城市交通规划毕业论文外文翻译.docx

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