The vast majority of rapid transit systems use 1,435 mm (4 ft 8+1⁄2 in) standard gauge.
Many rapid transit systems in countries where the main lines do not use standard gauges are built in standard gauge, including the Barcelona Metro, Santiago Metro, Taipei Metro, and many systems in India.
There are also systems that use 1,067 mm (3 ft 6 in) (some systems in Japan and Jakarta MRT), 1,524 mm (5 ft) (the standard in former Soviet Union), 1,600 mm (5 ft 3 in) (the standard in Brazil) and few others.
Some systems use monorail, the largest ones are in Chongqing Rail Transit and in São Paulo Metro.
For gauges used by systems that do not run in exclusive rights of way (trams, streetcars and light rail) see List of tram systems by gauge and electrification.