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Lesson7TransportationSystems交通运输系统Transportationsysteminadevelopednationconsistsofanetworkofmodesthathaveevolvedovermanyyears.Thesystemconsistsofvehicles,guideways,terminalfacilitiesandcontrolsystems:theseoperateaccordingtoestablishedproceduresandschedulesintheair,onland,andonwater.Thesystemalsorequiresinteractionwiththeuser,theoperatorandtheenvironment.Thesystemsthatareinplacereflectthemultitudeofdecisionsmadebyshippers,carriers,government,individualtravelers,andaffectednonusersconcerningtheinvestmentinortheuseoftransportation.Thetransportationsystemthathasevolvedhasproducedavarietyofmodesthatcomplementeachother.在发达国家，交通运输系统由网状结构组成的模式已经发展了好多年。这个系统由交通工具、轨道、站场设施和控制系统组成。这些依照空中、陆上和水上已制定的程序和计划运转。这个系统也需要和用户、司机和环境互动。现在的运输体系可以反映出与投资和使用有关的多方决定，包括运输业主、承运商、政府、每个出行者以及受影响的非使用者等。逐步发展的交通运输系统形成了各种互补模式。TheU.S.transportationsystemtodayisahighlydeveloped,complexnetworkofmodesandfacilitiesthatfurnishesshippersandtravelerswithawiderangeofchoicesintermsofservicesprovided.Eachmodeoffersauniquesetofservicecharacteristicsintermsoftraveltime,frequency,comfort,reliability,convenienceandsafety.Thetermlevelofserviceisusedtodescribetherelativevaluesoftheseattributes.Thetravelerorshippermustcomparethelevelofserviceofferedwiththecostinordertomaketradeoffsandmodeselection.Furthermore,ashipperortravelercandecidetouseapubliccarrierortouseprivate(orpersonal)transportation.Forexample,amanufacturercanshipgoodsthroughatruckingfirmorwithcompanytrucks,ahomeownerwhohasbeenrelocatedcanhireahouseholdmovingcompanyorrentatruck,andacommutercanelecttoridethebustoworkordriveacar.Eachofthesedecisionsinvolvesacomplexsetoffactorsthatrequiretradeoffsbetweencostandservice.当今美国的交通运输系统是一个高度发达，复杂的运输方式和设施构成的网络，他们为运输业主和出行者提供服务，并有很大的选择余地。每种模式按照行程时间、频率、舒适度、可靠性、方便性和安全性都具有一种独特的服务特性。服务水平被用来描述相对价值。旅客或运输业主对比同等费用下的服务水平来权衡和选择运输方式。此外，运输业主或旅客可以决定使用公共的或是私人运输方式。例如，厂商可以通过货运公司或者自己公司的卡车运货，要搬家的屋主可以选择雇佣搬家公司或者租赁卡车，通勤者可以选择乘公交或者开车去上班。每种决定都涉及一系列需要在费用和服务间权衡的复杂因素。Theprincipalmodesofintercityfreighttransportationarehighways,railroads,water,airandpipelines.Trafficcarriedbyeachmode,expressedaston-milesorpassenger-miles,hasvariedconsiderablyinthepast70years.ThemostcurrentinformationregardingmodalmarketshareisavailablefromtheBureauofTransportationStatistics(BST)website.Changesinton-milescarriedfrom1960through2005areillustratedinFig.7.1.主要的城际货运方式有铁路、公路、水运、空运和管道运输。在过去的70年里，表现为货运和客运的每一种运输方式发生了很大的改变。关于市场占有率的最新消息可以从BST网站获取。从1960年至2005年货运方式变化如图7.1所示。Thedistributionofpassengertransportationismuchdifferentfromthatforfreight:onemode-theautomobile-accountsforthehighestnumberofalldomesticintercitypassenger-milestraveledintheUnitedStates.Theremainingmodes-air,busandrail-shareamarketrepresentingaboutonequarterofthetotal,withairbeingthedominantmodeandintercitybus,privateaircarriersandrailrepresenting1percentorlessofthetotal.客运的分布与货运有很大不同：在美国，私家车这种方式在所有的家庭城际客运旅行中数量最多。剩下的方式（航空、公共汽车和铁路）占总数的四分之一，其中航空占优势，而城际公共汽车、私家人飞机和铁路占总量的百分之一或更少。Eachmodehasinherentadvantagesofcost,traveltime,convenienceandflexibilitythatmakeit“rightforthejob”underacertainsetofcircumstances.Theautomobileisconsideredtobeareliable,comfortable,flexibleandubiquitousformofpersonaltransportationformanypeople.Howeverwhendistancesaregreatandtimeisatapremium,airtransportationwillbeselected,supplementedbytheautoforlocaltravel.Ifcostisimportantandtimeisnotatapremium,orifanautoisnotavailable,thenintercitybusorrailmaybeused.在费用，旅行时间，方便性和灵活性等方面，每种方式都有自身的优势，从而使得它在特定情形下成为最佳选择。对很多人来说，汽车是一种可靠、舒适、灵活且普遍存在的私人运输方式。然而，当距离很远或者时间很宝贵时，人们将选择航空运输并在当地运输中补以汽车运输。如果费用很重要而时间并不紧，或者不能使用汽车时，可以使用城际巴士或火车。Selectingamodetohaulfreightfollowsasimilarapproach.Truckshavetheadvantagesofflexibilityandtheabilitytoprovidedoor-to-doorservice.Theycancarryavarietyofparcelsizesandusuallycanpickupanddelivertomeetthecustomer’sschedule.Waterwayscanshipheavycommoditiesatlowcost,butonlyatslowspeedsandbetweenpointsonariverorcanal.Railroadscanhaulanimmensevarietyofcommoditiesbetweenanytwopoints,butusuallyrequiretrucktransportationtodeliverthegoodstofreightterminalortotheirfinaldestination.Ineachinstance,ashippermustdecidewhetherthecostandtimeadvantagesaresuchthatthegoodsshouldheshippedbytruckaloneorbyacombinationoftruck,waterwayandrail.选择货运方式也可以遵循相似方法。卡车的优势在于灵活和提供门到门服务。卡车可以运送多种尺寸货物并可以按照客户时间表上门收取或交付货物。水运可以低价运送很重的货物，但是速度很低，并且只能在河流或运河的两点间运送。铁路可以在任意两地间运送大量货物，但往往需要卡车再将货物转运到终点或目的地。每种方式，托运商都要权衡花费和时间来决定只用卡车或者通过卡车、水运和火车联运。Manyindustrieshavebeentryingtoreducetheirpartsandsuppliesinventories,preferringtotransportthemfromthefactorywhenneededratherthanstockpilingtheminawarehouse.Thispracticehasmeantshiftingtransportationmodesfromrailtotruck.Railshipmentsareusuallymadeonceortwiceaweekincarloadlots,whereastruckdeliveriescanbemadeinsmalleramountsandonadailybasis,dependingondemand.Inthisinstance,lowerrail-freightratesdonotcompletewithtruckflexibility,sincetheoverallresultofselectingtruckingisacostreductionfortheindustry.Thereisatrendtowardintermodalismwhichhascombinedthecapabilitiesofbothmodes.许多公司都尝试减少零部件和原材料库存，相比把货物存积在仓库，商家更喜欢需要的时候直接从工厂运输。这种做法意味着运输方式从火车到卡车的转变。火车运输通常是以每周一到两次的频率整车运输，而卡车可以按需求每天少量的运送。这种情况下，较低的火车运输费用都难以