Busting Bus Bunching With Traffic Signals

Transportation officials equipped with increasingly sophisticated technology are considering ways they can use traffic signal-prioritization not just to speed the progress of buses, but to solve bus bunching.
Many cities are plagued by bus bunching at peak hours: one bus stops frequently to pick up and drop off passengers, slowing its progress. The bus behind it, finding stops cleared, goes increasingly fast, until the two meet.
It's not unusual for three or four buses to collect this way, frustrating riders who have to wait increasingly long intervals for a bunch of buses to arrive all at once.
The traditional solution—for the second or third bus to pull over and idle at the curb for several minutes—frustrates riders even more.
Emerging technology may offer a better solution.
Congested cities have come up with incentives to speed up the progress of their buses, making them more attractive to commuters who might otherwise choose to drive their own vehicles. Dedicated lanes give buses an uncongested path, and traffic-signal priority gives buses the power, once reserved for emergency vehicles, to switch signals from red to green as they approach.
Cities like Chicago have begun experimenting with traffic signal prioritization to speed buses generally:
"There's obviously a move toward traffic signal prioritization, having something on the signal that recognizes when a bus is coming so they can flip the light and give the transit user a faster ride," said Gabe Klein, commissioner of the Chicago Department of Transportation, at a public appearance earlier this year.
By modulating traffic-signal prioritization, cities may be able to solve bus bunching as well.
"I think transit signal priority could be helpful with that," said Steve Mortensen, a senior engineer with the Intelligent Transporation Systems program of the U.S. Dept. of Transportaation.
"It could be conditional, to try to move your bus that's holding every body up, to move them through, and then perhaps also being able to monitor passenger loads in real time, and conveying that information to passengers at the bus stop, to let them know this bus is filling up but there's another bus two minutes behind this one."
Mortensen spoke Thursday at a roundtable on Intelligent Transportation Systems sponsored by Chicago's Metropolitan Planning Council.
In an advanced system, transit system operators would be able to notice bus bunching conditions before the buses meet, give green lights to the front bus and alert riders to the presence of emptier buses following the first.
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