Emergency Brake

break used to stop the vehicle when the normal breaks don't work well or at all

An emergency brake is a separate brake system in a vehicle for use in case of failure of the regular (hydraulic or air) brakes and commonly used as a parking brake in automobiles. Also called hand brake, many people shorten emergency and call the devices e-brakes. In trains, control of emergency brakes is made available to the traveling passengers. Activating the brake will cause the train to automatically stop. Severe fines are often in place to dissuade people from activating the brake without good reason.
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Noun
1. a brake operated by hand; usually operates by mechanical linkage
(synonym) hand brake, emergency, parking brake
(hypernym) brake

A mechanism designed to stop a motor vehicle after a failure of the service brake system. (49CFR571)

FRENO D'EMERGENZA [FERROVIE]. FRENO A MANO [AUTOMOBILI]. FRENO DI STAZIONAMENTO [AUTOMOBILI]