搜索
1UrbantransportationPlanningAnurbantransportationsystemisbasiccomponentofanurbanarea'ssocial，economic，andphysicalstructure.Notonlydoesthedesignandperformanceofatransportationsystemprovideopportunitiesformobility，butoverthelongterm，itinfluencespatternsofgrowthandthelevelofeconomicactivitythroughtheaccessibilityitprovidestoland.Planningforthedevelopmentormaintenanceoftheurbantransportationsystemisthusanimportantactivity，bothforpromotingtheefficientmovementofpeopleandgoodsinanurbanareaandformaintainingthestrongsupportiverolethattransportationcanplayinattainingothercommunityobjectives.Thereareseveralbasicconceptsaboutanurbantransportationsystemthatshouldbekeptinmind.Mostimportant，atransportationsysteminanurbanareaisdefinedasconsistingofthefacilitiesandservicesthatallowtravelthroughouttheregion，providingopportunitiesfor:(I)mobilitytoresidentsofanurbanareaandmovementofgoodsand(2)accessibilitytoland.Giventhisdefinition，anurbantransportationsystemcanbefurthercharacterizedbythreemajorcomponents:thespatialconfigurationthatpermitstravelfromonelocationtoanother;thetransportationtechnologiesthatprovidethemeansofmovingoverthesedistances;andtheinstitutionalframeworkthatprovidesfortheplanning,construction,operation,andmaintenanceofsystemfacilities.TheSpatialConfigurationofaTransportationSystemOnewaytodescribethespatialdimensionofanurbantransportationsystemistoconsiderthecharacteristicsofindividualtripsfromanorigintoadestination.Forexample,atripcanconsistofseveraltypesofmovementundertakentoachievedifferentobjectives.Travelersleavinghomemightusealocalbussystemtoreachasuburbansubwaystation(atripcollectionprocess)，proceedthroughthestationtothesubwayplatform(atransferprocess)，ridethesubwaytoadowntownstation(aline-haulprocess)，andwalktoaplaceofemployment(adistributionprocess).Similarly，onecanviewahome-to-worktripbycarasconsistingofsimilarsegments，withthelocalstreetsystemprovidingthetripcollection2process,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:ThetransportationsystemshouldbeConsideredasanintegralpartofthesocialandeconomicsysteminanurbanarea.Viewedasasetofinterconnectedfacilitiesandservicesdesignedtoprovideopportunitiesfortravelfromonelocationtoanother.TheTechnologyofUrbanTransportationThetechnologyofurbantransportationiscloselyrelatedtothespatialconfigurationofthetransportationsysteminthatthedesigntransportationnetworksreflectsthespeed,operating,andcostcharacteristicsofthevehicleormodeoftransportationbeingused.Technologyincludesthemeansofpropulsion,typeofsupport，meansofguidance，andcontroltechnique.3ThedevelopmentandwidespreaduseofelectricstreetcarsinurbanareasduringthelatenineteenthcenturywasatechnologicalinnovationthatinitiatedthetransformationofmostNorthAmericancities.Theadventoftheelectricstreetcarpermittedurbanareastoexpandbeyondtheboundariesthathadbeendictatedbyprevioustransportationtechnologies(e.g.，walking，horse，horsecar)，spawning`streetcarsuburbs'withdramaticallylowerresidentialdensitiesalongstreetcarlinesradiatingfromthecentralcity.Whereasmanyindustrieshaddecentralizedalongrailroadlinesleadingfromthecentralcity，andworkersinitiallyhadtolivenearthesefactories,theintroductionofstreetcarsnowpermittedmoredistantliving.Thesuccessofthestreetcarinprovidingaccessfromselectedsuburbanareastocentralbusinessdistrictswasfollowedbypublicacceptanceofasecondmajortechnologicalinnovation-theautomobile，poweredbytheinternalcombustionengine.Increasingconsumerpreferencesforlower-densitylivingandforanabilitytotravelbeyondestablishedurbanboundariessparkedaphenomenalgrowthinautomobileownershipandusage，beginninginthe1920s.④Theautomobilecontinuesandacceleratedtheevolutionofurbanstru