Code of Federal Regulations Title 49. Transportation § 49.238.439 Doors

(a) The status of each powered, exterior side door in a passenger car shall be displayed to the crew in the operating cab. If door interlocks are used, the sensors used to detect train motion shall be nominally set to operate at 3 mph.

(b) Each powered, exterior side door in a passenger car shall be connected to an emergency back-up power system.

(c) For a passenger car ordered prior to January 28, 2014, and placed in service prior to January 29, 2018, a passenger compartment end door (other than a door providing access to the exterior of the trainset) shall be equipped with a kick-out panel, pop-out window, or other similar means of egress in the event the door will not open, or shall be so designed as to pose a negligible probability of becoming inoperable in the event of car body distortion following a collision or derailment.