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Public Transit Mechanics Explored: Breaking Up Bus Bunching

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The Ventra app launched last week, bringing some good reviews and lots of efficiency with it. They've even launched videos to show how you can use the app while you wait for the bus. Because waiting allows you to do other things. But there's a dark side of waiting for buses that often tempts the impatience among even the most zen of us. It's name is bus bunching.

Bunches of oats, bunches of flowers, bunches of grapes. These are all, in theory, good things. Except when you're talking about public transportation. Bus bunching is a real and cloying phenomenon that you've probably experienced without knowing the straightforward term for it. When you've been waiting for a late bus, and then two or three buses come in right behind each other, that's bus bunching. Though you may have added expletive terms to it in your head. Other terms for it are bus clumping, convoying, or platooning. And while it can also happen to trains, buses are often at highest risk for this to happen.

Bus bunching happens because, if a bus gets delayed, then there will be more people waiting at the next stop than anticipated. The extra passengers' boarding time makes the bus even later, and a downward spiral of delay commences. It's a cycle where a group of two or more transit vehicles, originally scheduled to be evenly spaced running along the same route, end up running right against each other, stopping at the same location. At the same time. Helping no one.

How does this happen? Sometimes it's through a natural course of events, such as when the first vehicle gets delayed by traffic, or takes longer time than anticipated when boarding someone in a wheelchair. If the vehicle ahead drives a bit slower than the one behind it, there's also an inevitable game of catch up. Try this interactive visualization game by Lewis Lehe to understand the phenomenon through two buses en route.

As a result, wait times can frustratingly grow, as the first vehicle gets crowded with people, while the second vehicle trails behind with a virtually empty car.

When it happens, measures need to be taken to correct it. One way is to create an express route, so that the bus ahead can stay ahead of the one behind it. Another approach is to abandon a schedule altogether, and keep buses equally spaced by strategically delaying them at designated stops. Both of these techniques can be frustrating, because riders who are already on board may get delayed by just sitting by. Or they'd need to get off if the express route is going to zip through their route.

Besides providing options of loading your Ventra app while you wait, Chicago has taken other steps to stop this. Through touch-screens and GPS on every bus, the Bus Transit Management System (BTMS) monitors buses in real-time and allows for improved two-way communication between drivers and the command center. The Command center can watch conditions from a high level and adjust courses because of perceived delays or bunching. They can also send mass messages to drivers in an area to advise for traffic and major events. BTMS replaces an outdated radio system, built upon the same system that powers Bus Tracker and automated bus announcements. While installing this system on all 1,800 buses is an estimated $8.8 million, it's supposed to pay off, particularly for the busiest south side bus routes. If you think you've been waiting for less time to get home or to work, then you may have technology to thank.

·Bus bunching [Wikipedia]
·Chicago busts bus bunching [GCN]
·Early Reviews Are In: Chicago's New Transit App Makes it Easy to Pay the Fare [Planetizen]
·Chicago Transit Authority introducing technology to help reduce chronic bus delays [Chicago Business Journal]
·Previous Bus Bunching coverage [Curbed Chicago]