# Giving the Green Light

When we drive on the road, we can’t all just go every which way. We have to stay on one side, and wait our turn where roads cross. Stop signs help, but really busy crossings need traffic lights. The traffic light, that cute red, yellow and green trio, was patented (made official as an invention) in 1923. Actually, the very first electric traffic light was invented in 1912 by Lester Wire, a policeman in Utah fed up with all the traffic. Wire borrowed the idea of railroad signals to make a traffic light, which had just red and green for stop and go. Then in 1920, Detroit cop William Potts built one with 3 colors (red, orange and green). Now we have LED traffic lights, but those don’t get warm enough to melt snow. As you see here, people have tried other designs, like this funny dial one from Australia, but the three-color light is what keeps most of us from crashing into each other today.

Wee ones: If a traffic light has a red light, a yellow, a green, and then a green left-turn arrow, how many lights does it have?

Little kids: Lester Wire’s light had 4 sides with a red and green light on each side. How many lights was that in total?  Bonus: Potts then built one with 3 colors on each of 4 sides. How many lights did that have?

Big kids: Most lights stay on red for only about 15 seconds, but some lights take forever. If the traffic light for your direction signal spends 15 seconds on green, 5 seconds on yellow, and 40 seconds on red, how long is a full cycle of green to yellow to red?  Bonus: If 8 cars can get through the green each time, how many cars make it through the light in 5 minutes?