Structural overlay thickness

1993 AASHTO Guide, Part III §5.4

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1993 AASHTO Guide, Part III §5.4

Units US customary SI (metric)

Future traffic

Future design ESALs

Reliability

Overall standard deviation, S₀

Serviceability after overlay, p₁

Terminal serviceability, p₂

Existing pavement

Design subgrade resilient modulus, M_R, psi

Back-calculated modulus × C (0.33 in the Guide).

Effective structural number of the existing pavement, SN_eff

Overlay layer coefficient, a_ol

Example values. Find SN_eff from a condition survey, component analysis or deflection testing.