3. Subject to articles 5 and 6, an exempt vehicle is authorised to be used for carriage on the Metropolitan Line even if it does not conform with, or it is used in a manner that does not conform with the requirements of—
(a)regulation 4(3)(b) (audible warning before door closes), but only in respect of the period of time for which the distinct sound should be emitted before the door starts to close;
(b)regulation 5(2) (control devices for doors), but only in respect of the period of time between the control device ceasing to be illuminated and the door starting to close;
(c)regulation 13(4) (passenger information when vehicle is stationary at a station), but only in so far as it applies to the systems inside the passenger saloon.