Semi-metro

Semi-metro is a form of urban rail transport in which trams run partly on a conflict-free track,[1][2] by using tunnels and viaducts.

Semi-metro routes are operated by regular trams (with or without low floor) or with specially developed tramcars (light rail vehicles), such as the Stadtbahn-car 'type B'.

It combines advantages of greater speed (from rapid transit) with a better coverage in suburban areas (from busses and trams).

The entanglement with the existing tram network is an advantage compared to constructing a separate light metro line.

[25] A rail transit system is firstly determined by its main right-of-way category[26] and secondly by other parameters like power supply and operating speed.

The reserved right-of-way is termed exclusive and a subtype is distinguished: semi-exclusive, which is an environment with reduced other modes of traffic.

A prominent example is the Tremont Street subway (1897) in Boston,[32][33] today part of the MBTA Green Line.

However, there is one clear distinguishing factor: premetro uses infrastructure that has been explicitly constructed with the ambition to transfer to use metro trains in the future.

In the United States, the most prominent examples are the San Francisco Muni Metro and Green Line in Boston.

[18]: 77  In the United Kingdom, the Tyne and Wear Metro is by definition a semi-metro system due to eight level crossings.