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Pavement Design for Heavy Traffic

This document discusses the calculation of equivalent single axle loads (ESALs) for pavement design. It provides reference materials and defines different vehicle classes and axle configurations. It also outlines the key steps in the traffic analysis: determining the initial ESAL based on traffic volume and mixture; applying directional, lane distribution and growth factors; and calculating the design ESAL over a 20-year period for a four-lane highway example assuming a 2% annual traffic growth rate. The example calculation shows applying these factors to the initial traffic data to determine the 20-year design ESAL of 10,358,354 for pavement structural design.

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289 views8 pages

Pavement Design for Heavy Traffic

This document discusses the calculation of equivalent single axle loads (ESALs) for pavement design. It provides reference materials and defines different vehicle classes and axle configurations. It also outlines the key steps in the traffic analysis: determining the initial ESAL based on traffic volume and mixture; applying directional, lane distribution and growth factors; and calculating the design ESAL over a 20-year period for a four-lane highway example assuming a 2% annual traffic growth rate. The example calculation shows applying these factors to the initial traffic data to determine the 20-year design ESAL of 10,358,354 for pavement structural design.

Uploaded by

gimanu
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Equivalent Single Axle Load Calculations

REFERENCES

AASHTO Guide for Design of Pavement Structures, 1993 and Huangs Pavement Analysis and Design, 1993

Traffic Analysis

We Need a Single Design ESAL Value

Axle Load Groups


Class 1 2 3 4 5 6 7 8 9 10 11 12 13 Description Motorcycles (optional) Passenger Cars Other Two-Axle, Four Tire Single Unit Vehicles Buses Two-Axle, Six Tire, Single Unit Trucks Three-Axle Single Unit Trucks Four or More Axle Single Unit Trucks Four or Less Axle Single Trailer Trucks Five-Axle Single Trailer Trucks Six or More Axle Single Trailer Trucks Five or Less Axle Multi-Trailer Trucks Six-Axle Multi-Trailer Trucks Seven or More Axle Multi-Trailer Trucks

Truck Configurations

ESAL Comparison Single Axles


80 kN 18,000 lb 100 kN 22,000 lb 18 kN 4,000 lb

1 ESAL

2.2 ESAL

.002 ESAL

ESAL Comparison (Tandem Axle Effects)


160 kN 36,000 lb Tandem Axle 160 kN 36,000 lb Single Axle

1.38 ESAL

13.93 ESAL

Little Truck

67 kN 27 kN 15,000 lb + 6,000 lb 0.48 ESAL 0.01 ESAL

0.49 ESAL

BIG TRUCK

151 kN 34,000 lb 1.10

151 kN 54 kN 34,000 lb + 12,000 lb 1.10 0.19

2.39 ESAL

10.5 ESALS (152,000 lbs)

Traffic Volume
We Need to Know:
Average Daily Traffic (ADT) Average Daily Truck Traffic (ADTT) Traffic Mixture (Number of Vehicles in
Each Class)

Average Weight of the Vehicles in Each


Class

Initial Year Traffic Volume

Given: ADT = 3500 VPD, Class 9 30%, Class 5 5% Use the ESAL Data from Previous Slide

ESALo = [(0.49)(0.05) + (2.39)(0.30)](3500)(365) ESALo = 947,266

Direction Distribution Factor

Initial Traffic in Two Directions Must Correct for One Direction Usually a Factor of 0.5 is Used This Can Vary Depending on the Traffic

Lane Distribution Factor



100% for Two Lane Highways Outside Lane is Design Lane for Multilane Facilities (Truck or Driving Lane) AASHTO, PCA, and Asphalt Institute all Recommend Slightly Different Methods

Lane Distribution Factor (L)


AASHTO

Lane Distribution Factor (L)


Asphalt Institute

Lane Distribution Factor (L)


PCA

Growth Factor


Used to Project Total Design Traffic from the Estimated First Year Traffic Multiply Initial Year Traffic by Appropriate Growth Factor (Table 6.13) Note that Growth Factors Can be Different for the Different Vehicle Classes

Growth Factor (G)

Growth Factor

Should Consider: Expected Traffic Attracted or Diverted Due to New/Improved Facility Normal Growth Due to Increased Activity Number of Motor Vehicles and Their Use Future Development (Land Use)

Example

Given

Four Lane Highway, Traffic Measured in Two


Directions

Flexible Pavement with Pt = 2.5 and SN = 5 Traffic Measurements over a 24 hour Period Traffic Data as Previously Shown Growth Factor = 2%
Find

20 Year Design ESAL ignoring Light Traffic


(eg. Passenger Cars) using AASHTO Method

Example Details
Assumptions:
Traffic Volume (All Vehicle Types) will
Increase at 2% per year

Axle Weights of Various Vehicle Types


will Remain Constant Over Design Period

Design ESAL
ESALD = (947,266)(0.5)(0.9)(24.30) ESALD = 10,358,354

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