajortypes,asillustratedinExhibit4‐4,IntersectionTypes.

4.4.1 Simple Intersections

Simpleintersectionsmaintainthestreet’stypicalcross‐sectionandnumberoflanesthroughouttheintersection,onboththemajorandminorstreets.Simpleintersectionsarebest‐suitedtolocationswhereauxiliary(turning)lanesarenotneededtoachievethedesiredlevel‐of‐service,orareinfeasibleduetonearbyconstraints.Generally,simpleintersectionsprovidetheminimumcrossingdistancesforpedestriansandarecommoninlow‐volumelocations.

4.4.2 Flared Intersections

Flaredintersectionsexpandthecross‐sectionofthestreet(main,crossorboth).Theflaringisoftendonetoaccommodatealeft‐turnlane,sothatleft‐turningbicyclesandmotorvehiclesareremovedfromthethrough‐trafficstreamtoincreasecapacityathigh‐volumelocations,andsafetyonhigherspeedstreets.Right‐turnlanes,lessfrequentlyusedthanleft‐turnlanes,areusuallyaresponsetolargevolumesofrightturns.Intersectionsmaybeflaredtoaccommodateanadditionalthroughlaneaswell.Thisapproachiseffectiveinincreasingcapacityatisolatedruralorsuburbansettingsinwhichlengthywideningbeyondtheintersectionis:notneededtoachievethedesiredlevel‐of‐service;notfeasibleduetonearbyconstraints;or,notdesirablewithinthecontextoftheproject.Intersectionapproachescanbeflaredslightly,notenoughforadditionalapproachlanesbutsimplytoeasethevehicleturningmovementapproachingordepartingtheintersection.Thistypeofflaringhasbenefitstobicycleandmotorvehicularflowsincehigherspeedturningmovementsattheintersectionarepossibleandencroachmentbylargerturningvehiclesintoothervehiclepathsisreduced.However,addingflaretoanintersectionincreasesthepedestriancrossingdistanceandtime.


Exhibit 4‐4 Intersection Types

Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 3 Elements of Design



4.4.3 Channelized Intersections

Channelizedintersectionsusepavementmarkingsorraisedislandstodesignatetheintendedvehiclepaths.Themostfrequentuseisforrightturns,particularlywhenaccompaniedbyanauxiliaryright‐turnlane.Atskewedintersections,channelizationislandsareoftenusedtodelineaterightturns,evenintheabsenceofauxiliaryrightturnlanes.Atintersectionslocatedonacurve,divisionalislandscanhelpdirectdriverstoandthroughtheintersection.Atlargeintersections,shortmedianislandscanbeusedeffectivelyforpedestrianrefuge.Channelizationislandsarealsousedinsupportofleft‐turnlanes,formingtheendsofthetaperapproachingtheturnbay,andoftenthenarrowdivisionalislandextendingtotheintersection.At“T”‐typeintersections,achannelizationislandcanguideoncomingtraffictotherightoftheleft‐turnlane.Channelizedintersectionsareusuallylargeand,therefore,requirelongpedestriancrosswalks.However,thechannelizationislandscaneffectivelyreducethecrosswalkdistanceinwhichpedestriansareexposedtomovingmotorvehicles.Thedesignofchannelizedintersectionsneedstoensurethattheneedsofpedestriansareconsidered,includingpedestriancurbcutrampsor“cut‐throughs”thatallowwheelchairusersthesamesafeharborasotherpedestriansonchannelizationislands.

4.4.4 Roundabouts

Theroundaboutisachannelizedintersectionwithone‐waytrafficflowcirculatingaroundacentralisland.Alltraffic—throughaswellasturning—entersthisone‐wayflow.Althoughusuallycircularinshape,thecentralislandofaroundaboutcanbeovalorirregularlyshaped.Roundaboutscanbeappropriatedesignalternativetobothstop‐controlledandsignal‐controlledintersections,astheyhavefewerconflictpointsthantraditionalintersections(eightversus32,respectively).Atintersectionsoftwo‐lanestreets,roundaboutscanusuallyfunctionwithasinglecirculatinglane,makingitpossibletofitthemintomostsettings.Roundaboutsdifferfrom“rotaries”inthefollowingrespects:

Size—Singlelaneroundaboutshaveanoutsidediameterbetween80and140feet,whereas,rotariesaretypicallymuchlargerwithdiametersaslargeas650feet.

Speed—Thesmalldiameterofroundaboutslimitscirculatingvehiclespeedsto10to25milesperhour,whereas,circulatingspeedsatrotariesistypically30to40milesperhour.


Capacity—Theslowercirculatingspeedsatroundaboutsallowenteringvehiclestoacceptsmallergapsinthecirculatingtrafficflow,meaningmoregapsareavailable,increasingthevolumeoftrafficprocessed.Atrotaries,vehiclesneedlargergapsinthecirculatingtrafficflowreducingthevolumeoftrafficprocessed.

Safety—Theslowerspeedsatroundaboutsnotonlyreducetheseverityofcrashes,butminimizesthetotalnumberofallcrashes,whereas,rotariestypicallyseehighnumbersofcrasheswithagreaterseverity.

Roundaboutsarealsoconsideredastraffic‐calmingdevicesinsomelocationssincealltrafficisslowedtothedesignspeedoftheone‐waycirculatingroadway.Thisisincontrastwithapplicationoftwo‐waystopcontrol,wherethemajorstreetisnotslowedbytheintersection,orall‐waystopcontrolwherealltrafficisrequiredtostop.Roundaboutscanalsobeconsideredforretrofitofexistingrotaries;however,incaseswithveryhightrafficvolumes,trafficsignalcontrolmaybemoresuitable.

4.4.5 Typical Intersection Configurations

Mostintersectionshavethreeorfourlegs,butmulti‐legintersections(five‐andevensix‐legintersections)arenotunusual.ExamplesofintersectionconfigurationsfrequentlyencounteredbythedesignerareshowninExhibit4‐5.Ideally,streetsinthree‐legandfour‐legintersectionscrossatrightanglesornearlyso.However,skewedapproachesarearegularfeatureofintersectiondesign.Whenskewanglesarelessthan60degrees,thedesignershouldevaluateintersectionmodificationstoreducetheskew.



Exhibit 4‐5 Intersecting Street Configuration and Nomenclature


4.5 Traffic Control

Trafficcontroldevices(signals,STOP,orYIELDsignsandpavementmarkings)oftencontroltheentryofvehiclesintotheintersection.Trafficcontroldevicesmayalsoberequiredatintersectionsofimportantprivatedrivewayswithpublicstreets.Examplesofimportantdrivewaysincludealleysservingmultiplehomes,commercialalleysaccessingparking,andcommercialdriveways.Thedesignershouldnotethatguidancefortheinstallationoftrafficcontroldevicesdiscussedinthissectionisbasedonthe2009MUTCD(notadoptedatthetimeofpublishingofthisGuidebook).


4.5.1 Traffic Control Measures

Potentiallyconflictingflows(vehicle‐to‐vehicleorvehicle‐to‐non‐vehicle)areaninherentfeatureofintersections.Atmostintersections,therefore,trafficcontrolmeasuresarenecessarytoassigntherightofway.Typesofintersectiontrafficcontrolinclude:

Wheresufficientvisibilityisprovidedinlowvolumesituations,someintersectionsoperateeffectivelywithoutformalizedtrafficcontrol.Inthesecases,normalrightofwayrulesapply.

Yieldcontrol,withtrafficcontrolledby“YIELD”signs(sometimesaccompaniedbypavementmarkings)ontheminorstreetapproaches.Majorstreettrafficisnotcontrolled.

All‐wayyieldcontrolonroundabouts.

Two‐waystopcontrol,withtrafficcontrolledby“STOP”signorbeaconsontheminorstreetapproaches.Majorstreettrafficisnotcontrolled.Theterm“two‐waystopcontrol”canalsobeappliedto“T”intersections,eventhoughtheremaybeonlyoneapproachunderstopcontrol.STOPcontrolshouldnotbeusedforspeedreduction.

All‐waystopcontrol,withtrafficonallapproachescontrolledbySTOPsignsorSTOPbeacons.All‐waystopcontrolcanalsobeatemporarycontrolatintersectionsforwhichtrafficsignalsarewarrantedbutnotyetinstalled.

Trafficsignals,controllingtrafficonallapproaches.

Flashingwarningbeaconsonsomeorallapproaches.

Generally,thepreferredtypeoftrafficcontrolcorrelatesmostcloselywithsafetyconcernsandvolumeofmotorvehicles,bicyclesandpedestrians.Forintersectionswithlowervolumes,STOPorYIELDcontrolonthecross(minor)streetisthemostfrequentlyusedformofvehiculartrafficcontrol.

4.5.1.1 Stop and Yield Control Warrants

PartTwooftheMUTCDshouldbeconsultedforguidanceonappropriateSTOPandYIELDsignusageandplacement.Ingeneral,STOPorYIELDsignscouldbeusedifoneormoreofthefollowingexist:

Anintersectionofalessimportantroadwithamainroadwhereapplicationofthenormalrightofwayrulewouldnotbeexpectedtoprovidereasonablecompliancewiththelaw;

Astreetenteringadesignatedthroughhighwayorstreet;and/or

Anunsignalizedintersectioninasignalizedarea.



Inaddition,theuseofSTOPorYIELDsignsshouldbeconsideredattheintersectionoftwominorstreetsorlocalroadswheretheintersectionhasmorethanthreeapproachesandwhereoneormoreofthefollowingconditionsexist:

Thecombinedvehicular,bicycle,andpedestrianvolumeenteringtheintersectionfromallapproachesaveragesmorethan2,000unitsperday;

Theabilitytoseeconflictingtrafficonanapproachisnotsufficienttoallowaroadusertostoporyieldincompliancewiththenormalright‐of‐wayruleifsuchstoppingoryieldingisnecessary;and/or

Crashrecordsindicatethatfiveormorecrashesthatinvolvethefailuretoyieldtheright‐of‐wayattheintersectionunderthenormalright‐of‐wayrulehavebeenreportedwithina3‐yearperiod,orthatthreeormoresuchcrasheshavebeenreportedwithina2‐yearperiod.

Atintersectionswhereafullstopisnotnecessaryatalltimes,considerationshouldbegiventousinglessrestrictivemeasures,suchasYIELDsigns.YIELDsignscouldbeinstalled:

Ontheapproachestoathroughstreetorhighwaywhereconditionsaresuchthatafullstopisnotalwaysrequired.

Atthesecondcrossroadofadividedhighway,wherethemedianwidthattheintersectionis30feetorgreater.Inthiscase,aSTOPorYIELDsignmaybeinstalledattheentrancetothefirstroadwayofadividedhighway,andaYIELDsignmaybeinstalledattheentrancetothesecondroadway.

Forachannelizedturnlanethatisseparatedfromtheadjacenttravellanesbyanisland,eveniftheadjacentlanesattheintersectionarecontrolledbyahighwaytrafficcontrolsignalorbyaSTOPsign.

AtanintersectionwhereaspecialproblemexistsandwhereengineeringjudgmentindicatestheproblemtobesusceptibletocorrectionbytheuseoftheYIELDsign.

Facingtheenteringroadwayforamerge‐typemovementifengineeringjudgmentindicatesthatcontrolisneededbecauseaccelerationgeometryand/orsightdistanceisnotadequateformergingtrafficoperation.

4.5.1.2 Multiway STOP Control

MultiwaySTOPcontrolcanbeusefulasasafetymeasureatintersectionsifcertaintrafficconditionsexist.Safetyconcernsassociatedwithmultiwaystopsincludepedestrians,bicyclists,andallroadusersexpectingotherroaduserstostop.MultiwaySTOPcontrolisusedwherethevolumeoftrafficontheintersectionroadsinapproximatelyequal.ThefollowingcriteriashouldbeconsideredformultiwaySTOPsigninstallation.


Wheretrafficcontrolsignalsarejustified,themultiwaySTOPisaninterim

measurethatcanbeinstalledquicklytocontroltrafficwhilearrangementsarebeingmadefortheinstallationofthetrafficcontrolsignal;

Fiveormorereportedcrashesina12‐monthperiodthataresusceptibletocorrectionbyamultiwaySTOPinstallation.Suchcrashesincluderight‐turnandleft‐turncollisionsaswellasright‐anglecollisions;

Minimumvolumes:

Thevehicularvolumeenteringtheintersectionfromthemajorstreetapproaches(totalofbothapproaches)averagesatleast300vehiclesperhourforanyeighthoursofanaverageday,and

Thecombinedvehicular,pedestrian,andbicyclevolumeenteringtheintersectionfromtheminorstreetapproaches(totalofbothapproaches)averagesatleast200unitsperhourforthesameeighthours,withanaveragedelaytominorstreetvehiculartrafficofatleast30secondspervehicleduringthehighesthour,but

Ifthe85thpercentileapproachspeedofthemajorstreettrafficexceeds40mph,theminimumvehicularvolumewarrantsare70percentoftheabovevalues.

Wherenosinglecriterionissatisfied,butwherethesecondandthirdcriteriaareallsatisfiedto80percentoftheminimumvalues.The85thpercentilespeedcriterionisexcludedfromthiscondition.

Athighercombinationsofmajorstreetandminorstreetvolume,trafficsignalsbecomethecommontrafficcontrolmeasure.Roundaboutsshouldalsobeconsideredinthesesituations.Thedecisiontousetrafficsignalsshouldfollowthe“signalwarrants”specifiedintheMUTCD.Thesewarrantsaresummarizedinthefollowingsection.

4.5.1.3 Traffic Signal Warrants

TrafficsignalsshouldonlybeconsideredwheretheintersectionmeetswarrantsintheManualonUniformTrafficControlDevices(MUTCD).Wherewarrantedandproperlyinstalled,trafficsignalscanprovideforanorderlymovementoftraffic.Comparedtostopcontrol,signalscanincreasethetrafficcapacityoftheintersection,reducefrequencyandseverityofcrashes,particularlyright‐anglecrashes,andinterruptheavytrafficflowtopermitothermotorvehicles,pedestriansandbicyclestocrossthestreet.Unwarrantedorpoorlytimedtrafficsignalscanhavenegativeimpacts,includingexcessivedelaytovehicularandpedestriantraffic,disrespectfortrafficcontroldevices

The satisfaction of a traffic signal

warrant or warrants shall not, in

itself, require the installation of a

traffic control signal. The traffic

signal warrant analysis provides

guidance as to locations where

signals would not be appropriate

and locations where they could

be considered further.



ingeneral,increased“cutthrough”trafficoninappropriateroutes,andincreasedfrequencyofcrashes.KeyfeaturesoftheMUTCDwarrantsare:

Warrant1:8‐hourvehicularvolume,metby500to600vehiclesperhouronthemajorstreet(bothdirections,two‐fourlanesrespectively)and150to200vehiclesontheminorstreet(majordirection,one‐twolanesrespectively),foranycombinationof8hoursdaily.Avariation(“interruptionofcontinuoustraffic”)warrantismetwith750to900vehicleshourlyonmajorstreet(two‐fourlanes,bothdirections),and75to100vehicleshourly(majordirection,one‐twolanes),ontheminorstreet.Thesevolumescanbereducedundercertaincircumstances(seePart4oftheMUTCDfordetails).

Warrant2:four‐hourvehicularvolume,metwhentheplottedpointsforeachofanyfourhoursrepresentingthevehiclesperhouronthemajorstreet(totalofbothapproaches)andthecorrespondingvehiclesperhouronthehigher‐volumeminor‐streetapproach(onedirectiononly)allfallabovetheapplicablecurveintheMUTCD.

Warrant3:peakhour,metwhentheplottedpointsforonehourrepresentingthevehiclesperhouronthemajorstreet(totalofbothapproaches)andthecorrespondingvehiclesperhouronthehigher‐volumeminor‐streetapproach(onedirectiononly)fallabovetheapplicablecurveintheMUTCD.

Warrant4:pedestrianvolume,metwhentheplottedpointsforeachofanyfourhoursofthevehiclesperhouronthemajorstreet(totalofbothapproaches)andthecorrespondingpedestriansperhourcrossingthemajorstreet(totalofallcrossings)allfallabovethecurveintheMUTCDforthePedestrianFourHourWarrant;orwhentheplottedpointsforonehourofthevehiclesperhouronthemajorstreet(totalofbothapproaches)andthecorrespondingpedestriansperhourcrossingthemajorstreet(totalofallcrossings)allfallabovethecurveintheMUTCDforthePedestrianPeakHourWarrant.

Warrant5:schoolcrossing,metwithaminimumof20studentscrossinginthehighestcrossinghour,andlessthanoneacceptablegapinthetrafficstreamperminuteduringthehighestcrossinghour.Engineeringjudgmentandattentiontootherremedies(suchascrossingguards,improvedsignage,andcrossingislands)arestronglyrecommended.

Warrant6:coordinatedtrafficsignalsystem,whereexistingtrafficsignalspacingdoesnotprovidethenecessarydegreeofplatooning(grouping)oftraffic,asneededtoprovideaprogressiveoperation.

Warrant7:crashexperience,metwhencrashdataindicatesaproblemremediablebytrafficsignalinstallation.

Warrant8:roadwaynetwork,metwhenthestreethasimportanceasaprincipalroadwaynetworkorisdesignatedasamajorrouteonanofficialplan.

Warrant9:intersectionnearagradecrossing,metwhenagradecrossingexistsonanapproachcontrolledbyaSTOPorYIELDsignandthetrackis


within140feetofthestoplineoryieldlineontheapproach;andwhenduringthehighesttrafficvolumehourduringwhichrailtrafficusesthecrossing,theplottedpointrepresentingthevehiclesperhouronthemajorstreet(totalofbothapproaches)andthecorrespondingvehiclesperhourontheminor‐streetapproachthatcrossesthetrack(onedirectiononly,approachingtheintersection)fallsabovetheapplicablecurveintheMUTCD.

Aspartoftheintersectiondesignprocess,thedetailedwarrants,aspresentedintheManualonUniformTrafficControlDevices,shouldbefollowed.Evenifwarrantsaremet,asignalshouldbeinstalledonlyifitisdeterminedtobethemostappropriatetrafficcontrolbasedonthecontextoftheintersection,assignalsdonotaddcapacitytoanintersection,theyareintendedtoprovideorder.Inmanyinstances,trafficsignalinstallationwillrequiresomewidening.

4.5.1.4 Pedestrian Travel at Traffic Signals

Trafficsignaldesignshouldencompassthefollowingprinciplesforaccommodatingpedestrians:

Ingeneral,theWALKindicationshouldbeconcurrentwiththetrafficmovingontheparallelapproach.ItshouldbenotedthatConnDOTdoesnotutilizeconcurrentpedestriansignalphasingatStateownedandmaintainedsignalizedintersections.

TimingofpedestrianintervalsshouldbeinaccordancewithMUTCDandADArequirements.

Pedestriansshouldbegiventhelongestpossiblewalktime,whilemaintainingbalancebetweenmotorvehicleflowandpedestriandelay.Inmostcases,theWALKintervalshouldincludeallofthetimeinthevehiclegreenphase,exceptfortherequiredclearanceinterval.Althoughnotpreferred,theminimumlengthfortheWALKintervalonapedestriansignalindicationis7seconds,longenoughforapedestriantostepoffthecurbandbegincrossing.Insomelimitedcircumstances,wherepedestrianvolumeissmall,walkintervalsasshortas4secondsmaybeused.

Signalsshouldbetimedtoaccommodatetheaveragewalkingspeedsofthetypeofpedestrianthatpredominantlyusestheintersection.(Thelengthoftheclearanceintervaliscalculatedbasedoncrossingtheentirestreetfromcurbramptocurbrampwithanassumedcrossingspeedof3.5feetpersecond).Inareaswhereasignificantportionofexpectedpedestriansareolderorhavedisabilities,awalkingspeedoflessthan3.5feetpersecondshouldbeconsideredindeterminingthepedestrianclearancetime.

Signalcyclesshouldbeasshortaspossible.Shortsignalcyclesreducedelay,andthereforeimprovelevelofserviceforpedestrians,bicyclistsandmotorvehiclesalike.



Simpletwo‐phasesignalsminimizepedestrianwaitingtimeandarethereforepreferableforpedestrianservice.Insomecases,simpletwo‐phasesignalsalsoprovidethebestserviceformotorvehicletraffic.

Leadingpedestrianintervals(LPI)givepedestriansanadvanceWALKsignalbeforethemotoristsgetaconcurrentgreensignal,givingthepedestrianseveralsecondstostartinthecrosswalk.Thismakespedestriansmorevisibletomotorvehiclesandallowspedestrianstoinitiatetheircrossingwithoutconflictwithothertraffic.

Goodprogressionformotorvehiclesthroughaseriesofsignalscanbeobtainedoverawiderangeofvehiclespeeds.Inareaswithhighvolumesofpedestrians,alowbutwell‐coordinatedvehicleprogressionspeed(20‐30mph)canbeusedwithlittleornonegativeimpactonvehicularflow.

Pedestrianphasesincorporatedintoeachsignalcycle,ratherthanon‐demandthroughacallbutton,maybepreferableforsomeconditions.

Callbuttonuseshouldbelimitedtoonlythoselocationswithtraffic‐actuatedsignals(i.e.,wherethesignaldoesnotcycleintheabsenceofminorstreettraffic).

Wherecallbuttonsareused,anotificationsignshouldbeprovided.

Pedestriancallbuttonactuationshouldprovideatimelyresponse,particularlyatisolatedsignals(i.e.,notinaprogressionsequence),atmid‐blockcrossings,andduringlow‐trafficperiods(night,forexample).

Atfour‐wayintersections,curbextensionscouldbeprovidedtodecreasethepedestriancrossinglength.

Pedestriancallbuttonsandthesignalstheyactivateshouldbemaintainedingoodrepair.Thisrequiresreliableandpredictablebuttonoperation,functionalsignaldisplays,andthecorrectorientationofpedestriansignalheads.

TheMUTCDrequiresthatallpedestriansignalheadsusedatcrosswalkswherethepedestrianchangeintervalismorethan7secondsshallincludeapedestrianchangeintervalcountdowndisplayinordertoinformpedestriansofthenumberofsecondsremaininginthepedestrianchangeinterval.Thecountdownishelpfultopedestriansbyprovidingtheexactamountofcrossingtimeremaining,therebyallowingthemtomaketheirowninformedjudgmentoninitiatingacrossing,ratherthansimplyfollowingtheWALK/DON’TWALKphases.GuidelinesforthedisplayandtimingofcountdownindicatorsareprovidedintheManualonUniformTrafficControlDevices.Accessiblepedestriansignalsanddetectorsprovideinformationinnon‐visualformatssuchasaudibletones,speechmessages,and/orvibratingsurfaces.GuidelinesfortheinstallationofsuchfeaturesareprovidedintheManualonUniformTrafficControlDevices.


Locating Pedestrian Call Buttons

Pedestriansignalcallbuttonsareusedtoinitiateapedestriancrossingphaseattrafficsignals.Whereneeded,pedestriancallbuttonsshouldbelocatedtomeetthefollowingcriteria:

Theclosestcallbuttontoacrosswalkshouldcallthepedestriansignalforthatcrosswalk.

Anarrowindicatorshouldshowwhichcrosswalkthebuttonwillaffect.

Thecallbuttonshouldalignwiththecrosswalkandbevisibletoapedestrianfacingthecrosswalk,unlessspaceconstraintsdictateanotherbuttonplacement.

Pedestrianactuatedcallbuttonsshouldbeplacedinlocationsthatareeasytoreach,atapproximately3.5feetbutnomorethanfourfeetabovethesidewalk.

Accessible Pedestrian Signal Systems

Atsignalizedintersections,peoplewithvisionimpairmentstypicallyrelyonthenoiseoftrafficalongsidethemasacuetobegincrossing.Theeffectivenessofthistechniqueiscompromisedbyvariousfactors,includingincreasinglyquietcars,permittedrightturnsonred,pedestrianactuatedsignalsandwidestreets.Further,lowtrafficvolumesmaymakeitdifficulttodiscernsignalphasechanges.Technologiesareavailablethatenableaudibleandvibratingsignalstobeincorporatedintopedestrianwalksignalsystems.TheManualonUniformTrafficControlDevicesoffersguidelinesontheuseofaccessiblepedestriansignals.TheFederalAccessBoard’sreviseddraftversion(2005)oftheADAAccessibilityGuidelinesforPublicRight‐of‐Wayrequirestheuseofaudiblesignalswithallpedestriansignals.

4.6 Intersection Capacity and Quality of Service

The“capacity”ofanintersectionforanyofitsusers(motorvehicles,pedestrians,bicyclists,transitvehicles)isthemaximumrateofflowofthatusertypethatcanbeaccommodatedthroughtheintersection.Typically,capacityisdefinedforaparticularusergroupwithoutotherusergroupspresent.Thus,forexample,motorvehicularcapacityisstatedintermsofvehiclesperhour,undertheassumptionthatnootherflows(pedestrians,bicycles)aredetractingfromsuchcapacity.Multimodalcapacityistheaggregatecapacityoftheintersectionforallusersoftheintersection.Insomecases,themaximummultimodalcapacitymaybeobtainedwhilesomeindividualuserflowsareatlessthantheirindividualoptimumcapacity.Qualityofservicecanbedefinedinacoupleofdifferentways.Onemeasureofeffectivenessthatcanbeusedtounderstandthequalityoftransportationatanintersectionforagivenmodeisthecontroldelayencounteredbytheuseratthe



intersection.Controldelay,aresultoftrafficcontroldevicesneededtoallocatethepotentiallyconflictingflowsattheintersection,reflectsthedifferencebetweentraveltimethroughtheintersectionatfreeflowversustraveltimeundertheencounteredconditionsoftrafficcontrol.Fordrivers,controldelayconsistsoftime“lost”(fromfree‐flowtime)duetodeceleration,waitingatsignals,STOPorYIELDsigns,waitingandadvancingthroughaqueueoftraffic,andacceleratingbacktofree‐flowspeed.Forpedestriansandbicyclists,decelerationandaccelerationtimesareinsignificant,andcontroldelayislargelythetimespentwaitingatsignals,STOP,orYIELDsigns.Anotherwayistodefinethequalityofserviceistodeterminethe“Levelofservice”whichisdefinedbytheHighwayCapacityManual,foreachtypeofintersectionuser.Foreachuser,levelofserviceiscorrelatedtodifferentfactorsbecauseeachmodehasuniqueissuesthatimpactthequalityofitsusers.Forautomobileslevelofserviceisgovernedbycontroldelay.Forbicyclesandpedestriansthelevelofserviceisdeterminedbyseveralfactorsthatdescribetheconditionsofthebicycleandpedestriansfacilities,theimpactsofmotorvehicletrafficonthesemodes,andthecharacteristicsofbicycleandpedestriantraffic.Eachoftheseanalysesisdescribedfurtherinsection4.6.2anddetaileddiscussionsoftheanalysesmethodologyarepresentedintheHighwayCapacityManual.Levelsofserviceanddelayaresomewhatcorrelatedtocapacityinthatlevelsofservicedeclinedascapacityisapproached.

4.6.1 Capacity

“Capacity”(themaximumpossibleflow)differsimportantlyfrom“servicevolumes”(flowsassociatedwiththequalityofflow,typicallystatedas“LevelofService”or“LOS”).Thesetwotermsarediscussed,forpedestrian,bicycle,andmotorvehicleflow,inthefollowingsections.

4.6.1.1 Pedestrian Flow Capacity

Unlikemotorvehiclesandbicycles,pedestrianfacilities(sidewalksandcrosswalks)donothaveadefaultcapacityforanalysispurposes.Onemeasurethatcanprovideinsightintothequalityandconditionofpedestrianfacilitiesisthepedestrianspacemeasuredinsquarefeetperpedestrian(ft2/p).TheHighwayCapacityManualsuggeststhatoncepedestrianspacefallsbelow15ft2/p,pedestrianspeedsbegintofallandtheabilityforpedestrianstomoveontheirdesiredpathbecomesrestricted.MethodsforcalculatingpedestrianspaceforsidewalksandcrosswalksarepresentedintheHighwayCapacityManual.Atsignalizedintersections,eachapproachwillaccommodatepedestriancrossingsfor10to20percentofthetime,reflectingtheintervalsthatpedestrianscanbegintocrosswithassuranceofcompletingtheircrossingwhiletrafficisstoppedfortheirapproach.Atunsignalizedlocations,thetimeavailableforpedestrianflowisdictatedbymotorvehiclevolumeandlengthofthecrossing.Thesetwofactors,whichgovernthenumber


of“gaps”inthemotorvehiclestreamavailableforsafepedestriancrossing,mustbemeasuredon‐sitetoestablishthepedestrianflowcapacityofanunsignalizedintersection.ThesignalwarrantsintheMUTCDofferguidanceoncombinationsofmotorvehicleandpedestrianvolumesthatmayjustifyasignal,andthereforereflectthepedestriancapacityofunsignalizedintersections.

4.6.1.2 Bicycle Flow Capacity

Abicyclelane(4‐6feetinwidth)can,withuninterruptedflow,carryavolumeofaround2,000bicyclesperhourinonedirection.Atsignalizedintersections,bicyclelanesreceivethesamegreensignaltimeasmotorvehicles,typically20‐35percentofthetotaltime.Thehourlycapacityofabicyclelane,atasignalizedintersection,istherefore400to700bicyclesperhour.Atsignalizedintersectionswithoutbicyclelanes,bicyclesarepartoftheapproachingvehiculartrafficstream.Thecombinedvehicularcapacity(motorvehiclesaswellasbicycles)isestablishedasdefinedinSection4.6.1.3.Atunsignalizedintersectionswithbicyclelanesonthemajorstreet,thebicycleflowcapacityistheuninterruptedflowvolumeof2,000bicyclesperhour.FortheSTOP‐controlled(minorstreet)approach,theflowcapacityforbicycles,whetherinbicyclelanesornot,isgovernedbythespeed,motorvehiclevolume,andnumberoflanesofmajorstreettraffic.Thesefactorsrequiremeasurementon‐sitetoestablishthebicycleflowcapacityofSTOPcontrolledapproaches.

4.6.1.3 Motor Vehicle Capacity

Atunsignalizedintersections,motorizedvehiclecapacityisgovernedbytheabilityofmotorvehicles(ontheminorstreet)underSTOPcontrolorYIELDcontroltoenterorcrossthestreamofmovingmotorvehiclesonthemajorstreet.Thiscapacityisreachedasthenumberofmotorvehiclesonbothmajorstreetapproaches,plusthenumberonthebusiestminorstreetapproachtotals1,200motorvehiclesinasinglepeakhour,ortotals900motorvehicleshourlyoveracontinuous4‐hourperiod.Atthesepoints,enteringorcrossingthemajorstreetfromtheSTOPcontrolledorYIELDcontrolledminorstreetbecomesdifficultorimpossible.FurtherincreasesinintersectioncapacityatSTOPcontrolledorYIELDcontrolledintersectionscanbegainedbyreplacingstoporyieldcontrolwithsignalcontroloraroundabout.Trafficsignalwarrants1,2,and3discussedpreviouslyprovidedetailedguidanceonspecificcombinationsofmajorandminorstreetvolumesassociatedwiththetransitionfromSTOPcontrolorYIELDcontroltotrafficsignalcontrol.Atsignalizedintersections,motorvehiclecapacityisgovernedbythenumberoflanesapproachingtheintersection,thenumberofreceivinglanes,andtheamountofgreensignaltimegiventotheapproach.Thetotalgreentimeavailabledecreasesasmoresignalphasesandthereforemoreredandyellow“losttime”areincludedinthesignalsequences.



Asimplebutreliablemeasureofasignalizedintersection’scapacityisits“criticallanevolume”capacity(CLVcapacity),definedasthemaximumsumofconflictingmovementsthatcanbemovedthroughtheintersectionatagivenlevelofserviceasshowninExhibit4‐6.SignalizedintersectioncapacityisnearedastheCLVreaches1,500hourlymotorvehiclesforintersectionswithtwosignalphases(theminimumpossible)or1,375to1,425forintersectionswithmorethantwosignalphases.ThissimpleCLVmeasurecanbeusedforinitialassessmentofanintersection’scapacity,andalsoasareasonablenesscheckonproceduresintheHighwayCapacityManual.TherelationshipbetweenCLVcapacityandlevelofservice(describedinmoredetailinSection4.6.2)issummarizedinExhibit4‐7.Atroundabouts,motorvehiclecapacityisgovernedbytheabilityofenteringtraffictoenterthestreamofmotorvehiclesinthecirculatingroadway.Thiscapacityisnearedasthevehicularvolumeinthecirculatingroadway(singlelane)approaches1,800motorvehicleshourly.Atthispoint,enteringthestreamofcirculatingmotorvehicleswithintheroundaboutbecomesdifficultorimpossible.Atthisthreshold,additionallanesononeormoreapproachesandasecondcirculatinglaneshouldbeconsidered.


Exhibit 4‐6 Computing Critical Lane Volume

Notes: Critical lane volume (CLV) is the sum of main street CLV plus the cross street CLV. The main street CLV is the greater of either: (A) eastbound through and right per lane + westbound left, or (B)

westbound through and right per lane + eastbound left. Similarly, the cross street CLV is the greater of either: (A) northbound through and right per lane + southbound left, or (B)

southbound through and right per lane + northbound left. Total intersection CLV = main street CLV + cross street CLV = 390 + 480 = 870. Source: Transportation Research Board, Circular Number 212, TRB 1980.



Exhibit 4‐7 Traffic Flow Related to Critical Lane Volumes1

Flow Condition

Corresponding Highway Capacity

Manual Level of Service

Corresponding Critical Lane Volume (CLV) Vehicles Per Hour

Signal Phases

2 Phase 3 Phase 4 Phase

Free Flowing (no loaded cycles)

A, B, C Less than 1200 Less than 1140 Less than 1100

Prevailing Level of Peak-Hour Congestion in Towns and Urban Areas

D 1200 – 1350 1140-1275 1100-1225

Approaching Capacity E, F 1350 – 1500 1275 - 1425 1225 – 1375

Source: CLV/LOS relationship from Table 6, Transportation Research Circular Number 212, Transportation Research Board, 1980. 1 Based on a peak hour factor of 0.9, limited heavy vehicles, limited turning volumes, and somewhat flat grades.

4.6.1.4 Multimodal Capacity

Undersomecombinationsofusersandintersectionconfiguration,achievingadesiredflowforoneusergroupdiminishesthecapacityforanothergroup.Typicalsituationsinclude:

Signalswithnumerousphases(5to6ormore)wherethe“walk”phaseisconstrainedbythegreentimeneededforvehiclesonotherapproachespermittedduringthe“walk”phase.

Wherebusesandothertransitvehiclesstopforpassengerloading/unloadinginalaneoftrafficapproachingordepartinganintersection.

Whereexceptionallylargevolumesofpedestrianscrossinganapproachrequirea“walk”phasetimegreaterthanthegreensignaltimeneededformotorvehiclespermittedtomoveduringthesamephase.

Insituationslikethese,intersectiondesignshouldflowfromacarefullyconsideredbalancingoftheneedsofthevarioususergroups.However,whendeterminingthisbalance,thedesigneralsoneedstoconsiderthatexcessivemotorvehicledelayscanleadtoundesirablecut‐throughtrafficpatternsonstreetsnotintendedforhighthroughvolumes.Alternatively,byprovidingmoreefficientmultimodalopportunities,themotorvehicledemandmaybereducedthroughusermodalchoice.

4.6.2 Level of Service (LOS)

Levelofserviceisonemeasureofusersatisfactionwithanintersection.Exhibit4‐8presentsthemeasuresusedtodeterminelevel‐or‐servicebymode.Formotorvehicles,levelofserviceislinkedtoaveragedelaywhileforbicyclesandpedestrianstheLOSisderivedfromanLOSscorewhichincorporatesseveralfactorsthatimpacttravelforthesemodes.


Exhibit 4‐8 Measures to Determine Level of Service by Mode

Intersection Type Mode

Pedestrian Bicycle Automobile

Signalized LOS score LOS score Delay

Unsignalized Delay N/A Delay and v/c ratio

Roundabout Delay N/A Delay and v/c ratio Source: Highway Capacity Manual, 2010

4.6.2.1 Pedestrian Level of Service

PedestrianlevelofserviceisdefinedbythepedestrianLOSscoreordelay,dependingonintersectiontype.Exhibit4‐8summarizespedestrianlevelofserviceforintersections.

Exhibit 4‐8 Pedestrian Level‐of‐Service (LOS) Criteria at Intersections

Intersection Type

LOS Signalized Intersection

LOS score Unsignalized Intersection

Delay (s) Roundabout

Delay (s)

A ≤ 2.00 0 – 5 0 – 5

B > 2.00 – 2.75 5 – 10 5 – 10

C > 2.75 – 3.50 10 – 20 10 – 20

D > 3.50 – 4.25 20 – 30 20 – 30

E > 4.25 – 5.00 30 – 45 30 – 45

F > 5.00 >45 >45

Source: Highway Capacity Manual, 2010

Forsignalizedintersections,thepedestrianLOSscoreiscalculatedbasedonseveralfactors.Thecrosswalkadjustmentfactorrepresentsthedeteriorationinpedestriantravelqualitycausedbyconflictingmotorvehicleandpedestrianpaths.Themotorizedvehiclevolumeadjustmentfactorrepresentsthevolumesofvehiclesthatwillconflictwiththepedestriancrosswalk.Themotorizedvehiclespeedadjustmentfactorrepresentstheimpactofvehiclespeedonpedestrian’sabilitytocrossanintersection.Lastly,thepedestriandelayfactorturnsthepedestriandelaycausedbyatrafficsignalintoafactorintheLOSscore.AtunsignalizedintersectionsdelayistheonlyfactorthatdeterminestheLOSforpedestrians.Thedelayincrossingthemajorstreet(i.e.,approachesnotcontrolledbySTOPcontrol)isthetimeneededforpedestrianstoreceiveagapintrafficadequatetocrosssafely.Gapsare,inturn,relatedtothevolumeoftrafficandthelikelihoodofdriver’syieldingtherightofwaytoapedestrianinthecrosswalk.PedestrianscrossingSTOPcontrolledorYIELDcontrolledapproachesdonothavetowaitforagapintraffic,butwaitforthefirstvehicleinlinetoyieldrightofway.PedestriancrossingsacrossSTOPcontrolledorYIELDcontrolledapproachesarelikelytohaveasignificantlybetterlevelofservicethancrossingsattheuncontrolledapproaches.



Atroundabouts,pedestriansmaywalkfurtherthanatasignalizedintersectionduetothediameterofthecirculatingroadway.However,pedestrianscrossonlyasinglelaneoftrafficatatime,takingrefugeinthesplitterisland.Actualdelayislikelytobecomparableorlessthanatanormallysituatedcrosswalk.PedestrianLOSatroundaboutsiscalculatedusingthesamemethodasforunsignalizedintersections.

4.6.2.2 Bicycle Level of Service

Unlikeautomobiles,bicyclistsintheirlane(orshoulder)“bypass”stoppedmotorvehicles,andthereforeseldomexperiencedelayduetoqueuing.Delayduetoqueuingofbicyclesisafactoronlywithextraordinaryvolumes.Therefore,LOSforbicyclesisdeterminedbyanLOSscoremuchlikethepedestrianLOSatsignalizedintersections.LevelofserviceforbicyclesatsignalizedintersectionsissummarizedinExhibit4‐9.ThefactorsthatcontributetothebicycleLOSscorearethecross‐sectionadjustmentfactorandthemotorvehicleadjustmentfactor.HavingbicyclelanesandwideshoulderswillimprovetheLOSscorewhilelargevolumesofvehiclesorpoorlymanagedvehicleswillworsenthescore.

Exhibit 4‐9 Bicycle Level‐of‐Service (LOS) Criteria at Signalized Intersections

Level of Service LOS Score

A ≤ 2.00

B > 2.00 – 2.75

C > 2.75 – 3.50

D > 3.50 – 4.25

E > 4.25 – 5.00

F > 5.00 Source: Highway Capacity Manual, 2010

Atunsignalizedlocations,bicyclesonthemajorstreetarenotlikelytobedelayedbecausetheyhavepriorityoverminorstreetvehicles.BicyclistscrossingorenteringthemajorstreetfromaSTOPcontrolledminorstreetaredelayedbytheamountoftimerequiredtofindanacceptablegap.Fieldmeasurementofthistime,duringpeakaswellasoff‐peakperiods,isthepreferredmethodofestablishingthisdelay.Atroundabouts,bicyclesgenerallyexperiencethesamedelaysasmotorvehiclesasthey“takethelane”inapproachingthecirculatingroadway.Currently,thereisnotaHighwayCapacityManualrecommendedmethodforanalyzingbicycleLOSatunsignalizedintersectionsorroundabouts.


4.6.2.3 Motor Vehicle Level of Service (LOS)

Motorvehiclelevelofservice(LOS)atanintersectionisdefinedbytheHighwayCapacityManualintermsofdelayexperiencedbyamotorvehicletravelingthroughtheintersectionduringthebusiest(peak)15minutesoftrafficoftheday.Typically,delayisaveragedoverallapproacheswithtrafficcontrols(STOP,YIELD,orsignal).Itcanalsobecomputedseparatelyforeachapproachoreachlanegroup(adjacentlaneswithatleastonemovementincommon;forexampleonelanewiththroughmovementadjacenttoalanewiththrough/right‐turnmovement).Exhibit4‐10providesmotorvehicularlevel‐of‐servicecriteriaatintersections.Forunsignalizedintersectionsandroundaboutsitisimportanttonotethatifthefacilityisoperatingatavolume‐to‐capacityratioexceeding1.0,regardlessofcalculateddelay,thefacilityisautomaticallyassignedanLOSF.Also,althoughthecriteriaforunsignalizedintersectionandroundaboutarethesamethemethodologyfordeterminingdelayisdifferentforeachfacility.

Exhibit 4‐10 Motor Vehicular Level of Service (LOS) Criteria at Intersections

Intersection Type

LOS Measure Signalized Intersection

Delay1 (s)

Unsignalized Intersection2

Delay (s)

Roundabout2

Delay (s)

A Less than 10.0 Less than 10.0 Less than 10.0

B 10.1 to 20.0 10.1 to 15 10.1 to 15

C 20.1 to 35.0 15.1 to 25 15.1 to 25

D 35.1 to 55.0 25.1 to 35 25.1 to 35

E 55.1 to 80.0 35.1 to 50 35.1 to 50

F Greater than 80.0 Greater than 50.0 Greater than 50.0

Source: Highway Capacity Manual, (HCM 2010) Transportation Research Board, 2010 1 Delay is “control delay” as defined in HCM 2010, and includes time for slowing, waiting in queues at the intersections,

and accelerating back to free-flow speed. 2 If the v/c ratio of the intersection being analyzed exceeds 1.0 the LOS is automatically F regardless of delay.

Improving Vehicular Level of Service at Intersections

Whenattemptingtoimprovethemotorvehicularlevel‐of‐serviceatintersections,thedesignershouldworktoensurethatthemeasurestoimprovemotorvehicularlevelofservicedonothaveadisproportionatelynegativeimpactonotherintersectionusers.Thereareseveraltechniquescommonlyusedtoachievethisobjectiveasdescribedinthefollowingparagraphs.Changingthetypeoftrafficcontrol(forexample,transitioningfromSTOPcontroltosignalizationortoaroundabout)mayaddmotorvehicularcapacityatintersections.Atintersectionsalreadysignalized,morecapacitymaybegainedfromreplacingfixed‐timesignalcontrolwithmotorvehicle,bicycleandpedestrian‐actuatedcontrol.Auxiliaryleft‐turnandright‐turnlanes(seeSection4.4.2)increaseintersectioncapacitybyremovingslowingorstoppedvehiclesfromlanesotherwiseusablebythroughtraffic.Auxiliarythroughlanes(seeSection4.4.2)canbeappropriateatisolatedsignalizedintersectionsand



increaseintersectioncapacity.However,thelengthoftheauxiliarylanesforthereceivinglegwilldeterminetheabilityofthisextrathroughtraffictomerge.Ifauxiliarylanesaretooshort,theymaycongesttheintersectionandblocktheminorstreettraffic,andfailtoreducedelay.Thedesignershouldalsonotethataddingauxiliarylanesincreasesthecrossingdistanceforpedestrians.ThedesignershouldensurethatthelevelofserviceincreasesprovidedformotorvehiclesdonotresultinlargedegradationsinLOSforotherusers.Wherewideningtoprovideauxiliarylanesisplanned,thedesignershouldconsidercrossingislandsandotherfeaturestoensuretheabilityforpedestrianstocross.Atroundabouts,capacitycanbeincreasedbyanadditionalapproachlaneandacorrespondingsectionofadditionalcirculatinglane.Addingparallellinksofstreetnetworkmayreducetrafficvolumesatanintersection,therebyeliminatingorpostponingtheneedtoincreaseitscapacity.

4.6.2.4 Multimodal Level of Service

Asdescribedthroughoutthissection,thedesignershouldstrivetoachievethehighestlevelofserviceforallintersectionusers,giventhecontextanddemandsencountered.TheintersectionlevelofservicecommonlyfoundinvariousareatypesisshowninExhibit4‐11.Thedesignerneedstounderstandthepotentialimpactthatintersectiongeometricsandtrafficcontrolwillhaveonlevelofserviceforallmodes.Generally,thedesignershouldtrytoimproveormaintainexistinglevelsofservice.Inmostinstances,thedesignershouldnotproposeadesignthatprovidesalevel‐of‐serviceimprovementforoneusergroupattheexpenseofanother.

Exhibit 4‐11 Common Intersection Level‐of‐Service Ranges by User Group and Area Type

Level-of-Service Ranges Pedestrian Bicycle Motor Vehicle

Rural Natural A-B A-C A-C Rural Village A-C A-D A-E(1) Rural Developed A-C A-C A-C Suburban High Density B-E C-E C-E Suburban Village/Town Center A-D C-E C-F(1) Suburban Low Density A-C A-C A-D Urban Park A-C A-D B-E Urban Residential A-C B-D C-E Urban Central Business District A-D B-E D-F(1) 1 In these instances, queuing at intersections becomes critical in that there should not be impacts that extend to adjacent

intersections.


4.7 Geometric Design Elements

Thefollowingsectionsdescribemanyofthedetaileddesignelementsassociatedwithintersectionsincludingintersectionalignment,pavementcornerradii,auxiliarylanes,channelizationislands,roundabouts,medianopenings,pedestriancurbcutrampsandcrosswalks,bicyclelanetreatments,andbusstops.

4.7.1 Intersection Alignment

Intersectionalignmentguidelinescontrolthecenterlinesandgradesofboththemajorandminorstreets,inturnestablishingthelocationofallotherintersectionelements(forexample,edgeofpavement,pavementelevation,andcurbelevation).

4.7.1.1 Horizontal Alignment

Ideally,streetsshouldintersectasclosetorightanglesaspractical.Skewedintersectionscanreducevisibilityofapproachingmotorvehiclesandbicycles,requirehigherdegreesoftrafficcontrol,requiremorepavementtofacilitateturningvehicles,andrequiregreatercrossingdistancesforpedestrians.GuidelinesforthemaximumcurvatureatintersectionsaregiveninExhibit4‐12.Curvaturethroughanintersectionaffectsthesightdistanceforapproachingmotorists,andmayrequireadditionaltrafficcontroldevices(warningsigns,stopsigns,signals,pavementmarkingsorroundabouts).Onhigher‐speedroads,superelevationoncurvesmayinclinethecrossslopeoftheintersectioninamanneruncomfortabletomotorists,orinconflictwithintersectionverticalalignmentguidelinesdescribedbelow.Theminimumtangentatcross‐streetapproach(TA)showninExhibit4‐12helpstoassurenecessarysightdistanceattheintersection,andtosimplifythetaskofdrivingformotoristsapproachingtheintersection.Often,insteepterrain,apermissiblegradecannotbeachievedwiththehorizontalalignmentguidelines.Typically,thisdesignchallengeisresolvedbyadheringtoverticalalignmentcriteria,whileincorporatingthenecessaryflexibilityinthehorizontalguidelines.



Exhibit 4‐12 Horizontal Alignment Guidelines at Intersections

Design Speed (MPH)

Minimum Angle of Intersection (AI, degrees) Minimum Curve

Radius, Main Street (RM, feet)

Minimum Tangent Cross

Street Approach (TA, feet)

Arterial Major Street

Collector Major Street

Local Major Street

15 60 60 60 45 30 20 60 60 60 85 30 25 60 60 60 155 30 30 60 60 60 250 30 35 60 60 60 365 45 40 60 60 60 500 45 45 65 60 60 660 45 50 65 65 60 835 60 55 65 65 65 1065 60 60 70 65 65 1340 60

Source: MassDOT

4.7.1.2 Vertical Alignment

Themajorstreetandminorstreetprofileinfluencetheverticalalignmentofanintersection.

Major Street Profile

Theintersectionapproachgradeintheuphilldirection,asshowninExhibit4‐13,affectstheaccelerationofmotorvehiclesandbicyclesfromastoppedcondition,andthereforecanhaveanimpactonvehiculardelayattheintersection.Theintersectionapproachgradeinthedownhilldirectionaffectsthestoppingdistanceofapproachingmotorvehiclesandbicycles.


Theintersectiongradeistheslopeofthepavementwithintheintersectionitself.Excessiveintersectiongradecancausetallvehicles(trucks,buses)totipwhileturning.Intersectiongradecanalsohaveanimpactonaccessibilityforpedestrianswithdisabilities,bycreatingagradeoncrosswalks.

Exhibit 4‐13 Vertical Alignment Guidelines

Source: MassDOT

Minor Street Profile

Theprofileoftheminorstreet,asshowninExhibit4‐14,issubjecttothesameverticalalignmentcriteriaasthemajorstreet;however,severalinherentfeaturesofaminorstreet,particularlyitslowerlevelofusage,willmostlikelypermitalowerdesignspeedfortheminorstreetcomparedtothemajorstreet.WheretheminorstreetisunderSTOPorYIELDcontrol(Exhibit4‐14,PartA),thecrownofthemajorstreetistypicallycarriedthroughtheintersection.Meetingthismajorstreet



cross‐sectioncanresultinminorstreetgradesneartheintersectionthataresteeperthanthatwhichwouldoccurwiththemajorstreetcrownremoved.Atintersectionswherethemajorstreetretainsthecrownthroughtheintersection,theminorstreetcrownisgraduallyreduced,typicallystartingatthebeginningoftheapproachgrade,andcompletedslightlyoutsidetheintersection.Atintersectionswithsignalcontrol,itiscustomarytoremovethecrownfromboththemajorstreetandtheminorstreet.Thisremovalofthecrownisadvisableforthecomfortandsafetyofmotorvehicledriversandbicyclistsproceeding,oneitherstreet,atthedesignspeedthroughagreensignalindication.Atintersectionswithall‐waySTOPcontrol,itmaybedesirabletoremovethecrownfrombothintersectingstreets,toemphasizethatallapproachesareequalintermsoftheirtrafficcontrol.Eliminatingthecrownonthemajorstreetcan,undermanycircumstances,reducetheamountofmodificationthatmustbedonetotheminorstreetprofile(Exhibit4‐14PartB).Themajorstreetcrossslopecanbeinclinedinthesamedirectionattheminorstreetprofile,therebypermittingapproachgradesontheminorstreettobeaccommodatedwithminimalalterationtotheoriginalminorstreetprofile.Wherebothmajorstreetandminorstreetcrownsareeliminated,theirremovalisaccomplishedgradually,typicallyoverthelengthoftheapproachgrade.Whethercrownedornot,pavementgradeswithintheintersectionshouldnotexceedthevaluesgiveninExhibit4‐13.Inadditiontomeetingtheverticalprofileguidelinesasstatedabove,intersectionapproachesonbothmainandminorstreetsaresubjecttotheintersectionsighttrianglerequirements(seeChapter2).Undersomecircumstances,thesesighttrianglerequirementsmaydictateapproachgradesorlengthofapproachgradesdifferingfromthoseindicatedintheverticalalignmentguidelinesabove.


Exhibit 4‐14 Pavement Cross‐slope at Intersections

Source: Transportation Association of Canada

A. Major Street Retains Crown (Stop or Yield control on cross street)

B. Major Street Crown Removed: Signal Control

major street profile

minor street gradeadjusted to reduceapproach grade

minor street crownflattened at approach

to intersection

minor street gradeadjusted to reduce

approach grade

major street crowncarried throughintersection

major streetpavement

major streetpavement

minor streetapproach grade(see Exhibit 6-13for minimum length)

original minor street profile

minor street profile

minor street gradeadjusted to reduceapproach grade

minor streetapproach grade(see Exhibit 6-13for minimum length)

original minor street profile

minor street

major street

minor street crownflattened at approach

to intersection

minor street crowneliminated throughintersection

minor street

minor street



4.7.2 Pavement Corner Radius

Thepavementcornerradius—thecurveconnectingtheedgesofpavementoftheintersectingstreets—isdefinedbyeitherthecurbor,wherethereisnocurb,bytheedgeofpavement.Thepavementcornerradiusisakeyfactorinthemultimodalperformanceoftheintersection.Thepavementcornerradiusaffectsthepedestriancrossingdistance,thespeedandtravelpathofturningvehicles,andtheappearanceoftheintersection.Excessivelylargepavementcornerradiiresultinsignificantdrawbacksintheoperationofthestreetsincepedestriancrossingdistanceincreaseswithpavementcornerradius.Further,thespeedofturningmotorvehiclesmakingrightturnsishigheratcornerswithlargerpavementcornerradii.Thecompoundedimpactofthesetwomeasures—longerexposureofpedestrianstohigher‐speedturningvehicles—yieldsasignificantdeteriorationinsafetyandqualityofservicetobothpedestriansandbicyclists.Theunderlyingdesigncontrolinestablishingpavementcornerradiiistheneedtohavethedesignvehicleturnwithinthepermitteddegreesofencroachmentintoadjacentoropposinglanes.Exhibit4‐15illustratesdegreesofencroachmentoftenconsideredacceptablebasedontheintersectingroadwaytypes.Thesedegreesofencroachmentvarysignificantlyaccordingtoroadwaytype,andbalancetheoperationalimpactstoturningvehiclesagainstthesafetyofallotherusersofthestreet.AlthoughtheExhibitprovidesastartingpointforplanninganddesign,thedesignermustconfirmtheacceptabledegreeofencroachmentusingvehicleturningtemplatespresentedearlierinthischapterandinAASHTO’sAPolicyontheGeometricDesignofHighwaysandStreets.ForStateroadways,cornerradiishouldbeconsistentwiththeConnecticutDepartmentofTransportation’sHighwayDesignManual.Atthegreatmajorityofallintersections,whethercurbedorotherwise,thepavementcornerdesignisdictatedbytheright‐turnmovement.Leftturnsareseldomacriticalfactorincornerdesign,exceptatintersectionsofone‐waystreets,inwhichcasetheircornerdesignissimilartothatforrightturnsatintersectionsoftwo‐waystreets.ThemethodforpavementcornerdesigncanvaryasillustratedinExhibit4‐16anddescribedbelow.

Simplecurbradius:Atthevastmajorityofsettings,asimpleradius(curborpavementedge)isthepreferreddesignforthepavementcorner.Thesimpleradiuscontrolsmotorvehiclespeeds,usuallyminimizescrosswalkdistance,generallymatchestheexistingnearbyintersectiondesignsandiseasilydesignedandconstructed.

Compoundcurvesortaper/curvecombinations:Whereencroachmentbylargermotorvehiclesmustbeavoided,whereturningspeedshigherthanminimumaredesirable,orwhereangleofturnisgreaterthan90degrees,compoundcurvescandefineacurb/pavementedgecloselyfittedtotheouter(rear‐wheel)vehicletrack.Combinationsoftaperswithasinglecurveareasimple,andgenerallyacceptable,approximationtocompoundcurves.


Turningroadways:Aseparateright‐turnroadway,usuallydelineatedbychannelizationislandsandauxiliarylanes,maybeappropriatewhereright‐turnvolumesarelarge,whereencroachmentbyanymotorvehicletypeisunacceptable,wherehigherspeedturnsaredesired,orwhereangleofturniswellabove90degrees.

4.7.2.1 Simple Curb Radius

Pavementcornerdesignatsimpleintersectionsiscontrolledbythefollowingfactors:

Theturningpathofthedesignmotorvehicle.DesignmotorvehiclesappropriateforthevariousroadwaytypesaresummarizedinSection4.3.3ofthischapter.

Theextent(ifany)ofencroachment,intoadjacentoropposingtrafficlanes,permittedbythedesignmotorvehicledeterminedfromExhibit4‐15.

The“effective”pavementwidthonapproachanddeparturelegsisshowninExhibit4‐17.Thisisthepavementwidthusable,bythedesignmotorvehicle,underthepermitteddegreeofencroachment.Ataminimum,effectivepavementwidthisalwaystheright‐handlaneandthereforeusuallyatleast11‐12feet,onboththeapproachanddeparturelegs.Whereon‐streetparkingispresent,theparkinglane(typically7‐8feet)isaddedtotheeffectivewidthonthoselegs(approach,departureorboth)withon‐streetparking.Typically,legswithon‐streetparkinghaveaneffectivepavementwidthofaround20feet.Theeffectivewidthmayincludeencroachmentintoadjacentoroppositelanesoftraffic,wherepermitted.Amaximumof10feetofeffectivewidth(i.e.,asinglelaneoftraffic)maybeassumedforsuchencroachment.



Exhibit 4‐15 Typical Encroachment by Design Vehicle

To (Departure Street)

For Tractor/Trailer (WB 50) For Single-Unit Truck (SU) For Passenger Car (P)

F

rom

(App

roac

h St

reet

)

Arterial Collector Local Arterial Collector Local Arterial Collector Local

Arterial (Art)

A B C A B C A A A

Collector (Col)

B B C B B C A A A

Local (Loc)

B D D C C D A B B

A, B, C, D defined in above diagrams. Note: Cases C and D are generally not desirable at signal controlled intersections because traffic on stopped street has

nowhere to go. Source: Adapted from ITE Arterial Street Design Guidelines.


Exhibit 4‐16 Methods for Pavement Corner Design

Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 9 Intersections

Exhibit 4‐17 Effective Pavement Widths

Note: The letters A, B, C, and D refer to the typical encroachment conditions illustrated in Exhibit 4-15. Source: MassDOT



Exhibit4‐18summarizesthesimplecurbradiusneededforvariousdesignmotorvehicles,reflectingtheextentofencroachmentandeffectivepavementwidth.Generalguidelinescanbeconcludedforright‐angle(90degree)intersections:

A15‐footsimplecurbradiusisappropriateforalmostallright‐angle(90degree)turnsonlocalstreets.Thisradiuspermitspassengercarstoturnwithnoencroachmentandaccommodatesthesingleunit(SU)truckwithacceptabledegreesofencroachment.Theoccasionaltractor/trailertruck(WB‐50)canalsonegotiatethe15‐footcornerradiuswithinitsacceptabledegreeofencroachment.

Wherethemajorstreetisacollectorstreet,a20‐30footradiusislikelytobeadequate.Whereparkingispresent,yieldinganeffectivewidthof20feet,thetypicaldesignmotorvehiclefortheintersection(theSUtruck)canturnwithlessthana20footcornerradius,withoutencroachment.Onsinglelaneapproachesanddepartures,withnoon‐streetparking,theSUvehiclecanbeaccommodatedwitha25‐footradiusandan8‐footencroachment(i.e.,a20footeffectivewidth)onthedeparture.Atlocationswherenoencroachmentcanbetolerated,aradiusof40feetwillpermittheSUtrucktoapproachanddepartwithinasinglelane.

ForarterialstreetswheretheWB‐50truckisthedesignvehicle,a35‐footradiusisadequateundermostcircumstancesofapproachanddepartureconditions.However,withasingleapproachanddeparturelane,andwithnoencroachmenttolerated,aradiusashighas75feetisrequired.Inthissituation,aturningroadwaywithchannelizationislandmaybeapreferablesolution.

OnStateroadways,cornerradiidesignshouldbeconsistentwiththeCTDepartmentofTransportation’sHighwayDesignManual.Atskewedintersections(turnanglegreaterthan90degrees),thesimpleradiusrequiredfortheSUandWB‐50vehicleissignificantlylargerthanthatneededfor90degreeintersections.Curve/tapercombinationsorturningroadwaysmaybeappropriateinthesesituations.


Exhibit 4‐18 Simple Radius for Corner Design (Feet)

Turn Angle and Effective Width on Approach Leg (feet)

Effective Width on Departure Leg (Feet)

Passenger Car (P)

Single-unit Truck (SU)

Tractor-Trailer (WB-50)

12 20 12 20 24 12 20 24

90O Turn Angle 12 Feet 10 5 40 25 10 75 35 30 20 Feet 5 5(a) 30 10 5 70 30 20

24 Feet (b) (b) 25 5 5(a) 70 25 15

120O Turn Angle

12 Feet 25 10 60 35 25 105 65 50

20 Feet 10 5(a) 50 25 20 95 50 40

24 Feet (b) (b) 45 20 15 95 50 35

150O Turn Angle

12 Feet 50 25 130 90 75 170 130 105

20 Feet 30 10 110 75 60 155 115 95

24 Feet (b) (b) 100 65 55 155 110 80

Source: P, SU and WB-50 templates from A Policy on Geometric Design of Highways and Streets, AASHTO, 2011. (a) Minimum buildable. Vehicle path would clear a zero radius. (b) Maximum of 20 feet (one lane plus parking) assumed for passenger car operation.

4.7.2.2 Curve/Taper Combinations

Thecombinationofasimpleradiusflankedbytaperscanoftenfitthepavementedgemorecloselytothedesignmotorvehiclethanasimpleradius(withnotapers).Thiscloserfitcanbeimportantforlargedesignmotorvehicleswhereeffectivepavementwidthissmall(dueeithertonarrowpavementorneedtoavoidanyencroachment),orwhereturningspeedsgreaterthanminimumaredesired.Exhibit4‐19summarizesdesignelementsforcurve/tapercombinationsthatpermitvariousdesignmotorvehiclestoturn,withoutanyencroachment,fromasingleapproachlaneintoasingledeparturelane.



Exhibit 4‐19 Curve and Taper Corner Design


Exhibit 6‐4‐20 Turning Roadways and Islands

Turning Roadway, Edge of Pavement Angle of Turn

(Degrees) Design Vehicle

Radius (feet) R1-R2-R1

Offset (OS feet)

75 P 100-75-100 2.0 SU 120-45-120 2.0 WB -50 150-50-150 6.5

90 P 100-20-100 2.5 SU 120-40-120 2.0 WB -50 180-60-180 6.5

105 P 100-20-100 2.5 SU 100-35-100 3.0 WB -50 180-45-180 8.0

120 P 100-20-100 2.0 SU 100-30-100 3.0 WB -50 180-40-180 8.5

150 P 75-20-75 2.0 SU 100-30-100 4.0 WB -50 160-35-160 7.0

Note: W (width) should be determined using the turning path of the design vehicle. Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 9 Intersections


4.7.3 Auxiliary Lanes

Thedesignelementsofthreeauxiliarylanestypesaredescribedinthefollowingsections:left‐turnlanes,right‐turnlanes,andthroughlanes.Decelerationandtaperdistancesprovidedbelowshouldbeacceptedasadesirablegoalandshouldbeprovidedforwherepractical.However,inurbanareasitissometimesnotpracticaltoprovidethefulllengthofanauxiliarylane.Insuchcases,atleastpartofthedecelerationmustbeaccomplishedbeforeenteringtheauxiliarylane.Chapter9ofAASHTO’sGeometricDesignofHighwaysandStreetsprovidesmoreinformationforthedesigner.ThedesignofauxiliarylanesonaStateroadwaysshouldbeconsistentwiththeCTDepartmentofTransportation’sHighwayDesignManual.

4.7.3.1 Left‐Turn Lane Design Elements

Left‐turnlanesremovestoppedorslow‐movingleft‐turningmotorvehiclesfromthestreamofthroughtraffic,eliminatingtheprimarycauseofrear‐endcrashesatintersections.Thesafetybenefitsofleft‐turnlanesincreasewiththedesignspeedoftheroad,astheygreatlyreduceboththeincidenceandseverityofrear‐endcollisions.Left‐turnlanesalsoimprovecapacitybyfreeingthetravellanesforthroughtrafficonly.Thesafetyandcapacitybenefitsofleft‐turnlanesapplytoallvehiculartraffic,motorizedaswellasnon‐motorized.However,left‐turnlanesaddtothepedestriancrossingdistanceandpedestriancrossingtime.Theadditionalstreetwidthneededforleft‐turnlanesmayrequirelandtakingorremovalofon‐streetparking.Thelengthsofleft‐turnlanes,illustratedinExhibit4‐21,dependonthevolumeofleft‐turningmotorvehiclesandthedesignspeed.Thelengthoftaperrequiredtoformtheleft‐turnlanevarieswithdesignspeed.Atsignalizedintersections,aconservativeguidelinefordeterminingthestoragelengthofaleft‐turnlaneis150percent(1.5times)ofthelengthoftheaveragenumberofleft‐turningvehiclesarrivingduringasinglesignalcycleinthepeakhour.Amoreanalyticalguidelineforthelengthofrequiredstoragelaneistoobtaintheexpectedlengthoftheleft‐turnqueueandassociatedprobabilitiesfromintersectionanalysiscomputations(computerizedversionsofHighwayCapacityManualmethodologyorderivativeprogramssuchasSYNCHRO).Typically,left‐turnlanesaresizedtoaccommodatethemaximumlengthofqueueforthe95thpercentiletrafficvolumes,aqueuelengththatisexceededononly5percentofthepeak‐hourtrafficsignalcycles.



Exhibit 4‐21 Left‐Turn Lane Design Guidelines

Dimensions for Left-Turn Lane Elements (feet)

Design Speed (mph)

Lane Width

(W, feet)

Deceleration Distance

(feet)1

Storage Distance2

(feet)

Length of Lane2

(L, feet)

Taper Length

(T, feet)3

Widened Taper Length (T, feet)

15-25 10 115 50 165 100 See Note 4 30-35 10 170 50 220 100 See Note 4 40 10-11 275 75 350 110 See Note 4 45 10-11 340 75 415 150 See Note 4 50 11-12 410 75 485 180 See Note 4 55 11-12 485 75 560 180 See Note 4 60 12 530 75 605 180 See Note 4

Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 9 Intersections 1 For deceleration grades of 3 percent or less. 2 Storage distance and therefore total lane length (L) are based on an unsignalized left-turn volume of 100 vehicles hourly.

For larger volumes, compute storage need by formula or from intersection analysis queue calculation. 3 This taper length is not applicable for “widened for turn lane” cases, see note 4. 4 For “widened for turn lane” cases, use T = WS2/60 for speeds less than 45 mph and T = WS for speeds 45 mph and greater.


4.7.3.2 Right‐Turn Lane Design Elements

Rightturnlanesareusedtoremovedeceleratingright‐turningmotorvehiclesfromthetrafficstream,andalsotoprovideanadditionallaneforthestorageofright‐turningmotorvehicles.Wheretheright‐turnvolumeisheavy,thisremovaloftheturningmotorvehiclefromthetrafficstreamcanalsoremoveaprimarycauseofrear‐endcrashesatintersections.Designelementsforright‐turnlanesaresummarizedinExhibit4‐22.

Exhibit 4‐22 Right‐Turn Lane Design Guidelines

Dimensions for Right-Turn Lane Elements (feet)

Design Speed1 (mph)

Lane Width

(W. feet)

Turning Lane Width (WT, feet)

Deceleration Distance

(feet)

Storage Distance2

(feet)

Length of Lane2

(L, feet)

Taper Length (T, feet)

15-25 10 14 115 50 165 100

30-35 10 14 170 50 220 100

40 10-11 15 275 60 335 110

45 10-11 15 340 60 400 150

50 11-12 15 410 60 470 180

55 11-12 16 485 60 545 180

60 12 16 530 60 590 180 Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2004. Chapter 9 Intersections 1 Based on grades of less than three percent for speeds less than 60 mph. Based on grades of less than two percent for

speeds greater than 60mph. 2 Storage distance and therefore total lane length (L) are based on an unsignalized right-turn volume of 100 vehicles

hourly. For larger volumes, compute storage need by formula or from intersection analysis queue calculation.

Right‐turnlanesprovideasafetyandcapacitybenefitformotorizedtraffic.However,inareasofhighpedestrianorbicyclistactivity,thesebenefitsmaybeoffsetbytheadditionalpavementwidthintheintersection,higherspeedsofmotorvehicularturningmovements,



andvehicle/bicyclistconflictcreatedasmotoristsenteraright‐turnlaneacrossanon‐streetbicyclelaneoracrossthepathofbicycletrafficoperatingnearthecurb.

4.7.3.3 General Criteria for Right‐Turn and Left‐Turn Lanes

Criteriaforconsideringinstallationofleft‐turnlanesaresummarizedinExhibit4‐23.Thesecriteriaarebasedonacombinationofleft‐turningmotorvehiclevolumesplusopposingthroughmotorvehiclevolumesatunsignalizedlocations.Forexample,if330vehiclesperhourtraveleastboundat40mphandfivepercentareturningleft,anexclusiveleft‐turnlaneiswarrantedoncethewestboundvolumeexceeds800vehiclesperhour.

Exhibit 4‐23 Criteria for Left Turn Lanes

A. Unsignalized Intersections, Two-Lane Roads and Streets1:

Design Speed

Opposing Volume (motor vehicles

per hour)

Advancing Motor Vehicle Volume (vehicles per hour) 5%

Left Turns 10%

Left Turns 20%

Left Turns 30%

Left Turns 30 mph or less 800 370 265 195 185 600 460 345 250 225 400 570 430 305 275 200 720 530 390 335 40 mph 800 330 240 180 160 600 410 305 225 200 400 510 380 275 245 200 640 470 350 305 50 mph 800 280 210 165 135 600 350 260 195 170 400 430 320 240 210 200 550 400 300 270 60 mph 800 230 170 125 115 600 290 210 160 140 400 365 270 200 175 200 450 330 250 215

B. Signalized Intersections2: Left-Turn Lane Configuration Minimum Turn Volume

Single exclusive left-turn lane 100 motor vehicles per hour Dual exclusive left-turn lane 300 motor vehicles per hour

1 AASHTO Green Book (1990) 2 Source: Highway Capacity Manaual (2000)

Considerableflexibilityshouldbeexercisedinconsideringleft‐turnlanes.Typically,theyinvolvelittleimpacttothesetting,whilegenerallyyieldinglargebenefitsinsafetyanduserconvenience.Left‐turnlanesmaybedesirableinmanysituationswithvolumeswellbelowthosestated.Theseincludetodestinationsofspecialinterest(shopping,majorinstitutions,etc.),orforlocationswithmarginalsightdistanceonthemainroadoraconsistentoccurrenceofrear‐endcrashes.


Wherethereisaneedformultiple,closelyspacedleft‐turnlanes(duetodrivewaysorsmallblocks),itmaybeadvisabletodesignateacontinuouscenterlaneasa“two‐wayleftturnlane”(TWLTL)asdiscussedinChapters3and7.Criteriafortheinstallationofright‐turnauxiliarylanesaremorejudgmentalthanthenumericalguidelinesfortheirleft‐turnlanecounterpart.Positiveandnegativeindicators(i.e.,conditionsfavoringorarguingagainstright‐turnlanes)aresummarizedinExhibit4‐24.

Exhibit 4‐24 Criteria for Right‐Turn Lane Placement

Positive Criteria (Favoring Right-Turn Placement)

Negative Indicators (Arguing Against Right-Turn Lane Placement)

High speed arterial highways In residential areas

High right-turn motor vehicle volumes In urban core areas

High right-turn plus high cross-street left-turn volumes On walking routes to schools

Long right-turn queues Where pedestrians are frequent

Intersection capacity nearly exhausted Low right turn volumes

History of crashes involving right-turning vehicles

Little to no pedestrian activity


4.7.3.4 Auxiliary Through Lane Design Elements

Shortsegmentsofadditionalthroughlane(wideningastreetthroughasignalizedintersection)canbeaneffectivewayofincreasingintersectioncapacityatrelatively“isolated”intersections(forexample,inruralareasandinsettledareaswithaminimumofaboutone‐milespacingbetweensignalizedintersections).Wherethroughlanesareprovided,motoristsapproachingtheintersectionarrangethemselvesintotwolanesoftrafficandmergebacktoasinglelaneoftrafficonthedeparturesideoftheintersection.Mergingunderacceleration(i.e.,onthedeparturesideoftheintersection)workswell,sincegaps(spacesbetweenmotorvehicles)areincreasingasvehiclesaccelerate,leavingnumerousopportunitiestomergeasthetrafficstreamleavestheintersection.DesignelementsforauxiliarythroughlanesaregiveninExhibit4‐25.



Exhibit 4‐25 Auxiliary Through Lane Design Guidelines

Dimensions for Auxiliary Through-Lanes (feet)

Design Speed (mph)

Lane Width (feet)

Taper Length

(T, feet)1

Length of Lane

(L, feet)

15-25 10 WS2/60 See Note 2

30-35 10 WS2/60 See Note 2

40 10-11 WS2/60 See Note 2

45 10-11 WS See Note 2



60 12 WS See Note 2 1 W is the lateral shift required to form the additional through lane. 2 L should be based on anticipated queue derived from intersection operations analysis. Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 9 Intersections and

the Manual on Uniform Traffic Control Devices

4.7.4 Channelization Islands

Channelizationislandsareusedto:

Delineatetheareainwhichmotorvehiclescanoperate; Reducetheareaofmotorvehicleconflict; Bringmotorvehiclemergingintoasafer(smaller)angleofmerge;and Providepedestrianrefuge.

Ideally,channelizationislandsareraisedabovepavementlevel,typicallytocurbheight(6inches).Lesspreferably,theymaybeflushwiththepavementlevel.Bothraisedandflushislandsmaybeconstructedofavarietyofmaterials,includingconventionallyfinishedconcrete,scoredconcrete,orrigidpaversofvarioustypes.Somegeneralcriteriaforthedimensionsofchannelizationislandsinclude:


Triangularislandsshouldbeaminimumof100squarefeetinsurfaceareawithonesideatleast15feetinlength.Linearislandsshouldbeatleast2,andpreferably3feetormorewide.Iftheycontainsigns,theyshouldbeatleast4feetwide.Iftheyintersectpedestriancrosswalksorcontainsigns,theyshouldbeatleast6feetwidewithmaximum1.5percentslope.Theminimumlengthoflinearislandsshouldbe25feet.

Channelizationislandsshouldcontainat‐gradepassagesforbicyclelanes,wheelchairandpedestrianpaths,andshouldgenerallybeplacedtoavoidimpedingbicyclemovement,whetherornotbicyclelanesarepresent.

Theedgesofchannelizationislandsshouldbeoffsetfromthetravellanes,toguidedriverssmoothlyintothedesiredpath.Typically,a2‐footoffsetisappropriate.

TypicalarrangementsandapplicationsofchannelizationareshowninExhibit4‐26.

4.7.4.1 Right‐turn Channelization Islands

Asmallchannelizationislandcandelineatearight‐turnlaneatasimpleintersection(i.e.,whereneithertheapproachnordeparturelaneisflared).Thistypeofchannelizationisappropriateforlarge‐radiuscorners.Amorecommonusefortheright‐turnchannelizationislandisatflaredintersections,whereadecelerationlaneflareisprovidedontheapproachtotheintersection,sometimescombinedwithanaccelerationlaneflareonthedepartureside.Thelargestchannelizationislandsaretypicallyfoundwhereanauxiliaryright‐turnlaneisprovidedonboththeapproachanddeparturesideoftheintersection.Right‐turnchannelizationislandscanbenefitpedestrianscrossingtheaffectedapproachesbyprovidinganinterimrefugeinthecrosswalk.Thisrefugepermitspedestrianstodevotefullattentiontocrossingtheright‐turnlanewithoutneedingtoassureasafecrossingfortherestofthestreet.Fromthechannelizationisland,pedestrianscanthenproceedacrossthethroughlanesoftrafficwithoutthecomplicatingfactorofcrossingtheright‐turnmovement.

4.7.4.2 Divisional Islands

Divisionalislandsareusefulindividingopposingdirectionsoftrafficflowatintersectionsoncurves,orwithskewedanglesofapproach.Insuchinstances,theycanimprovethesafetyandconvenienceforapproachingmotorists.Althoughsuperficiallysimilartomedians,divisionalislandsdifferfromthemintheirshortlengthandrelativelynarrowwidthandarediscussedfurtherlaterinthischapterandinChapter6.

4.7.4.3 Left‐Turn Lane Delineator Islands

Theleft‐turndelineatorislandresemblesashortsectionofmedianisland,withtriangularstripingtoguidetrafficaroundit.Attheintersectionendoftheisland,itisnarrowedtoprovidestorageforleft‐turningmotorvehiclesandbicycles.



Onundividedstreets,theleft‐turnlanedelineatorislandisusedtoformtheleft‐turnbay.Atitsupstreamnose(i.e.,ontheapproachtotheintersection),theislandandassociatedstripingshiftsthethroughtrafficlanetotheright,creatingroomforthetaperandleft‐turnbay.


Exhibit 4‐26 Channelization Islands




4.7.5 Roundabout Geometric Design Elements

ThekeyelementsofgeometricdesignforroundaboutsareshowninExhibit4‐27andinclude:

Thecirculatingroadway,whichcarriesmotorvehiclesandbicyclesaroundtheroundaboutinacounterclockwisedirection.

Thecentralisland,definingtheinnerradiusofthecirculatingroadwayaroundit.

Acoreareawithinthecentralisland,fromwhichmotorvehiclesareexcluded.

Atruckapronareaontheouterperimeterofthecentralisland,traversablebylargemotorvehicles.

Theinscribedcircle,definedbytheouteredgeofthecirculatingroadway.

Splitterislands,onallapproaches,separatingtheenteringfromtheexitingtraffic.

Crosswalksacrossapproachanddepartureroadways.

Thekeydesignelementoftheroundaboutisitsouterdiameter,theinscribedcirclediameter(ICD).Thisdimensiondeterminesthedesignofthecirculatingroadwayandcentralislandwithinit.Thealignmentofapproachanddepartureroadwaysandtheresultingsplitterislandsarealsoestablishedbytheinscribedcircle.ForfurtherinformationonroundaboutdesignrefertotheFHWApublicationRoundabouts:AnInformationalGuide,2010.

4.7.5.1 Inscribed Circle

TheICDisderivedfromthemotorvehicle.Theinscribedcircleisestablishedbytheouterturningradiusofthedesignvehicle,plusamarginforcontingenciesencounteredinnormaloperation.

4.7.5.2 Width of Circulating Roadway

Thewidthofthecirculatingroadwayisestablishedfromtheturningpathofthedesignvehicleplusamargintoallowfornormaloperatingcontingencies.Thecriticalturningmovementistheleftturn,requiringa270degreemovementaroundthecirclewhich,inturn,producesthelargestsweptmotorvehiclepathandtherebyestablishesthewidthofthecirculatingroadway.


Exhibit 4‐27 Circle Dimensions, Single Lane Roundabout

Note: The design vehicle should be the largest vehicle expected to be accommodated on the street. Source Roundabouts: An Informational Guide, FHWA 2010.

4.7.5.3 Central Island

Thediameterofthecentralislandisderivedfromthediameteroftheinscribedcirclelessthewidthofthecirculatingroadway.Typically,centralislandsconsistofacoreareanotintendedtobetraversedbymotorvehiclesandbicycles,borderedbyatruckapronofaslightlyraisedpavementnotintendedtobeusedbyvehiclessmallerthanaschoolbus,butavailablefortheinnerrearwheeltrackoflargermotorvehicles.

4.7.5.4 Entry and Exit Curves

Theentryradiuscanbevariedasdesiredtoachievethedesiredentryspeed.Curvatureislimitedonlybytheneedtoprovidesufficientclearanceforthedesignvehicle.Entranceroadwaysaredesignedsothatthecontinuationoftheinsideedgeoftheentrycurvejoinstangentiallytothecentralisland,whiletheoutsideedgeoftheentrycurvejoinssmoothlyandtangentiallytotheoutsideedgeofthecirculatingroadway.Typically,theentryradii(measuredattheoutsidepavementedge)rangefrom30to100feet.Exitcurvesjointangentiallytotheinnerandouterdiametersoftheroundaboutinthesamemannerastheentrycurve.Theoutsideexitcurvejoinssmoothlyandtangentiallytotheoutsideedgeofthecirculatingroadway,whiletheinsidecurve,ifcontinued,wouldjointangentiallytothecentralisland.Aswiththeentrycurve,thewidthoftheroadwayshouldaccommodatethedesignmotorvehicle.Theexitpathradius(measured



atthecenterlineoftheexitcurve)shouldbeatleastasgreatasthemotorvehiclepatharoundthecirculatingroadway,sothatdriversdonotreducespeeduponleavingthecircle,or,failingthat,overruntheexitcurveandcollidewiththesplitterisland.Frequently,exitcurveshavelargerradiithanentrycurves,toreducethepossibilityofcongestionattheexitpoints.However,theexitspeedshouldalsobeinfluencedbytheaccommodationofpedestriansandbicyclists.

4.7.5.5 Splitter Islands

SplitterislandsareformedbytheseparationbetweentheentryandexitlanesasillustratedinExhibit4‐28.Splitterislandsguidemotorvehiclesandbicyclesintotheroundabout,separatetheenteringandexitingtrafficstreams,assureamergebetweenenteringandcirculatingtrafficatanangleoflessthan90degrees,andassistincontrollingspeeds.Further,splitterislandsprovidearefugeforpedestriansandbicyclists,andcanbeusedasaplaceformountingsigns.Largersplitterislandsaffordtheopportunityforattractivelandscaping,butsignsandlandscapingmustnotobstructsightdistanceforapproachingmotorists.Splitterislandsshouldbeatleast50feetintotallengthtoproperlyalertdriverstotheroundabout.Thesplitterislandshouldextendbeyondtheendoftheexitcurvetoassurethatexitingtraffichascompleteditsturn,andtopreventitfromcrossingintothepathofon‐comingtraffic.


Exhibit 4‐28 Entry/Exit Lanes, Single Lane Roundabouts

Source: Roundabouts: An Informational Guide, FHWA, 2010.

4.7.6 Intersection Median Openings

Atintersectionswhereoneorbothofthestreetshavedividedroadwaysseparatedbyamedian,thedesignofthemedianbecomesanelementintheintersectiondesign.Twofactorscontrolthedesignoftheendsofmediansatintersections:

Theturningpathofmotorvehiclesandbicyclesmakingaleftturnfromtheminorstreetintothemajorstreetcontrolsthelocationandshapeoftheendofthemedianinthedeparturelegofthemajorstreet;and,

Theleftturnfromthemajorstreetintotheminorstreetdeterminesthelocationandconfigurationofthemedianendontheapproachlegofthismovement.

Right‐turnmovementsareseldomafactorinmedianopeningdesign.However,thepresenceofamedianmaylimittheeffectivepavementwidthformotorvehiclesandbicyclesmakingarightturn.Effectivepavementwidth,aspreviouslydiscussed,hasalargebearingonthecornerradiusneededforrightturns.



4.7.6.1 Design Vehicles for Median Openings

Thedesignvehicleformedianopeningsisthesameasthedesignvehicleselectedfortheintersection.Roadswithmediansarelikelytobeclassifiedasarterialroads,withtheappropriatedesignvehiclethereforebeingtheWB‐50truck.However,forsomemedianopenings,thepassengercar(P)orsingleunittruck(SU)designvehiclemaybeappropriate.

4.7.6.2 Permitted Encroachment at Median Openings

Atintersectionsofstreetswithmedians,turningvehiclesmaybepermittedtoencroachintoadjacentlanes,accordingtoguidelinesdiscussedearlier.However,ondividedhighways,encroachmentintoopposinglanesoftrafficisphysicallyimpossible,duetothemedian.Somecategoriesofencroachment,therefore,eventhoughpermissible,maynotbeavailablefortheturninquestion.

4.7.6.3 Median and Design Controls

Theleft‐turnmovementfromtheminorstreetintothedeparturelegofthemajorstreetcontrolstheplacementandshapeoftheaffectedmedianisland.Similarly,theleftturnfromthedividedmajorstreetintotheminorstreetcontrolstheplacementandshapeoftheaffectedmedianislandonthatapproachlegoftheintersection.Whereboththemajorstreetandtheminorstreetaredivided,thefourpossibleleftturnscontrolthelocationandshapesofallfourmedianislands.

4.7.6.4 Median Openings

Animportantdesignelementisthelengthofthemedianopening,assummarizedinExhibit4‐29.Openingdimensionsaregivenfortwoconfigurationsofmedianend:semi‐circularandbullet‐nose.Medianopeningsaregivenforthethreecategoriesofdesignvehicleaddressedthroughoutthischapter:passengercar(P),singleunittruck(SU),andthetractor/50‐foottrailer(WB‐50).


Exhibit 4‐29 Median Openings

Note: R1, R2 and NL determined by design vehicle turning paths. Source: Adapted from A Policy on the Geometric Design of Streets and Highways, AASHTO, 2011. Chapter 9 Intersections



4.7.7 Pedestrian Crosswalks

Crosswalksareacriticalelementofintersectiondesign.Crosswalksareessentialfordesignatingtheappropriatepathoftravelforapedestrianthroughtheintersection.Crosswalksaredefinedbypavementmarkings,texturedpavement,andcoloredpavementasdescribedbelow.Severaltechniquesareavailabletoshortenpedestriancrossingsandforimprovingcrosswalkvisibility,asdescribedbelow.

4.7.7.1 Crosswalk Pavement Markings

Pavementmarkingsindicatetopedestrianstheappropriaterouteacrosstrafficandremindturningmotorvehicledriversandbicyclistsofpotentialconflictswithpedestrians.Thecrosswalkedgenearesttotheintersectionshouldbealignedwiththeedgeofthesidewalknearesttotheroad.Whendifferentpavementtreatmentsareused,crosswalksmustbeboundedbyparallelbars.Atsignalizedintersections,allcrosswalksshouldbemarked.TobeconsistentwithConnDOTpolicy,crosswalksatsignalizedintersectionsshouldbe8‐feetwidewith16‐inchbarsandspaces(forstandardcrossings)or24‐inchbarsandspaces(forschool/elderlyandhandicappedcrossings)ifpossible.Atunsignalizedintersections,crosswalksshouldbemarkedwhenthey:

Helporientpedestriansinfindingtheirwayacrossacomplexintersection;

Helpshowpedestrianstheshortestrouteacrosstrafficwiththeleastexposuretomotorvehiclesandbicycles,andtotrafficconflicts;or

Helppositionpedestrianswheretheycanbestbeseenbyon‐comingtraffic.Whenusedwithoutotherintersectiontreatments,crosswalksaloneshouldnotbeinstalledwithinuncontrolledenvironmentswhenspeedsaregreaterthan40mph.Allcrosswalksontheentriesandexitsofroundaboutsshouldbemarked.Crosswalksaretypicallylocatedonecarlengthbackfromtheyieldlineorcirculatingroadwayatsingle‐laneroundabouts.Crosswalkstobe10‐feetwidewith16‐inchbarsandspaces(forstandardcrossings)or24‐inchbarsandspaces(forschool/elderlyandhandicappedcrossings)atmidblockandunsignalizedlocations.Formoreinformation,refertotheManualonUniformTrafficControlDevices.

4.7.7.2 Vehicular Stop Bar Placement

Wherecrosswalksareprovidedacrossastreetwithastoplineorwithtrafficsignals,thereshouldbeaminimum4‐footspacingbetweentheouteredgeofthecrosswalkandthenearestedgeofthestopbar.StopbarsshouldbedimensionedinaccordancewithguidelinesintheMUTCD.Atsignalizedintersections,theinstallationofloopdetectorswithincrosswalksshouldbeavoided.


4.7.7.3 Methods to Reduce Pedestrian Crossing Distance

Markedorunmarked,crosswalksshouldbeasshortaspossible.Atallintersections,reducingthetimepedestriansareinthecrosswalkimprovespedestriansafetyandmotorvehicleandbicyclemovement.Atsignalizedintersections,reducingthepedestriancrossingdistancecanimprovecapacityforbothmotorvehicles(longergreentime)andforpedestrians(longerWALKinterval).

Curb Extensions

Curbextensionsshortenthecrossingdistance,provideadditionalspaceatthecorner,allowpedestrianstoseemotorvehiclesandbeseenbymotorvehicledriversbeforeenteringthecrosswalk,andkeepparkingawayfromcrosswalks.CurbextensionsarediscussedfurtherinChapter6.

Crossing Islands and Medians

Raisedmediansandtriangularchannelizationislandscanbeusedtointerruptextremelylongcrosswalks.Theseraisedareas:

Allowpedestrianstocrossfewerlanesatatime,reducingexposuretime;

Providearefugesothatslowerpedestrianscanwaitforabreakinthetrafficstream;

Allowpedestrianstofocusontrafficfromonlyonedirectionatatime;

Reducethetotaldistanceoverwhichpedestriansareexposedtoconflictswithmotorvehicles;and,

Mayprovideeasilyaccessiblelocationforpedestriansignalcallbuttons.Ingeneral,fiftyfeetisthelongestuninterruptedcrossingapedestrianshouldencounteratacrosswalk,butislandsandmediansarealsoappropriateforshorterdistances.Islandsandmediansshouldnotbeusedtojustifysignaltimingthatdoesnotallowpedestrianstocompletetheircrossinginonecycle.CrossingislandsarediscussedfurtherinChapter6.

4.7.7.4 Improving the Visibility of Pedestrian Crossings

Safepedestriancrossingisdependentonawarenessbymotoristsofthepedestrian.Methodstoimprovethevisibilityofpedestrians,inadditiontocurbextensions,sometimesincludetexturedcrosswalks,raisedcrosswalks,andflashingbeaconsatmid‐blocklocationsasdiscussedfurtherinChapter6.

4.7.7.5 Pedestrian Crossing Prohibitions

Someintersectioncrossingsincludeconflictsbetweenpedestriansandmotorvehicletrafficthatareespeciallydangerous;however,prohibitingpedestriancrossingshouldbeconsideredonlyinverylimitedcircumstances,forexample:



Whereitwouldbeverydangerousforpedestrianstocross,aswherevisibility

(forpedestrians,motoristsorbicyclists)isobstructedandtheobstructioncannotbereasonablyremoved,andwheresignalizationisnotanoption.

Wheresomanylegalcrosswalksexistthattheyconflictunreasonablywithothermodes,asonanarterialstreetwithmultipleoffsetor"T"intersections.

Crosswalksat“T”andoffsetintersectionsshouldnotbeclosedunlessthereisasafercrosswalkwithin100feetoftheclosedcrosswalk."PedestriansUseMarkedCrosswalk"signsshouldbeusedforcrosswalksclosedtoreduceanexcessofcrosswalksonastreetwith“T”oroffsetintersections."NoPedestrianCrossing"signsshouldbeusedforcrosswalksclosedforpedestriansafety.ThesesignsneedtobeapprovedbytheOfficeofStateTrafficAdministration(OSTA)onroadwaysunderStatejurisdiction.

4.7.8 Pedestrian Curb Cut Ramps

Therearetwopreferredconfigurationsofpedestriancurbcutramps.Theseconfigurationsincludeseveraldesignelements.Boththeconfigurationsanddesignelementsaredescribedinthefollowingsections.

4.7.8.1 Ramp Types

Pedestriancurbcutrampsatmarkedcrossingshallbewhollycontainedwithinthemarkings,excludinganyflaredsides.Twotypesoframpconfigurationsarepreferred—perpendicularrampsandparallelramps.Thefirsthasarampleadingatrightanglesfromthesidewalkintoacrosswalk,whilethesecondhasarampleadingintoalandingthatisflushwiththestreetsurface.Athirdtype,adiagonalramp,isdiscouragedbutpermissibleforcertainspecificintersectionconditions(seebelow)underspecificconditions.

Perpendicular

Wheneverpossible,requiresthatapedestriancurbcutrampisorientedsothatthefalllineoftherampisinlinewiththecrosswalkandperpendiculartothecurb.Whereconditionsarenotconstrained,thedesignershouldlocatetherampsothatbothconditionscanbemet.Aminimumfourfeetlevellandingwithacrossslopedesignedatamaximumof1.5%foreachapproachatthesidewalkandstreetlevelwithinthedesignatedcrosswalkisrequired.

Parallel

Parallelcurbcutrampsareusedwheretheavailablespacebetweenthecurbandthepropertylineistootighttopermittheinstallationofbotharampandalanding.Aminimumfourfootlandingisnecessarybetweenthetworamps.


Diagonal or Apex

Diagonalor“apex”curbcutrampsaresingleperpendicularpedestriancurbcutrampslocatedattheapexofthecorner.Diagonalrampsareonlypermittedunderthefollowingspecificconditionsby:a. Driverorpedestrianlineofsighttoorfromthefrontofthelevellandingontheramp

isimpaired,preventingsafeobservationofcrosswalksorapproachingtrafficattheintersectionbyasignificantimmovableorunalterablestreetscapefeaturesuchasabuildingstructureorhistoricelement,etc.

b. StoplineisbeyondtheallowedlimitasstatedintheManualonUniformTrafficControlDevices.

c. Vaultscontainingelectrical,telecommunication,etc.thatareunderorontheexistingsidewalk.

d. Largeradiuscorners(30feetorgreater).Whenusingdiagonalorapexcurbcutramps,theremustbea4footlevellandingatthebase(street)leveloftherampthatiswithinthemarkedcrosswalk.

4.7.8.2 Design Elements

Keydesignelementsofpedestriancurbcutrampsincludetherampedsection,landingareasandsideflaresasdescribedbelow.

Ramp Section

Theminimumslopepossible(givencurbheightsandsidewalkwidth)shouldbeusedforanypedestriancurbcutramp.Themaximumcurbcutrampslopeis8.33%inthebuiltconditionwithacrossslopeofnomorethan2%inthebuiltcondition.Toensurethatthebuildconditionsdonotexceedtheemaximums,designersshouldusestandardsspecificationsof7.5percentforslopesand1.5percentforcross‐slopes.Theminimumwidthofapedestriancurbcutrampisatleast3feet,with4feetpreferred,exclusiveofflaredsides.Acurbcutrampshallhaveadetectablewarningthatextendsthefullwidthandlengthofthecurbramp.DetectablewarningsshallcomplywiththeADAAccessibilityGuidelinesforBuildingsandFacilities.Curbcutrampsandtheirapproachesshallbedesignedsothatwaterwillnotaccumulateonwalkingsurfaces.Surfacesofpedestriancurbcutrampsshallbestable,firm,andslip‐resistant.

Landings

Thebasicprincipleisthateverycurbcutrampmusthavealandingatthetopandatthebottom.Thelandingatthetopofarampshouldbeaminimumoffourfeetlong(5feetpreferred)andatleastthesamewidthasthecentercurbcutrampitself.Itshouldbedesignedtoslopenomorethan1.5%inanydirection,allowingthebuiltconditionto



slopenomorethan2%.Asinglelandingmayserveasthetoplandingforonerampandthebottomlandingforanother.Whenperpendicularrampsrundirectlyintoacrosswalk,thelandingatthebottomwillbeintheroadway.Thelanding,atleast4feetlong,shouldbecompletelycontainedwithinthecrosswalkpavementmarkingsandshouldnothavearunningslopewhenbuiltnogreaterthan5percent.Whentheparallelramplandingiswithinthesidewalkorcornerareawhereapersonusingawheelchairmayhavetochangedirection,thelandingmustbeaminimumoffivefeetlongandatleastaswideastheramp,althoughawidthoffivefeetispreferred.Thelandingmaynotslopemorethan2%whenbuilt(1.5%indesign)inanydirection.

Flares

Flaresaregradedtransitionsfromtherampsectiontothesurroundingsidewalk.Flaresaretypicallynotpartoftherouteforpeopleusingwheelchairs.Flaresmaybesteeperthantherampwherethereisa4‐footdeeplevellandingatthetopoftheramp’scenterlanding.Themaximumslopeoftheflareshallbe10%(9%indesign).Ifthelandingdepthatthetopofapedestriancurbcutrampislessthanfourfeet,thentheslopeoftheflaredsideshallnotexceed8.33%inthebuiltcondition(7.5%design).Whenintersectionsarelocatedonahill,itispossiblethatthesideflaresrampcannevermeetthe8.33%maximumsloperequirement.

Returned Curbs

Flaresarenotnecessarywherepedestrianswouldnotnormallywalkacrosstheramp,suchaswheretherampedgeabutsgrass,otherlandscaping,orothernon‐walkingsurface.Pedestriancurbcutrampsmayhavereturnedcurbsorotherwell‐definededgesonlywhentherampitselfisslopedat8.33%maximum,andthereisnopedestrianapproachfromeithersideoftheramp.Suchedgesshallbeparalleltothedirectionofpedestrianflow,andtheadjacentareashouldclearlyprohibitpedestrianusewith,forexample,plantings,railings,streetfurniture,etc.Thebottomoframpswithreturnedcurbsshallhaveafourfootminimumclear,levellandingthatdoesnotextendintoatravellaneandiswithinthecrosswalkmarkings.

4.7.9 Bicycle Lanes at Intersections

Onstreetswithoutbicyclelanes,abicyclist’stravelthroughintersectionsreflectsthebicyclist’saccommodationatadjacentnon‐intersectionstreetsegments.Wherebicyclistssharealanewithmotorists,theycontinuethroughintersectionsinthisshared‐lanemodeofaccommodation.Wherearoadshoulderispresentandusedbybicyclists,theyapproachanddepartintersectionsontheroadshoulderorinthetravellane.Onstreetswithbicyclelanes,thedesignofbicyclelanesatintersectionsiscomplicatedbytheneedtoaccommodatenumerousturningmovementsbybothmotoristsand


bicyclists,oftenwithlimitedavailablespace.Intersectiondesignisbasedontheassumptionthat:

Motoristsmakingrightturnsshouldmaketheirturnfromasclosetotheright‐handcurbaspractical;

Bicyclistsgoingstraightaheadshouldbetotheleftofrightturningtraffic;and,

Bicycliststurningleftshouldturnfromaleftturnlaneortheleftsideofacombinationthrough/leftlane.

Thebicyclelanemarkingisa6‐inchwidewhitesolidstripe.Nearintersections,thesolidstripeshouldbereplacedbyabrokenlinestripe(two‐foot–longstripesseparatedbysix‐foot‐longspaces)wherebicyclesandvehiclesmerge.Theouterbicyclelanemarkingisskipstripedallthewaytothestopbaratcontrolledintersections,andtotheextensionofthepropertylineatuncontrolledintersections.Theskipstripealertsbicycliststothepotentialformotoriststobecrossingtheirpathandencouragessafemerginginadvanceoftheintersection.Thelanesshouldresumeonthefarsideoftheintersection.Whenabicyclelaneintersectswithaone‐waystreet,orwhererightturnsareprohibited,thebicyclelanemarkingsaresolidallthewaytotheintersection.Bicyclelanestripesshouldnotbeextendedthroughapedestriancrosswalkoranystreetintersection.Exceptionsincludedashedlinesthroughsomecomplexintersections,andthebicyclelanestripingonthesideacrossfromtheT‐intersectionshouldcontinuethroughtheintersectionareawithnobreak.AtypicalconfigurationforbicyclelanesatasimpleintersectionisillustratedinExhibit4‐30.ItshouldbenotedthatbicyclelanesonroadwaysunderStatejurisdictionrequireapprovalfromtheOfficeofStateTransportationAdministration(OSTA).



Exhibit 4‐30 Typical Bicycle Accommodation at a Simple Intersection

Source: Guide for the Development of Bicycle Facilities, AASHTO, 2012.

4.7.9.1 Intersections with Bus Stops

Wherethereisabusorothertransitstop,eithernearsideorfarside,the6‐inchsolidlineshouldbereplacedbytwo‐inchdotsseparatedbysix‐footspacesforthelengthofthebusstop.

bike lane symbol and arrow

bike lane stripe issolid to intersection

parking lanes

sight distance requirementsrestrict vehicle parking within20’ of all intersections

For streets with no on-streetparking, the bike lane will beadjacent to the curb with noother necessary changes.

parking lanes

20’


4.7.9.2 Intersections with Bus Stops

Wherethereisabusorothertransitstop,eithernearsideorfarside,the6‐inchsolidlineshouldbereplacedbytwo‐inchdotsseparatedbysix‐footspacesforthelengthofthebusstop.

4.7.9.3 Flared Intersections

Rightturnlanesshouldbeusedonlywherejustifiedbyatrafficstudysincetheyforceright‐turningvehiclesandthroughbicycliststocrosspaths.WhererightturnlanesareonstreetswithbicyclelanesasshowninExhibit4‐31,thecurblaneisdesignatedwithmarkingsandsignsindicating“RightTurnOnlyExceptforBicycles.”Thisimprovessafetyforbicyclistsbypreventingthroughmotoristsfrompassingontherightwhilestillallowingthroughbicycliststousethelane.Signsalsoindicatethatmotoristsshouldyieldthesharedlanetothebicyclist.Whenthewidthallows,thebicyclelaneisdottedtoencourageright‐turningvehiclestomergeright.Thebicyclelanethencontinuesforaminimumof30feetuntilthestopbar.Thebicyclelaneshouldnotbeplacedtotheleftofarightturnlaneinthreecircumstances:

Heavyrightturnvolumes‐Atfour‐leggedintersectionswithheavyright‐turnvolumesandwhereitisexpectedthatmostbicyclistswillmakearight‐turn(suchaswherethestraightthroughmoveleadstoaminorsidestreet),thebicyclelaneshouldbeplacedontheright.

T‐intersections‐Bicyclelanesshouldbeplacedtotherightoftheright‐turnlane.Whereleft‐turnvolumesareheavy,abicycleleft‐turnlanemaybeplacedbetweenthevehicleleft‐turnandright‐turnlanes.

Optionalright/straightandright‐turnonlylanes‐Stripedbicyclelanesshouldendwiththebeginningofthetaperfortheright‐turnlane,resumingonthefarsideoftheintersection.



Exhibit 4‐31 Typical Bicycle Accommodation at a Flared Intersection


4.7.9.4 Bicycle Lanes at Roundabouts

Roundaboutdesignshouldaccommodatebicyclistswithawiderangeofskillsandcomfortlevelsinmixedtraffic.Bicyclistshavetheoptionofeithermixingwithtrafficorusingtheroundaboutasapedestrian,asillustratedinExhibit4‐32.

Wherebikelanesarepresent,low‐speed(approximately12to15mph)andsingle‐laneroundaboutsallowforsafemixingofbicyclesandmotorvehicleswithinthe


roundabout.Thisoptionwilllikelybereasonablycomfortableforexperiencedbicyclists.Bicyclistswilloftenkeeptotherightontheroundabout;theymayalsomergelefttocontinuearoundtheroundabout.Motoristsshouldtreatbicyclistsasothervehiclesandnotpassthemwhileonthecirculatoryroadway.Thebicyclelaneshouldbediscontinuedabout100feetpriortolow‐speedroundaboutstoindicatethatbicyclistsshouldeithermixwithmotorvehicletrafficorexittothesharedusepath.

Ontheperimeterofroundabouts,thereshouldbeasidewalkthatcanbesharedwithbicyclists.Less‐experiencedbicyclists(includingchildren)mayhavedifficultyanddiscomfortmixingwithmotorvehiclesandmaybemoresafelyaccommodatedaspedestriansinsomeinstances.Bicyclelanesleadingtowardaroundaboutshouldbediscontinuedatthebeginningoftheentrycurveoftheroundabout,endinginarampleadingtowardasharedusebicyclepedestrianpatharoundtheroundabout.Bicyclelanesshouldresumeontheendoftheexitcurve,beginningwitharampfromasharedusepath.

Exhibit 4‐32 Bicycle Accommodations at Roundabouts


Bicyclistsrequireparticularattentionwithinhigherspeedanddoublelaneroundabouts,especiallyinareaswithmoderatetoheavymotorvehiclevolume.Itmaysometimesbepossibletoprovidebicyclistswithgradeseparationoranalternativeroutealonganotherstreetthatavoidstheroundabout,whichshouldbeconsideredaspartofoverall



planning.Theprovisionofalternativeroutesshouldnotbeusedtojustifycompromisingthesafetyofbicycletrafficthroughtheroundaboutbecauseexperiencedbicyclistsandthosewithimmediatelyadjacentdestinationswilluseit.

4.8 Other Considerations

Severalotherconsiderationsimportantforintersectiondesignaredescribedinthefollowingsectionsincluding:sighttriangles;intersectionspacing;busstopconsiderations;othertypesofroadwaycrossings;mid‐blockpathcrossings;andhighway‐railroadgradecrossings;anddriveways.

4.8.1 Intersection Sight Triangles

Theintersectionsighttriangleisatriangular‐shapedzone,sufficientlyclearofvisualobstructionstopermitdriversenteringtheintersectiontodetectanyhazardsorconflictsandreactaccordingly.IntersectionsightdistanceandsighttrianglesarediscussedfurtherinChapter2.

4.8.2 Intersection Spacing

Aprimarypurposeofintersectionspacingguidelinesistominimizethepossibilityofconflictsintrafficoperationsbetweenadjacentintersections.Examplesofsuchconflictsarequeuesoftrafficextendingfromoneintersectionthroughanadjacentintersection,orintersectionspacingthatprecludesthepossibilityoftrafficsignalprogressionbetweenintersections.Onarterials,intersectionspacingrequirementsareintendedtominimizethe“friction”arisingfromsignalcontrolandturningmovementsatintersections.Intersectionspacingcanalsoinfluencethepedestrianconnectivityalongacorridorsincecrossingopportunitiesareoftenlocatedatintersections.

4.8.2.1 Spacing Between Public Street Intersections

GuidelinesforspacingbetweenpublicstreetsaregiveninExhibit4‐33.Inmostsituations,onlyaminimumspacingisrecommended.However,forstreetsinurbanareas,maximumspacingarealsorecommendedtoenableaproperdensityofconnectingstreetnetwork.


Exhibit 4‐33 Intersection Space Guidelines

Source: Adapted from Congress for the New Urbanism (CNU), AASHTO, 2005Frequently,intersectionspacingisnotacontrollableelementofintersectiondesign,andthespacingis“given”asafixedcondition.Insuchcircumstances,spacingguidelinesarenotapplicable.However,inmanysituations,particularlyinvolvingareasofnewdevelopment,intersectionspacingisanimportantpartofthecontext,andshouldbeconsideredinlightoftheaboveguidelines.

4.8.2.2 Spacing between Signalized Intersections

Frequently,criteriaforthedesirablespacingofsignalizedintersectionsareconfusedwiththatforspacingofallintersections,whethersignalizedornot.Goodsignalprogressioninbothdirectionssimultaneouslyrequiressignalspacingofapproximately1,200feetormore,wellbeyondtheidealspacingforintersectionsinvillage,towncenter,andurbansettings.However,signalizedintersections,spacedforgoodsignalprogression,canbecombinedwithnon‐signalizedintersections,yieldingoverallintersectionspacingwithsmallblocks(ideallyaround200feet)appropriateforurbansettings.Mid‐blockcrossingsshouldbespacednocloserthan300feetfromasignalizedintersection,unlesstheproposedcontrolsignalwillnotrestricttheprogressivemovementsoftraffic.Goodconnectivitytothesignalizedintersectionsalongthemajorstreetcanbeassuredwithawellconnectednetworkoflocalandcollectorstreetsparalleltothemajorstreet.Withsuchanetworkinplace,turningmovementscanbemadeatalllocations,signalized



andunsignalized,duringnon‐peakhours.Duringpeakhours,motoristsandbicyclistswantingtoenterorcrossthemajorstreetcanchoosetousethesignalizedintersections.

4.8.3 Transit Stop Considerations

Fromthepointofviewofbusoperations,itisdesirabletohavebusstopslocatednearintersectionssothatbusriderscanapproacheasilyfromboththestreetcarryingthebusrouteandfromtheminorstreets.Further,itisdesirabletointegratebusstopswiththeadjoiningpedestriansystem(sidewalks,sharedusepathsandcrosswalks)andalsowithanyadjoiningbikepath/lanesystem.Withrespecttointersections,busandothertransitstopsmaybeeither:

Nearside,locatedontheapproachlegoftheintersection;or,

Farside,locatedonthedeparturelegoftheintersection.

Busandothertransitstopsatintersections,whileadvantageousforbusservice,createchallengesforothervehicleflows,aswellasnon‐motorizedtravel:

Ifthebusstopisinitsownlane(typicallyanextensionofparkinglanestowardtheinterioroftheblock),itmustreenterthetrafficstreamaftercompletingastop.If,ontheotherhand,thebusstopsinalaneoftraffic,itblocksthatlaneforthedurationofthestop.

Atfar‐sidestops,astoppedbusmaycausefollowingvehiclestobackupthroughtheintersection.

Atnear‐sidestops,wherethestoppedbusisoutsidethetrafficstream,thereentryofthebusintothetrafficstreamislikelytooccuratapedestriancrosswalk.Atunsignalizedlocations,thispresentsavehicle/pedestrianconflictpossibility.Evenatsignalizedintersections,busdriversmaybegintheirexitfromtheirloadingspaceduringtheredsignalphase,thusconflictingwithcrossingpedestrians.

Busstopsandaccessibleon‐streetparkingwillcompeteforthelocationnearesttheintersection.Thelocationsofbothshouldberesolvedwithinputfromthelocaldisabilitycommission,regionalindependentlivingcenter,andtransitagency.

Thechallengesassociatedwithbusstopsatintersectionsareaddressedthroughthefollowingdesignguidelines:

Far‐sidebusstopsaregenerallypreferabletonear‐sidestops.

Itisdesirabletoseparatebusloadingareasfrommovinglanesoftraffic.Whereon‐streetparkingisgenerallypresentonthestreet,suchaloadingareacanbegainedbyrestrictingtheparkinginthevicinityoftheintersection.Onstreetswithouton‐streetparking,busbaysmaybeconsidered.


Parkingshouldberestrictedforadistanceof60feetfromthebeginningofthepavementcornerradius.Thedesignatedbusloadingareashouldnotextendcloserthan20feettothepavementcornerradius.Thesedimensionsapplytobothnear‐sideandfar‐sidebusstops.

Buspullouts,undersomecircumstances,maybeappropriateatintersectionareas.However,thedrawbackofpullouts—difficultyforthebusinreenteringthetrafficstream—canbeproblematicnearintersections.Pulloutsaremorelikelytobeacceptableatfar‐sidestops,wheretheexitingbusvehicleismorelikelytoencounteracceptablegapsinthetrafficstream,comparedtoanear‐sidestopontheapproachlegoftheintersection.BuspulloutsonStateroadwaysshouldbeconsistentwiththeCTDepartmentofTransportation’sHighwayDesignManual.

4.8.4 Mid‐Block Path Crossings

Atintersections,sharedusepaths(forpedestrians,bicyclistsandothernon‐motorizedusers)areaccommodatedasintersectioncrosswalks,asdescribedinSection4.7.8.Wherepathscrossstreetsatlocationsotherthanatintersections,theyshouldconformtothefollowingguidelinesfor“mid‐block”crossings(theMUTCDprovidesfurtherguidanceonplacementandspacing):

Mid‐blockpathcrossingsshouldbeusedonlywhereneeded.Factorslikelytoproducethisneedareexistingrouteofpaths,availabilityofright‐of‐wayforpathextensions,distancetoalternatecrossinglocationsatintersections,andtopography.

Mid‐blockpathcrossingsshouldbeinstalledonlywherestoppingsightdistanceisfullyadequateforvehiculartrafficonthestreetbeingcrossed.

Mid‐blockpathcrossingsshouldprovideadequatesightdistanceforpedestrians,bicyclesandotherusersofthepath.

Wheremid‐blockpathcrossingsexceed60feetinlength,amedianislandshouldbeconsidered.Medianislandsprovidethedualbenefitofprovidingarefugeforcrossingpathusers,reducingthesizeofgapintrafficneededtocrossthestreetsafely,andmayhelpalertapproachingmotoristsandbicycliststothepresenceofthecrossing.

Medianislandsshouldbeatleast6feetwide,toshieldbicyclesormorethanonepedestrian.

Treesalongtheroadsideatthepathcrossing,andinlargermedians,cancallattentionofon‐comingmotoriststothepresenceofthetrailcrossing.However,treesandotherlandscapingshouldnotbeallowedtoinfringeonthesightdistanceofpedestriansormotoristsinthevicinityofthecrossing.

Allmedianorchannelizingislandsshouldhavepedestriancurbcutrampsorat‐gradecut‐throughs.At‐gradecut‐throughsshouldbeslopedgently(maximumof2percentinthebuildconditionand1.5%indesign))toallowdrainage.



Onmulti‐lanearterialstreets,pedestriancallbutton‐actuatedtrafficsignalsmaybeappropriate.Wheninstalled,suchsignalinstallationsshouldhaveasupplementarycallbuttonatthemedian,aswellasateithercurb.TheFederalAccessBoard’scurrentreviseddraftversion(2005)oftheADAAccessibilityGuidelinesforPublicRight‐of‐way(notadoptedatthetimeofthisGuidebook)requiresaudibletrafficsignalswhereverwalksignalsareinstalled.Althoughnotyetrequired,these,alongwithdetectablewarnings,willprovidestrongcuesforpeoplewithlimitedsight.

Pedestriancallbuttonsshouldhavelocatortonesforpedestrianswithlimitedsight.

Pathsshouldbemarkedbywhitecontinentalcrosswalkmarkings(longitudinalstripes).

On‐streetparkingshouldberemovedforadistance(typically40to60feet)adequatetoassuresightdistanceforpathuserswaitingonthecurb.

Analternativetreatmentwhereparkingispresentistoprovideacurbextension,typically6feetdeepfora7to8footparkinglane.Curbextensionsreduceoreliminatetheneedforremovingparking,anddecreasethecrossingdistanceforthepath.

Atcrossingswithmarginalsightdistance,advancesigningorevenadvanceflashingindicatorsmaybeappropriate.

4.8.5 Railroad‐Highway Grade Crossings

Thefollowingguidelinesaffectthehorizontalalignmentofstreetsatarailroad‐highwaygradecrossing:

Crossingsshouldbeavoidedonbothhighwayandrailroadcurves.Railroadcurvespresentaproblemofsuperelevatedtrackcrossingtheroadway.Acurveonthecrossinghighwaypreventsanysuperelevationonthehighway,resultinginanawkwardorunsafecurve.

Thehighwayshouldintersecttracksasnearaspossibleto90degrees.

Ideally,thereshouldnotbenearbyintersectionswithstreetsordriveways.Whereitisnotpossibletoprovidesufficientdistancebetweenthecrossingandnearbyintersections,trafficsignalsatthenearbyintersectioncanbeinterconnectedwiththegradecrossingsignal,toenablevehiclestoclearthegradecrossingasatrainapproaches.

Thecrossingshouldbewideenoughtopermitbicycliststocrossthetracksatrightangles,whilestayingintheirtrafficlane.

Thefollowingguidelinesapplytotheverticalalignmentofstreetsatrailroadhighwaygradecrossings:


Thestreetsurfaceshouldbeatthesameplaneasthecross‐slopeofthetopoftherails(levelfortangentrailandadoptingthegradeofsuper‐elevatedrail)foradistanceof2feetoutsideeitherrail.Beyondthispoint(i.e.,2feetfromoutsideedgeofrail),thegradeshouldnotbemorethan1percentgreaterthanthegradeacrossthetracks.

Verticalcurvesshouldbeusedtomakethetransitionfromthestreetgradetotherailcross‐slopeplanedescribedabove.

Trafficcontroldevicesforrailroad‐highwaygradecrossingsrangefrompassive(signs,pavementmarkings)toactive(flashinglightsignals)torestrictive(automaticgates).ConsulttheMUTCDfordetailedcriteriaforthedesignandoperationofthesedevices.Atcrossingsprotectedbyactivesignalsorgates,thesightdistancerequirementisdeterminedbythedesignspeedofthecrossingstreet(seeChapter2ofthisGuidebook).AtgraderailcrossingsshouldbeconsistentwiththeDepartmentofTransportation’sHighwayDesignManual.Atcrossingswithouttrainactivatedwarningdevices,thesightdistancemustallowthedriverorbicyclisttoobservetheapproachingtrainatsufficientdistancetopermitstoppingpriortoreachingthecrossing.Thedistanceneededforthiscasedependsonthespeedofthevehicleandthespeedofthetrain.DetailedsightdistancesaregivenfortheWB‐65designvehicleintheAASHTOGreenBook.Wherepublicsidewalkscrossrailsystemsat‐grade,thesurfaceofthecontinuouspassageshallbelevelandflushwiththerailtopattheouteredgeandbetweentherails.

4.8.6 Driveways

Drivewaysarepointsofaccessfrompublicstreetstoprivateproperty,andarethereforenotintersections,asdefinedinthischapter,althoughsomelargevolumedrivewaysshouldbedesignedasintersections.GuidelinesfordrivewaydesignandspacingareofferedinChapter7.

4.9 For Further Information

HighwayCapacityManual,TransportationResearchBoard,Washington,D.C.,2010.

ManualonUniformTrafficControlDevices,FederalHighwayAdministration,2009.

APolicyonGeometricDesignofHighwaysandStreets,AASHTO,2011.

Roundabouts:AnInformationalGuide,FederalHighwayAdministration,2010.

GuideforthePlanning,DesignandOperationofPedestrianFacilities,AmericanAssociationofStateHighwayandTransportationOfficials(AASHTO),2004.



GuidefortheDevelopmentofBicycleFacilities,AmericanAssociationofStateHighwayandTransportationOfficials(AASHTO),2012

UrbanBikewayDesignGuide,NACTO,2011.

ADAAccessibilityGuidelinesforBuildingsandFacilities,TheAccessBoard,amendedthroughAugust2005.

GuidelinesforDrivewayLocationandDesign,InstituteofTransportationEngineers(ITE),1987.

Chapter 1-4 - Intersection Design - VHB.com

Documents

Transcript of Chapter 1-4 - Intersection Design - VHB.com