The train

Its job in the system

Rolling stock is the railway term for vehicles that run on the track. In an urban electric train, the passenger space is only one visible part. Beneath and around it are wheel assemblies, motors, power electronics and braking equipment. The train must work with the particular line’s physical dimensions, electrical supply and control system.

How it works

Electric traction converts electrical energy into mechanical motion. The available force at the wheels, the train’s mass, speed restrictions and the distance to the next stop all influence acceleration. Maximum speed alone says little about a short urban journey: there may be limited time between accelerating and braking for the next station.

Doors, interior layout and passenger information are operational equipment too. A train with ample floor space but narrow or badly positioned passenger flows can take longer to exchange its load. On lines with communications-based train control, compatible onboard equipment also exchanges movement information with the railway. Replacing a fleet can therefore require changes beyond the vehicles themselves.

What it connects to

The train sits at the meeting point of power, track, signalling and stations. Its length must fit the available stopping and platform arrangements. Its control equipment must understand the line’s movement permissions. Its operating pattern must leave time for inspection and maintenance, so the number of trains owned is not the number always available for service.

Different places, different designs

Metros commonly use electric multiple units, with traction equipment distributed along the train. Other urban services may use locomotive-hauled vehicles, trams, rubber-tyred metros or different automation arrangements. This explanation follows a steel-wheel electric urban train; it is a connected example, not a definition of every railway.