trains

A train is a collection of connected vehicles that run on rails and are moved by locomotives or by self-propelled multiple-unit sets. They are used to transport passengers or freight over land and operate on fixed track networks that include stations, yards, and signaling systems.

Historically, trains emerged in the early 19th century with steam-powered locomotives and rapidly expanded rail networks. Subsequent generations adopted diesel and electric propulsion, increasing range, efficiency, and speed. Modern trains use a variety of propulsion systems, including steam (historically), diesel-electric, and electric traction. Rolling stock ranges from locomotive-hauled passenger coaches to electric and diesel multiple units, along with specialized freight cars. High-speed trains are designed for sustained speeds well above conventional regional services.

Infrastructure and operations focus on the interaction between rolling stock and the fixed network. Tracks vary in gauge, with standard gauge being the most widely used worldwide. Electrification through overhead wires or third rails supplies power to electric trains. Signaling, traffic control, and automated safety systems coordinate operations to maintain schedules, manage capacity, and prevent collisions. Services are organized to meet passenger demand and freight needs, with timetables, crew rosters, and maintenance planning guiding daily use.

Impact and trends include energy efficiency and emissions reduction when trains run on clean electricity, as well as ongoing developments in electrification, lightweight materials, regenerative braking, and autonomous train control.