“why we shouldnt pull emrgency cord on subway trains” (1/26/08)

But if you really must know:

The emergency brakes are released when a passenger pulls the dangling cord at either end of the subway car, or when the steel lever attached to the undercarriage of the lead car — called a trip cock — strikes an object lying on the tracks or track bed. Each time this occurs, a train operator must leave the cabin, inspect the tracks under each car and clear any obstacles before beginning the 10-minute process of repressurizing the brakes, according to Jared Lebow, a Transit Authority spokesman. It can take a while.

In most emergencies — when a passenger is ill or caught in the doors — the brake cord should be pulled only to prevent the train from leaving a station, Mr. Lebow said. Passengers shouldn’t pull the cord while the train is in a tunnel, he said, unless a passenger falls onto the tracks.

. . .

The emergency brakes are pressurized to 110 pounds per square inch. Although they won’t stop the train on a dime, they can bring a 400-ton string of cars moving 30 miles an hour to a halt in about 250 feet.