城市道路设计10

SchoolofCivilEngineering孙仁娟12/18/2023URBANROADDESIGNLecture8-GradeSeparationsandInterchangesOutlinesInterchangesRampsInterchanges

InterchangeConfigurationsThree-legdesignsFour-legdesignsApproachestothestructureThegeneralcontrolsforhorizontalandverticalalignmentandtheircombinationshouldbeadheredtoclosely.Inparticular,anyrelativelysharphorizontalorverticalcurvesshouldbeavoided.Gradientsthatmayslowdowncommercialvehiclesorthatmaybedifficulttonegotiateundericyconditionsshouldbeavoided.Reductionofvehiclespeedsbylongupgradesencouragespassing,whichisundesirableinthevicinityoframpterminals.SightdistanceSightdistanceontheroadsthroughagradeseparationshouldbeatleastaslongasthatneededforstoppingandpreferablylonger.Thehorizontalsightdistancelimitationsofpiersandabutmentsatcurvesusuallypresentamoredifficultproblemthanthatofverticallimitations.InterchangeSpacingInterchangespacinghasapronouncedeffectonroadoperations.Inareasofconcentratedurbandevelopment,properspacingusuallyisdifficulttoattainbecauseoftrafficdemandforfrequentaccess.Minimumspacingofarterialinterchanges(distancebetweenintersectingstreetswithramps)isdeterminedbyweavingvolumes,abilitytosign,signalprogression,andlengthsofspeed-changelanes.Ageneralruleofthumbforminimuminterchangespacingis1.5km[1mi]inurbanareasand3.0km[2mi]inruralareas.Inurbanareas,spacingoflessthan1.5km[1mi]maybedevelopedbygrade-separatedrampsorbyaddingcollector-distributorroads.UniformityofInterchangePatternsWhenaseriesofinterchangesarebeingdesigned,attentionshouldbegiventothegroupofinterchangesasawhole,aswellastoeachindividualinterchange.Consideringtheneedforhighcapacity,appropriatelevelofservice,andmaximumsafetyinconjunctionwithexpresswayoperations,itisdesirabletoprovideuniformityinexitandentrancepatterns.Becauseinterchangesarecloselyspacedinurbanareas,shorterdistancesareavailableinwhichtoinformdriversofthecoursetofollowwhenexitingaroad.Aninconsistentarrangementofexitsbetweensuccessiveinterchangescausesdriverconfusion,resultingindriversslowingdownonhigh-speedlanesandmakingunexpectedmaneuvers.ExamplesofinconsistentexitarrangementsareillustratedinExhibit10-45Aandincludeinconsistencyofexitramplocationswithrespecttothestructure(nearandfarsideofstructure)andexitrampsontheleftsideofthetraveledway.Exceptinhighlyspecialcases,allentranceandexitrampsshouldbeontheright.Totheextentpractical,allinterchangesalongaexpresswayshouldbereasonablyuniformingeometriclayoutandgeneralappearance,asshowninExhibit10-45B.BasicNumberofLanesThebasicnumberoflanesisdefinedasaminimumnumberoflanesdesignatedandmaintainedoverasignificantlengthofaroute,irrespectiveofchangesintrafficvolumeandlane-balanceneeds.Asillustratedinexhibit,thebasicnumberoflanesonexpresswaysismaintainedoversignificantlengthsoftheroutes,asAtoBorCtoD.Thenumberoflanesispredicatedonthegeneralvolumeleveloftrafficoverasubstantiallengthofthefacility.ThevolumeconsideredhereistheDHV(normally,representativeofthemorningoreveningweekdaypeak).CoordinationofLaneBalanceandBasicNumberofLanesTorealizeefficienttrafficoperationthroughandbeyondaninterchange,thereshouldbeabalanceinthenumberoftrafficlanesontheexpresswayandramps.Designtrafficvolumesandacapacityanalysisdeterminethebasicnumberoflanestobeusedontheexpresswayandtheminimumnumberoflanesontheramps.Thebasicnumberoflanesshouldbeestablishedforasubstantiallengthofexpresswayandshouldnotbechangedthroughpairsofinterchanges,simplybecausetherearesubstantialvolumesoftrafficenteringandleavingtheexpressway.Inotherwords,thereshouldbecontinuityinthebasicnumberoflanes.Afterthebasicnumberoflanesisdeterminedforeachroadway,thebalanceinthenumberoflanesshouldbecheckedonthebasisofthefollowingprinciples:Atentrances,thenumberoflanesbeyondthemergingoftwotrafficstreamsshouldnotbelessthanthesumofalltrafficlanesonthemergingroadwaysminusone,butmaybeequaltothesumofalltrafficlanesonthemergingroadway.Atexits,thenumberofapproachlanesontheexpresswayshouldbeequaltothenumberoflanesontheexpresswaybeyondtheexit,plusthenumberoflanesontheexit,minusone.Thetraveledwayoftheexpresswayshouldbereducedbynotmorethanonetrafficlaneatatime.RampsTypesandExamplesTheterm“ramp”includesalltypes,arrangements,andsizesofturningroadwaysthatconnecttwoormorelegsataninterchange.Thecomponentsofarampareaterminalateachlegandaconnectingroad.Thegeometryoftheconnectingroadusuallyinvolvessomecurvatureandagrade.Generally,thehorizontalandverticalalignmentoframpsisbasedonlowerdesignspeedsthantheintersectingroads,butinsomecasesitmaybeequal.RampterminalsTheterminalofarampisthatportionadjacenttothethroughtraveledway,includingspeed-changelanes,tapers,andislands.StandardandSpecification《城市道路交叉口规划规范》GB50647-2011，2012年1月1日CodeforPlanningofIntersectionsonUrbanRoad《城市道路工程设计规范》

CJJ37-2012,2012年5月1日Codefordesignofurbanroadengineering《城市道路交叉口设计规程