ABSTRACT
The useful life of an infrastructure component or system is often defined as the time to physical failure of the asset. Clearly there are limitations to such an approach, since an asset may become obsolete, that is, it may not live up to current needs or expectations even though its physical condition is fine. A perfect example is the Roman aqueduct, physically sturdy yet functionally obsolete. Hence, Lemer (1996) draws a distinction between the physical life of an infrastructure asset and its service life, and concludes that the only meaningful definition of “design service life” would be one defined in terms of obsolescence, where obsolescence is defined as the inability to meet performance requirements that are changing. Lemer captures the situation elegantly in Figure 1. There is a performance function that is constant for a period of time and then proceeds to slope downward with time due to normal aging of the structure. Also represented is an expectations curve, upwardly sloping due to increasing expectations with time. Where the two intersect defines the design service life conceptually. In discussing notions of service life, the perspective must be broadened from one focused narrowly on condition and deterioration to a broader view that accounts for technological, regulatory, economic, and social change.
