quality:corruption, quality:correction
Rapid transit trains

A number of types of trains are used to provide rapid transit to urban areas. These are distinct from traditional passenger trains in that they operate more frequently, typically do not share tracks with freight trains, and cover relatively short distances. Many different kinds of systems are in use globally.

Rapid transit trains that operate in tunnels below ground are known as subways, undergrounds, or metros. Elevated railways operate on viaducts or bridges above the ground, often on top of city streets. "Metro" may also refer to rapid transit that operates at ground level. In many systems, two or even all three of these types may exist on different portions of a network.