What is an ESAL?
- Definition: ESAL = Equivalent Single Axle Load
- Standard: One ESAL is the damage from a single 18,000-lb (80 kN) single axle with dual tires.
- Purpose: Convert mixed traffic into a common damage unit for pavement design.
ESAL Formula
Where:
- Ni = number of passes for vehicle class i
- LEFi = Load Equivalency Factor for vehicle class i
Typical Load Equivalency Factors (LEFs) (based on AASHTO & typical LEFs)
| Vehicle Type | Axles | Typical Load (kips per axle) | Approx. ESAL per Pass |
|---|---|---|---|
| Passenger Car (sedan) | 2 | 2–3 | 0.0004 |
| Pickup / SUV | 2 | 3–4 | 0.001 |
| Delivery Van (2-axle, light) | 2 | 4–5 | 0.005 |
| Single-Unit Truck (2-axle, 6-tire) | 2 | 6–9 | 0.02 |
| Single-Unit Truck (3-axle) | 3 | 8–10 | 0.40 |
| City Bus | 2–3 | 10–12 | 0.50 – 1.50 |
| Tractor-Trailer (4-axle) | 4 | 12–14 | 0.80 – 1.50 |
| Tractor-Trailer (5-axle standard semi) | 5 | 16–18 | 1.0 – 4.0 |
| Tractor-Trailer (6-axle) | 6 | 18–20 | 3.0 – 6.0 |
| Heavy Haul Truck (7+ axles, overloaded) | 7+ | 20+ | 5.0 – 10.0+ |
(Values vary by pavement type and standard — AASHTO, IRC, etc.)
How to Use This Table
- Classify vehicles (cars, pickups, buses, trucks, semis, heavy haul).
- Multiply the number of vehicles by the ESAL factor in the table.
- Sum across all vehicle classes to get the total daily ESALs.
- Apply growth factor & design life to get design ESALs.
Or use the Traffic to ESAL Converter
ESAL Conversion Table (by Vehicle & Load Condition)
| Vehicle Type | Axles | Load Condition | Typical Axle Load (kips) | Approx. ESAL per Pass |
|---|---|---|---|---|
| Passenger Car | 2 | Normal | 2–3 | 0.0004 |
| Pickup / SUV | 2 | Empty | 3–4 | 0.0005 |
| 2 | Loaded | 4–5 | 0.001 | |
| Delivery Van (2-axle, light) | 2 | Empty | 4–5 | 0.003 |
| 2 | Loaded | 5–6 | 0.005 | |
| Single-Unit Truck (2-axle, 6-tire) | 2 | Empty | 6–7 | 0.01 |
| 2 | Medium | 8–9 | 0.02 | |
| 2 | Fully Loaded | 10–12 | 0.05 | |
| Single-Unit Truck (3-axle) | 3 | Empty | 8–10 | 0.2 |
| 3 | Medium | 10–12 | 0.4 | |
| 3 | Fully Loaded | 12–14 | 0.8 | |
| City Bus | 2–3 | Light Load (off-peak) | 10–11 | 0.5 |
| 2–3 | Peak Load (crowded) | 12–14 | 1.0 – 1.5 | |
| Tractor-Trailer (4-axle) | 4 | Empty | 10–12 | 0.3 |
| 4 | Medium | 12–14 | 0.8 | |
| 4 | Fully Loaded | 14–16 | 1.5 | |
| Tractor-Trailer (5-axle, standard semi) | 5 | Empty | 12–14 | 0.5 |
| 5 | Medium | 14–16 | 1.5 | |
| 5 | Fully Loaded | 16–18 | 2.5 – 4.0 | |
| 5 | Overloaded | 18–20+ | 5.0+ | |
| Tractor-Trailer (6-axle) | 6 | Medium | 16–18 | 3.0 |
| 6 | Fully Loaded | 18–20 | 4.0 – 6.0 | |
| Heavy Haul Truck (7+ axles) | 7+ | Legal Load | 20+ | 5.0 |
| 7+ | Overloaded | 22–25+ | 8.0 – 12.0+ |
Passenger cars ≈ negligible impact → engineers usually ignore them in ESAL calculations.
Axle load matters more than vehicle type (a single overloaded truck can equal thousands of cars).
Buses can rival trucks in ESAL impact, especially in urban corridors.
Overloaded trucks are ESAL monsters → 1 pass can equal 5–10+ passes of a legal semi-truck.
Step-by-Step Conversion Example
Problem:
- Road AADT = 20,000
- 8% trucks (1,600 trucks/day)
- Design life = 20 years
- Assume truck mix avg. LEF = 2.0
Solution:
- Total trucks over design life = 1,600×365×20=11.68 million1,600 \times 365 \times 20 = 11.68 \text{ million}1,600×365×20=11.68 million
- ESALs = 11.68×106×2.0=23.36 million11.68 \times 10^6 \times 2.0 = 23.36 \text{ million}11.68×106×2.0=23.36 million
Pavement must be designed for 23.4 million ESALs.
Typical ESAL Ranges for Roads
| Road Type | Design ESALs (lifetime) |
|---|---|
| Low-volume rural | 10⁴ – 10⁵ |
| Urban arterial | 10⁶ – 10⁷ |
| Expressway / Highway | 10⁸+ |
Quick Reference Notes
- Cars contribute negligible ESALs compared to trucks.
- Pavement failure risk grows exponentially with axle load (fourth power law).
- Always check local design codes (AASHTO 1993, MEPDG, IRC, etc.).
Free Download ESAL Cheat Sheet
(Compact, printable version for students & engineers.)
