Section 16(2) in The Delhi Metro Airport Express Line, General Rules, 2010
(2)Fixed Signals- (i) on main lines, fixed signals are color light signals capable of showing a "red" or a "white"(ii)a "Red" aspect indicates that a train must be brought to STOP short of the signal;(iii)a "White" aspect indicates that the route is set and locked but may not be fully clear and a train operating under cab signals may proceed under the authority of the cab signals but a train operating on the sole authority of line side signals must stop and seek instructions from the Traffic Controller;(iv)when a fixed signal is not in use, the aspect shall be covered and the cover shall display two crossed white bars on a b lack background, the bars being not less than thirty centimeters long and ten centrimeters wide.
