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Highway administrators, engineers, and researchers often face problems for which infor- mation already exists, either in documented form or as undocumented experience and prac- tice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway commu- nity, the American Association of State Highway and Transportation Officialsâthrough the mechanism of the National Cooperative Highway Research Programâauthorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Project 20-5, âSynthesis of Information Related to Highway Problems,â searches out and synthesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. This synthesis reports on the state of the practice of falling weight deflectometer (FWD) usage as it involves state departments of transportation (DOTs) using these devices to mea- sure pavement deflections in response to a stationary dynamic load, similar to a passing wheel load. The data obtained are used to evaluate the structural capacity of pavements for research, design, rehabilitation, and pavement management practices. It is anticipated that this synthesis will provide useful information to support guidelines, advancing the state of the practice for state DOTs and other FWD users, as well as equipment manufacturers and other involved in pavement research, design, rehabilitation, and management. Based on a survey conducted for this report, 45 state highway agencies (SHAs) reported using 82 FWDs, produced by 3 different manufacturers. The importance of FWDs among SHAs appears to be reflected in the survey results, as it was noted that SHAs conduct FWD tests on up to 24 100 lane-km (15,000 lane-miles) annually. Survey information presented in this report is supplemented by an extensive literature search, as well as communication with FWD calibration centers and FWD manufacturers. Individual SHA websites were also searched. Although current practice was limited to the United States, research published internationally was considered for historical context and for potential future research topics. A series of case studies share lessons learned from utilizing FWDs. Sirous Alavi, Sierra Transportation Engineers, Reno, Nevada, collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand. ForeWord By Donna Vlasak Senior Program Officer Transportation Research Board preFace
