Regulation 4 Doors
Each passenger doorway in the side of a regulated rail vehicle shall be indicated clearly by doors (excluding any window in or control device on the doors) rendered to contrast with the exterior of the vehicle to each side of that doorway.
Each passenger doorway in the side of a regulated rail vehicle shall be fitted with an audible warning device which shall emit warning sounds in accordance with paragraph (3) inside and outside the vehicle in the proximity of each control device for that doorway or, if there is no such control device, adjacent to that doorway.
The audible warning device shall—
emit a distinct sound for a period of not less than 3 seconds commencing when the door becomes openable by a passenger;
only if the door is operated by a member of the operator’s staff, emit a different distinct sound commencing not less than 3 seconds before the door starts to close.
In this regulation “sound” includes the spoken word.