Complete Guide to Pavement Design (AASHTO)
The Pavement Design Calculator implements AASHTO 1993/1998 empirical methods for flexible and rigid pavements. It computes ESALs, required structural number (SN), and slab thickness based on traffic, subgrade, and reliability. Essential for highways, airports, and parking lots. Our free Pavement Design Calculator integrates with Traffic Volume for complete roadway projects.
What is Pavement Design?
Structural design of roadway layers to support traffic loads over design life without excessive deformation or cracking.
- Flexible: Asphalt layers over granular base
- Rigid: PCC slab with or without base
Why Design Pavements?
Required for:
- Durability: 20+ year life
- Safety: Smooth ride, skid resistance
- Cost: Balance initial vs. maintenance
Link with Traffic Volume for ESALs.
Key Equations
ESALs
\( W_{18} = 365 \times AADT \times T \times G \times D \times LEF \times (1+r)^n \)
Flexible SN
\( \log_{10} W_{18} = Z_R S_0 + 9.36 \log_{10}(SN+1) - 0.20 + \frac{\log_{10}(\Delta PSI / 4.2-1.5)}{0.40 + \frac{1094}{(SN+1)^{5.19}}} + 2.32 \log_{10} M_R - 8.07 \)
Rigid Thickness
\( \log_{10} W_{18} = Z_R S_0 + 7.35 \log_{10}(D+1) - 0.06 + \frac{1 + \frac{1.624 \times 10^7}{(D+1)^{8.46}}}{(4.22 - 0.32 p_t)^{1.00}} + \frac{\log_{10}(p_t / 4.5-1.5)}{1 + \frac{18.32}{(D+1)^{1.57}}} \)
Step-by-Step Process
- Estimate Traffic: AADT, T%, growth
- Convert to ESALs: Use LEF ≈ 1.0–4.0
- Determine Subgrade Mr
- Select Reliability: 85–99%
- Solve for SN or D
Example: Flexible Pavement
AADT=5000, T=15%, r=3%, n=20, Mr=10,000 psi, R=95%, ΔPSI=2.5:
- ESALs ≈ 7.3 million
- SN required ≈ 4.8
- Layers: 5" HMA + 10" base + 12" subbase
Typical Values
| Parameter | Flexible | Rigid |
|---|---|---|
| Design Life | 15–30 years | 20–40 years |
| Reliability | 85–95% | 90–99% |
| ΔPSI | 2.0–2.5 | — |
| Mr (psi) | 5,000–30,000 | — |
Applications
- Highways: Interstates, arterials
- Airports: Runways, aprons
- Parking Lots
- Industrial Roads
Best Practices
- Use local traffic data
- Perform FWD testing
- Include drainage
- Consider climate
Common Mistakes
- Underestimating ESALs
- Ignoring drainage
- Wrong Mr value
- No reliability factor
Advanced Topics
- Mechanistic-Empirical (MEPDG)
- Perpetual pavements
- Full-depth asphalt
- Composite pavements
Conclusion
Proper pavement design ensures long-term performance. Our Pavement Design Calculator delivers AASHTO-compliant SN and slab thickness instantly. Combine with Traffic Volume and other tools for end-to-end roadway design. Build durable, cost-effective pavements!