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A Nifty Visualization of the 'Vicious Cycle' of Bus Bunching

See how small delays can lead to big commuting headaches in this interactive.

Lewis Lehe/Dennys Hess.

As a video game, “Why Do Buses Bunch?” is about as pulse-pounding as those municipal simulators about street cleaning and garbage collection. But as an interactive visualization, it’s a clean, beautiful explanation for how small delays can lead to big headaches in your commute.

The viz, created by Berkeley transportation-engineering student Lewis Lehe and designer Dennys Hess, presents a simplified city where two buses run a circular route. By clicking on one, you can cause it to momentarily pause—something that might happen if the driver was loading a wheelchair, say, or letting somebody put a bike on the rack.

But here’s the nifty part: No matter how short of a delay you create, the buses eventually wind up running back-to-back, an annoying phenomenon known as “bus bunching.” The creators explain:

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 systems have to build slack into the system, but that slack involves extra buses and labor and longer travel times.

Bunching might seem esoteric to non-transportation scholars, but it’s something cities are taking seriously. Chicago is testing out a nearly $9 million anti-bunching system, and Miami recently teamed up with IBM to tackle the problem, which reportedly can ding cities’ economies by millions every year.

About the Author

  • John Metcalfe
    John Metcalfe is CityLab’s Bay Area bureau chief, based in Oakland. His coverage focuses on climate change and the science of cities.