This synthesis on the use of recycled rubber tires in highways will be of interest to administrators and policy-makers; pavement, materials, geotechnical, environmental, and traffic operations engineers; and research engineers involved with highway design and construction issues. Information is provided on the uses of rubber tires in asphalt paving materials as well as other uses, such as on fills and embankments, for erosion control and on railroad grade crossings. Specifically, information is included which identifies the agencies using or implementing applications for recycled rubber tires and defines the design parameters, technical and construction limitations, performance, costs, benefits, environmental limitations, specifications, and availability. This synthesis of information defines the use of recycled rubber tires in highways and is based on a review of nearly 500 references and on information recorded from state highway agency responses to a 1991 survey of practice. Updates are included for as much of the state practice information possible through 1993. The use of scrap tires for highway applications is dynamic with regard to policy and technical issues. Therefore, the reader should keep in mind that the information presented reflects the best available data at a particular time. The synthesis also identifies current research in the topic area, critical research needs, and legislative issues that affect application and use of recycled rubber tires.