【正文】 （ 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 mon 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 mon 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 parison purposes. From the diagram, it is clear that highway construction costs change erratically and even display different short and longterm 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. Past Methods of Forecasting Highway Construction Cost Forecasting future highway construction costs has been achieved in basically three ways in the past. First, unit rates of construction such as dollars per mile by highway type have been used to estimate construction costs in the short term. However, this method has generally been found to be unreliable, because site conditions such as topography, in situ soil, land prices, environment, and traffic loads vary sufficiently from location to location to make average prices inaccurate estimates of the price of individual projects or even of all projects in a particular year. Second, extrapolation of past trends, or timeseries analysis, has been used to forecast future overall construction costs （ Koppula 1981。 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 ment and review. Ultimately, a program will be approved by the state legislature and will bee 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 mon 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 inpetence 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. 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。 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 costcutting 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 2020. Applying costcutting policies and assuming input costs are 20% less than anticipated, the model estimates highway construction costs will increase by 75% between 1998 and 2020. Key words: Highway construction。 本 科 生 畢 業(yè) 設 計（論文） 外文翻譯 題目Ⅰ： Estimating Future Highway Construction Costs Estimating Future Highway Construction Costs C.