本 科 生 毕 业 设 计（论文）
题目Ⅰ：
外文翻译
Estimating Future Highway Construction Costs
2009年 2 月 19 日
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Estimating Future Highway Construction Costs
C. G. Wilmot, M.ASCE,1 and G. Cheng, P.E.2
Abstract: The objective of this research was to develop a model that estimates future highway construction costs in Louisiana. The model describes overall highway construction cost in terms of a highway construction cost index. The index is a composite measure of the cost of construction labor, materials, and equipment; the characteristics of contracts; and the environment in which contracts are let. Future construction costs are described in terms of predicted index values based on forecasts of the price of construction labor, materials, and equipment and the expected contract characteristics and contract environments. The contract characteristics and contract environments that are under the control of highway agency officials, can be manipulated to reflect future cost-cutting policies. Application of the model in forecasting to highway construction costs in Louisiana shows that the model closely replicates past construction costs for the period 1984–1997. When applied to forecasting future highway construction costs, the model predicts that highway construction costs in Louisiana will double between 1998 and 2015. Applying cost-cutting policies and assuming input costs are 20% less than anticipated, the model estimates highway construction costs will increase by 75% between 1998 and 2015.
Key words: Highway construction; Costs; Estimation.
Introduction
State Departments of Transportation are required to prepare highway construction programs that describe their planned construction activity in the short term. There is usually considerable interest in the program from local authorities, politicians, and interest groups. Draft programs are typically presented to the public and to various agencies at the local, regional, state, and federal level for comment and review. Ultimately, a program will be approved by the state legislature and will become the formal program of construction of the state Department of Transportation until a new program is developed in the next cycle a few years later.
Because individual projects are of considerable importance to politicians and individual interest groups, it is common that progress on a construction program is closely monitored. Any deviation is likely to be queried, and the Secretary of the state Department of Transportation or a senior official in the department will often have to defend the situation publicly or in the state legislature. This can lead to perceptions of incompetence and erosion of support from the legislature and the public.
To prepare reliable highway construction programs, road authorities must have accurate estimates of future funding and project costs. While future funding is obviously never known witha great deal of certainty, it is often the estimation of project costs that cause upsets in the execution of construction programs.
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Inaccurate cost estimation is one source of error, but another, the escalation in cost of a project over time, is another source disruption to the program that is usually not anticipated and catered for. Typically, when projects are costed, their costs are estimated in terms of the current cost of the project, and this estimate is not adjusted for the year in which the project is scheduled for implementation. These cost increases can be significant and are, of course, cumulative across projects; also, they rise at an increasing rate each year into the future. Estimating future highway construction is the focus of this paper. The model developed in this study was developed with data from the Louisiana Department of Transportation and Development ~DOTD! and is therefore particular to that state. However, the methodology employed could be employed in other areas.
Measuring Project Costs
When construction in the field lags behind planned construction in the construction program, it is usually because the projects that have been constructed have cost more than anticipated. This is not random variation of actual costs about estimated costs, because, clearly, underestimates would cancel out overestimates over time in such a situation. Rather, it is evidence of a consistent underestimateof all projects collectively. The benefit of this is that it can be measured at the overall level, which is much easier to measure than at the individual project level.
In the past, change in overall construction costs has been measured in terms of construction indices. These indices are weighted averages of the cost of a set of representative pay items over time. They have been used to display cost trends in the past. However, there is no reason why cost indices must be restricted to displaying past trends; they can also portray future overall costs, provided the representative pay items on which the index is based can be forecast. A predictive construction cost index was adopted in this study to describe the change in overall construction costs in the future. The formulation of the index is described later in the paper.
Past Increases in Construction Costs
When the change in overall construction costs in the past is observed（as measured by popular construction cost indices）, it is apparent that they change significantly from year to year and that the changes can sometimes be quite erratic. The common assumption that construction costs change with the rate of inflation can lead to poor estimates of future construction cost. To illustrate, the Federal Highway Administration‘s Composite Bid Price Index, an index of overall highway construction costs, is plotted in Fig. 1 together with the Consumer Price Index （CPI）, a common expression of general inflation. The FHWA CBPI for the entire nation and for Louisiana alone is plotted in the diagram. All indices have been normalized to a value of 100 in 1987 for comparison purposes. From the diagram, it is clear that highway construction costs change erratically and even display different short and long-term trends from to those of the CPI. It is also apparent that construction cost changes are different in Louisiana from those in the nation as a whole. While not shown here, review of the FHWA CBPI from other states shows that many of them show a deviation from national values.
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土木工程建筑外文翻译外文文献英文文献公路建设造价的未来
