There is some confusion as to how the U.S. treats articulated buses, but the general agreement in professional circles seems to be that they're treated as combination vehicles, and therefore requires that drivers hold a Class A commercial driver license (CDL) with a passenger (P) endorsement, which requires the passage of both a written and driven exam. The driven exam must be completed in the highest class of vehicle the driver wishes to operate, else restrictions are issued on the driver's license disallowing them to operate higher classes of vehicles than they tested on (e.g. a driver with a Class A CDL performs their P endorsement test on a class B bus, resulting in their license bearing the "no class A passenger vehicle" restriction, which is notated with an 'M', in addition to their P endorsement). These restrictions can be removed through further testing at a later date.