In road vehicles, the parking brake, also called hand brake, emergency brake, or e-brake, is used to keep the vehicle stationary and in many cases also perform an emergency stop. Parking brakes on older vehicles often consist of a cable connected to two wheel brakes at one end and the other end to a pulling mechanism which is operated with the driver’s hand or foot. The mechanism may be a hand-operated lever, at floor level beside the driver, or a straight pull handle located near the steering column, or a (foot-operated) pedal located beside the drivers leg.
In most automobiles the parking brake operates only on the rear wheels, which have reduced traction while braking. Some automobiles have the parking brake operate on the front wheels, for example most Citroens manufactured since the end of World War II, and the early models of the Saab 900.The most common use for a parking brake is to keep a vehicle motionless when it is parked. The parking brake has a ratchet or other locking mechanism that will keep it engaged until manually released. On vehicles with automatic transmissions, this is usually used in concert with a parking pawl in the transmission.
A recent variation is the electric parking brake. First installed in the 2001 BMW 7 Series (E65), electric parking brakes have since appeared in a number of vehicles. Two variations are available: In the more-traditional “cable-pulling” type, an electric motor simply pulls the parking brake cable on the push or pull of a button rather than a mechanical pedal or handle in the cabin. A more complex unit (first seen on the 2003 Audi A8) uses a computer-controlled motor attached to each of the two rear brake calipers referred to as the Motor on Caliper(MoC) system.
It is expected that these systems will incorporate other features in the future. Jaguar, Land Rover, BMW, Renault, Subaru and VW already have a system where the parking brake engages when the engine is stopped and is released when the gas pedal is pressed. An extension of this system, called the hill-hold function, prevents roll-back when stopping and starting on a hill. The OEM can easily turn off the system. Some electric parking brakes function similar to “park” on an automatic transmission and will not engage when the vehicle is in motion, there is no emergency brake in this case.