Bus bunching

This effect is often theorised to be the primary cause of reliability problems on bus and metro systems.

[1] Clumping can be caused by random heavy usage of any particular vehicle, resulting in it falling behind schedule.

[2][3][4] Clumping can be prevented or reduced as follows: A different approach is to abandon the idea of a schedule and keep buses equally spaced by strategically delaying them at designated stops.

[5] This is used to control the buses on the campus of Northern Arizona University, where it outperforms the previously scheduled system.

[7] Merely adding more vehicles to the schedule without making other changes has been proven not to be a reliable solution to the problem of bunching.