Ga Tech Develops System to Eliminate “Bus Bunching”

April 21st, 2012

It’s the Murphy’s Law of buses. Yours runs late because of traffic. When it arrives, lots of folks pile in. Then another bus pulls up just a few seconds later to an empty stop.

Now, a team of researchers and students at Georgia Tech have come up with a system they say fixes the problem known as “Bus Bunching.”

“The schedule is always wrong,” opines Georgia Tech grad student Blake Thornberry, who stands near the campus student center.

To get to class, he takes the Tech Trolley (That’s what Georgia Tech’s transit system calls several buses built to look like old-style trolleys.). And when the Tech Trolleys are late—as the often are–“Everybody will be waiting to get on that first trolley, and it’s packed,” explains Thornberry.

And sure enough, as soon as that trolley pulls off, another pulls in. Empty.

“That’s what happens when you have bunching. And basically, you’re wasting a trolley,” says Thornberry.

“Bus bunching,” the phenomenon is called.

And on Tech’s campus, Thornberry says it’s about to be a thing of the past.

As Tech Trolley Bus #405 pulls in to pick up waiting students, driver Clarence July looks down at a small, tablet notebook attached to the dashboard. On its display is a clock counting down.

“Three minutes and ten seconds,” says July, explaining what the tablet computer is telling him. “This gives me an appropriate time how long I’ll be staying at this stop.”

When the timer ends, Clarence shuts the doors and heads on.

Meanwhile, the tablet computer is busy calculating away. It’s using built-in GPS and cellular phone technology to space itself evenly relative to the other buses running the same route. No more ”bus bunching.”

John Bartholdi is professor of Industrial and Systems Engineering at Georgia Tech, and helped design the bus separation system. He says the idea came a few years ago, sparked by a math problem.

“The mathematics behind it came about when we were modeling the movement of buses, and looking the effects of delaying the buses at the endpoints of the route. And we saw a pattern in the mathematics that we recognized as expressing a mathematical concept known as a ’Markov chain,’” Bartholdi says.

Named for 19^thCentury Russian Mathematician Andrey Markov, a Markov chain is a set of random events that are influenced by the random events that just happened.

Bartholdi says Markov chains are well-studied and understood. They tend to behave in certain, predictable ways.

“So once we had that realization, we worked out the rest of the mathematics.”

Understanding the patterns allowed Bartholdi to craft an algorithm, which in simple terms, is just the formula the computer uses to calculate spacing.

The system can run on any commercial cellular network.

And it’s working so well, he says mass transit systems across the US and around the world are in touch wanting to see for themselves.