Then computers were invented. Here’s a really neat little video explaining how the old style traffic lights work. The ones that use regular light bulbs, and moving parts, and lots of other breakable items. Right off the bat, I used to notice burned out traffic lights all the time, but I live in a town, not a big city, so maybe that’s the difference.
I looked for a video explaining how the newer LED based traffic lights work, and look, but couldn’t find one. Probably because as the guy said above, it looks much like the computer you’re reading this on, and does everything you can think of and then some.
Still it’s neat to see how things worked before we had computers to do everything for us.