To ensure more regular transit service, the on-campus buses at Georgia Tech are running in relation to one another instead of following strict schedules.
It's a bid to prevent against "bus bunching" -- a phenomenon that occurs when multiple buses driving a fixed route all try to meet their schedules by hurrying to the next stop. Usually, stops end up with no service for a long period of time until multiple buses arrive all at once.
An interdisciplinary team of students developed a system of tablet computers and GPS transponders that track the flow of buses and let drivers know when to wait extra time at a stop to ensure even service. The process is known as "self equalizing," and it relies on an equation instead of a fixed schedule.
Each bus' departure time is calculated using an average of its own headway (the distance between the bus and the one in front of it) and the headway of the trailing bus. Drivers wait at each stop until their new dynamically calculated departure times, and bunching is avoided. Even if a bus goes out of service or a route is changed due to traffic or construction, headways will eventually equalize.
"The equation computes a wait time for each bus arriving at a control point in such a way that gaps between buses tend to equalize," said John Bartholdi, the professor of Industrial and Systems Engineering who is leading the project. "Exactly how that happens is the magic of the mathematics."
So far, trials of the system have been successful on the Georgia Tech campus trolley system, which serves more than 5,000 riders a day. While it's surely frustrating to wait at a bus stop as other traffic passes by, riders have reported favorable opinions on the frequency of service, and drivers have offered positive feedback as well.
"Because of its simplicity, our scheme is easy to implement and easy to adapt," Bartholdi said. "We expect it to be useful for other transportation systems with short headways, such as subway trains or airport shuttles."
Photo: Flickr/l0st2
