Pavement Impact Assessment Due to Overloading of Commercial Vehicles in Pakistan

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SEQUENCE

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INTRODUCTION

Pavement Design – ESALs

Pavement performance – strongly influenced by the actual traffic loading.

Commercial traffic – more structural and functional deterioration of the pavements.

Average Daily Truck Traffic (ADTT) or the Truck ESAL Factor – minimum information required for the pavement design.

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INTRODUCTION (cont…)

National Highway Authority (NHA) – Design and rehabilitation procedures for flexible & rigid pavements – NTRC Study

Equivalent Standard Axles

Equivalent Single Axle Load (ESAL)

Load Equivalency Factor (LEF) or Equivalent Axle Load Factor (EALF).

NHA – weigh stations – actual load applied - continuous availability data – better representation traffic loading.

Weigh Station Data – data of greater time period – more accurate Truck ESAL Factors.

Truck ESAL Factors – design new pavements and pavement rehabilitation more accurately.

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Pakistan - suffering from the early pavement deterioration - overloading of the vehicles.

Pavements in Pakistan - designed on – NTRC truck ESAL factors - NTRC Study 1995.

Re-evaluate the damaging factors based on the actual vehicle loading obtained from the weigh station data so that the damage caused by the overloaded vehicles on the national highway network can be evaluated and accordingly pavement design be prepared and loading restrictions be imposed strictly.

PROBLEM STATEMENT

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To develop a computer program that will use a standard weigh station data as input and outputs the Truck ESAL Factor for the data.

Calculation of Truck ESAL factors

Calculated Truck ESAL factors and NTRC Truck ESAL factors.

Trend of Truck ESAL Factor

OBJECTIVES

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Development of software that uses a standard weigh station data as input and calculates the Truck ESAL factors.

Observation of trend of Truck ESAL factors over time and comparison of the calculated Truck ESAL factor with NTRC Study.

As a case study, data of in-service Mullan Mansoor weigh station located on Attock Khurd – Hattian section of National Highway (N-5) is used for analysis.

SCOPE

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WEIGH STATIONS OF N-5 CONSIDERED FOR STUDY

TORKHAM

KARACHI

N-5

MULLAN MANSOORMULLAN MANSOOR

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COMMERCIAL VEHICLES (TRUCKS) CONSIDERED

TRUCK TYPELOAD LIMIT

(TONS)

2 – Axle Single 17.5

3 – Axle Tandem 27.5

4 – Axle Single Tandem 39.5

5 – Axle Tandem

Tandem49.5

6 – Axle Tandem Tridem 58.5

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DATA COLLECTION

N-5 – longest highway – starting from Karachi and terminating at Torkham Border – total length of 1,819 Km.

Weigh station data – several months duration including all the national holidays.

Source of weigh station data – Operation’s Wing of the NHA.

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WEIGH STATION DATA

Weigh station data – loaded and unloaded vehicles – single excel sheet – several months duration – weight of each individual axle mentioned.

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DATA ANALYSIS STRATEGY

The Gross weight of the commercial vehicles observed at the weigh station is categorized and the EALF or LEF for each axle are calculated which is then converted to the ESALs.

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Calculation of Truck ESAL Factors for Flexible Pavement:

= a function of the ratio of loss in serviceability at time, t, to the potential loss taken at a point where pt = 1.5.

= function which determines the relationship between serviceability and axle load applications.

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Calculation of Truck ESAL Factors for Rigid Pavement:

= a function of the ratio of loss in serviceability at time, t, to the potential loss taken at a point where pt = 1.5.

= function which determines the relationship between serviceability and axle load applications.

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Calculated Truck ESAL factors (Flexible & Rigid, Calculated Truck ESAL factors (Flexible & Rigid, Mullan Mansoor, NB & SB)Mullan Mansoor, NB & SB)

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Truck TypeFlexible Rigid

North South North South

2-Axle Single 5.31 5.68 6.78 7.20

3-Axle Tandem 8.47 9.35 18.05 19.98

4-Axle Single Tandem 10.21 7.06 17.04 11.30

5-Axle Tandem Tandem 15.21 9.95 32.88 21.00

6-Axle Tandem Tridem 12.69 12.18 31.79 30.22

Trend of Truck ESAL factors over Time Trend of Truck ESAL factors over Time (Flexible, (Flexible, Mullan Mansoor, NB)Mullan Mansoor, NB)

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Trend of Truck ESAL factors over Time Trend of Truck ESAL factors over Time (Flexible, (Flexible, Mullan Mansoor, SB)Mullan Mansoor, SB)

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COMPARISON OF CALCULATED TRUCK ESAL COMPARISON OF CALCULATED TRUCK ESAL FACTORS WITH NTRC’S TRUCK ESAL FACTORSFACTORS WITH NTRC’S TRUCK ESAL FACTORS

NTRC Truck ESAL Factors – 24 hours traffic volume – portable weigh bridge

Calculated Truck ESAL Factors – weigh station data collected for over months.

Therefore, a comparison of the calculated Truck ESAL Factors and NTRC Truck ESAL Factors for Flexible Pavement Design using the AASHTO Design Guide is made for all the weigh stations.

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COMPARISON OF NTRC AND CALCULATED TRUCK COMPARISON OF NTRC AND CALCULATED TRUCK ESAL FACTORS FOR FLEXIBLE PAVEMENT AT ESAL FACTORS FOR FLEXIBLE PAVEMENT AT MULLAN MANSOOR WEIGH STATION (NB & SB)MULLAN MANSOOR WEIGH STATION (NB & SB)

Truck Type

Weighted Average Truck ESAL Factor on

North South

NTRCCalculate

d

Increase or

Decrease(%)

NTRC Calculated

Increase or

Decrease(%)

2-Axle Single4.64 5.31 14.44 4.32 5.68 31.37

3-Axle Tandem10.35 8.47 -18.21 10.22 9.35 -8.51

4-Axle Single Tandem18.74 10.21 -45.54 - 7.06 -

5-Axle Tandem

Tandem

- 15.21 - - 9.95 -

6-Axle Tandem Tridem- 12.69 - - 12.18 -

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a. The calculated average Truck ESAL Factor for 2-Axle Truck is approximately 1.1 times more than the NTRC Study calculated Truck ESAL Factor for north bound and 1.3 times more for south bound.

b. The calculated average Truck ESAL Factor for 3-Axle Tandem Truck is approximately 0.8 times lesser than the NTRC Study calculated Truck ESAL Factor for north bound and 0.9 times lesser for south bound.

c. The calculated average Truck ESAL Factor for 4-Axle Single Tandem Truck is approximately 0.5 times lesser than the NTRC Study calculated Truck ESAL Factor for north bound.

MULLAN MANSOOR WEIGH STATIONMULLAN MANSOOR WEIGH STATION

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Overloading tendency of the commercial vehicles – reduces the haulage cost – economic benefit to the country – early pavement deterioration.

Weigh Station Data can be used to develop more accurate Truck ESAL Factors than NTRC’s ESAL Factors because these data more accurately represent the loading conditions prevailing on the pavement.

Truck ESAL Factor increases over time due to changing vehicle characteristics such as the loading and the axle configuration.

Use of the developed LoadAnalyst Software can help in quicker and accurate analysis of the weigh station data.

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Construct stronger pavements or impose and enforce load limits. Which is appropriate?

Most of the highway engineers are of the opinion that without enforcement of load regulations, the overloading will continue and as a result the pavements will continue failing.

In order to solve the overloading problem and save the pavements from early deterioration, following is recommended:

Imposition of the appropriate axle load limits and strict enforcement of the legal load limits.

If not, then, the calculated Truck ESAL factors be used by the pavement designers and pavement management engineers to design new pavements and pavement rehabilitation accordingly.

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Calculated Truck ESAL factors be linked with the pavement deterioration in terms of cost of pavement deterioration per unit overloading for each class of commercial vehicle and accordingly fine for overloading be imposed.

Weigh station data be supplied in either of the formats specified and a database be developed in order to track the monthly, yearly and seasonal variation in the Truck ESAL factors for rigid and flexible pavements.

The NTRC Axle Load Study on National Highways, 1995 must be revised and updated using the weigh station data of all the weigh stations to obtain more accurate Truck ESAL Factors and to design the flexible & rigid pavements and pavement rehabilitation based on the actual loading conditions.

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American Association of State Highway and Transportation Officials. (1993). “Guide for Design of Pavement Structures”, Washington, DC.

ERES Consultants Inc., (2000). “Introduction to Mechanistic-Empirical Design of New and Rehabilitated Pavements”, Reference Manual NHI, U.S. Department of Transportation, Federal Highway Administration, Course No. 131064.

National Transport Research Centre. (1995).”Axle Load Study on National Highways”, Islamabad.

Smith, B. C., Diefenderfer, B. K. (2009). “Development of Truck Equivalent Single Axle Load (ESAL) Factors based on weigh in motion data for Pavement Design in Viriginia”, Virginia Transportation Research Council, VRTC 09-R18.

Thorell, I. (1997). "The impact of heavy duty trucks on Pakistan roadnet". Economic Review: Issues from 1997, http://findarticles.com/p/articles/mi_hb092/is_n9_v28/ai_n28693655, 01/24/12.

Transport and Road Research Laboratories, “Road Note 31 – A Guide to the Structural Design of Bitumen – Surfaced Roads in Tropical and Sub-Tropical Countries”

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