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Are current design service lives for asphalt concrete pavements suboptimal? An analytic argument for longer design service lives

ABSTRACT One would expect the service life to be treated as an endogenous variable to be optimized in design procedures, but this is often not the case. This article provides a solution to the net-benefit maximizing choice of the design service life as a closed form equation. Using the 1993 AASHTO Design Equation, it is shown that for real discount rates under 4%, design service lives over 72 years are net-benefit maximizing given constant traffic loads. For lower discount rates, optimal service lives are considerably longer. This finding is consistent with perpetual pavement design as well as with optimal maintenance strategies involving multiple resurfacing cycles. Discounting is shown to be a key driver of the solution. Additionally, a simple method is shown on how to calculate an economically maximum pavement thickness that is independent of physical parameters. A methodology to simplify the AASHTO equation for use in analytic modelling is shown.