Designing a durable and cost-effective road starts with a strong pavement foundation. In Pakistan, flexible pavement remains the most common choice for urban roads, highways, and access streets. But how do engineers determine the thickness of each pavement layer — from subgrade to asphalt?
This article walks you through the basics of flexible pavement design using the AASHTO 1993 method and introduces a free, web-based calculator that simplifies the process.
🔍 What is Flexible Pavement?
Flexible pavements are composed of multiple layers, typically:
- Asphalt Concrete (AC)
- Base Course (e.g., crushed aggregate)
- Sub-base Course
- Compacted Subgrade Soil
Each layer is designed to distribute traffic loads downward while maintaining strength and durability.
📐 The AASHTO 1993 Method
The AASHTO (American Association of State Highway and Transportation Officials) 1993 design method is widely used across Pakistan due to its practicality and reliability. It estimates required pavement thicknesses based on:
- Traffic Load (in ESALs)
- Subgrade Strength (CBR or resilient modulus)
- Reliability Level
- Drainage Conditions
- Serviceability Loss
🚛 Understanding ESALs (Traffic Loading)
Traffic volume is converted to Equivalent Single Axle Loads (ESALs) to standardize loading effects. For example:
- A single 18,000 lb axle = 1 ESAL
- A 10-wheel truck may cause 1.5–3.0 ESALs per pass
You can estimate cumulative ESALs using our free tool below.
👉 Try it here: Traffic to ESALs Converter
🧮 Try the Pavement Design Calculator (Free)
We’ve built a simple web-based calculator based on AASHTO 1993 to help engineers and planners in Pakistan:
👉 Use the Pavement Design Calculator
Just input:
- Design ESALs
- Subgrade CBR
- Desired reliability
- Drainage and layer coefficients
The tool will output:
- Required asphalt thickness
- Base and sub-base thicknesses
- All values in inches, ideal for use in design BOQs and construction drawings
📌 Disclaimers
- The tool provides preliminary estimates — always verify with a qualified pavement engineer for final designs.
- Values like CBR and layer coefficients should be based on site-specific testing when available.
- ESAL values must reflect actual projected traffic — don’t guess!
🛠 Need Help With Road Design?
At Arterials.co, we provide:
- Custom pavement design reports
- Material estimates and BOQs
- Traffic studies and ESAL forecasting
- Construction material sourcing
📩 Contact us for road design, BOQs, or construction material supplies anywhere in Pakistan.
💡 Final Thoughts
With tools like the AASHTO-based pavement design calculator and ESAL converter, early-stage road design can be much faster, more transparent, and easier to communicate. Whether you’re a consultant, engineer, or client, understanding the design logic helps you build roads that last.
