毕业设计外文资料及翻译智能交通信号灯模拟控制系统设计精品Word文档格式.docx

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Thequalityof（urban）trafficcontrolsystemsisdeterminedbythematchbetweenthecontrolschemaandtheactualtrafficpatterns.Iftrafficpatternschange,whattheyusuallydo,theeffectivenessisdeterminedbythewayinwhichthesystemadaptstothesechanges.Whenthisabilitytoadaptbecomesanintegralpartofthetrafficcontrolunititcanreactbettertochangesintrafficconditions.Adjustingatrafficcontrolunitisacostlyandtimelyaffairifitinvolveshumanattention.Thehypothesisisthatitmightofferadditionalbenefitusingself-evaluatingandself-adjustingtrafficcontrolsystems.Thereisalreadyamarketforanurbantrafficcontrolsystemthatisabletoreactiftheenvironmentchanges;

thesocalledadaptivesystems."

Real"

adaptivesystemswillneedpro-activecalculatedtrafficinformationandcycleplans-basedonthesecalculatedtrafficconditions-tobeupdatedfrequently.

Ourresearchoftheusabilityofagenttechnologywithintrafficcontrolcanbesplitintotwoparts.Firstthereisatheoreticalpartintegratingagenttechnologyandtrafficcontrol.Thefinalstageofthisresearchfocusesonpracticalissueslikeimplementationandperformance.Herewepresenttheconceptsofagenttechnologyappliedtodynamictrafficcontrol.Currentlywearedesigningalayeredmodelofanagentbasedurbantrafficcontrolsystem.Wewillelaborateonthatinthelastchapters.

Adaptiveurbantrafficcontrol

Adaptivesignalcontrolsystemsmusthaveacapabilitytooptimisethetrafficflowbyadjustingthetrafficsignalsbasedoncurrenttraffic.Allusedtrafficsignalcontrolmethodsarebasedonfeed-backalgorithmsusingtrafficdemanddata-varyingfromyearstoacoupleofminutes-inthepast.Currentadaptivesystemsoftenoperateonthebasisofadaptivegreenphasesandflexibleco-ordinationin（sub）networksbasedonmeasuredtrafficconditions（e.g.,UTOPIA-spot,SCOOT）.Thesemethodsarestillnotoptimalwheretrafficdemandchangesrapidlywithinashorttimeinterval.Thebasicpremiseisthatexistingsignalplangenerationtoolsmakerationaldecisionsaboutsignalplansundervaryingconditions;

butalmostnoneofthecurrentavailabletoolsbehavepro-activelyorhavemeta-rulesthatmaychangebehaviourofthecontrollerincorporatedintothesystem.Thenextlogicalstepfortrafficcontrolistheinclusionofthesemeta-rulesandproactiveandgoal-orientedbehaviour.Thekeyaspectsofimprovedcontrol,forwhichcontributionsfromartificialintelligenceandartificialintelligentagentscanbeexpected,includethecapabilityofdealingwithconflictingobjectives;

thecapabilityofmakingpro-activedecisionsonthebasisoftemporalanalysis;

theabilityofmanaging,learning,selfadjustingandrespondingtonon-recurrentandunexpectedevents（Ambrosinoetal..,1994）.

Whatareintelligentagents?

Agenttechnologyisanewconceptwithintheartificialintelligence（AI）.TheagentparadigminAIisbaseduponthenotionofreactive,autonomous,internally-motivatedentitiesthatinhabitdynamic,notnecessarilyfullypredictableenvironments（Weiss,1999）.Autonomyistheabilitytofunctionasanindependentunitoveranextendedperiodoftime,performingavarietyofactionsnecessarytoachievepre-designatedobjectiveswhilerespondingtostimuliproducedbyintegrallycontainedsensors（Ziegler,1990）.Multi-AgentSystemscanbecharacterisedbytheinteractionofmanyagentstryingtosolveavarietyofproblemsinaco-operativefashion.BesidesAI,intelligentagentsshouldhavesomeadditionalattributestosolveproblemsbyitselfinreal-time;

understandinformation;

havegoalsandintentions;

drawdistinctionsbetweensituations;

generalise;

synthesisenewconceptsand/orideas;

modeltheworldtheyoperateinandplanandpredictconsequencesofactionsandevaluatealternatives.Theproblemsolvingcomponentofanintelligentagentcanbearule-basedsystembutcanalsobeaneuralnetworkorafuzzyexpertsystem.Itmaybeobviousthatfindingafeasiblesolutionisanecessityforanagent.Oftenlocaloptimaindecentralisedsystems,arenottheglobaloptimum.Thisproblemisnoteasilysolved.Thesolutionhastobefoundbytailoringtheinteractionmechanismortohaveasupervisingagentco-ordinatingtheoptimisationprocessoftheotheragents.

IntelligentagentsinUTC,ahelpfulparadigm

AgenttechnologyisapplicableindifferentfieldswithinUTC.Theonesmostimportantmentioningare:

informationagents,agentsfortrafficsimulationandtrafficcontrol.Currently,mostapplicationsofintelligentagentsareinformationagents.Theycollectinformationviaanetwork.Withspecialdesignedagentsuserspecificinformationcanbeprovided.Inurbantraffictheseintelligentagentsareuseableindeliveringinformationaboutweather,trafficjams,publictransport,routeclosures,bestroutes,etc.totheuserviaaPersonalTravelAssistant.Agenttechnologycanalsobeusedforaggregatingdataforfurtherdistribution.Agentsandmultiagentsystemsarecapableofsimulatingcomplexsystemsfortrafficsimulation.Thesesystemsoftenuseoneagentforeverytrafficparticipant（inasimilarwayasobjectorientedprogramsoftenuseobjects）.Theapplicationofagentsin（Urban）TrafficControlistheonethathasourprimeinterest.Hereweultimatelywanttouseagentsforpro-activetrafficlightcontrolwithon-lineoptimisation.Signalplansthenwillbedeterminedbasedonpredictedandmeasureddetectordataandwillbetunedwithadjoiningagents.Themostpromisingaspectsofagenttechnology,theflexibilityandpro-activebehaviour,giveUTCthepossibilityofbetteranticipationoftraffic.CurrentUTCisnotthatflexible,itisunabletoadjustitselfifsituationschangeandcan'

thandleun-programmedsituations.Agenttechnologycanalsobeimplementedonseveraldifferentcontrollayers.ThisgivestheadvantageofbeingclosetocurrentUTCwhileleavingconsiderablefreedomatthelower（intersection）level.

Designingagentbasedurbantrafficcontrolsystems

Theidealsystemthatwestriveforisatrafficcontrolsystemthatisbasedonactuatedtrafficcontrollersandisabletoproactivelyhandletrafficsituationsandhandlingthedifferent,sometimesconflicting,aimsoftrafficcontrollers.Theproposeduseoftheconceptofagentsinthisresearchisexperimental.

Assumptionsandconsiderationsonagentbasedurbantrafficcontrol

Therearethreeaspectswhereagentbasedtrafficcontroland-managementcanimprovecurrentstateoftheartUTCsystems:

-Adaptability.Intelligentagentsareabletoadaptitsbehaviourandcanlearnfromearliersituations.

-Communication.Communicationmakesitpossibleforagentstoco-operateandtunesignalplans.

-Pro-activebehaviour.Duetotheproactivebehaviourtrafficcontrolsystemsareabletoplanahead.

Tobeacceptableasreplacementunitforcurrenttrafficcontrolunits,thesystemshouldperformthesameorbetterthancurrentsystems.TheagentbasedUTCwillrequireon-lineandpro-activereactiononchangingtrafficpatterns.AnagentbasedUTCshouldbedemandresponsiveaswellasadaptiveduringallstagesandtimes.Newmethodsfortrafficcontrolandtrafficpredictionshouldbedevelopedascurrentonesdonotsufficeandcannotbeusedinagenttechnology.Theadaptabilitycanalsobedividedinseveraldifferenttimescaleswherethesystemmayneedtohandleinadifferentway（Rogier,1999）:

-gradualchangesduetochangingtrafficvolumesoveralongerperiodoftime,

-abruptchangesduetochangingtrafficvolumesoveralongerperiodoftime,

-abrupt,temporal,changesduetochangingtrafficvolumesoverashortperiodoftime,

-abrupt,temporal,changesduetoprioritisedtrafficoverashortperiodoftime

Onewayofhandlingthebalancebetweenperformanceandcomplexityistheuseofahierarchicalsystemlayout.Weproposeahierarchyofagentswhereeveryagentisresponsibleforitsownoptimalsolution,butmaynotonlybeinfluencedbyadjoiningagentsbutalsoviahigherlevelagents.Theseagentshavethetaskofsolvingconflictsbetweenlowerlevelagentsthattheycan'

tsolve.Thisrepresentscurrenttrafficcontrolimplementationsandidea'

s.Onefinalaspecttobementionedistherobustnessofagentbasedsystems（ifallcommunicationfailstheagentrunson,iftheagentfailsafixedprogramcanbeexecuted.

Tobeabletokeepourfirsturbantrafficcontrolmodelassimpleaspossiblewehavemadethefollowingassumptions:

welimitourselvestoinnercitytrafficcontrol（roadsegments,intersections,corridors）,wehandleonlycontrolledintersectionswithdetectors（intensityandspeed）atallroadsegments,weonlyhandlecarsandweusesimplerulebasesforknowledgerepresentation.

Typesofagentsinurbanintersectioncontrol

Aswedividethesysteminseveral,recognisable,partswedefinethefollowing4typesofagents:

-Roadsarerepresentedbyspecialroadsegmentagents（RSA）,

-Controlledintersectionsarerepresentedbyintersectionagents（ITSA）,

-Forspecific,defined,areasthereisanareaagent（higherlevel）,

-Forspecificroutestherecanberouteagents,thatspansseveraladjoiningroadsegments（higherlevel）.

Wehavenotchosenforoneagentpersignal.Thismayresultinamoresimplesolutionbutavailabletrafficcontrolprogramsdonotfitinthatkindofagent.Wedeliberatelychooseamorecomplexagenttobeabletousestandardtrafficcontroldesignalgorithmsandprograms.Theideastillistheoptimisationonalocallevel（intersection）,butwithlocalandglobalcontrol.Thereforweuseareaagentsandrouteagents.Allcommunicat