This synthesis will be of interest to state department of transportation (DOT) roadway design, traffic, structural, maintenance, and research engineers and others concerned with highway safety issues. This synthesis describes the current state of the practice for the use of guardrails and median barriers and their crashworthiness. It includes information about the crashworthiness and typical applications of the most common, permanently installed, nonproprietary guardrail and median barrier systems used in the United States today. A significant amount of detail is included in the text to aid the design, selection, and locating processes for safe and effective guardrails and median barriers. The report presents data obtained from a review of the literature and a survey of state DOTs. The synthesis presents a description of the typical longitudinal barriers in use today, including drawings, the extent of their use, and the most recent testing on each guardrail and barrier system, with particular emphasis on NCHRP Report 230 and 350 requirements. In addition, it discusses the maintenance issues, cost constraints, and common problems with each type of barrier. The synthesis only discusses the crashworthiness of guardrails and median barriers; their transitions and terminals are not discussed.  The report for this topic can be purchased at https://www.trb.org/news/blurb_detail.asp?id=3313