North Reading Transportation (ÂNRTÂ) operates a fleet of school buses at a number of different locations in Massachusetts. NRT violated the federally-enforceable motor vehicle idling limits contained in the Massachusetts (MA) state implementation plans. The applicable regulations establish requirements for all motor vehicles operating in MA, and, with very few exceptions, limit idling to no more than five minutes in MA. The violations occurred at bus lots owned or operated by NRT in Methuen, Lowell, Lynn, and, Wilmington.