[bmslieght]

I am a traffic signal engineer. They don't.

They may have a detector (ir-red/mircowave/inductive loop) that detects your approach. At night, as they may be no conflicting demands - the side road will change Green ASAP.

[paulbennett]

Do they, or did they used to, have light sensors to detect emergency vehicles coming through? Perhaps that was just an urban myth.