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But Why: A Podcast for Curious Kids

Why does green mean go and red mean stop?

But Why: A Podcast for Curious Kids

Vermont Public

Nature, Kids & Family, Science, Language

4.35.6K Ratings

🗓️ 1 May 2026

⏱️ 37 minutes

🧾️ Download transcript

Summary

Why is there traffic? How do traffic lights work? How do they know when to turn red and green? Why does green mean go and red mean stop? Why are cars able to go faster than they are allowed to go with the speed limit? Why do we drive on the right side of the road in the United States? Why are some roads bigger than others?  Answers to your traffic questions with Mike Knodler, professor and director of the Transportation Center at the University of Massachusetts.


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Transcript

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0:00.0

Want to help shape future episodes of But Why?

0:03.0

Join the But Why Fan Club.

0:05.0

Along with other great perks, fan club members now get previews of upcoming episodes

0:09.0

and can send questions on the topics we're working on.

0:12.0

Beyond the perks, But Why Fan Club members play a big role in supporting our work

0:17.0

and help keep this show free for curious kids everywhere.

0:20.0

To learn more or join the fan club,

0:22.1

head to butyKids.org slash donate.

0:25.0

Thanks and stay curious.

0:27.4

Music This is But Why a podcast for Curious Kids.

0:51.3

I'm Jane Lindholm.

0:52.3

And right now, I am actually standing on an overpass in Los Angeles, California.

0:58.0

Maybe you can hear the traffic behind me. I'm here in Los Angeles talking about traffic, partly because Los Angeles is known for traffic.

1:06.0

There are almost 8 million cars registered in Los Angeles County, which includes more than just the city.

1:14.6

There are only about 10 million people who live here, so that's a lot of cars.

1:19.6

And when you think about all the miles that people drive around this city and around this county every day, it's astronomical.

1:26.6

In fact, one of the most crowded highways

1:30.2

in the whole world is here. The 405 freeway, close to 400,000 vehicles go on it every single day,

1:39.1

and its congestion problems are pretty legendary. Some people call it Carmageddon when the cars are just stopped on the freeway.

1:46.0

Other times people say it's called the 405 because people can only go about four or

1:51.0

five miles per hour. Los Angeles has a lot of cars and a lot of drivers and

1:57.0

it's a good place to start our conversation today, which is all about traffic.

...

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