Dango unten (bus bunching)

The word for buses on the same route running strung together in a line. It happens when the lead bus falls behind through congestion or a rush of boardings and the buses behind catch up. Typically the second bus and those after it are lightly loaded.

What dango unten means

Dango unten is the colloquial name for the state in which two or three buses on the same route end up running strung together in a line. The name comes from the way they look like 団子 (dango), dumplings threaded on a skewer. You wait for ages, and then they arrive all at once. Every bus rider has met this phenomenon at least once, and it is the most visible form that a disturbance in the service interval can take. It is not a formal technical term, but it is widely understood as a word you cannot do without when talking about bus operations.

Why it happens

Bunching is not the result of anyone slacking off; it arises structurally. The mechanism goes like this. The lead bus falls slightly behind because of congestion or a traffic light, and at the next stop a longer-than-planned span of waiting passengers has piled up. Boarding and alighting take time, and the delay grows wider still. Meanwhile, almost no waiting passengers are left in front of the bus following close behind. With boarding done in moments, the follower presses steadily ahead until at last it catches the bus in front. A small delay creates the split of "heavy and slow in front, light and quick behind," and that automatically closes the gap.

Once the catch-up has happened, it is hard for the two buses to drift apart again by themselves, and it is not unusual for them to run coupled together almost to the terminus. The operations side does make adjustments to restore the interval, but there is a limit to what a bus on ordinary streets can do. For the full picture of what causes delays, see our article on why buses run late.

What riders gain from knowing this

Knowing the mechanism hands you a practical trick for avoiding crowds. The lead bus in a bunch draws all the waiting passengers to itself and gets packed, while the second and later buses are often nearly empty. So when two buses pull up one after the other, deliberately letting the first go and taking the second sharply raises your chances of a seat. They reach the same place at almost the same moment, so there is no reason to rush.

Likewise, when you look at bus positions in the approach information and see buses on the same route clustered close together, that is a sign of bunching. Just being able to predict that "the first bus after a long wait will be crowded" and brace for it gives you a little breathing room.