It's my understanding that it is quite specifically installed on every traffic light (in the sense that it's both the purpose of the device and that it's legall

It's my understanding that it is quite specifically installed on every traffic light (in the sense that it's both the purpose of the device and that it's legally required). Note that this does not control the lights, it simply monitors and switches to flashing-yellow (until a manual reset) if there's an error. Mind you, none of this is first hand.