Section 20(1)(iv) in The Bangalore Metro Railway (General) Rules, 2011
(iv)normally signaling system shall permit only one train at a time in one Tunnel Ventilation Section, more than one train in one Tunnel Ventilation section can be sent only in case of emergencies, and in a case the Traffic Controller decides to send additional trains in a Tunnel Ventilation section already occupied by a train, he shall set the route manually for additional trains and shall advise train operators about this before authorizing them to proceed;