Thane Vashi Metro Line
Western Metro Line
Central Metro Line
Harbor Metro Line
Mumbai (formerly Bombay, approx. 10 million inh.) currently has four rail corridors exclusive to the mass transit system (with separate tracks) totalling 149 Km. Trains run from 4:00am to 1:00am with a headway of 3 mins during peak hours and ranging from 5 to 10 mins during the rest of the hours of operation (except late at night, when headway is about 20-30 mins).
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Further, there are currently regular operations with a headway between 10 and 30 mins on other lines not exclusively for mass transit use (shared with long distance trains) totalling to 154 Km, in addition to the 149 km system. Alongside much of the mass transit tracks, the long distance tracks also carry 'fast' trains which do not stop at all stations.

The major sections of the exclusive MRTS system are (not including those shared with long distance trains)

a. Churchgate to Borivali on the Western Railway (WR) - 34 Km. A further 26 Km on this line from Borivali to Virar has regular suburban trains running on the main line tracks (shared with long distance trains). The separate line from Borivali to Virar is under construction.

b. Mumbai CST to Kalyan on the Central Railway (CR) Main Line (54 Km). Further, there are regular suburban trains going further and using the main line tracks (shared with long-distance trains). The two different lines from Kalyan onwards are Kalyan to Karjat (61 Km) and Kalyan to Kasara (67 Km).

c. Mumbai CST to Panvel on the Harbour Line (CR) (50 Km)

d. Wadala to Andheri linking the Harbour Line to the Western Railway Corridor.(11 Km)

Information Source: UrbanRail.net