1993 AASHTO flexible pavement design

1993 AASHTO Guide, Part II §3.1

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1993 AASHTO Guide, Part II §3.1

Finds the structural number the traffic needs, then the layer depths that provide it, layer by layer from the top.

Units US customary SI (metric)

Traffic and reliability

Design ESALs

Total 18-kip (80 kN) ESALs in the design lane over the design period.

Reliability

Overall standard deviation, S₀

Typically 0.40 to 0.50 for flexible pavements.

Serviceability

Initial serviceability, p_i

Terminal serviceability, p_t

Structure

Layers above the subgrade

Subgrade resilient modulus, M_R, psi

HMA surface

HMA layer coefficient, a₁

Base

Base layer coefficient, a₂

Base drainage coefficient, m₂

Base resilient modulus, psi

Subbase

Subbase layer coefficient, a₃

Subbase drainage coefficient, m₃

Subbase resilient modulus, psi

Example values. Layer coefficients and drainage coefficients come from your agency’s design manual.