Equipment for Collecting Traffic Load Data (2004)

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