When we drive on the road, 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 very first electric traffic light was invented in 1912 by Lester Wire, but his light had just two colors: red for stop and green for go. Then in 1920, Detroit cop William Potts built one with 3 colors (red, orange and green). 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?

Answers:

*Wee ones:* 4 lights.

*Little kids:* 8 lights in total. *Bonus:* 12 lights in total.

*Big kids:* 60 seconds, or 1 minute. *Bonus:* 40 cars.