They call it the dead-man feature.

In the spartan, phone-booth-size motorman’s cab in a subway train, there is a metal arm a few inches long called the controller.

To set the train in motion, the operator presses down on the controller arm with several pounds of pressure, swivels it and holds on. If he lets go, for whatever reason, the emergency brakes are applied. This is the dead-man feature. It has been part of every New York City subway train for as long as there have been New York City subway trains, according to New York City Transit.

On Wednesday, it worked. At 8:08 a.m., at the Long Island City-Court Square Station in Queens, the northern terminus of the G line, Domenick Occhiogrosso turned a lever on the ancient-looking black console, depressed the controller and eased the crowded train out of the station. His first stop was to be 21st Street, barely a quarter-mile away.

The train was not even completely out of the station when it ground to a halt. The conductor walked to the front car and found Mr. Occhiogrosso — who had spent the past 23 years of his working life in a train cab — unconscious.