dead man’s handle
In the motorman’s cab there are two levers, a braking lever operated by the right hand and the controller lever, equivalent to an accelerator, which is operated by the left hand. The controller is also called the “dead man’s handle’” because it must constantly be pressed downward against a spring to accelerate the train. When the motorman’s hand is lifted from the lever, the lever springs upward and the train automatically brakes.
» —“Brakes Were Off On Subway Train Involved In Crash” by Edward A. Gargan New York Times July 6, 1981. (source: Double-Tongued Dictionary)