Method, and what needs calibrating before you use this

The curve is a two-parameter Weibull survival form: PCI(t) = PCI₀ · exp(−(t/τ)^β), where τ (characteristic life) is derived from cumulative ESALs, the climate multiplier and the structural adequacy factor, and β (shape) sets how sharply deterioration accelerates. β is fixed at 2.0, which produces the slow-then-steep profile typical of flexible pavements.

This is a parametric family, not a published standard. AASHTO and the HDM-4 family of models use different formulations with locally fitted coefficients. The τ scaling here is calibrated to give roughly 12–15 years to PCI 70 for a well-built urban arterial under moderate heavy-vehicle loading, which is a reasonable default and nothing more. Before this drives a budget submission, fit τ and β to your own repeat-survey PCI history — two surveys on the same sections five or more years apart is enough to do it.

ESALs are computed as AADT × truck% × truck factor × 365 × lane distribution, with directional split taken as 0.5. No traffic growth is applied, so cumulative loading is linear in time; if your corridor is growing, the curve here is optimistic.