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毕业设计(论文)外文资料翻译院（系）：机电工程学院专业：电气工程及其与自动化姓名：学号：外文出处：Geo-spatialInformationScience10(3):213-217附件：1.外文原文；2.外文资料翻译译文。完成日期：2011年5月23日外文原文TrafficAssignmentForecastModelResearchinITSIntroductionTheintelligenttransportationsystem(ITS)developsrapidlyalongwiththecitysustainabledevelopment,thedigitalcityconstructionandthedevelopmentoftransportation.OneofthemainfunctionsoftheITSistoimprovetransportationenvironmentandalleviatethetransportationjam,themosteffectivemethodtogaintheaimistoforecastthetrafficvolumeofthelocalnetworkandtheimportantnodesexactlywithGISfunctionofpathanalysisandcorrelationmathematicmethods,andthiswillleadabetterplanningofthetrafficnetwork.Trafficassignmentforecastisanimportantphaseoftrafficvolumeforecast.Itwillassigntheforecastedtraffictoeverywayinthetrafficsector.Ifthetrafficvolumeofcertainroadistoobig,whichwouldbringontrafficjam,plannersmustconsidertheadoptionofnewroadsorimprovingexistingroadstoalleviatethetrafficcongestionsituation.Thisstudyattemptstopresentanimprovedtrafficassignmentforecastmodel,MPCC,basedonanalyzingtheadvantagesanddisadvantagesofclassictrafficassignmentforecastmodels,andtestthevalidityoftheimprovedmodelinpractice.1Analysisofclassicmodels1.1ShortcuttrafficassignmentShortcuttrafficassignmentisastatictrafficassignmentmethod.Inthismethod,thetrafficloadimpactinthevehicles’travelisnotconsidered,andthetrafficimpedance(traveltime)isaconstant.Thetrafficvolumeofeveryorigination-destinationcouplewillbeassignedtotheshortcutbetweentheoriginationanddestination,whilethetrafficvolumeofotherroadsinthissectorisnull.Thisassignmentmethodhastheadvantageofsimplecalculation;however,unevendistributionofthetrafficvolumeisitsobviousshortcoming.Usingthisassignmentmethod,theassignmenttrafficvolumewillbeconcentratedontheshortcut,whichisobviouslynotrealistic.However,shortcuttrafficassignmentisthebasisofalltheothertrafficassignmentmethods.1.2Multi-waysprobabilityassignmentInreality,travelersalwayswanttochoosetheshortcuttothedestination,whichiscalledtheshortcutfactor;however,asthecomplexityofthetrafficnetwork,thepathchosenmaynotnecessarilybetheshortcut,whichiscalledtherandomfactor.Althougheverytravelerhopestofollowtheshortcut,therearesomewhosechoiceisnottheshortcutinfact.Theshorterthepathis,thegreatertheprobabilityofbeingchosenis;thelongerthepathis,thesmallertheprobabilityofbeingchosenis.Therefore,themulti-waysprobabilityassignmentmodelisguidedbytheLOGITmodel:njiiiFFp1)exp()exp((1)Whereipistheprobabilityofthepathsectioni;iFisthetraveltimeofthepathsectioni;θisthetransportdecisionparameter,whichiscalculatedbythefollowprinciple:firstly,calculatetheipwithdifferentθ(from0to1),thenfindtheθwhichmakesipthemostproximatetotheactualip.Theshortcutfactorandtherandomfactorisconsideredinmulti-waysprobabilityassignment,therefore,theassignmentresultismorereasonable,buttherelationshipbetweentrafficimpedanceandtrafficloadandroadcapacityisnotconsideredinthismethod,whichleadstotheassignmentresultisimpreciseinmorecrowdedtrafficnetwork.Weattempttoimprovetheaccuracythroughintegratingtheseveralelementsaboveinonemodel-MPCC.2Multi-waysprobabilityandcapacityconstraintmodel2.1RationalpathaggregateInordertomaketheimprovedmodelmorereasonableintheapplication,theconceptofrationalpathaggregatehasbeenproposed.Therationalpathaggregate,whichisthefoundationofMPCCmodel,constrainsthecalculationscope.Rationalpathaggregatereferstotheaggregateofpathsbetweenstartsandendsofthetrafficsector,definedbyinnernodesascertainedbythefollowingrules:thedistancebetweenthenextinnernodeandthestartcannotbeshorterthanthedistancebetweenthecurrentoneandthestart;atthesametime,thedistancebetweenthenextinnernodeandtheendcannotbelongerthanthedistancebetweenthecurrentoneandtheend.Themulti-waysprobabilityassignmentmodelwillbeonlyusedintherationalpathaggregatetoassigntheforecasttrafficvolume,andthiswillgreatlyenhancetheapplicabilityofthismodel.2.2Modelassumption1)Trafficimpedanceisnotaconstant.Itisdecidedbythevehiclecharacteristicandthecurrenttrafficsituation.2)Thetrafficimpedancewhichtravelersestimateisrandomandimprecise.3)Everytravelerchoosesthepathfromrespectiverationalpathaggregate.Basedontheassumptionsabove,wecanusetheMPCCmodeltoassignthetrafficvolumeinthesectoroforigination-destinationcouples.2.3CalculationofpathtrafficimpedanceActually,travelershavedifferentunderstandingtopathtrafficimpedance,butgenerally,thetravelcost,whichismainlymadeupofforecasttraveltime,travellengthandforecasttraveloutlay,isconsideredthetrafficimpedance.Eq.(2)displaysthisrelationship.aaaaFLTC(2)WhereaCisthetrafficimpedanceofthepathsectiona;aTistheforecasttraveltimeofthepathsectiona;aListhetravellengthofthepathsectiona;aFistheforecasttraveloutlayofthepathsectiona;α,β,γaretheweightvalueofthatthreeelementswhichimpactthetrafficimpedance.Foracertainpathsection,therearedifferentα,βandγvaluefordifferentvehicles.Wecangettheweightedaverageofα,βandγofeachpathsectionfromthestatisticpercentofeachtypeofvehicleinthepathsection.2.4ChosenprobabilityinMPCCActually,travelersalwayswanttofollowthebestpath(