Section 15(3) in The Delhi Metro Airport Express Line, General Rules, 2010
(3)A fixed signal be placed, where practicable, on the left hand side of the track to which it refers and shall be visible from such a distance as will enable a train operator to brake a train from forty kilometer per hour speed to stop before reaching the fixed signal and a repeater signal shall be provided at locations where due to obstructions such visibility is not available, except in depot.
