8 Scientific Reasons Why You're Having One Of Those Days
5. Your Bus Is Late Then Three Turn Up
As well as being a well known saying, the fact that you can wait forever for a bus and then three will turn up at once is a genuine phenomenon known as platooning.
It famously plagues buses, but it can occur in trains and even elevators and it's all down to the witless public (and some complex system dynamics).
Even if each bus/train/whatever begins evenly spaced, all it takes is a small delay to the frontmost one, perhaps some idiot holding the doors open, and it causes a runaway effect. If the leading vehicle is delayed, it leaves more time for passengers to accumulate on the platform. This, in turn means that it takes longer for them to board, causing further delays.
What's more, this means that there are fewer passengers for the subsequent vehicles to pick up, which means that they will eventually end up either stuck behind their painfully slow leader, or overtaking them and picking up the crowd that has accumulated at the next stop, slowing it down.