You wait and you wait and you wait for a bus. Then, just as your patience is exhausted, three empty vehicles arrive at your stop. It's a common problem with urban bus routes. But if two math researchers have their way, it may not be a problem for long.
John Bartholdi of the Georgia Institute of Technology and Don Eisenstein of the University of Chicago have devised a mathematical formula to prevent "bus bunching" — the stacking of vehicles delayed by traffic and other obstacles.
The system relies on Android tablets and GPS systems inside each bus. As the vehicle reaches the end of its route, an app checks the location of the bus immediately behind it, then delays the first bus's departure, telling the driver when to leave so the vehicles are all evenly spaced.
"The trick is knowing how big a correction to make," Bartholdi explains. "That's where our formula comes in."
The system has been successfully tested on the central trolley line cutting through the Georgia Tech campus, though more testing is needed before it's rolled out full time, says David Williamson, associate director for transportation at Georgia Tech.
"On our campus, most trolleys run six to seven minutes apart, so bus bunching is one of the more common complaints," he says. "When you're running that high a level of service, it doesn't take long for some vehicles to be two or three minutes apart followed by a big gap.
"But Williamson cautions that abandoning fixed schedules for a more dynamic system won't work for all bus lines. He notes that the public wants services that run 20 to 30 minutes apart to adhere to a fixed schedule. "When they're running less than 10 minutes apart, there's an opportunity to improve service for customers. That's what this is really all about."