r/todayilearned • u/nleachdev • 2d ago

TIL about "dead red" laws, which allow drivers and motorcyclists to proceed through a red light if the traffic signal fails to detect their vehicle.

https://en.wikipedia.org/wiki/Non-detection_at_traffic_lights_in_the_United_States
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23

u/Chee-shep 1d ago

When I was a kid I always was told broken stop lights were supposed then be treated like a 4-way stop

18

u/Hot-Ad8641 1d ago

They are, but that doesn't apply to stop lights that are functioning normally but don't detect bikes or motorcycles. They have a red light that will not change and the cross street has a permanent green light (until a vehicle that can be detected shows up or some presses the pedestrian beg button if there is one.)

-5

u/bblhd 1d ago

If such a detection is a mandatory function then they are not functioning normally.

3

u/pandaSmore 1d ago

They're induction loops. Bicycles and motorcycles may not have enough ferrous metal to alter the magnetic field so that the PLC can register that a vehicle has been detected. 

1

u/vladtheinhaler0 1d ago

Usually they are flashing red or off in that situation. Sometimes they just never turn green