Pavement
AASHTO Pavement Design
AASHTO 1993 flexible pavement design calculator — structural number from ESALs, reliability, DPSI, and subgrade resilient modulus.
Pavement · AASHTO 1993
AASHTO Pavement Design (SN)
The AASHTO 1993 method determines the required structural number (SN) for flexible pavement. SN is a composite index reflecting the combined strength of all pavement layers above the subgrade.
Key inputs: 18-kip ESAL loading (W₁₂) for the design period, reliability level (R), overall standard deviation (S₀ = 0.45 typical), change in serviceability index (ΔPSI), and subgrade resilient modulus (MR). SN is solved iteratively from the AASHTO design equation. SN is then converted to layer thicknesses using structural coefficients (a₁D₁ + a₂m₂D₂ + a₃m₃D₃).
AASHTO 1993 Design Equation
log₁₀(W₁₂) = Z𝑹·S₀ + 9.36·log₁₀(SN+1) − 0.20
+ log₁₀(ΔPSI/2.7) / [0.40 + 1094/(SN+1)^5.19]
+ 2.32·log₁₀(M𝑹) − 8.07
Reference: AASHTO Guide for Design of Pavement Structures, 1993. SN solved via bisection method.
AASHTO Pavement Design Calculator
Flexible pavement structural number (SN)
Local ~0.5M Arterial ~5M Highway 20M+
Urban arterial: 85–95% Rural: 75–85%
Flexible: 0.44–0.49
pᵢ=4.5 − pₜ=2.5 → 2.0
Poor: 3,000–6,000 Typical: 8,000–15,000
Pavement Design Results
Required Structural Number (SN)—
Z𝑹 (Reliability Factor)—
Min. HMA Surface (a₁=0.44)—
log₁₀(W₁₂)—
SN is a minimum design value. Layer thickness design and drainage coefficients must be per AASHTO 1993 Part II and applicable state DOT supplements. Requires PE review and seal.