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1.0 Introduction The AASHTO Technical Committee on Pavements has undertaken an effort to develop an improved guide for the design of pavements. This effort, undertaken under NCHRP Project 1-37A, Development of the 2002 Guide for the Design of New and Rehabilitated Pavement Structures1 (the "Pavement Design Guide"), will provide engineers with practical and realistic pavement design procedures and software that use existing mechanistic-empirical principles. The mech- anistic-based distress prediction models used in the Pavement Design Guide will require the input of specific data for each axle type and axle-load group. Under NCHRP Project 1-39, a software system, TrafLoad, has been developed for generating the traffic data required by the Pavement Design Guide software. This part of the report pre- sents guidelines for collecting traffic data required by TrafLoad and provides brief descrip- tions of some of the analyses that TrafLoad performs in the course of converting these data into inputs required by the Pavement Design Guide software. The presentation is designed to complement the more extensive discussion of the collection of traffic data that is contained in the FHWA's Traffic Monitoring Guide (2001).2 A user's manual for TrafLoad is presented as Part 3, which is available online at http://trb.org/news/blurb_detail.asp?id=4403. This introduction presents a brief summary of the data required by the Pavement Design Guide software, followed by an outline of the remainder of Part 2. 1.1 Traffic Data Requirements for the Pavement Design Guide Software The Pavement Design Guide distinguishes three broad levels of input data that vary with the quality of information that the designer has about the loads to be applied at the site. These input levels are described as sites for which the designer has 1) good, 2) fair, or 3) poor infor- mation about the truck volumes and axle loads to be applied, with Level 3 further divided into Levels 3A and 3B. Corresponding to each input level, the Pavement Design Guide software requires site-specific, region-specific, or default values for several types of traffic data. In addition, there are other types of optional traffic data for which the software can use state-supplied values, or the software can use default values that have been developed in NCHRP Project 1-37A from national data. 1 http://www.2002designguide.com/ 2 http://www.fhwa.dot.gov/////ohim/tmguide/index.htm 2-1