Idea of the Day: Bus Bunching

12 Jul
bus_bunching

Flickr photo by skew-t

If you’d come out of Buckhead Station’s north exit around 6:00 p.m. Tuesday you would have noticed two things: first, that there were far more people waiting for the route 110 bus than normal; second, that traffic was sitting absolutely still on Peachtree as far as you could see in both directions.
At 6:15, with the traffic creeping forward a few feet every few minutes and the bus scheduled to arrive at 6:13 nowhere in sight, you would have probably calculated that walking to the gym about a mile south of the station would be the quicker way to get there. But after walking south for about 10 minutes, around the time you were crossing Maple Drive, you would have noticed a route 110 bus heading north, toward the station you just left. You would have then noticed another one – directly behind the first. The first bus was very, very late. The second was almost on schedule.
What you would have seen is called bus bunching.
Bus bunching occurs when traffic or another delay slows down a bus’ progress along its route so much that the amount of the delay, as it’s compounded by the time required to stop and pick up passengers, exceeds the scheduled time between that bus and the one behind it. As the first bus continues along the route, it falls farther and farther behind schedule, as it has to keep stopping to pick up passengers. The second bus rarely has to stop, as there are very few or no passengers at all to pick up. Eventually the second bus is moving along the route so quickly that it catches up to the first one.  The shorter the headway, the more risk there is for bunching.
WABE and CNN recently posted stories about scientists at Georgia Tech who have developed an anti-bunching technique that relies less on schedules and more on calculated, adjustable delays coordinated by GPS. The system will be fully rolled out for the university’s Stinger Shuttle Tech Trolley system this fall and the developers say they’ve already been contacted by transit authorities here and abroad who are interested in implementing something similar.
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