As used in this compact:
(a) "Vehicle" means every device in, upon, or by which any person or property is or may be transported or drawn upon a highway, excepting devices moved by human power or used exclusively upon stationary rails or tracks.
(b) "State" means a State, territory or possession of the United States, the District of Columbia, or the Commonwealth of Puerto Rico.
(c) "Equipment" means any part of a vehicle or any accessory for use thereon which affects the safety of operation of such vehicle or the safety of the occupants.