年平均日交通量).ppt

Chapter3.Volume,DensityMaxV10=360;MaxV15=364Hourlyvolume=307,Peakhourfactor（高峰小时系数）-isdefinedastheratioofhourlyvolumedividedbymaximumrateofflow,PHFisusedtoreflectthefluctuationofvolumedistributioninanhour!,PHF5=307/504=0.61;PHF10=307/360=0.85;PHF15=307/364=0.84;,Peak-Hour-Factor(PHF),The30thhourlyvolume(第30位小时交通量)-definedasanhourlyvolumeatwhichitsrankingonyearly-countingcurvecounts30thamong8760hourlyvolumesinayearDDHV(DirectionalDesignHourlyVolume设计小时流量)-DDHV=AADTKDwhere:Kisproportionofdailytrafficoccurringduringthepeakhour,expressedasadecimal;Disproportionofpeak-hourtraffictravelinginthepeakdirection,expressedasadecimal,D=ratioofdesignhourvolumeinthemajordirectiontothetotal(方向性系数）,K=ratioofdesignhourvolumetothe24hourvolume（设计小时系数）,RelationshipBetweenDDHVandAADT,IngeneralDandKisconstant!,VMT(VehicleMilesTraveled=车英里)orVKT(VehicleKilometersTraveled车公里)-definedasaproductofnumberofvehiclesandmiles(orkilometer)traveledbythesevehicles,EstimationofVehicle-MilesTraveledonaLimitedNetwork:AnExample,PCEandPCU（小汽车当量）-definedasthenumberofpassengercarsdisplacedbyonetruck,bus,orRVinagiventrafficstreamTrafficintensitycanbeusedascriteriontodeterminepassengercarequivalent,2.Speed,Timemeanspeed(TMS，时间平均车速)-definedastheaveragespeedofallvehiclespassingapointonahighwayoversomespecifiedtimeperiodSpacemeanspeed(SMS，空间平均车速)-definedastheaveragespeedofallvehiclesoccupyingagivensectionofahighwayoversomespecifiedtimeperiod,TMSisapointmeasure,whileSMSisameasurerelatingtoalengthofhighwayorlaneSMSisoftenusedintrafficflowtheorystudyatmacroscopiclevelwhileTMSisusedforengineeringstudyTMSSMS,Averagetravelspeedandaveragerunningspeed（平均行程，行驶速度)-Averagetravelspeed=distance/traveltimeAveragerunningspeed=distance/runningtimeRunningtime=traveltime-stoppeddelays,Operatingspeed（运营速度）-definedasthemaximumsafespeedatwhichavehiclecanbeconductedinagiventrafficstream,withoutexceedingthedesignspeedofthehighwaysegment.CriticalspeedorOptimalspeed(临界车速)-definedasthespeedatwhichmaximumflowrate(capacity通行能力)canbeachieved(oratwhichgasconsumptionofvehiclesisatthelowest),Percentilespeeds（百分位速度）-isaspeedbelowwhichthestatedpercentofvehiclesinthetrafficstreamtravel,Intrafficengineering,85thpercentilespeedisoftenusedasameasureofthemaximumreasonablespeedforthetrafficstream(upperlimit),whilethe15thpercentilespeedmaybeusedasameasureoftheminimumreasonablespeedforthetrafficstream.The50thpercentileormedianspeedisusedtodescribethemidpointofthespeeddistribution.,3.Density,Itisdefinedasthenumberofvehiclesoccupyingagivenlengthofhighwayorlaneandisgenerallyexpressedasvehiclesperkilometerperlane.Difficulttoobtainfromthefield-usingoccupancy(占用率）whichisdefinedastheproportionoftimethatadetectoriscoveredbyavehicleinthespecifiedperiodoftime,CloselyrelatedtotrafficdemandItiseasyfordriverstoperceiveSpacing(车头间距）andheadway（车头时距）spacingisdefinedasthedistancebetweensuccessivevehiclesinatrafficlane;headwayisdefinedasthetimeintervalbetweensuccessivevehiclesastheypassapointalongthelane,Differentdensityonbothdirectionsoffreeway,USA,FreewayofI-15inSanDiego,USA,Differentdensityoneachdirectionofexpressway,Beijing,Differentdensityonbothdirectionsofmainstreet,Beijing,Itshouldbenotedthatdensityandvolumearedifferent.Theformerrepresentsdistributionofvehiclesintermsofspaceoccupyingtheroadway;whereasthelaterexpressesthefrequencyofvehiclespassingapointofroadway.,4.Relationshipamongvolume,speedanddensity,Thisequationisvalidforuninterruptedflowonly!,TheGreenshieldslinearmodel,GraphicalRelationshipAmongThreeParameters,CongestionZone,Greenbergslogarithmicmodel,Underwoodsexponentialmodel,NorthwesternUniversityModel,Summary,Derivationofflow-speedandflow-densityrelationshipsunderGreenshields,Capacity,Capacityisdefinedasthemaximumrateofflowthatcanbeachievedonroadwayfacilitiesunderprevailingroadway,traffic,andcontrolconditions.,Similarlywecanget:,ThreeimportanttrafficstatesFreeflow(uf,q=0,k=0)Optimastate(qmax,uo,ko)Trafficjam(km,q=0,u=0),Flow-SpeedCurveUnderDifferentConditions,Flow-SpeedCurveForMajorArterialofBeijing,Flow-SpeedCurveForMinorArterialofBeijing,Someconclusions,Whendensitylessthan20,GreenbergandUnderwoodmodelsoverestimatespeedWhendensitybetween20to60,allmodelsunderestimatespeedandflowthatmayleadtounderestimatecapacityWhendensitybiggerthan90,Greenshieldsmodelstartstodeviatefromthedata,atdensity125,Greenshieldsmodelhaszerospeedandflowrate,Discussionofthemodels,GreenbergandUnderwoodmodelshavehigherfreeflowspeedthantheobservedGreenbergunderestimatesoptimal(cri