WHY DO BUSES OFTEN COME IN THREES?

Why do buses often come in three?

A common complaint of people who use public transportation is that of waiting at a bus stop for ages and then three buses arrive all at once. In fact, mathematicians have attempted to explain this everyday conundrum by means of applying complex formulae based on queuing models, correlation and renewal theories, random matrixes and bunching. However, the phenomenon can be explained in fairly simply terms.

Buses leave the depot at regular intervals, but the number of people waiting at the various bus stops tends to vary considerably, and it’s these variations at the bus stops that play an important role in “bus bunching”. For example, if there’s an excessive number of passengers waiting at one bus stop, the first bus will take longer than normal to load these passengers. In this time, the second bus catches up a little. When this second bus arrives at the same stop, it’s likely that there won’t be as many passengers waiting, as most of them are on the first bus, so the second bus won’t stay at the bus stop for as long. Also, because the first bus has taken longer at the first stop, it’s likely that more passengers will be waiting at the next stop. The process then repeats itself, with the second bus eventually catching the first until they travel in tandem, acting as one. The longer the route, the more buses that are likely to join the convoy, although experiments have shown that the most common bunching number is two buses.

Despite there being such a scientific basis for bus bunching, some claim that it rarely occurs and that people forget how often single buses arrive.