This recommended practice is specifically limited to tractor scrapers, wheel loaders, wheel tractors, graders, and dumpers (as defined in SAE J1116 (January, 1977) and J1057a (June, 1975)) which are designed to operate at a maximum rated speed in excess of 20.0 km/h (12.4 mph) and which employ power source(s) in addition to the operator control effort to effect machine steering.