Lesson 7 Transportation Systems交通运输系统Transportation system in a developed nation consists of a network of modes that have evolved over many years. The system consists of vehicles, guideways, terminal facilities and control systems: these operate according to established procedures and schedules in the air, on land, and on water. The system also requires interaction with the user, the operator and the environment. The systems that are in place reflect the multitude of decisions made by shippers, carriers, government, individual travelers, and affected nonusers concerning the investment in or the use of transportation. The transportation system that has evolved has produced a variety of modes that complement each other.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。
The U. S. transportation system today is a highly developed, complex network of modes and facilities that furnishes shippers and travelers with a wide range of choices in terms of services provided. Each mode offers a unique set of service characteristics in terms of travel time, frequency, comfort, reliability, convenience and safety. The term level of service is used to describe the relative values of these attributes. The traveler or shipper must compare the level of service offered with the cost in order to make tradeoffs and mode selection. Furthermore, a shipper or traveler can decide to use a public carrier or to use private (or personal) transportation. For example, a manufacturer can ship goods through a trucking firm or with company trucks, a homeowner who has been relocated can hire a household moving company or rent a truck, and a commuter can elect to ride the bus to work or drive a car. Each of these decisions involves a complex set of factors that requiretradeoffs between cost and service.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。
The principal modes of intercity freight transportation are highways, railroads, water, air and pipelines. Traffic carried by each mode, expressed as ton-miles or passenger-miles, has varied considerably in the past 70 years. The most current information regarding modal market share is available from the Bureau of Transportation Statistics (BST) website. Changes in ton-miles carried from 1960 through 2005 are illustrated in Fig. 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。
The distribution of passenger transportation is much different from that for freight: one mode-the automobile-accounts for the highest number of all domestic intercity passenger-miles traveled in the United States. The remaining modes-air, bus and rail-share a market representing about one quarter of the total, with air being the dominant mode and intercity bus, private air carriers and rail representing 1 percent or less of the total.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。
Each mode has inherent advantages of cost, travel time, convenienceand flexibility that make it “right for the job” under a certain set of circumstances. The automobile is considered to be a reliable, comfortable, flexible and ubiquitous form of personal transportation for many people. However when distances are great and time is at a premium, air transportation will be selected, supplemented by the auto for local travel. If cost is important and time is not at a premium, or if an auto is not available, then intercity bus or rail may be used.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。
Selecting a mode to haul freight follows a similar approach. Trucks have the advantages of flexibility and the ability to providedoor-to-door service. They can carry a variety of parcel sizes and usually can pick up and deliver to meet the customer’s schedule. Waterways can ship heavy commodities at low cost, but only at slow speeds and between points on a river or canal. Railroads can haul an immense variety of commodities between any two points, but usually require truck transportation to deliver the goods to freight terminal or to their final destination. In each instance, a shipper must decide whether the cost and time advantages are such that the goods should he shipped by truck alone or by a combination of truck, waterway and rail.选择货运方式也可以遵循相似方法。