Avoiding Bus Bunching
The Atlantic Cities has a cool, nerdy post on the science behind avoiding bus "bunching." You know, that thing where you wait and wait for a bus and then two or three show up at the same time.
Transportation analysts say that the traditional way of managing bunching—building in periods of "slack time" and forcing the driver to make adjustments—doesn't really work, especially during periods of bad weather and traffic.
Instead, they suggest eliminating the set schedule and required "headway" (time between buses), and have bus drivers simply follow the flow of traffic. Using that model in several studies, they discovered that buses naturally found an equilibrium and reduced bunching.
Here in D.C., that's sort of what makes the Circulator work so well (well, that and the $1 fare). And back in September, the 90, 92, and 93 buses were switched over from a fixed schedule to a Circulator-style interval schedule. At stops that both buses serve, they're supposed to arrive every 7-8 minutes. This was an effort to avoid bunching—a big problem with these buses. Shortly after implementation, I observed that the new schedule didn't seem to do much to help the problem.
Still, in recent months it seems like things have gotten better. I've reached out to WMATA to see if they've measured any improvement in the way buses are running since the schedule change.
Photo by Darrow Montgomery