Traffic information is one of the key data elements required for the design and analysis of pavement structures. In the procedure used in the 1993 AASHTO Guide for Design of Pavement Structures, a mixed traffic stream of different axle loads and axle configurations is converted into a design traffic number by converting each expected axle load into an equivalent number of 18-kip, single-axle loads, known as equivalent single-axle loads (ESALs). Equivalency factors are used to determine the number of ESALs for each axle load and axle configuration. These factors are based on the present serviceability index (PSI) concept and depend on the pavement type and structure. Studies have shown that these factors also are influenced by pavement condition, distress type, failure mode, and other parameters. A more direct and rational approach to the analysis and design of pavement structures involves procedures that use mechanistic-empirical principles to estimate the effects of actual traffic on pavement response and distress. This approach has been used to develop a guide for the mechanistic-empirical design of new and rehabilitated pavement structures as part of NCHRP Project 1-37A. The mechanistic-based distress prediction models used in this guide will require specific data for each axle type and axle load group. Recognising the constraints on resources available in state and local highway agencies for traffic data collection, the guide will allow for various levels of traffic data collection and analysis. Because the anticipated guide will use traffic data inputs that differ from those currently used in pavement design and analysis, there was an apparent need for research to provide clear information on traffic data and forecasting and to provide guidance on selection and operation of the equipment needed for collecting these data. This information will facilitate use of the anticipated guide. NCHRP Project 1-39 was conducted to address this need. Under NCHRP Project 1-39, “Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design,” Cambridge Systematics, Inc., was assigned the objectives of (1) developing guidelines for collecting and forecasting traffic data to formulate load spectra for use in procedures proposed in the guide for mechanistic empirical design and (2) providing guidance on selecting, installing, and operating traffic data collection equipment and handling traffic data. This report is concerned with the latter objective; the first objective will be addressed in detail in the agency’s final report on the project. To accomplish the latter objective, the researchers identified the steps required to select the equipment necessary for collecting traffic load data. In these steps, the researchers identified the types of equipment available for collecting classification counts and for weighing vehicles in motion and provided detailed descriptions of various technologies. As part of these descriptions, the researchers reviewed the strengths and weaknesses of each technology. Finally, the researchers provided guidance on selection of equipment by considering (1) data collection needs of users, (2) data handling requirements and capabilities, and (3) characteristics of available technologies. To facilitate implementation and use of equipment, the researchers also provided information on best practices for equipment use. The information contained in this report should be of interest to those involved in the planning and design of highway pavements and structures. It will be particularly useful to agencies contemplating collection of traffic data for use in conjunction with the guide for the mechanistic-empirical design of new and rehabilitated pavement structures. (Author/publisher) This report may be accessed by Internet users at http://gulliver.trb.org/publications/nchrp/nchrp_rpt_509.pdf
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