This synthesis will be of interest to geologists; geotechnical, construction, and maintenance engineers; other state department of transportation (DOT) personnel involved with the planning, design, and permit issuance for conduits beneath roadways; local transportation agencies; utility contractors and consultants; and trenchless construction equipment manufacturers. It describes the current state of the practice for the use of trenchless technology for installing conduits beneath roadways. Trenchless construction is a process of installing, rehabilitating, or replacing underground utility systems without open-cut excavation. The synthesis is focused on trenchless technology for new installations. This report of the Transportation Research Board describes the trenchless installation technologies ( methods, materials, and equipment) currently employed by state DOTs and other agencies to install conduits beneath roadways. The synthesis presents data obtained from a review of the literature and a survey of transportation agencies. For each technology identified, information is provided to describe the range of applications, basis for technique selection, site specific design factors to be considered, relative costs, common environmental issues, and example specifications. In addition, information on emerging technologies and research needs is presented.