BEYOND CONVENTIONAL LCCA: LONG TERMRETURNON PAVEMENT INVESTMENTS

摘要

It is becoming increasingly necessary in life cycle analysis (LCA) of infrastructure assets,rnincluding pavements, to take a longer term approach than in past, conventional practice. This isrnlargely for reasons of ensuring sustainability and assessing the future impacts of today'srndecisions.rnLife cycle analysis can be primarily in terms of life cycle cost analysis (LCCA) but can alsorninclude considerations of resource conservation, environmental impacts, energy balance, etc. Inrnany case, a key question is what constitutes a reasonable time horizon for life cycle analysis. Thernsuggestion is that it should involve short, medium and long term periods, in the order of 25, 50rnand 100 years, respectively. Further, using this approach, it is possible to develop a context forrnLCA of likely and uncertain societal activities, including transportation, over the short, mediumrnand long terms.rnConventional LCCA is directed to comparing competing alternative investment strategies andrncan involve a range of stakeholders, from the elected level to the public at large to suppliers andrnconsultants. Of the methods available, present worth of costs is almost exclusively the methodrnused in the pavement field. However, when medium to longer term life cycle periods arerninvolved, rate-of-return and cost-effectiveness formulations can be applicable and should bernconsidered.rnA numerical example is provided which shows how an agency can determine the internal rate ofrnreturn (IRR) for two investment alternatives involving different pavement designs and a life cyclernperiod of 50 years. As well, a cost-effectiveness example is provided for a sidewalk network andrnagain a life cycle period of 50 years which shows how the best investment alternative has beenrnidentified.rnConventional LCCA for calculating present worth of costs will undoubtedly continue to be usedrnin the pavement field as a primary tool. However, going beyond conventional LCCA and using arnrate-of-return or cost-effectiveness formulation, especially for medium to longer term life cyclernperiods, should be given more consideration.