Obscure knowledge from my first job to the rescue! Flashing/blinking red actually exists everywhere...there are two systems monitoring the output of the traffic signal controller: the conflict monitor unit and the master malfunction unit. The CMU detects if the controller outputs an invalid signal, like giving a green light to every direction of traffic at the same time, and the MMU monitors the CMU for failures and also looks out for general failures of the entire cabinet's traffic hardware setup.
If either unit detects a failure, the traffic light controller attempts to reset itself. While the controller attempts to clear the error condition, the output signal is transitioned over to a series of relays which cause the red lights to flash. This continues until the error condition clears or a technician is able to fix the cabinet issues.
That’s amazing! I never would have known this. Isn’t the internet fantastic that I get wonderfully surprising comments like this? 🥰
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