Revolving doors

Revolving doors are widely used by shops; they are quite effective at keeping heat in during Winter, and cool, conditioned air inside during Summer.  Since shops are keen on not getting sued by people losing a limb or suffering other injury in doors of this type, the doors are fitted with some kind of emergency stop, whereby they cease revolving if anything untoward is happening.

Around here, a few supermakets have fitted shiny new, larger revolving doors with super-sophisticated safety systems: if you touch the door it stops, and a proximity detector works such that if you get within 30cm, it slows down to a snail's pace.  This works fine if there are only a few people in the door at once, but the fun starts at busy times.

Since the new doors are larger than the old ones, the temptation is to fill them to capacity with people and trolleys.  The problem is then that the proximity detector trips and slows down the door to almost stationary.  Arguments then ensue as to who might be responsible - the people at the front, or the people at the back, each group defending itself vigorously.

To correct the problem, those at the front just have to stand still and wait for the door to move on a bit, but those at the back have to shuffle forwards in the limited space, compressing the people in the middle, until the door catches up with them again and slows down.  Although it's easy to stay 30cm away from a door that is moving away from you, it is remarkably difficult to do the same with a door that is creeping up behind, especially if there are people in front of you.

Meanwhile, since it's a busy time, queues are forming outside of the door, with encouragement to the occupants from people who are keen to get on with their shopping.