Traffic and Axle Loads

Typical Axle Combinations

Single Axle Tridem AxleTandem Axle

Typical Weight Limits

Weigh Stations

Axle Load Histogram

0

100

200

300

400

500

600

3000-6999 7000-7999 8000-11999

12000-15999

16000-17999

18000-19999

20000-21999

22000-23999

24000-25999

26000-29999

Single Axle Load (lbs)

F

r

e

q

u

e

n

c

y

Axle Load Histogram

0

50

100

150

200

250

6000-11999

12000-17999

18000-23999

24000-29999

30000-31999

32000-33999

34000-35999

36000-37999

38000-39999

40000-41999

Tandem Axle Load (lbs)

F

r

e

q

u

e

n

c

y

Standard Axle Load

Single Axle, Dual Wheels

Source: WSDOT Pavement Guide Interactive CD-ROM

9 kips

9 kips

GENERIC METHOD

Mazda Miata

1 consumption per passageMM

dN

Curb weight = 2300 lb

Assume NM = 12,000,000

Ford Excursion

1 consumption per passageFF

dN

Curb weight = 6300 lb

Assume NF = 200,000

Standard Vehicle

1 consumption per passageSS

dN

Assume NF = 1,000,000

Mazda Equivalency Factor

11

M M SMS S M

d N NFd N N

1,000,000 0.08312,000,000

MF

Ford Equivalency Factor

11

F F SFS S F

d N NFd N N

1,000,000 5.0200,000

FF

MECHANISTIC METHOD

Pavement Life (Fatigue)

21

kf tN kAsphaltTensileStrain

AsphaltFatigue

Life

LEF (Fatigue)

1 sii

kNLEFN

21

kstk

2

2

kit

k sitt

3 k2 6

Pavement Life (Rutting)

43

kf cN kSubgrade

CompressiveStrain

SubgradeFatigue

Life

LEF (Rutting)

3 sii

kNLEFN

43

ksck

4

4

kic

k sicc

3.5 k4 4.5

Pavement Life (Rigid)

4

225,000

tfN MOR

ConcreteModulus of

Rupture

ConcreteTensile Strain

LEF (Rigid)

sts

ii

MORNLEFN

4it MOR

4

4

itst

LEF Summary

4 4 4 4

18

i i it t c i

i s s st t c

LLEFL

18-kipStandardAxle Load

MeasuredAxle Load

AASHTO METHOD

AASHTO LEF

18

10 10 22 18

18 1log 4.79log 4.33log

xt t t

t x x

W G GLW L L

Flexible Pavements

18

10 10 22 18

18 1log 4.62log 3.28log

xt t t

t x x

W G GLW L L

Rigid Pavements

Pavement Performance

p

W

i i f Wp p p p

failure

pi

pf

Pavement Performance

p

W

failure

pi

pf

(failure)

Pavement Performance

p

W

xi i fx

Wp p p p

pi

pffailure

Pavement Performance

x xti ft ix

p p pW

p

Wt x

Serviceability Limit

pi

pf

ptp

x

failure

W

x

Flexible Pavement Performance

xxx

tt 4.2 4.2 1.5

Wp

Wt x

Serviceability Limit

4.2

1.5

ptp

x

failure

W

x

Flexible Pavement Performance

xxttx

Wp 4.2 4.2 1.5

3.23

25.19 3.23

2

0.0810.41

x

xL L

SN L

9.365.93 4.332

4.792

10 1 x xSN LL L

Flexible Pavement Performance

xxttx

Wp 4.2 4.2 1.5

xt t x xW p , , f

AASHTO LEF

18 18 18

, ,, ,

x

t ts

x t t x x

W f pNLEFN W f p

Flexible Pavement Performance

xxttx

Wp 4.2 4.2 1.5

x

xtt

x

W4.2 p4.2 1.5

x

t

tt

G

10 x 10x

W4.2 plog log4.2 1.5

Pavement Performance

xtt x 10

x

WG log

10 10log log xt t xx

G W

10 10log log x tt xx

GW

Pavement Performance

10 10log log x tt xx

GW

1010loglog10 10

txtx xG

W

10t

x

x

G

t xW

AASHTO LEF

1818 1818 1810 10

10

t

t t

x

txx

GG G

tG

t xx

WLEF

W

xLEF e EALF

AASHTO LEF

18

1818

log log log

xt t tx

t x

W G GW

1: log xx

NOTE this is not ee

This is the equation in the textbook

Rigid Pavement Performance

xxttx

Wp 1.54.5 4.5

5.20

8.46 3.52

22

3.6311

.0 x

x LDL L

7.352

5.85 3.28

62

4. 210 1 x x

LL LD

Rigid Pavement Performance

xxttx

Wp 1.54.5 4.5

x

xtt

x

Wp1

4.54.5 .5

t

xtt10

G

x 10x

Wplog log1.

4.54. 55

TRUCK LOAD FACTORS

Equivalent Single Axle Loads

12,000 32,000 32,000

ESAL = ??

AASHTO Equivalency Factors

Axle Load Histogram

0

50

100

150

200

250

6000-11999

12000-17999

18000-23999

24000-29999

30000-31999

32000-33999

34000-35999

36000-37999

38000-39999

40000-41999

Tandem Axle Load (lbs)

F

r

e

q

u

e

n

c

y

Single AxlesLoad Group

(lbs)Axle Count

per 1000 trucks LEF ESALs3000-6999 557 0.005 2.79

7000-7999 140 0.027 3.78

8000-11999 493 0.088 43.38

12000-15999 154 0.360 55.44

16000-17999 75 0.796 59.70

18000-19999 33 1.24 40.9

20000-21999 5 1.83 9.15

22000-23999 2 2.58 5.16

24000-25999 1 3.53 3.53

26000-29999 1 5.39 5.39

TOTAL = 229.2

Tandem AxlesLoad Group

(kips)Axle Count

per 1000 trucks LEF ESALs6000-11999 227 0.010 2.3

12000-17999 162 0.037 6.0

18000-23999 108 0.150 16.2

24000-29999 140 0.429 60.1

30000-31999 58 0.757 43.9

32000-33999 25 0.97 24.3

34000-35999 6 1.23 7.4

36000-37999 3 1.54 4.6

38000-39999 1 1.89 1.9

40000-41999 1 2.29 2.3

TOTAL = 169.0

Average Truck Load Factor

229 169 0.401000 f ESALsT Vehicles

FHWA Truck Classes

FHWA Class 4

Source: WSDOT Pavement Guide Interactive CD-ROM

FHWA Class 5

Source: WSDOT Pavement Guide Interactive CD-ROM

FHWA Class 6

FHWA Class 7

FHWA Class 8

Source: WSDOT Pavement Guide Interactive CD-ROM

FHWA Class 9

Source: images.encarta.msn.com

FHWA Class 10

Source: WSDOT Pavement Guide Interactive CD-ROM

FHWA Truck ClassesClass Type EALF1 Motorcycles negligible2 Passenger Cars negligible3 Other Two-Axle, Four-Tire Single Unit Vehicles negligible4 Buses 0.575 Two-Axle, Six-Tire, Single Unit Trucks 0.266 Three-Axle Single Unit Trucks 0.427 Four or More Axle Single Unit Trucks 0.428 Four or Less Axle Single Trailer Trucks 0.309 Five-Axle Single Trailer Trucks 1.2010 Six or More Axle Single Trailer Trucks 0.9311 Five or Less Axle Multi-Trailer Trucks 0.8212 Six-Axle Multi-Trailer Trucks 1.0613 Seven or More Axle Multi-Trailer Trucks 1.39

Typical Traffic Data

Source: WSDOT Pavement Guide Interactive CD-ROM

WSDOT Simplified System

WSDOT Category FHWA Classes Assumed EALF

Single Units 4, 5, 6, 7 0.40

Double Units 8, 9, 10 1.00

Trains 11, 12, 13 1.75

Daily ESALs = 0.40(single units) + 1.00(double units) + 1.75(trains)

Source: WSDOT Pavement Guide Interactive CD-ROM

TDOT Simplified System

VehicleType

FHWAClass

FlexibleEALF

RigidEALF

Cars & Motorcycles 1, 2 0.001 0.001

Pickups, Panel Vans 3 0.004 0.005

Buses 4 0.300 0.300

2-axle, 6-tire Singles 5 0.170 0.170

3-axle or more Singles 6, 7 0.700 1.000

4-axle Combos 8 0.700 0.780

5-axle or more Combos 9 -11 1.100 1.780

Design ESALS

fESAL 365 ADT T T D L GTruck Load

Factor

LaneDistribution

Factor

DirectionDistribution

Factor

GrowthFactor

PercentTrucks

AverageDaily Traffic(two-way)

Design ESALS

fESAL 365 ADT T T D L GTruck Load

Factor

LaneDistribution

Factor

DirectionDistribution

Factor

GrowthFactor

AverageDaily Truck

Traffic

Design ESALS

m m m mi 1

ESAL 365 L D N T G

DirectionDistribution

Factor

DailyTruck Count(two-way)

GrowthFactor

TruckLoad

Factor

LaneDistribution

Factor

Traffic GrowthCOMPARISON OF GROWTH IN VOLUME AND

LOADINGS ON THE INTERSTATE SYSTEM

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 020

100

200

300

400

500

600

700

P

E

R

C

E

N

T

G

R

O

W

T

H

(

3

-

Y

E

A

R

M

O

V

I

N

G

A

V

E

R

A

G

E

)

RURALAVERAGE DAILYLOAD

RURALAVERAGE DAILYTRAFFIC

YEARSource: Truck Weight Study and HPMS

Growth Factor

1 1G 0 ng for gg

Lane Distribution FactorsNumber of Lanesin Each Direction

Percent of Loadsin Design Lane

1 100

2 80-100

3 60-80

4 50-75