law: 20. Use of rolling stock.
  The metro railway administration may use such rolling stock as it may consider necessary for operation and working of the metro railway:
  Provided that before using any rolling stock of a design or type different from that already running on any section of the metro railway, the previous sanction of the Central Government shall be obtained for such use:
  Provided further that before giving any such sanction, the Central Government shall obtain a report from the Commissioner that he has made a careful inspection of the rolling stock and, in his opinion, such rolling stock can be used.