How do they do the minute countdown at the bus stops? I can imagine how they do it for the Tube, but I don’t get the buses. It must be GPS, right?
It’s not GPS, not yet. At the moment Countdown relies on about 5,000 beacons attached to lampposts along each bus route. A bus goes by one every 30-60 seconds and beams its location to the beacon via microwave signals. Central command in Chingford also gets the information, and they can communicate with the bus driver by radio if necessary. This system is known as AVL, Automatic Vehicle Location, and has been around for about a decade. But AVL wasn’t designed for a city as large as London, and Ken’s continuing promise to add buses to the streets will only make tracking more difficult. TFL is working on switching over to a GPS system, which will make the Countdown screen more accurate, as well as help stop the old wait-for-30-minutes-and-then-three-come-along-at-once problem. (Though we have to point out this means holding back buses that have gotten ahead of themselves, and which is more annoying: waiting forever at a bus stop or waiting forever on a stopped bus that should to be getting you to work on time?) TFL expects the GPS Countdown to be set up around 2008 or 2009. That’s about 2.5 million minutes, if you’re waiting.
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