Today's standard freight-car coupler is the Type E, a Janney ?clasped-hand? device that couples automatically when one or both knuckles are open and cars are pushed together. Upon impact, the knuckle swings into the closed position and a lock drops in place, securing the coupling.

Train cars stay together using specialized mechanical devices known as couplers. In North America, the standard is the Janney coupler (also called a "knuckle" or "automatic" coupler), which looks like two interlocking hands. When one car is pushed into another, the "knuckles" swing shut and are locked in place by a heavy steel pin. To uncouple, a crew member pulls a lever that lifts the pin, allowing the knuckles to swing open. In Europe and parts of Asia, many trains still use screw couplings, where a large metal link is placed over a hook and tightened with a threaded spindle to bring the "buffers" (shock absorbers) together. Modern high-speed and commuter trains often use Janney or Scharfenberg couplers, which are fully automatic and also connect the train's electrical and pneumatic (air brake) lines simultaneously. This ensure that if the cars were to accidentally separate, the air pressure in the brake lines would drop immediately, automatically triggering the emergency brakes on the entire train.