Link: Bus Bunching Explained Visually

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Have you ever been waiting for a late bus, and all of a sudden two or three buses arrive at the same time? That's called bus bunching.

 

Bus bunching happens because, if a bus gets delayed, then there will be more people waiting at the next stop than anticipated. The extra passengers' boarding time makes the bus even later, and so on in a vicious cycle.

 

To combat bus bunching, bus sytems have to build slack into the system, but that slack involves extra buses and labor and longer travel times.