I’d always assumed they must be connected to support the ability of fire engines to setup route plans or the central traffic management teams to be able to override light sequences.
I see now there are other novel ways of supporting preemption for emergency vehicles, although I’m still unconvinced that’s what our city uses as the lights often preempt several minutes in advance and from over a kilometre away.
Most US preemption devices are just a visible (and sometimes optional infrared) stroke at 80Hz. Visibility to the sensor/receiver device is largely subject to prevailing light (bright day, more challenging, night/shade, then it's easy to pick out the strobe).
In Queensland, Australia it's all an (internal) networked thing, relies on a lot of hardware interacting on IP networks. I can't imagine what'll happen in the 2038 situation - hopefully they've got a good vendor :)
Question, since I've always been curious about this: How difficult would it be to make your own preemption device? Are such things available on online stores?
I'm assuming it's illegal to use one obviously, but I wonder what precautions are used to prevent unauthorized usage, if that can even be disclosed to the public. What's stopping the average joe from getting one from Alibaba?
Honestly, pretty little, other than the risk of being observed. There may be systems that allow for authentication, but I've not seen them (though I'm not an expert).
There is an encoding standard for prioritization that some larger systems use, that mass transit may utilize, but can be overrode by Fire/EMS/LE.
I see now there are other novel ways of supporting preemption for emergency vehicles, although I’m still unconvinced that’s what our city uses as the lights often preempt several minutes in advance and from over a kilometre away.