SAE J1455 is the recommended practice of the Society of Automotive Engineers for the design of electronic equipment used in heavy-duty vehicles, a category that covers trucks, buses, off-road machines and the trailers and bodies they carry, and it is unusual among the documents on this site because it is addressed to the design engineer rather than to the test engineer. Its purpose is to describe the environment that equipment in this class of vehicle actually meets, so that a product can be designed for it from the outset: the vibration and shock of a vehicle working on poor roads, the extremes of temperature in a cab roof or an engine compartment, the humidity, the salt used on winter roads, and the electrical conditions of the supply, which in a heavy vehicle differs from that of a passenger car because of the size of the loads, the number of separately wired body functions and the practice of connecting and disconnecting trailers.