(U//FOUO) Threats to the U.S. highway system (including tunnels, bridges, long-haul buses, school buses, and commercial trucks) emanate from transnational and domestic terrorist organizations, as well as from insiders and special interest groups. However, the primary threat stems from al-Qa’ida, its affiliates, and other Sunni Muslim extremists, whether foreign or domestic. No reporting indicates a current, credible, and specific terrorist threat to U.S. highway interests. However, since 1993 at least three terrorist plots to bomb tunnels and bridges in the United States have been disrupted, aborted, or abandoned. Further, recurring suspicious incidents involving U.S. highway infrastructure and assets could reflect pre-operational terrorist planning. Thus far, however, no definitive link has been established between any of the suspicious incidents and terrorism.