Trapdoor

I decided to use the local bus service into Cambridge today. First problem: they have recently changed the route at the city end so I needed to check the stops. Second problem: timetable has changed - but they do that twice a year anyway. Third problem: I had to download 7 different documents (from three different websites) to get the full picture of bus services in this area.

Anyway I caught the bus, but then I spotted the trapdoor in today's picture. Is this for awkward or difficult passengers? You might think I'm joking but today's driver sailed past two stops where people were waiting. OK, no change there. I'm going to be careful next time I step onto a bus.