Who is the carrier responsible?:
John Smith is driving a tractor/semi-trailer owned and operated by ABC Trucking
Answer: ABC Trucking is the motor carrier. John Smith is just a driver for ABC Trucking.
John Smith is driving a tractor owned by ABC Trucking, which has been leased to XYZ Trucking. XYZ uses the tractor to pull XYZ trailers in its regular shipping service.
Answer: In this case, XYZ is the motor carrier becauxe XYZ is directing the carrying of the load.