Aspects of IVHS Architecture Design

AspectsofIVHSArchitectureDesignPravinVaraiyaDepartmentofElectricalEngineeringandComputerSciencesUniversityofCalifornia,BerkeleyCA9472017September1991ThispaperisprepareddfordiscussionattheIVESSystemArchitectureWorkshop,UniversityofMichigan.AnnArbor,October24-25,1991.IamgratefultoSteveShladover,TonyHitchcock,andotherparticipantsofthePATEseminaronAVCSfordiscussions;however,theydonotnecessarilyendorsealltheviewsexpressedhere.AbstractIVHSsystemsinfluencefourkindsofdecisionsthatdriversmakeduringtheirtrip.ThecorrespondingtasksthatIVHSsystemscarryoutarerouteandflowcontrol,congestioncontrol,vehiclecoordination,andspacing.AcomparisonoftwoscenariosshowshowIVHSinfluenceovervehiclebehaviorcanrangefromminor(underastrategylimitedtoprovidinginformationandadvice)tomajor(underfullautomationwhichpreemptsdrivercontrol).ThefourIVHStaskshavethreedifferentiatingfeatures:timescaleorthetimeavailabletocarryoutthetask;spatialscopeortheimpactofexecutingthetaskonthetrafficsystem;andinformationspanortheextentofinformationneededtocarryoutthetask.AnIVHSarchitectureorganizedinahierarchyoffourlayers-network,link,co-ordination.andregulation-isproposed.Thishierarchyresolvesinanaturalwaythethreedifferentiatingfeatures.Thearchitecturecanaccommodateawiderangeofautoma-tionstrategiesfromthesimplest,whichlimitsitselftoprovidingdriverinformation.tothemostcomplex.whichachievestotalcontrolofthevehicle.Thearchitecturepermitstheincorporationofnewfunctionalcapabilitiesovertime,andencouragesadecentralizedimplementationofIVHStasks.AnopenarchitecturespecificationisurgedasameanstopromoterapiddevelopmentofIVHSandtoensuretheinterworkingofindependent,subsystemimplementations.ItisalsosuggestedthatIVHSstandardsshouldbespecifiedinaformal-mathematicallanguagetosimplifylaterproblemsofdesignvalidationandconformancetestingofproducts.1IntroductionEngineersfacedauntingchallengesastheyattempttomeetagrowingdemandfortravelatatimewhenthetraditionalresponseofbuildingmoreroadsislessacceptablebecauseitistoocostlyortoodamagingtotheenvironment.Thereisagrowingconsensusthatanappropriatecombinationofintelligentvehiclesandintelligenthighwaysmayassistdriversinwaysthatleadtogreatercapacityandsafetywithoutbuildingnewroads.However,thereisawidediversityofopinionabouttheformofthis‘intelligence’.Thisdiversityhasseveraldimensionsincluding:lFunction-therangeandextentoftransportationanddrivingfunctionsthatshouldbeautomated;lArchitecture-thefunctionaldecompositionofIVHSsystems,theassignmentoftaskstovarioussubsystems,theinformationflowsbetweensubsystems,andtheirinterfaces;lDesign-theappropriateforms,includingthedivisionofintelligencebetweenvehicleandhighway,inwhichcontrol,computingandcommunicationtechnologiesshouldbecombinedtorealizethisarchitecture;lEvolution-thetimingofsystemdevelopment,theextenttowhichearlierarchitecturesshouldbecapableofaccommodatingnewfunctions;lEvaluation-theeffectiveness,costsandbenefitsofdifferentNHSproposals.§2presentsaframeworkfordescribingIVHSfunctions,theirrelationtokeydecisionsthatdriversmake,andthedegreeofinfluencethatIVHScanhaveonthosedecisions.ThisframeworkprovidesaquickcomparisonofdifferentIVHSproposals.§3proposesoneIVHSarchitecture.Thearchitecturearrangessubsystemstasksinahierarchythatcorrespondstothefunctionsintroducedin§2.ThearchitecturesupportslUniformity-itaccommodatesawiderangeofIVHSautomationcapabilities;lEvolution-itpermitstheincorporationofnewfunctions;oDecentralization-itencouragesanimplementationinwhichthetasksarecarriedoutinadecentralizedmanner;consequentlymostoftheintelligenceisinthevehicle..§4urgesthespecificationofanopenarchitecture,i.e.theformulationofstandardsintheformofreferencemodelsforeachlayerofthearchitecturehierarchy.Italsourgestheconsiderationofformal-mathematicalmethodsforstandardsspecification,designvalidationandconformancetesting.§5arguesthatsignificantsafetyandcapacitygainsfromIVHSwillonlybeachievedbymuchlargerdegreeofautomaticvehiclecontrol(AVC)thanmostproponentsofIVHSareatpresentwillingtocontemplate.Werecommend,therefore,thatIVHSarchitecturesbedesignedwiththeexplicitrequirementthattheybeabletoaccommodateAVCfunctions.12IVHSfunctionsTable1listsasequenceofsixdecisionsmadebyanautomobiledriverinthecourseofatrip.lThedecisionsaredividedintothreephases-pretrip,in-trip,andpost-trip.IVHSsystemsseektoimprovethesedecisionsandNHSsubsystemsmustcarryoutcorrespondingtasks.Generallyspeaking,driverdecisionsmaybeinfluencedbyfourstrategiesofintervention-providinginformation,offeringadvice,takingdirectcontrolofthedecision,andchangingincentivesbypricing,eg.tolls.IPhaseDriverdecisionIVHSgoalIVHStaskStrategyA=Advice,C=Control,I=Information,P=PricingTable-l:DriverdecisionsandIVHSfunctionsHenceforthwerestrictattentiontothefourin-tripdecisions.Notethatasthestrategyadoptedtoinfluencedriverdecisionsshiftsfromgivinginformationtoofferingadvicetoexertingpreemptivecontrol,thedecisionsbecomemoreautomaticandpredictable.andtheburdenonsystem‘intelligence’increases.AbetterappreciationofthisshiftofresponsibilityfromthedrivertotheIVHSsystemisgainedbycomparingascenarioofa