Medium-capacity rail transport system

In rail transport, a "Medium-capacity system" (MCS), commonly called "light metro" in European countries is a non-universal term coined to differentiate an intermediate system between light rail and rapid transit/metro. It is commonly regarded as a medium-capacity rapid transit system and sometimes called "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.