This synthesis will be of interest to maintenance, construction, and traffic engineers, and others interested in the use of safety apparatus for highway operations. Information is provided on the performance and operational experience of truck-mounted attenuators, including physical characteristics, test results, and guidelines for use. There is growing use of truck-mounted attenuators (TMAs) for highway traffic, maintenance, and construction operations. This report of the Transportation Research Board describes the current state of the practice with respect to the use of TMAs. Experience with TMA design is summarized, and field experience and guidelines for use are discussed based on a review of the literature and a survey of the states.  The report for this topic can be purchased at https://www.trb.org/news/blurb_detail.asp?id=3375