CFR > Title 49 - Transportation > SUBTITLE B—Other Regulations Relating to Transportation > CHAPTER V—NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (Parts 501–599) > PART 570—VEHICLE IN USE INSPECTION STANDARDS > SUBPART B—Vehicles With GVWR of More Than 10,000 Pounds (§570.51 to §570.63) > 570.54—Definitions.

570.54—Definitions.

Unless otherwise indicated, all terms used in this part that are defined in part 571 of this chapter, Motor Vehicle Safety Standards, are used as defined in that part.
Air-over-hydraulic brake subsystem means a subsystem of the air brake that uses compressed air to transmit a force from the driver control to a hydraulic brake system to actuate the service brakes.
Electric brake system means a system that uses electric current to actuate the service brake.
Vacuum brake system means a system that uses a vacuum and atmospheric pressure for transmitting a force from the driver control to the service brake, but does not include a system that uses vacuum only to assist the driver in applying muscular force to hydraulic or mechanical components.