Why buses come in threes

Driving along the road the other day I realised why buses do come in threes and thought I would share this. As it is so obvious I'm not sure if I am here demonstrating my incredible perception or my ignorance at only just realising this.

As a bus pulls into a bus stop just before me I pull out and go round it as do all the other cars. The problem is that when a bus comes up to this it can't get passed and so we now have two buses in convoy. Observing this occur made me realise why buses all come together and that it wasn't just to spite and irritate the person who has been sat in the bus stop for half an hour waiting for any bus!

Anyway I thought I'd share!