TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 515: Practices for Preventing Roadway Departures identifies and summarizes practices being used by state departments of transportation (DOTs) to prevent roadway departure crashes and to identify the data-driven advantages and disadvantages of these practices. More than half of all traffic fatalities result from roadway departure crashes. This type of crash occurs after a vehicle crosses an edge line or centerline or otherwise leaves the traveled way. A variety of engineering strategies, often referred to as countermeasures, have been implemented by state and local agencies to prevent roadway departure crashes and reduce the severity of injuries if crashes do occur. Appendices A through F have been combined into one file and are available separate from the report.