What is "bus bunching"?

M: There is a strange phenomenon regarding buses. You wait ages for one, then three come along at once!
    But why does this happen? "Bus bunching" (two or three buses coming at once) is caused by random fluctuations in the running of and demand for buses. Once a bus is delayed, by the time it arrives at the next stop there is likely to be more than the usual number of passengers queueing. This leads to further delay while they all board. Meanwhile, the bus behind will have fewer passengers than normal to pick up, causing it to accelerate and eventually catch up with the first bus. This continues with the two buses taking stops alternately, with no way of breaking out of being stuck together. This can happen a few times on a bus journey until quite a few buses are stuck together in this way.
    An even stranger phenomenon is the English obsession with queueing. Throughout the 1960s, a huge bus queue, the longest people had seen, would appear at Easter in Sloane Street when Londoners waited for a 137A bus to take them to the funfair at Battersea Park. The route was just over one mile long, and one of London Transport’s shortest. It was quicker to walk, but the English prefer to queue!
    This was the time when London Transport was short of staff and so the route was normally run as voluntary overtime, meaning the drivers and conductors might not be used to working with each other which sometimes led to some fun and games. The conductors would take fares before giving the driver the departure bell, making the driver late, and drivers would get their own back by going like the clappers when given the starting signal, leaving conductors only halfway through fare collection by the end of the journey!