交通工程专业外语第七单元.doc

Unit7 Economics and Transportation EngineeringAn economic analysis should not be carried out as an afterthought. It should be used as part of a continuous process, starting with the objectives of the proposed trarrsportation project (can these objectives be satisfied in any other way?), running through the entire planning and design process, and only ending, as a final summing up, with the overall evaluation. It should consider the following questions: (_T)Project identification. Which projects or policies should be considered as possible solutions to a particular transport need? ()Establishing rough priorities. Which projects and policies should be considered in detail? ()Detailed evaluation. Which costs and benefits are relevant to the evaluation, how should they be measured, and how can they best be presented as an index of priority? ()Project selection. Should this project be selected, should it be rejected, or should it be postported? Economics is often overlooked as an aid to transportation planning and design. Yet any transportation engineering problem involves a whole series of essentially economic decisions. In the area of design, for example, the transportation engineer must choose materials, select an overall design concept, and then combine the component parts of the scheme into an effective, and economical, whole. A river crossing could thus beby ferry beat, causeway, or bridge. In the latter case it could be in steel, concrete, or timber. It could be suspended, arched, or simply supported. What should the engineer choose? The range of choice is not usually as large as this. Some solutions will be physically infeasible (e. g., by lack of suitable foundations for an arched bridge), but important choices will remain. In the absence of a rigorous economic analysis, the designer may make these choices on the basis of: (1)Experience, which may or may not cover an adequate range of options. (2)Preconceptions as to what is desirable (e. g., one solution uses less material). (3)An innate view of mathematical or structural elegance (e. g., an arch is a more elegant structural form). Economics avoids the need for these arbitrary rules by providing a tangible criterion-cost-for choosing between alternative solutions. In many cases this can be done quite simply by drawing envelopes of cost curves of, for example, steel girder bridges versus reinforced concrete bridges versus prestressed concrete bridges. By plotting cost (y) against span length (x) the engineer can choose which type is most economic over a given range of span lengths. In practice, the engineer does not usually carry the economic analysis to this level of detail, although curves like this commonly form part of the standard highway design repertoire. It is more a question of the economic attitude of mind that asks: Is this the only possible solution, and if not, is there a better one? It is this general principle which eventually ensures that the final design is the most economical and the one which, if justified in aggregate terms, offers best value for money.Economic efficiency and distribution Economics is not concerned solely with the optimum allocation of resources, hut with wider questions of equity and the distribution of costs and benefits among individuals, regions, etc. It is thus concerned with the question: who does what, to whom, and at whose expense? In a nse this concern complements the intertemporal considerations noted above. A dollar to one person is not necessarily worth the same amount to another. Since economies assumes that marginal values decline as income increases, interpersonal differences in income may thus affect any overall measure of consumer benefit. Questions of distribution nevertheless go beyond mere differences in income. Institutional constraints usually prevent beneficiaries, defined in the broadest sense, from compensating people who are adversely affected. It is therefore often appropriate to separate the impact of a transport improvement into its effect on different interest groups, in addition to its effect on different income groups.翻译：经济分析不应该进行一勺面糊。它应该是作为一个连续的过程,从客观的提议trarrsportation项目(可以实现这些目标被满意的任何其他方式?),贯穿整个规划和设计过程,并只结束,最后总结,以综合评价。它应该考虑以下问题:(_T)。项目鉴定。哪些项目或政策应被视为未解的问题的可能解决特定运输需要吗?()。建立粗糙的优先权。哪些项目和政策应考虑的细节吗?()。详细的评估。相关的成本与效益的评价,应该如何衡量,他们如何才能最好被看作一个指数的优先级吗?()。项目的选择。该项目被选中,应该被拒之门外,应该还是postported吗?经济学是经常被忽视的帮助交通规划和设计。然而任何交通工程问题涉及到整个系列的本质上的经济决策。在设计领域,例如,交通工程师必须选择材料,选择了一个整体设计概念,然后把部件成一种有效的方案,经济、整体。一条河穿越能因此beby渡轮击败,堤,或桥。后者的例子中,它可能在钢铁、混凝土、或木材。它能暂停,拱型,或简单地支撑着。应该如何选择?工程师,这个范围的选择通常不一样大。一些方案将身体上不可行(e)。通过分析j.缺乏合适的基础,为一个拱形桥),但最重要的选择。在缺乏严格的经济分析,设计人员做出这些选择的基础上。(1)。经验,这也许是,也许不是一个适当的选择范围。(2)。什么是一个理想的偏见(如一个解决方案使用较少的资料)。(3)。一个天生的数学或结构优雅(如一道拱门是一种更优雅的结构形式)。避免这些经济规则提供了一种切实任意criterion-cost-for之间的选择可能的解决方案。在很多情况下,这可以很简单地用信封的成本曲线,为例,对钢板梁桥的钢筋混凝土桥梁和预应力混凝土桥梁。通过对成本(y轴)的跨度(x)工程师可以选择何种类型是最经济在给定范围的跨度的长度。在实践中,工程师通常不会把经济分析,这个水平的细节,但这样的曲线的标准的一般形式的公路设计套路。它更是一个问题的经济的态度,问:这是唯一可能的解决方案,如果没有,有较好的吗?这是一般的原则,最终保证最终的设计是最经济的