3 ms·
Moving arms also predate traffic lights for the same function - see trains https://en.wikipedia.org/wiki/Railway_semaphore_signal https://en.wikipedia.org/wiki/
by kzrdude 4y ago
Moving arms also predate traffic lights for the same function - see trains https://en.wikipedia.org/wiki/Railway_semaphore_signal https://en.wikipedia.org/wiki/Railway_semaphore_signal