train

A train is a connected line of railroad cars, often pulled by a locomotive. The word "train" originally referred to the part of a gown that trailed behind the wearer, stemming from the French verb "trainer," meaning "to draw" or "drag".12

Trains operate on fixed tracks, and their control differs from other vehicles because operators primarily adjust speed. The low friction between wheels and rails allows for efficient propulsion but results in long stopping distances, requiring operators to anticipate events far in advance. Railroads have pioneered advanced communication and control systems, including telegraphs, computers, and automation, to manage operations spread over vast distances.34

Modern control systems include automatic block systems, which use track circuits to prevent trains from entering occupied sections of track. Automated systems like "moving block" systems, common in urban rapid-transit, use continuous data transmission to calculate safe stopping distances and maximum speeds, increasing throughput. Automatic train protection (ATP) systems further enhance safety by continuously monitoring and controlling train speed, automatically applying brakes if the operator doesn't respond to restrictive signals.4