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Comment by helterskelter | Hacker News Reader

If you're in America, take a look at the strobe on top of school busses. I'm not sure if they still have them (they used to). It would flash at a specific frequency and trip a photovoltaic sensor connected to the traffic light, which would turn it green so the kids aren't late for class. If you had a bright enough strobe which flashed at the same frequency...you get the idea.

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Is that actually true? I've heard of ambulances & police cars having such devices, but they were supposed to be infrared.

The last time I saw the strobe on top of a school bus active, it was when I was a passenger in one, driving down the freeway at night, and it wasn't strobing particularly fast. It's possible that our driver just forgot to turn it off, I suppose - he was that kind of guy.

School buses in my state are legally required to run the strobe when passengers are onboard.

No two strobes I have seen strobe at the same frequency. I think this traffic control story is urban legend.

I never heard about this being used on school busses. This was always something for emergency services like firetrucks/ambulances to not have to sit in traffic at a red light, but it was only active if they were actively responding to a call with their lights on. Otherwise, they sit at the lights too.

A newspaper article told of a mayor of some city that had one installed so he could zip along to emergencies.

Emergency vehicles have devices that announce their presence to get traffic lights to change in their favor. “Kids being late to class” is not on the order of importance to create a complex scheme to change traffic lights based on strobe lights from a bus.

Sounds like urban legend.

We definitely have this system in place in some cities in Canada, primarily for express bus routes.

So as a driver, you want to follow an express route bus when you can?

Bus priority lanes and traffic lights that give priority to busses are definitely a thing. Usually for municipal busses and not school busses, but I'd expect a community that had priority lights for busses would allow school busses onto the system as well.

Not specifically to avoid late arrivals of pupils, but because prioritizing many passenger vehicles is valuable.

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