城市交通规划毕业论文外文翻译.docx
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城市交通规划毕业论文外文翻译.docx
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城市交通规划毕业论文外文翻译
UrbantransportationPlanning
Anurbantransportationsystemisbasiccomponentofanurbanarea'ssocial,economic,andphysicalstructure.Notonlydoesthedesignandperformanceofatransportationsystemprovideopportunitiesformobility,butoverthelongterm,itinfluencespatternsofgrowthandthelevelofeconomicactivitythroughtheaccessibilityitprovidestoland.Planningforthedevelopmentormaintenanceoftheurbantransportationsystemisthusanimportantactivity,bothforpromotingtheefficientmovementofpeopleandgoodsinanurbanareaandformaintainingthestrongsupportiverolethattransportationcanplayinattainingothercommunityobjectives.
Thereareseveralbasicconceptsaboutanurbantransportationsystemthatshouldbekeptinmind.Mostimportant,atransportationsysteminanurbanareaisdefinedasconsistingofthefacilitiesandservicesthatallowtravelthroughouttheregion,providingopportunitiesfor:
(I)mobilitytoresidentsofanurbanareaandmovementofgoodsand
(2)accessibilitytoland.Giventhisdefinition,anurbantransportationsystemcanbefurthercharacterizedbythreemajorcomponents:
thespatialconfigurationthatpermitstravelfromonelocationtoanother;thetransportationtechnologiesthatprovidethemeansofmovingoverthesedistances;andtheinstitutionalframeworkthatprovidesfortheplanning,construction,operation,andmaintenanceofsystemfacilities.
TheSpatialConfigurationofaTransportationSystem
Onewaytodescribethespatialdimensionofanurbantransportationsystemistoconsiderthecharacteristicsofindividualtripsfromanorigintoadestination.Forexample,atripcanconsistofseveraltypesofmovementundertakentoachievedifferentobjectives.Travelersleavinghomemightusealocalbussystemtoreachasuburbansubwaystation(atripcollectionprocess),proceedthroughthestationtothesubwayplatform(atransferprocess),ridethesubwaytoadowntownstation(aline-haulprocess),andwalktoaplaceofemployment(adistributionprocess).Similarly,onecanviewahome-to-worktripbycarasconsistingofsimilarsegments,withthelocalstreetsystemprovidingthetripcollectionprocess,afreewayprovidingtheline-haulcapability,aparkinglotinthecentralbusinessdistrictservingasatransferpoint,andwalking,asbefore,servingthedistributionfunction.
Thefacilitiesandservicesthatprovidetheseopportunitiesfortravel,wheninterconnectedtopermitmovementfromonelocationtoanother,formanetwork.Thus,anotherwayofrepresentingthespatialdimensionofanurbantransportationsystemisasasetofroadandtransitnetworks.Eveninthesmallesturbanareas,wheremasstransitisnotavailable,thelocalstreetnetworkprovidesthebasicspatialcharacteristicofthetransportationsystem.
Thetransportationsystemofacitycaninfluencethewayinwhichthecity'ssocialandeconomicstructure,oftencalledtheurbanactivitysystem,develops.Atthesametime,changesinthisstructurecanaffecttheabilityofthetransportationsystemtoprovidemobilityandaccessibility.Thus,thetransportationsystemiscloselyrelatedtotheurbanactivitysystemand;historically,hasbeenanimportantdeterminantofurbanform.
Becauseoftherelationbetweentransportationandurbanactivities,manyofthemethodsusedbytransportationplannersdependonestimatesoftripsgeneratedbyspecificlanduses.Therelationalsosuggeststhattheoptionsavailabletopublicofficialsdealingwithtransportationproblemsshouldincludenotonlythoserelateddirectlytothetransportationsystem,butalsoactionssuchaszoningthataffectthedistributionoflanduse,andthusinfluencetheperformanceofthetransportationsystem.
Theforegoingconsiderationspointtotwoimportantprinciplesfortransportationplanning:
Thetransportationsystemshouldbe
Consideredasanintegralpartofthesocialandeconomicsysteminanurbanarea.
Viewedasasetofinterconnectedfacilitiesandservicesdesignedtoprovideopportunitiesfortravelfromonelocationtoanother.
TheTechnologyofUrbanTransportation
Thetechnologyofurbantransportationiscloselyrelatedtothespatialconfigurationofthetransportationsysteminthatthedesigntransportationnetworksreflectsthespeed,operating,andcostcharacteristicsofthevehicleormodeoftransportationbeingused.Technologyincludesthemeansofpropulsion,typeofsupport,meansofguidance,andcontroltechnique.
ThedevelopmentandwidespreaduseofelectricstreetcarsinurbanareasduringthelatenineteenthcenturywasatechnologicalinnovationthatinitiatedthetransformationofmostNorthAmericancities.Theadventoftheelectricstreetcarpermittedurbanareastoexpandbeyondtheboundariesthathadbeendictatedbyprevioustransportationtechnologies(e.g.,walking,horse,horsecar),spawning`streetcarsuburbs'withdramaticallylowerresidentialdensitiesalongstreetcarlinesradiatingfromthecentralcity.Whereasmanyindustrieshaddecentralizedalongrailroadlinesleadingfromthecentralcity,andworkersinitiallyhadtolivenearthesefactories,theintroductionofstreetcarsnowpermittedmoredistantliving.
Thesuccessofthestreetcarinprovidingaccessfromselectedsuburbanareastocentralbusinessdistrictswasfollowedbypublicacceptanceofasecondmajortechnologicalinnovation-theautomobile,poweredbytheinternalcombustionengine.Increasingconsumerpreferencesforlower-densitylivingandforanabilitytotravelbeyondestablishedurbanboundariessparkedaphenomenalgrowthinautomobileownershipandusage,beginninginthe1920s.④Theautomobilecontinuesandacceleratedtheevolutionofurbanstructurestartedbytheelectricstreetcar.Itsavailabilitypermittedfurtherexpansionofurbanareasand,moreimportant,providedaccesstolandbetweentheradialstreetcarandrailroadlinesleadingintothecentralcity.
Thetechnologyoftheinternal-combustionengine,however,alsoledtothedeclineofothertransportationmodesusedinurbanareasbyprovidingalessexpensiveandmoreflexiblereplacementforrail-basedmodes.Whiletheautomobileprovidednewopportunitiesforpersonalmobilityandurbangrowth,motorbusesrapidlyreplacedelectricstreetcars,totheextentthatonlyfiveNorthAmericancitiestodaystilloperatelarge-scalestreetcarsystems-Boston,Philadelphia,Pittsburgh,Toronto,andSanFrancisco(althoughthistrendhasreversedsomewhatinrecentyearswithnew`lightrail'systemsinoperationinEdmonton,Calgary,SanDiego,andBuffalo).Atthesametime,thegrowthofprivateautomobileusehasdramaticallyreducedtheuseofpublictransportationingeneral,particularlysincetheendofWorldWarII.Accordingtothelatestcensusfigures,in1980,62.3millionAmericansnormallydrovealonetoworkeachday,another19millioncar-pooled,and6millionusedpublictransportation.
Thetechnologiesandtheresultingmodesavailabletodayforurbantransportationarecommontomostcitiesbutareoftenappliedindifferentwaystoservedifferentpurposes.Itshouldbenotedthatcertaintypesofmodesareappropriatethanothersinservingdifferenttypesofurbantrips.
Thetechnologicaldimensionoftheurbantransportationsystemsuggestsathirdprincipleforurbantransportationplanning:
Transportationplannersmustconsiderthetransportationsystemasconsistingofdifferentmodes,eachhavingdifferentoperationalandcostcharacteristics.
From;MichaelD.MeyerandEricJ.Miller"UrbanTransportationPlanning",1984
Trafficsignals
IntheUnitedStatesalone,some250,000intersectionshavetrafficsignals,whicharedefinedasallpower-operatedtraffic-controldevicesexceptflashers,signs,andmarkingsfordirectingorwarningmotorists,cyclists,orpedestrians.
Signalsforvehicular,bicycle,andpedestriancontrolare‘pretimed’wherespecifictimesintervalsareallocatedtothevarioustrafficmovementsandas'trafficactuated'wheretimeintervalsarecontrolledinwholeorinpartbytrafficdemand.
PretimedTrafficSignals
'Pretimed'trafficsignalsaresettorepeatregularlyagivensequenceofsignalindicationsforstipulatedtimeintervalsthroughthe24-hrday.Theyhavetheadvantagesofhavingcontrollorsoflowerfirstcostandthattheycanbeinterconnectedandcoordinatedtovehiclestomovethroughaseriesofintersectionswithaminimumofstopsandotherdelays.Also,theiroperationisunaffectedbyconditionsbroughtonbyunusualvehiclebehaviorsuchasforcedstops,which,withsometraffic-actuatedsignalinstallationsmaybringatrafficjam.Theirdisadvantageisthattheycannotadjusttoshort-timevariationsintrafficflowandoftenholdvehiclesfromonedirectionwhenthereisnotrafficintheother.Thisresultsininconvenience,andsometimesadecreaseincapacity.
‘Cyclelength’thetimerequiredforacompletesequenceofindications,ordinarilyfallsbetween30and120s.Shortcyclelengthsaretobepreferred,asthedelaytostandingvehiclesisreduced.Withshortcycles,howeverarelativelyhighpercentageofthetotaltimeisconsumedinclearingtheintersectionandstartingeachsucceedingmovement.Ascyclelengthincreases,thepercentageoftimelostfromthesecausesdecreases.Withhighvolumesoftraffic,itmaybenecessarytoincreasethecyclelengthtogainaddedcapacity.
Eachtrafficlaneofanormalsignalizedintersectioncanpassroughlyonevehicleeach2.1sofgreenlight.Theyellow(caution)intervalfollowingeachgreenperiodisusuallybetween3and6s,dependingonstreetwidth,theneedsofpedestrians,andvehicleapproachspeed.Todetermineanapproximatecycledivision,itiscommonpracticetomakeshorttrafficcounts
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