"This information bulletin is provided to sensitize state and local authorities and the private sector responsible for security of critical infrastructure and key resources to the potential for terrorists to use heavy transport vehicles as vehicle-borne improvised explosive devices (VBIEDs) against a range of attractive targets in the United States. Although there is currently not specific information to discern the exact location or timing of a planned attack, indicators are such that increased diligence is warranted within the commercial trucking transportation sector and around Canadian and Mexican border crossings. Extra vigilance is also warranted at transportation node connections with other modes at seaports and rail yards. Sector authorities and operators should also be sensitive to irregular activity or circumstances out of the norm for a particular situation especially in connection with large public gatherings or significant public or private facilities with high economic or symbolic value. Examples include unusual activity around highway tunnels, bridges, or non-transportation high value buildings or facilities without substantial protective defenses in place."