ESAL Calculator
Calculates 20-year design ESALs using Alaska DOT&PF five-category truck classification and Table 6-1 load equivalency factors. Per AKFPD Chapter 6.
📊 Traffic Inputs
Both directions, all vehicles
Percent of AADT that are trucks (Classes 4–13)
Projects opening date relative to base count year
Usually 0.5 for 2-lane roads
1.0 for 2-lane roads; 0.8–0.9 for multi-lane
🚛 Truck Mix — Load Factors (Table 6-1)
Enter percent of truck fleet in each class. Must total 100%. Load factors per AKFPD Table 6-1.
Type
Classes
LEF
% of fleet
ESALs/day
2-axle
Class 5
0.30
—
3-axle
Class 6
0.55
—
4-axle
Class 7
0.78
—
5-axle
Class 8,9,11
1.11
—
6+-axle
Class 10,12,13
2.24
—
Fleet total: 100%
ESAL Design Summary
Construction Year AADT
—
Trucks/Day (Design Lane)
—
ESALs/Day
—
Design ESALs (×1,000)
—
Recommended Method
—
📐 Growth Factor Formula
Ndesign = AADT × D × L × (T%/100) × LEFavg × GF × 365
GF = [(1+r)n+y − (1+r)y] / r
r = annual growth rate, n = design period, y = years to construction
Weighted LEF: —
Growth Factor (GF): —
📋 Design Method Thresholds
| Design ESALs | Method |
|---|---|
| \x3C 100,000 | Excess Fines (low-volume) |
| 100,000 – 1,000,000 | Excess Fines preferred |
| \x3E 1,000,000 | Mechanistic Required |
| Overlay design | Mechanistic Required |
❄ Need frost depth & Casagrande check? subgrade-frost.html →
Excess Fines Design Method
Empirical method for new highway pavements with ESALs < 1.0 million per AKFPD Chapter 3. Calculates required AC thickness from P200 content of aggregate layers. Step-by-step mode shows calculations building layer by layer.
Method Applicability: Design ESALs < 1.0 million AND standard asphalt concrete with P200 within allowable limits. Mechanistic design required for ESALs > 1.0M or overlay design.
🚛 Traffic
From ESAL Calculator, or enter directly.
🪨 Aggregate Layers (below AC bottom, to 40")
Define each layer with P200 content. The method automatically subdivides into 1" sublayers. Include base, subbase, and select material.
#
Material
Top (in)
Bot (in)
P200 (%)
Status
📊 Calculation Results
Pavement Section Diagram
Diagram proportional to layer thicknesses
Shows SRF, EFFt calculation, and Pcr/Pmax check for each layer
Mechanistic Design
Based on AKFPD Chapter 4. Required for ESALs > 1.0 million or overlay design. Uses TAI fatigue equation and Per Ullidtz functional failure criterion with Alaska R=2.75. Miner's Law seasonal damage summation.
🚛 Traffic
🛣️ AC Layer
🪨 Structural Layers (define to subgrade)
#
Material
Top (in)
Bot (in)
E (ksi)
🌱 Subgrade
Spring thaw weakening typically reduces MR to 30–50% of summer value
Design Results
Damage Ratio (Total)
—
Design Status
—
Critical Season
—
Total damage ratio ≤ 1.0 required. Per Miner's Law, D = Σ(ni/Ni).
📅 Seasonal Damage Breakdown — Miner's Law
Alaska seasonal distribution: Spring 10% · Summer 35% · Fall 20% · Winter 35%
📊 Layer Damage Visualization
Bar length = relative damage contribution. Red = dominant damage season. Wider bars = higher damage fraction.
📐 Key Equations
TAI Fatigue: Nf = 0.0795 × εt−3.291 × EAC−0.854
Per Ullidtz: Nr = C × (1/εv)R where C=1.365×10⁻⁹, R=2.75 (Alaska)
Miner's Law: Dtotal = Σ (ni / Ni) ≤ 1.0
Strain (simplified): ε = σ / E
Materials Reference
Condensed reference tables from AKFPD Chapter 5 (structural layer coefficients and moduli) and Chapter 6 (load factors). For full tables see the AKFPD Manual directly.
Table 5-1 — Structural Layer Moduli (Typical)
| Material | E Summer (ksi) | E Spring (ksi) | E Winter (ksi) | SRF |
|---|---|---|---|---|
| Asphalt Concrete (AC) | 300–500 | 200–300 | 800–1500 | — |
| D-1 Aggregate Base | 30–40 | 15–25 | 50–80 | 1.0 |
| Select Material Type A | 20–30 | 12–20 | 35–60 | 0.9 |
| Select Material Type B | 15–25 | 8–15 | 25–50 | 0.8 |
| Select Material Type C | 10–18 | 6–12 | 18–35 | 0.7 |
| Subbase F (granular) | 12–20 | 7–14 | 20–40 | 0.75 |
| Native Subgrade (good) | 8–15 | 3–8 | 30–80 | — |
| Native Subgrade (poor) | 4–8 | 1–4 | 15–50 | — |
| ATB (Asphalt Treated Base) | 200–400 | 150–300 | 600–1000 | — |
SRF = Structural Reduction Factor (Excess Fines method). Source: AKFPD Table 5-1.
P200 Specification Limits by Layer
| Material / Layer | Max P200 (%) | AKFPD Ref |
|---|---|---|
| D-1 Aggregate Base (0–8") | 7.0 | Fig 3-4 |
| Select Material Type A (8–20") | 10.0 | Fig 3-4 |
| Select Material Type B (20–40") | 15.0 | Fig 3-4 |
| Select Material Type C (>40") | 20.0 | Fig 3-4 |
| Subbase F | 12.0 | Spec D-1 |
| Common Borrow / Fill | 35.0 | Spec |
Limits are position-dependent — P200 allowable increases with depth from AC. ❄ For Casagrande frost check: subgrade-frost.html
Table 6-1 — Load Equivalency Factors
| Truck Type | Classes | LEF | Typical Use |
|---|---|---|---|
| 2-axle (single-unit) | Class 5 | 0.30 | Pickup/delivery, light trucks |
| 3-axle (single-unit) | Class 6 | 0.55 | Medium delivery, dump trucks (small) |
| 4-axle (single-unit) | Class 7 | 0.78 | Larger single-unit trucks |
| 5-axle combination | 8, 9, 11 | 1.11 | Semi-trucks, standard 18-wheelers |
| 6+-axle combination | 10, 12, 13 | 2.24 | Tandem semi, multi-trailer |
Source: AKFPD Table 6-1. LEF = Load Equivalency Factor relative to standard 18-kip axle load.
AC Thickness Minimums by ESAL
| Design ESALs | Min AC (in) | Method |
|---|---|---|
| \x3C 10,000 | 2.0 | Excess Fines |
| 10,000 – 100,000 | 2.5 | Excess Fines |
| 100,000 – 500,000 | 3.0 | Excess Fines |
| 500,000 – 1,000,000 | 4.0 | Excess Fines or Mech. |
| > 1,000,000 | 4.0+ | Mechanistic |
Seasonal Moduli Reduction Factors (Alaska)
| Season | Months | Portion of Year | MR Factor (typical) |
|---|---|---|---|
| Spring (thaw) | May–Jun | 10% | 0.3–0.5 × summer |
| Summer | Jul–Sep | 35% | 1.0 (baseline) |
| Fall | Oct–Nov | 20% | 0.8–1.0 × summer |
| Winter (frozen) | Dec–Apr | 35% | 5–15 × summer |
Spring thaw weakening is the critical design season for most Alaska subgrades. ❄ Frost depth and thaw settlement: subgrade-frost.html