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3 CHAPTER ONE Introduction Purpose Ninety percent of all SHAs responded to this synthesis sur- vey. Responding agencies are listed in Table 1. The number Falling weight deflectometers (FWDs) have been in use of FWDs in use and the importance of their role in pavement since the 1980s. These devices are used to measure pave- engineering practice are expected to increase as agencies ment deflections in response to a stationary dynamic load, move toward mechanistically based pavement design. The similar to a passing wheel load. The data obtained are used interpretation of FWD data is a key method for estimating to evaluate the structural capacity of pavements for research, the in situ moduli of pavement layer materials. design, rehabilitation, and pavement management purposes. Based on a survey conducted for this synthesis, 45 state high- The importance of FWDs among SHAs was reflected in way agencies (SHAs) reported using 82 FWDs produced by survey results. SHAs conduct FWD tests on up to 24,100 three different manufacturers (Appendix B, Questions 26). lane-km (15,000 lane-mi) annually (Appendix B, Question TABLE 1 RESPONDING STATE HIGHWAY AGENCIES State Responding Agency State Responding Agency Alabama Alabama Department of Transportation Montana Montana Department of Transportation Alaska Department of Transportation Nebraska Nebraska Department of Roads Alaska and Public Facilities New New Hampshire Department of Transportation Arizona Arizona Department of Transportation Hampshire* Arkansas Highway and Transportation New Jersey New Jersey Department of Transportation Arkansas Department New Mexico New Mexico Department Of Transportation California California Department of Transportation New York New York State Department of Transportation Colorado Colorado Department of Transportation North Carolina North Carolina Department of Transportation Connecticut* Connecticut Department of Transportation North Dakota North Dakota Department of Transportation Florida Florida Department of Transportation Ohio Ohio Department of Transportation Hawaii Hawaii Department of Transportation Oregon Oregon Department of Transportation Idaho Idaho Transportation Department Pennsylvania Pennsylvania Department of Transportation Illinois Illinois Department of Transportation Rhode Island Rhode Island Department of Transportation Indiana Indiana Department of Transportation South Carolina South Carolina Department of Transportation Iowa Iowa Department of Transportation South Dakota South Dakota Department of Transportation Kansas Kansas Department of Transportation Tennessee Tennessee Department of Transportation Kentucky* Kentucky Transportation Cabinet Texas Texas Department of Transportation Louisiana Louisiana Department of Transportation Utah Utah Department of Transportation Maine Maine Department of Transportation Vermont Vermont Department of Transportation Maryland Maryland State Highway Administration Virginia Virginia Department of Transportation Michigan Michigan Department of Transportation Washington State Department of Washington Minnesota Minnesota Department of Transportation Transportation Mississippi Mississippi Department of Transportation West Virginia West Virginia Department of Transportation Missouri Missouri Department of Transportation Wisconsin Wisconsin Department of Transportation *Responded by stating that the agency does not have an FWD program.