potential implications of nafta truck traffic:. for better or for worse? potential implications of...

Potential Implications of Potential Implications of NAFTA Truck Traffic:NAFTA Truck Traffic:

for better or for worse? for better or for worse?


for better or for worse? for better or for worse?

Dr. Jorge A ProzziDr. Jorge A ProzziThe University of TexasThe University of Texas

Border Partnership Working GroupBorder Partnership Working Group7 September 2006, Austin, Texas7 September 2006, Austin, Texas


Presentation OutlinePresentation Outline

Effect of Loads on Pavement DamageEffect of Loads on Pavement Damage• Historical (ESAL)Historical (ESAL)• Recent Findings (TxDOT Research 0-4510)Recent Findings (TxDOT Research 0-4510)

Data AnalysisData Analysis Preliminary ResultsPreliminary Results Preliminary FindingsPreliminary Findings

Historical: ESALHistorical: ESAL

Where,Where, LEFLEFi i : load equivalency factor for load i-th: load equivalency factor for load i-th nni i : number of axles of load i-th: number of axles of load i-th xxi i : axle load i-th: axle load i-th LLS S : standard axle load: standard axle load m m : power, usually 4.0: power, usually 4.0

k

iii nLEFESAL

1

m

s

ii L

xLEF


Power value, m: Power value, m: 4.0 according to analysis of the AASHO Road Test 4.0 according to analysis of the AASHO Road Test

(based on (based on riding qualityriding quality)) 3.0-5.0 for fatigue 3.0-5.0 for fatigue crackingcracking Around 1.0-2.0 for rutting or surface Around 1.0-2.0 for rutting or surface deformationdeformation Other research studies found values varying from Other research studies found values varying from

less than 1.0 to 6.0 or even largerless than 1.0 to 6.0 or even larger So, which exponent (power) should we use?So, which exponent (power) should we use? Is it safe to use a higher power value? Is it safe to use a higher power value?


00.20.40.60.8

11.21.4

0 2 4 6 8 10

Power

LSF

+0+1+2+4


0

0.5

1

1.5

2

2.5

15 20 25 30 35 40 45AXLE LOAD (kips)

EDF

or "

wei

ght"

EDF1EDF2EDF3EDF4


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60 70 80

Axle Weight (kip)

Nor

mal

ized

Fre

quen

cy

Type II

Type III

Type I

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60 70 80

Axle Weight (kip)

Nor

mal

ized

Fre

quen

cy

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60 70 80

Axle Weight (kip)

Nor

mal

ized

Fre

quen

cy

Mixed Lognormal distributionMixed Lognormal distribution

WhereWhere• xx: axle load, kip: axle load, kip• kk: the : the kk-th peak-th peak• KK: number of peaks, (1-3): number of peaks, (1-3)• λλkk, , ζζkk: parameters: parameters• WWkk: weights, : weights, ∑∑WWkk = 1 = 1

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 10 20 30 40 50

Axle Load (kip)

Nor

mal

ized

Fre

quen

cypk1pk2pk3all

K

k k

k

k

kkkk

xLnx

WWxf

1

2)(

21exp

2),,;(

Recent Findings: TxDOT 0-4510Recent Findings: TxDOT 0-4510


WhereWhere MM : total number of axles: total number of axles f(x)f(x) : relative frequency of axle load i-th,: relative frequency of axle load i-th, LSFLSF : load spectra factor, which represents the : load spectra factor, which represents the

number of ESALs of a “representative” axle.number of ESALs of a “representative” axle.

k

i

ii MnLEF

MESAL

1

mi

k

i

mim

s

k

ii

m

s

i LSFxfxL

xfLx

)(1)(11

Advantages of the log-normal random variable X:Advantages of the log-normal random variable X: The logarithm of X (axle load) is normal.The logarithm of X (axle load) is normal. X is non-negative, as axle loads are.X is non-negative, as axle loads are. The parameters have physical meaning.The parameters have physical meaning. It has a close-form expression for the LSF, which It has a close-form expression for the LSF, which

captures the damaging effect of loads on captures the damaging effect of loads on pavements:pavements:

22

222

21

211 expexp mmWmmWLSF


Data AnalysisData Analysis

TxDOT operates approximately 15-20 TxDOT operates approximately 15-20 permanent WIM stations, mostly on rural permanent WIM stations, mostly on rural interstate and US highwaysinterstate and US highways

Selection criteria:Selection criteria:• enough time series data, andenough time series data, and• close to US-Mexico borderclose to US-Mexico border

D522, near McAllen (Hidalgo), on US 281D522, near McAllen (Hidalgo), on US 281 D516, near San Antonio, on IH 35 D516, near San Antonio, on IH 35

Data AnalysisData Analysis

Class 9 (3S2) and Class 5 were analyzed in Class 9 (3S2) and Class 5 were analyzed in detail; they account for +80% of the volumedetail; they account for +80% of the volume

Analysis was doneAnalysis was done• per direction (north- and southbound)per direction (north- and southbound)• per axle type (steering, single, and tandem)per axle type (steering, single, and tandem)• per year (to establish and document trends)per year (to establish and document trends)

We calculated pavement damage by applying We calculated pavement damage by applying the LSF concept explained earlierthe LSF concept explained earlier

Preliminary ResultsPreliminary Results

D522 – US 281, McAllenD522 – US 281, McAllen

Class 9, Class 9, steeringsteering axle load distribution for axle load distribution for northboundnorthbound and and southboundsouthbound lanes lanes

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 5 10 15 20 25 30

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Year98

Year99

Year00

Year01

Year02

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 5 10 15 20 25 30

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Year98

Year99

Year00

Year01

Year02


Class 9, Class 9, tandemtandem axle load distribution for axle load distribution for northboundnorthbound and and southboundsouthbound lanes lanes

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 10 20 30 40 50

Axle Load (kip)

Nor

mal

ized

Fre

quen

cy

Year98

Year99

Year00

Year01

Year02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 10 20 30 40 50

Axle Load (kip)

Nor

mal

ized

Fre

quen

cy

Year98Year99Year00

Year01Year02


Class 9, Class 9, tandemtandem axle load distribution for axle load distribution for northbound and southbound lanes in northbound and southbound lanes in 20022002

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 10 20 30 40 50 60

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Northbound

Southbound

U.S. Legal Limit (34kip)

Mexico Legal Limit (40 kip)


Class 5, Class 5, steeringsteering and and singlesingle axle load axle load distribution for distribution for southboundsouthbound direction direction

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Year98

Year99

Year00

Year01

Year02

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 5 10 15 20 25 30

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Year98

Year99

Year00

Year01

Year02

Preliminary Findings (D522)Preliminary Findings (D522)

Class 9Class 9• bi-modal for tandem, uni-modal for steeringbi-modal for tandem, uni-modal for steering• small but steady rightward shiftsmall but steady rightward shift• northbound traffic is heavier than southboundnorthbound traffic is heavier than southbound• northbound is Type III; southbound, Type IInorthbound is Type III; southbound, Type II

Class 5Class 5• steering and single show uni-modal spectrasteering and single show uni-modal spectra• not significant directional distribution, nor load not significant directional distribution, nor load

increase (rightward shift)increase (rightward shift)


Class 9, LSF estimation for Class 9, LSF estimation for steeringsteering and and tandemtandem axles axles in northbound and southbound directions.in northbound and southbound directions.

Note that the “number of ESALs per vehicle” is Note that the “number of ESALs per vehicle” is increasing.increasing.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1997 1998 1999 2000 2001 2002 2003

Year

LSF Northbound

Southbound

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1997 1998 1999 2000 2001 2002 2003

Year

LSF Northbound

Southbound

D516 – IH 35, San AntonioD516 – IH 35, San Antonio

Class 9, Class 9, steeringsteering axle load distribution for axle load distribution for northbound directionnorthbound direction

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 5 10 15 20 25 30

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Y94

Y95

Y96

Y97

Y98

Y99

Y00

Y01

Y02

D516 – IH 35, San AntonioD516 – IH 35, San Antonio

Class 9, Class 9, tandemtandem axle load distribution for axle load distribution for northbound directionnorthbound direction

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 10 20 30 40 50

Axle Load (kip)

Norm

aliz

ed F

requ

ency

Y94

Y95

Y96

Y97

Y98

Y99

Y00

Y01

Y02


Class 9Class 9• bi-modal distribution for tandem axlesbi-modal distribution for tandem axles• uni-modal for steering axlesuni-modal for steering axles• consistent rightward shiftconsistent rightward shift• spectra is changing from Type II to Type IIIspectra is changing from Type II to Type III• no significant difference per directionno significant difference per direction

Class 5Class 5• similar findings as for D522similar findings as for D522

Preliminary ConclusionsPreliminary Conclusions In addition the volume increase, the LSF, ESAL per In addition the volume increase, the LSF, ESAL per

vehicle, should be closely monitored.vehicle, should be closely monitored. The LSF captures the load-associated pavement The LSF captures the load-associated pavement

damage damage “contained”“contained” in the load distribution. in the load distribution. We captured the change in the mid-1990s due to We captured the change in the mid-1990s due to

NAFTA, therefore, we should capture any future NAFTA, therefore, we should capture any future shift, even is it is smallshift, even is it is small

Small changes, however, may cause significant Small changes, however, may cause significant increase in pavement damage and, therefore, on increase in pavement damage and, therefore, on TxDOT maintenance and rehabilitation activities. TxDOT maintenance and rehabilitation activities.

What is next?What is next?

We will incorporate at least two more WIM We will incorporate at least two more WIM stations from the border region or I-10.stations from the border region or I-10.

We are trying to obtain similar data from We are trying to obtain similar data from Mexican bordering states to carry out a similar Mexican bordering states to carry out a similar analysis.analysis.

We want to evaluate the potential increase in We want to evaluate the potential increase in the proportion of six-axle trucks (3S3). the proportion of six-axle trucks (3S3).

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