SG - 1,435 mm (4 ft 8 1⁄2 in)
BG - 1,676 mm (5 ft 6 in)
Until 2010 (delhi) Metro used Broad gauge but post 2010 all metro's in the country are being built on SG. Although Delhi's Airport Express track is fit for 330 Kmph but due to some major goof ups by Reliance during construction of pillars the train now only runs at 80 kmph instead of prescribed 120 kmph.