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Traffic Data For Pavement

2012 FHWA Highway Information Seminar, Arlington, VATianjia Tang, PE, Ph.D.

Chief, Travel Monitoring and Surveys Division

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Objective

To enhance the knowledge of the traffic data collection and processing professionals on the needs of traffic data for pavement design

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Pavement Basics

Surface

Base

Sub-base

Sub-grade42

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Stress and Strain

tensiontension

compression

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Pavement Basics

Pavement is designed and constructed to meet

future needs.

Past Present Future

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Pavement Design

A set of plans covering types of materials to be used, depths of various layers, treatments of various layers, and ways to construct various layers to meet a set of performance goals (e.g., service life…) meaning to withstand cumulative deteriorations occurred during the entire design life (e.g., 25 years)

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Traffic Data For Existing Roadways

Past and present traffic data are obtained from field observations through collection.

Future traffic data are obtained through traffic demand modeling.

Past and present data are used for trend analysis and calibrate and validate traffic demand models.

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Traffic Data For New Roadways

Past and present traffic data do not exist.

Future traffic data are obtained through traffic demand modeling.

Past and present data are used for trend analysis and calibrate and validate traffic demand models.

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Concept of ESAL

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Equivalent Single Axle Load (ESAL)

One ESAL is known to cause a quantifiable and standardized amount of damage to the pavement structure equivalent to one pass of a single 18,000-pound, dual-tire axle with all four tires inflated to 110 psi.

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Compute Number of ESAL

AASHTO Guide for Design of Pavement of Structures

The ESAL method is the so called “empirical” method.

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Compute ESAL

W18= DD x DL X ẇ18

WhereW18 is the ESAL for the design lane. W18 represents the ultimate traffic data need for pavement designDD is the traffic directional factor for a two way roadway.

DL is a lane traffic splitting factor for a roadway having more than one lane in each directionẇ18 is cumulative two way ESAL projected for a roadway segment. 42

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Compute ẇ18

Information needed:

1. The number of axles for various axle configurations under various axle loads from Traffic Demand Modeling

2. Axle load equivalence factors - to be obtained from AASHTO’s Guide Appendix D

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Compute ẇ18

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Compute ẇ18

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Compute ẇ18

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Critical Traffic Data

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Mechanistic-Empirical Method

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Traffic Data Needed for Input

1: Opening Year Two Way Annual Average Daily Truck Traffic

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Traffic Data Needed for Input

2: Percent of Truck Traffic in Design Direction %

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Traffic Data Needed for Input

3: Percent of Truck Traffic in Design Lane %

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Traffic Data Needed for Input

4: Truck Monthly Adjustment FactorThe Truck Monthly Adjustment Factor

(MAF) reflects truck travel patterns throughout the year

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Traffic Data Needed for Input MAF

MADTT Class 4 Class 5 Class 6 Class 7 Class 8 Class 9 Class 10 Class 11 Class 12 Class 13January 588 2800 1216 502 250 527 485 51 142 124February 598 2851 896 498 263 654 493 38 152 108March 602 2864 1211 561 296 625 520 25 164 165April 630 3001 1321 598 299 692 586 62 159 154May 674 3213 1452 625 421 568 564 45 156 142June 717 3415 1621 740 465 587 652 65 187 165July 756 3602 1690 789 489 623 657 82 221 120August 810 3859 1699 785 620 621 678 32 235 95September 832 3962 1780 741 661 451 725 67 268 67October 755 3455 1795 645 561 482 712 12 189 64November 685 2699 1400 560 421 389 608 18 167 96December 598 2760 1324 495 412 462 527 19 152 116Total 8245 38481 17405 7539 5158 6681 7207 516 2192 1416

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Traffic Data Needed for Input MAF

MAF Class 4 Class 5 Class 6 Class 7 Class 8 Class 9 Class 10 Class 11 Class 12 Class 13January 0.86 0.87 0.84 0.80 0.58 0.95 0.81 1.19 0.78 1.05February 0.87 0.89 0.62 0.79 0.61 1.17 0.82 0.88 0.83 0.92March 0.88 0.89 0.83 0.89 0.69 1.12 0.87 0.58 0.90 1.40April 0.92 0.94 0.91 0.95 0.70 1.24 0.98 1.44 0.87 1.31May 0.98 1.00 1.00 0.99 0.98 1.02 0.94 1.05 0.85 1.20June 1.04 1.06 1.12 1.18 1.08 1.05 1.09 1.51 1.02 1.40July 1.10 1.12 1.17 1.26 1.14 1.12 1.09 1.91 1.21 1.02August 1.18 1.20 1.17 1.25 1.44 1.12 1.13 0.74 1.29 0.81September 1.21 1.24 1.23 1.18 1.54 0.81 1.21 1.56 1.47 0.57October 1.10 1.08 1.24 1.03 1.31 0.87 1.19 0.28 1.03 0.54November 1.00 0.84 0.97 0.89 0.98 0.70 1.01 0.42 0.91 0.81December 0.87 0.86 0.91 0.79 0.96 0.83 0.88 0.44 0.83 0.98Total 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00

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Traffic Data Needed for Input -MAF

MAF for month i and class j truck

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Traffic Data Needed for Input

5: Vehicle Class DistributionVehicle class distribution (VCD) refers to AADTT distribution among the 10 vehicle types

Class 4 Class 5 Class 6 Class 7 Class 8 Class 9 Class 10 Class 11 Class 12 Class 13 Total

AADTT 235 654 961 1620 1240 654 598 103 1245 4621 11931% 2.0 5.5 8.1 13.6 10.4 5.5 5.0 0.9 10.4 38.7 100.0

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Traffic Data Needed for Input

6: Truck Hourly Distribution Factor (THDF) Truck hourly distribution factor refers to the percentage of hourly AADTT among a 24 hour time period starting at midnight. There are 24 THDFs

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Traffic Data Needed for InputHourly-AADTT %

Midnight 1:00 AM 8 0.61:00 AM 2:00 AM 9 0.72:00 AM 3:00 AM 12 0.93:00 AM 4:00 AM 16 1.34:00 AM 5:00 AM 25 2.05:00 AM 6:00 AM 36 2.86:00 AM 7:00 AM 45 3.57:00 AM 8:00 AM 68 5.38:00 AM 9:00 AM 78 6.19:00 AM 10:00 AM 76 5.910:00 AM 11:00 AM 78 6.111:00 AM Noon 82 6.4

Noon 1:00 PM 98 7.71:00 PM 2:00 PM 98 7.72:00 PM 3:00 PM 86 6.73:00 PM 4:00 PM 88 6.94:00 PM 5:00 PM 74 5.85:00 PM 6:00 PM 78 6.16:00 PM 7:00 PM 64 5.07:00 PM 8:00 PM 52 4.18:00 PM 9:00 PM 54 4.29:00 PM 10:00 PM 26 2.010:00 PM 11:00 PM 18 1.411:00 PM Midnight 10 0.8

1279 100.0

Hourly Distribution

Total

Start Time End Time

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Traffic Data Needed for Input

Axle Load Factor FHWA vehicles in class 4 to 13 can have a variety of axle configurations including single axle, tandem axle, tridem axle, and quad axle

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Traffic Data Needed for Input

Single Axle Configuration Axle Load Factor There are 39 axle weight groups for single axle configuration vehicles. The axle weight group ranges from 3,000 lbs to 41,000 lbs with increments of 1,000 lbs. The computation of the ALF data is based on MAADT for a particular vehicle class and axle weight group

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Traffic Data Needed for Input

Tandem, Tridem, and Quad Axle Vehicles For tandem axle vehicles, the axle weight group starts at 6,000 lbs and ends at 82,000 lbs with increment s of 2000 lbs.

For both tridem and quad axle vehicles, the axle weight group start at 12,000 lbs and ends at 102,000 lbs with increments of 3000 lbs.

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Traffic Data Needed for Input – Single Axle1 1 1 1 1 1 1 1 1 1 2 124 5 6 7 8 9 10 11 12 13 4 13

100 100 100 100 100 100 100 100 100 100 100 1003000 1.8 10.05 2.47 2.14 11.65 1.74 3.64 3.55 6.68 8.88 1.8 8.884000 0.96 13.21 1.78 0.55 5.37 1.37 1.24 2.91 2.29 2.67 0.96 2.675000 2.91 16.42 3.45 2.42 7.84 2.84 2.36 5.19 4.87 3.81 2.91 3.816000 3.99 10.61 3.95 2.7 6.99 3.53 3.38 5.27 5.86 5.23 3.99 5.237000 6.8 9.22 6.7 3.21 7.99 4.93 5.18 6.32 5.97 6.03 6.8 6.038000 11.47 8.27 8.45 5.81 9.63 8.43 8.35 6.98 8.86 8.1 11.47 8.19000 11.3 7.12 11.85 5.26 9.93 13.67 13.85 8.08 9.58 8.35 11.31 8.35

10000 10.97 5.85 13.57 7.39 8.51 17.68 17.35 9.68 9.94 10.69 10.97 10.6911000 9.88 4.53 12.13 6.85 6.47 16.71 16.21 8.55 8.59 10.69 9.88 10.6912000 8.54 3.46 9.48 7.42 5.19 11.57 10.27 7.29 7.11 11.11 8.54 11.1113000 7.33 2.56 6.83 8.99 3.99 6.09 6.52 7.16 5.87 7.32 7.32 7.32

…30000 0.05 0.02 0.05 0.08 0.04 0.01 0.02 0.06 0.02 0.05 0.05 0.0531000 0.04 0.02 0.03 0.72 0.04 0.01 0.03 0.03 0.03 0.05 0.04 0.0532000 0.04 0.02 0.03 0.06 0.12 0.01 0.01 0.04 0.01 0.08 0.04 0.0833000 0.04 0.02 0.03 0.03 0.01 0.01 0.02 0.01 0.01 0.06 0.04 0.0634000 0.03 0.02 0.02 0.03 0.02 0.01 0.01 0 0.01 0.02 0.03 0.0235000 0.02 0.02 0.01 0.02 0.02 0 0.01 0 0 0.01 0.02 0.0136000 0.02 0.02 0.01 0.02 0.01 0.01 0 0 0 0.01 0.02 0.0137000 0.01 0.01 0.01 0.01 0.01 0 0.01 0 0.01 0.01 0.01 0.0138000 0.01 0.01 0.01 0.01 0 0 0 0.02 0.01 0.01 0.01 0.0139000 0.01 0 0.01 0.01 0.01 0 0.01 0.01 0 0.01 0.01 0.0140000 0.01 0 0.01 0.01 0 0 0.04 0.02 0 0 0.01 041000 0 0 0 0 0 0 0 0 0 0 0 0

Month Vehicle Class

Total %

…………………………………………………………………………………………………………………………………

……………Axle

Weight (lbs)

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Traffic Data Needed for Input

7: Number of Axle Types per Truck Class The number of axles per vehicle class for a given axle configuration is an annual average number of axles per vehicle category (per vehicle class and vehicle axle configuration).

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Traffic Data Needed for Input

Sinle Axle Tandem Tridem QuadClass 4 1.62 0.39 0Class 5 2 0 0Class 6 1.02 0.99 0Class 7 1 0.26 0.83Class 8 2.38 0.67 0Class 9 1.13 1.93 0Class 10 1.19 1.09 0.89Class 11 4.29 0.26 0.06Class 12 3.52 1.14 0.06Class 13 2.15 2.13 0.35

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Traffic Data Needed for Input

• 8: Axle Spacing

• Axle spacing data are only applicable to tandem, tridem and quad vehicles. It is the distance between two consecutive tandem, tridem, and quad axles.

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Traffic Data Needed for Input

• 9: Average Axle Width:

• The distance between the two outside edges of an axle is defined as axle width

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Traffic Data Needed for Input

10: Wheelbase

The distance between the steering and the first device axle of a tractor or a heavy single unit

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Traffic Data Needed for Input

Date Item #

Date Item Name# of Data

PointsFrequency

Foundation Data

Data Dimension

1Annual Average Daily

Truck Traffic1 annually AADTT by sum of all trucks

2% of Truck Traffic in

Design Direction1 annually AADTT

by sum of all trucks and travel direction

3% of Truck Traffic in

Design Lane1 annually AADTT

by sum of all trucks, travel direction and

travel lane

4Truck Monthly

Adjustment Factor120 monthly MADTT

MADTT by truck class for each month in a

year5 Truck Classification 12 annually AADTT AADTT by truck class

6Truck Hourly Distribution

24 annually AADTTAADTT by sum of all trucks by hour of the

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Traffic Data Needed for Input

Date Item #

Date Item Name# of Data

PointsFrequency

Foundation Data

Data Dimension

Axle Load factor- Single Axle

4680 monthly MADTTMADTT by truck class, axle

configuration, and axle weight group

Axle Load factor -tandem

4680 monthly MADTTMADTT by truck class, axle

configuration, and axle weight group

Axle Load Factor - tridem

3720 monthly MADTTMADTT by truck class, axle

configuration, and axle weight group

Axle Load factor- quad 3720 monthly MADTTMADTT by truck class, axle

configuration, and axle weight group

8 Number of Axles 40 annually AADTTAADTT by truck class and axle

configuration

9Axle Spacing-tandem,

tridem, and quad3 annually AADTT AADTT by axle configuration

10 Wheelbase 3 annually AADTT AADTT by wheelbase

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Summary

Time framePavement layersESALMechanistic and Empirical

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Q/A

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Thanks you!

Traffic Data For Pavement

2012 FHWA Highway Information Seminar, Arlington, VATianjia Tang, PE, Ph.D.

Chief, Travel Monitoring and Surveys Division

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