Light metro

A medium-capacity system (MCS) is a rail transport system with a capacity greater than light rail, but less than typical heavy-rail rapid transit. It is also known as light metro or light rapid transit.

Since ridership determines the scale of a rapid transit system, statistical modeling allows planners to size the rail system for the needs of the area. When the predicted ridership falls between the service requirements of a light rail and heavy rail or metro system, an MCS project is indicated. An MCS may also result when a rapid transit service fails to achieve the requisite ridership due to network inadequacies (e.g. single-tracking) or changing demographics.

In contrast with most light rail systems, an MCS usually (though not always) runs on a fully grade separated exclusive right-of-way. In some cases, the distance between stations is much longer than typically found on heavy rail networks. An MCS may also be suitable for branch line connections to another mode of a heavy-capacity transportation system, such as an airport or a main route of a metro network.

The definition of a medium-capacity system varies due to its non-standardization. Inconsistencies in international definitions are even reflected within individual countries. For example, the Taiwan Ministry of Transportation and Communications states that each MCS system can board around 6,000–20,000 passengers per hour per direction (p/h/d or PPHPD), while the Taiwan Department of Rapid Transit Systems (TCG) suggests an MCS has a capability of boarding around 20,000–30,000 p/h/d, and a report from the World Bank places the capacity of an MCS at 15,000–30,000 p/h/d. For comparison, ridership capacity of more than 30,000 p/h/d has been quoted as the standard for metro or "heavy rail" standards rapid transit systems, while light rail systems have passenger capacity volumes of around 10,000–12,000 p/h/d or 12,000–18,000 p/h/d. However, passenger capacity volume is just one possible criterion used to define a medium-capacity rail transit system.

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