I want to explain physics at
how can civil defense Change traffic lights from red to green ?
It's only a physics issue as regards electricity. Police and fire vehicles, and perhaps ambulances, have remote-control transmitters that override the normal programming of the lights. This only works on lights that are designed for the purpose.
Around here, traffic lights have a receiver mounted on them, emergency vehicles transmit a signal which is received by the light and sets the state according to where the emergency vehicle is going. Not sure how smart the system is but there is no reason (given sufficient money) that it could not be made very smart.
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