Section 236.205 - Signal control circuits; requirementsThe circuits shall be so installed that each signal governing train movements into a block will display its most restrictive aspect when any of the following conditions obtain within the block:
(a) Occupancy by a train, locomotive, or car,(b) When points of a switch are not closed in proper position,(c) When an independently operated fouling point derail equipped with switch circuit controller is not in derailing position,(d) When a track relay is in de-energized position or a device which functions as a track relay is in its most restrictive state; or when signal control circuit is deenergized.33 FR 19684, Dec. 25, 1968, as amended at 49 FR 3385, Jan. 26, 1984