NCHRP Report 538: Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design

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3.0 Vehicle Classification Data Chapter 2.0 discussed the collection of weigh-in-motion (WIM) data and the capabilities of the TrafLoad software for using these data to estimate the pavement loads produced by vehicles in various VCs. This chapter addresses the complementary topic of the data required by TrafLoad to estimate the number of vehicles in each class operating at a particular site. All data provided to TrafLoad are assumed to be quality checked. As in the case of WIM sites, in this chapter different levels of classification-count sites are iden- tified, reflecting the amount and quality of the counts collected at the sites. These levels are discussed in the first section of this chapter. The second section provides a brief summary of the traffic data produced by TrafLoad for use by the Pavement Design Guide software. Sec- tions 3.3�3.5 discuss in some detail the classification data that are required by TrafLoad in order to produce these outputs. And the final section presents a recommended procedure for forecasting volumes of heavy vehicles over the design life of the pavement. 3.1 Levels of Classification Site TrafLoad provides the user with substantial flexibility in the amount of vehicle classification data to be collected for any site. The options have been grouped into three levels: 1. Sites for which continuous data from an automatic vehicle classifier (AVC) are available for periods of at least 1 week for at least 12 consecutive months. A distinction is made between 1A. Data collected at the site in question and 1B. Data collected at a reasonably nearby site on the same road. 2. All other sites for which vehicle classification counts are available. A distinction is made between 2A. Sites for which at least one AVC count is available for a period of at least 48 weekday hours and 2B. Sites for which only a manual classification count is available for a period of at least 6 weekday hours. 3. Sites for which volume counts are available but not classification counts. A distinction is made between 2-23

Table of Contents

Front Matter R1-R70

1.1 Traffic Data Requirements for the Pavement Design Guide Software 1-1

1.2 The Remainder of Part 2 2-3

2.0 Weight Data 4-5

2.1 Sources of Estimation Error 6-7

2.2 Alternative Data-Collection Programs 8-11

2.3 Level 1 WIM Sites 12-16

2.4 Level 2 WIM Sites and TWRGs 17-19

2.5 Level 3 WIM Sites 20-20

2.6 Weight Data Collection 21-22

3.1 Levels of Classification Site 23-23

3.2 Data Produced for the Pavement Design Guide Software 24-24

3.3 Level 1 Classification Sites 25-33

3.4 Level 2 Classification Sites 34-36

3.5 Level 3 Classification Sites 37-38

3.6 Forecasts 39-44

4.1 Data Collection 45-46

4.2 Data Analysis 47-51

4.3 Administrative and Institutional Changes 52-53

Glossary 54-54

Levels of Classification Site 55-55

Levels of WIM Site 56-56

Abbreviations used without definitions in TRB publications 57-57