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16 CHAPTER 1 INTRODUCTION This report is designed to serve as a primer on the selec- Taken together, these observations make it clear that no tion and use of equipment for counting and classifying vehi- single technology is best and that simply purchasing all data cles and for collecting data on their axle weights. The data collection equipment from a reputable vendor will not ensure collected by this equipment are specifically required by the accurate data collection. Rather, the following is required: mechanistic-empirical pavement design procedures being developed under NCHRP Project 1-37A (Development of the A careful examination of equipment capabilities and lim- 2002 Guide for the Design of New and Rehabilitated Pave- itations relative to the data collection environment in ment Structures). These data are also required by other pro- which that equipment will be placed and cedures that incorporate estimates of expected pavement The deployment of a comprehensive data collection pro- stresses into the design of pavements. gram that includes, at a minimum, The most important finding of an extensive review of the Acceptance testing of purchased equipment; available literature on equipment performance is that wide Staff training in that equipment's placement, opera- variation exists in the reported error rates for any given tech- tion, and maintenance; nology. In fact, different results are often reported for dif- Quality assurance tests on the data that are collected; ferent tests of a specific device from the same manufacturer. The funding necessary to purchase and properly install, Closer examination of these results almost always leads to inspect, maintain, and operate the equipment; and the conclusion that the observed variation is a direct result of Sufficient vendor support to quickly resolve problems differences in the environment in which the devices were identified as the equipment is used. placed, as well as how well each specific piece of equipment This report provides a basic overview of the steps required was placed, calibrated, maintained, and operated. to select the equipment necessary to collect traffic load data. When the Minnesota Guidestar program examined non- The report also discusses all these data collection program intrusive sensors,1 one of its primary conclusions was that attributes. "the differences between devices from different manufactur- The report is organized into a summary and five chapters, ers were more significant than differences between technolo- including this introduction. Chapter 2 provides a brief intro- gies." The report also stated, "It is more important to select a duction to the types of equipment available for collecting well designed and highly reliable product than to narrow a classification counts and for weighing vehicles in motion, and selection to a particular technology." Chapter 3 contains more detailed descriptions of the various technologies. Chapter 4 provides guidance on the selection 1 Field Test of Monitoring of Urban Vehicle Operations Using Non-Intrusive Technolo- of equipment, and the final chapter offers additional guidance gies, FHWA, May 1997, FHWA-PL-97-018, by Minnesota DOT and SRF Consulting. on the implementation and use of the equipment.