Presumably the post was reference London... here at First Kernow we have 2 double door buses in a fleet of around 200!
Used to have more and unfortunately, when the bell rang, it could only be reset by using the middle door. No
CCTV▸ of course, poor visibility of the door & pupils (or all ages) used to try boarding un-noticed through them.
Most drivers would only use the front doors for boarding/exiting, and only when all were on would the middle doors be opened/closed as quickly as possible to reset the bell.
Double set of buttons on the floor/dash also confused the situation.
It also added to the dwell time.
Not popular to take on a run.
Would hope the modern ones would have sorted all those problems!