Ground Control

A Berkeley professor’s research could help buses stay on schedule.
By Elaine Tu

For passengers in a hurry, nothing is more frustrating than waiting for a late bus. Unless it’s waiting all that time only to watch two arrive at once. “Without any intervention, the natural state of the bus system is that they will pair up or cluster,” says Carlos Daganzo, a professor of civil and environmental engineering. This problem, called bus bunching, is being tackled by Daganzo and his colleagues at the Institution of Transportation Studies at Berkeley.

Anything that slows down the boarding process can delay a bus: a wheelchair, a large number of riders, or a late passenger who flags the bus down just as it’s pulling away. Too many setbacks can make the bus fall so far behind that it begins to collect passengers who should be picked up by the following bus. Meanwhile, the second bus doesn’t have to make as many stops and catches up.

To try to solve the problem, transit agencies build a time cushion into their schedules, and hold early buses at checkpoints along the route, while allowing late buses to drive on. But Daganzo’s research suggests that for high-demand lines such as those serving Berkeley, this strategy can slow the buses too much, almost doubling the total travel time.

Daganzo’s team calls for adjusting a bus’s speed at the moment they start to clump. “If they’re just beginning to bunch, then you can give them an aspirin before the problem gets worse,” says Daganzo. By tracking buses via GPS, drivers could maintain proper distances by slowing down slightly, speeding up, or waiting at stops. This approach would only slow buses by about 10–15 seconds per kilometer traveled for lines with moderate demand, compared to one minute per km with current methods.

Areas with the highest demand may require additional strategies to help buses keep to their schedules, according to Daganzo. Faster fare collection systems, for example, could help systemwide and spacing stops farther apart or closer together could smooth the schedule.

For now, the work on bunching buses is theoretical, but Daganzo hopes to implement a demonstration project in a year or two. “For a system like this to be deployed, the unions and transit agencies would have to be on board, so the bigger obstacles will be institutional,” Daganzo says. “The technical obstacles are there but are not insurmountable.”

From the Winter 2011 Taste issue of California.
Filed under: Science + Health
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