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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 require tradeoffs 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, convenience and 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 provide door-to-door service. They can carry a variety of parcel sizes and usually can pick up and deliver to meet the customers 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。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。Many industries have been trying to reduce their parts and supplies inventories, preferring to transport them from the factory when needed rather than stockpiling them in a warehouse. This practice has meant shifting transportation modes from rail to truck. Rail shipments are usually made once or twice a week in carload lots, whereas truck deliveries can be made in smaller amounts and on a daily basis, depending on demand. In this instance, lower rail-freight rates do not complete with truck flexibility, since the overall result of selecting trucking is a cost reduction for the industry. There is a trend toward intermodalism which has combined the capabilities of both modes.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和汽车的灵活性相竞争，因为厂商选择卡车的全部原因是开支的减少。有一种趋势指向将各种方式结合起来的联运制。The nations transportation system can be considered to be in a state of equilibrium at any given point in time as a result of market forces, government actions and transportation technology. As these change over time, the transportation system also will be modified. During recent decades, changes in gasoline prices, regulation by government, and new technology have affected the relative importance of each mode. The passenger or shipper thinks of each mode in terms of the level of service provided. Each mode offers a unique set of service characteristics at a given price: travel time, frequency, comfort, convenience, reliability and safety. The traveler or shipper selects the mode based on how these attributes are valued.国家的运输系统可以看作一种在市场压力、政府管控、运输新技术下的平衡。随着时间变化，运输系统也会改变。近几十年，油价的改变、政府的管控和新的技术已经对运输业造成了很大影响。旅客或托运商按照服务水平考虑每一种方式。每种方式在给定的价格下提供一种独特的服务特点：行程时间、频率、舒适度、方便性、可靠性和安全性。旅客和托运商按照这些属性的价值选择运输方式。A wide range of organizations and agencies provide the resources to plan, design, build, operate and maintain the nations transportation system. These include private companies that furnish transportation; regulatory agencies that monitor the safety and service quality provided; federal, state, local agencies that provide funds to build roads and airports and carry out legislation dealing with transportation at a national level; trade associations that represent the interests of a particular group of transportation providers or suppliers; professional organizations and transportation user groups.许多组织和代理机构提供计划、设计、建设、操作和维持国家交通运输系统的资源。这些组织和机构包括：运输业私人公司、兼管安全和服务质量的管理机构、提供资金修建道路和机场并为交通制定全国性法规的联邦、州以及地方公路局；代表某一特殊运输群体利益的行业协会；专业技术组织以及运输使用者群体。Lesson 8 Highway Location 公路定线The basic principle for locating highways is that roadway elements such as curvature and grade must blend with each other to produce a system that provides for the easy flow of traffic at the design capacity, while meeting design criteria and safety standards. The highway should also cause a minimal disruption to historic and archeological sites and to other land-use activities. Environmental impact studies are therefore required in most cases before a highway location is finally agreed upon.定线的基本原则是车行道要素如弯道和坡度必须互相组合，在满足设计规范和安全标准的要求的同时，提供满足设计通行能力并且平稳的交通流体系。公路应尽可能小的影响历史古迹及其他设施。绝大多数情况下，当公路路线位置最终确定前都要求进行环境影响评估。The highway location process involves four phases: Office study of existing information Reconnaissance survey Preliminary location survey Final location survey 公路定线包括四个阶段： 对已有信息进行室内研究 勘测设计 初步定线 最终定线Office Study of Existing InformationThe first phase in any highway location study is the examination of all available data of the in which the road is to be constructed. This phase is usually carried out in the office prior to any field or photogrammetric investigation. All the available data are collected and examined. These data can be obtained from existing engineering reports, map, aerial photographs and charts, which are usually available at one or more of the states departments of transportation, agriculture, geology,hydrology and mining. The type and amount of data collected and examined depend on the type of highway being considered, but in general, data should be obtained on the following characteristics of the area:已有信息室内研究所有公路选线第一阶段是对公路建设地区所有信息进行研究。这一阶段通常先于任何现场或图片调查在室内进行。所有可得数据被收集并考察。这些数据可以从现有工程报告、地图、航拍图片和图表中获取，这些东西通常都可以从一个或多个政府运输、农业、地理、水利及矿产部门获取。所收集并考察的数据类型和数量取决于拟建道路等级，但总体来说数据都要有该地区以下特征： Engineering, including topography, geology, climate and traffic volumes.Social and demographic, including land use and zoning patterns. Environmental, including types of wildlife; location of recreational, historic and archeological sites: the possible effects of air, noise and water pollution. Economic, including unit costs for construction and trend of agricultural, commercial and industrial activities. 工程上，包括地形、地质、气候和交通量 社会和人口，包括土地使用和区划特征 环境方面，包括野生动物类型；娱乐场所，历史遗迹的位置；可能产生的空气噪声和水污染 经济方面，包括单位建设花费，农业趋势，商业和工业活动Preliminary analysis of the data obtained will indicate whether any of the specific sites should be excluded from further consideration because of one or more of the above characteristics. For example, if it is found that a site of historic and archeological importance is located within an area being considered for possible route location, it maybe immediately decided that any route that traverses that site should be excluded from further consideration. At the completion of this phase of the study the engineer will be able to select general areas through which the highway can traverse. 初步分析所获取的数据将得出是否有地方由于上述因素的一个或多个被剔除在进一步考虑之外。例如，如果发现一个重要的历史古迹和建筑位于路线可能通过的区域，则应立即确定通过那个区域的任何线路下一步将不被考虑。在这一阶段结束后，工程师将能选择公路所能穿过的大体区域。Reconnaissance SurveyThe object of this phase of the study is to identify several feasible routes, each within a band of a limited width of a few hundred feet. When rural roads are being considered, there is often very little or no information available on maps or photographs, and therefore aerial photography is widely used to obtain the required information. Feasible routes are identified by a stereoscopic examination of the aerial photographs, taking into consideration factors such as:Terrain and soil conditionsServiceability of route to industrial and population areasCrossing of other transportation facilities, such as rivers, railroads and other highwaysDirectness of route勘测设计这一阶段的的目标是找出几条可行路线，每一条都在几百英尺有限宽度的带状区。当考虑郊外公路时，在照片或地图上通常很少或没有可用信息，因此航空摄影被广泛采用来获取所需信息。通过航拍照片生成的立体透视图来检查可行路线所考虑的因素包括：地貌及土质对工业及居民区服务能力与其他交通设施如水路、铁路及其他公路的交叉情况路线的直接性Control points between the two endpoints are determined for each feasible route. For example, a unique bridge site with no alternative may be taken as a primary control point. The feasible routes identified are then plotted on photographic base maps.两端点间的控制点对每条可行路线起控制作用。例如，无可选择的唯一的桥位就可被当作基本控制点。找出这些可行路线并标注在航拍照片的底图上。Preliminary Location Survey During this phase of the study, the positions of the feasible routes are set as closely as possible by establishing all the control points and determining preliminary vertical and horizontal alignments for each. Preliminary alignments are used to evaluate the economic and environmental feasibility of the alternative routes.初步定线在这一步的研究中，通过建立控制点和初步确定平纵线型，尽可能精确地确定可行路线的位置。初步定线用于评价备选路线的经济和环境可行性。Economic evaluation of each alternative route is carried out to determine the future effect of investing the resources necessary to construct the highway.对每条备选路线经济评价的目的在于确定投入资源修建的道路在未来所能产生的影响。The benefit-cost ratio method is used for this evaluation. Factors usually taken into consideration include road user costs, construction costs, maintenance costs, road user benefits and any disbenefits, which may include adverse impacts due to dislocation of families, businesses and so forth. The results obtained from the economic evaluation of the feasible route provide valuable information to the decision maker. For example, these results will provide information on the economic resources that will be gained or lost if a particular location is selected. This information is also used to aid the policy maker in determining whether the highway should be built, and if so, what type of highway it should be. 在这一评估中采用效益成本比的方法。通常所考虑的因素包括用户的花费，建设费用，养护费用，使用者受益和一些损失，这些损失包括居民拆迁、对商业和其他的不利影响。从经济苹果中获得的结果给决策者提供有价值的信息。例如，结果将提供特定位置确定后经济资源上的得失信息。这一信息也用来帮助政策制定者决定公路是否该修建，如果该修那又该修何种等级的道路。Construction of a highway at any location will have a significant impact on its surroundings. A highway is therefore an integral part of the local environment and must be considered as such. This environment includes plant, animal human communities and encompasses social, physical, natural and man-made variables. These variables are interrelated in a manner that maintains equilibrium and sustains the life style of the different communities. The construction of a highway at a given location may result in significant changes in one or more variables, which in turn may offset the equilibrium and result in significant adverse effects on the environment. This may lead to a reduction of the quality of the animals and/or human communities. It is therefore essential that the environmental impact of any alignment selected be fully evaluated.在任何地方修建道路都会对当地环境产生重要影响。因此公路应当被看成是当地环境完整的一部分。这一环境包括植物、动物、人类群体，同时包括社会的、物理的、自然的和认为的变量。这些变量是以一种维持平衡并维持不同群体间生活方式的方法相互关联的。在给定的区域内公路的修建可能会导致一个或多个变量的剧烈变化，这些变化反过来会试图修复平衡并会对环境产生非常不利的影响。这可能会导致动物与/或人类数量的减少。因此对任何线路的选择全面考虑对环境的影响是很必要的。Final Location SurveyThe final location survey is the detailed layout of the selected route. The horizontal and vertical alignments are determined and the positions of structures and drainage channels are located. The method used is to set out the points of intersections (PI) of the straight portions of the highway and fit a suitable horizontal curve between these. This is usually a trial-and-error process until, in the designers opinion, the best alignment is obtained, taking both engineering and aesthetic factors into consideration. Splines and curve templates are available that can be used in this process. The spline is a flexible plastic guide that can be bent into different positions and is used to lay out different curvilinear alignments, from which the most suitable is selected. Curve templates transparencies giving circular curves, three-center compound curves and spiral curves of different radii and different standard scales. The spline is used first to obtain a hand-fitted smooth curve that fits in with the requirements of grade, cross-sections, curvature and drainage. The hand-fitted curve is then changed to a more defined curve by using the standard templates.最终定线最终定线是对选定的路线进行详细设计。在这一阶段确定平纵面线形和排水沟位置。传统方法是设定公路直线部分的交点并在两直线之间设定合适的平曲线。这通常是一个反复试验的过程，直到在工程师看来找到了考虑了工程和美学的最好线形。活动曲线规可以被用在这一阶段。活动曲线规是一个活动的可被弯曲成不同形状并用来画出不同线条的塑料导轨，利用它可以选出最合适的线形。曲线模板是一种能画出不同曲率和不同标准比例的圆曲线、三心复曲线和螺旋曲线的透明板。活动曲线规最早用于获得能满足纵坡、横断面、曲率和排水要求的手绘光滑曲线。这条手绘曲线通过标准模板变成一条更加清晰的曲线。The availability of computer-based techniques has significantly enhanced this process since a proposed highway can be displayed on a monitor, enabling the designer to have a drivers eye view of both the horizontal and vertical alignments of the road. The designer can therefore change either or both alignments until the best alignment is achieved.计算机技术的实用性极大地提高了这一过程的效率，因为设计的公路可以显示在屏幕上，从而使设计者有了驾驶者的视线效果，既可以看到平面线形，又可以看到纵面线形。因此设计者可以改动平/纵面线形或者同时改动两者直到获得最好的线形。Lesson 9 Design of the Alignment线形设计The alignment of a highway is composed of vertical and horizontal elements. The vertical alignment includes straight (tangent) highway grades and the parabolic curves that connect these grades. The horizontal alignment includes the straight (tangent) sections of the roadway and the circular curves that connect their change in direction. 公路线形包括平曲线和竖曲线元素。竖曲线包括直坡线（切线）和连接这些直坡线的抛物线。平曲线包括公路的直线部分（切线）和连接两直线并转向的圆曲线。The design of the alignment depends primarily on the design speed selected for the highway. The least costly alignment is one that generally takes the form of the natural topography. It is not always possible to select the lowest cost alternative because the designer has to adhere to certain standards that may not exist on the natural topography. 线形的设计取决于公路的设计速度。最经济的线形是沿着自然地形展线。现实中设计师往往不能选择造价最低的方案，因为他们必须遵循特定的技术标准，而这些标准在自然地形中也许难以达到。It is important that the alignment of a given section has consistent standards to avoid sudden changes in the vertical and horizontal layout of the highway. It is also important that both horizontal and vertical alignments be designed to complement each other, since this will result in a safer and more attractive highway. 重要的是给定部分的线形必须符合规范来避免公路在水平和竖直布局上产生突变。同样重要的是设计的平曲线和竖曲线要相互协调，因为这样才能设计出安全并更有吸引力的公路。One factor that should be considered to achieve compatibility is the proper balancing of the grades of tangents with curvatures of horizontal curves and the location of horizontal and vertical curves with respect to each other. For example, a design that achieves horizontal curves with large radii at the expense of steep or long grades is a poor design. Similarly, if sharp horizontal curves are placed at or near the top of pronounced crest vertical curves or at or near the bottom of a pronounced sag vertical curve, a hazardous condition will be created at these sections of the highway. Thus, it is important that coordination of the vertical and horizontal alignments be considered at the early stages of preliminary design.为提高协调性应考虑的因素之一是保持直线坡度和曲线曲率均衡，处理好平曲线和竖曲线之间的相互位置。例如，大半径平曲线搭配长陡纵坡是一种较差的设计。同样，如果在凸形竖曲线的顶部及附近或在凹形竖曲线底部及附近设置小半径平曲线，那该路段就会变得很危险。因此，在初步设计阶段综合考虑平纵曲线很重要。The vertical alignment of a highway consists of straight sections known as grades, or tangents, connected by vertical curves. The design of the vertical alignment therefore involves the selection of suitable grades for the tangent sections and the appropriate length of the vertical curves. The topography of the area through which the road traverses has a significant impact on the design of the vertical alignment.公路竖曲线由纵坡线或称切线以及连接他们的竖曲线组成。因而，竖曲线的设计包括直线合适坡度的选择和竖曲线合适长度的设计。路线所穿越地区的地形对竖曲线的设计有十分重要的影响。The effect of grade on the performance of heavy vehicles must be considered. The speed of a heavy vehicle can be significantly reduced if the grade is steep and/or long. Note that steep grades not only affect the performance of heavy vehicles but also the performance of passenger cars. In order to limit the effect of grades on vehicular operation, the maximum grade on any highway should be selected judiciously.必须考虑到纵坡对重载交通的影响。如果纵坡很陡且/或很长，重交通车辆的车速将极大地降低。注意到坡度不仅影响重车的性能同时也影响轿车的性能。为限制纵坡对车辆运行的影响，任何公路都应恰当的选择最大坡度。The selection of maximum grades for a highway depends on the design speed and the design vehicle. It is generally accepted that grades of 4 to 5 percent have little or no effect on passenger cars, except for those with high weight/horsepower ratios, such as those found in compact and subcompact cars. As the grade increases above 5 percent, however, speeds of passenger cars decrease on upgrades and increase on downgrades.公路最大坡度的选择取决于设计速度和设计车辆。普遍认为4%-5%的坡度对客车的影响不大或没有影响，除非是（质量/功率）较高的车，例如那些小型车或微型车。然而，当坡度大于5%时，客车上坡速度进一步降低，下坡速度进一步增加。Grade has a
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