Like most cities in the U.S., Atlanta is plagued with horrendous traffic. Undoubtedly the congestion could be eased if more people used public transporation. But public transit is often slow and frustrating. Take riding the bus for example. It’s typical to wait a while, only to have several buses show up one after another. Fortunately, Georgia Tech's Industrial & Systems Engineering Professor John Bartholdi has an answer to the bus bunching dilemma. Abandon the fixed schedule, tell drivers to go with the flow of traffic and use a "self-equalizing" formula developed by Georgia Tech.
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. Exactly how that happens is the magic of the mathematics.
Under the “self-equalizing” plan, each bus is equipped with a GPS and cell phone. The GPS constantly reports the bus’ position to a central server. When the server recognizes the bus has reached a stop, it sends a message via cell phone telling the driver how long to wait and when to proceed.
That departure time is calculated through the “self-equalizing” equation, which changes the headway of each newly-arrived bus to an average of its former headway and the headway of the trailing bus. For example, if its former headway was larger, its new headway becomes smaller. Using the equation, gaps between buses will equalize even if a bus is added or removed, or if the bus route changes.
Because of its simplicity, our scheme is easy to implement and easy to adapt. We expect it to be useful for other transportation systems with short headways, such as subway trains or airport shuttles.
Bartholdi and his students will be testing the self-equalizing scheme tomorrow on Georgia Tech's trolley system, which carries more than 5,000 passengers a day. But the applications for this system go far beyond a college campus and could help provide better bus service in cities nationwide.
For more information, visit http://www.gatech.edu/newsroom/release.html?nid=124631
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