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MAKE subscriber Joe Kerman sent us a link to this video about how mechanical controllers for traffic lights work. This is from a Canadian kid’s TV show from the late 80s (I think), called the Acme School of Stuff. I watched a number of other episodes on YouTube and found them pretty engaging and educational. [Thanks, Joe!]
16 thoughts on “How (analog) traffic lights work”
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Fantastic! I thoroughly enjoyed that. I’m heading straight to eBay to see if they have any controllers…
Too bad this won’t do anything to quiet down the believers in pedestrian crosswalk “placebo” buttons or the people who say “you have to enter a secret code on the pedestrian walk button to make it actually work”.
What is the “advance green flasher”? I have never seen one. Does it warn you to get ready to beat the pedestrians? In my area I used to see burned out bulbs every month or so. They have replaced the red and green incandescents with LEDs. They didn’t replace the yellow because they don’t burn out as quickly.
The flashing advanced green is a thing that’s peculiar to Toronto where this was shot. It takes the place of an arrow, allowing you to make a left turn before the oncoming lane’s light turns green. I’m not sure how people from outside of Toronto are supposed to figure it out, since there’s no big sign at the city limits saying “We couldn’t afford arrows, but the green light blinks.”
They had them in Ottawa as well, but they’ve replaced most with actual arrows because it’s not quite so intuitive for out-of-province drivers.
Basically, it lets one direction go straight and/or turn before the oncoming direction. It’s the same as having a green light for straight traffic and a turn light for a turn lane both green at the same time.
I want to watch the rest of the video (or series!)
Also, in a world where analog is often used to mean “not electronic”, as in people referring to “analog cameras” (which are actually mechanical, and chemical, not analog!) it’s interesting to note what is analog and what is digital about that system. It’s a mix of both, actually. The changing of the speed by selecting gear sizes on the motor is a perfect example of an analog system.
They had one of these setups at the Canadian National Museum of Science and Technology in Ottawa here for a while, and you could press the crosswalk button and see all the electronic and electro-mechanical stuff going through the plexiglass.
I wonder if it’s still there.
I remember an episode of MacGyver where he cut some pieces off a credit card and used the pieces as additional keys to actuate the servo more frequently than it was supposed to (thus causing chaos at the intersection). I think his goal was to use this as both a distraction while he broke into some building (I believe it was somewhere in the Eastern Bloc), and to delay the police response to his break-in. I think a small clip of that was even in the opening credits of the show for awhile. Like so many other people, MacGyver was one of the things that influenced me to become an engineer.