Kai Ryssdal: Time now for a little Freakonomics Radio. It's that moment every couple of weeks where we talk to Stephen Dubner, the co-author of the books and the blog of the same name. It is the hidden side of everything. Dubner, welcome back.
Stephen Dubner: Hey, thanks Kai. You in a quiz mood today?
Ryssdal: You know how I feel about that, but OK if I have to.
Dubner: All right. You love them. All right here we go. I was in California not so long ago. I saw someone doing something that I hadn't seen in a good while, even though I used to see it a lot. In fact, I used to do it myself out of necessity during college. What was it that I saw?
Ryssdal: Um, I don't know. We do a lot of things out here, man. I don't know.
Dubner: The answer is hitchhiking. I saw two guys, thumbs out. This was in Half Moon Bay.
Ryssdal: See I was in Tahoe two weeks ago -- hitchhikers all over the place.
Dubner: You're kidding. Well, I never see them anymore, at least on the East Coast here. And it got me to thinking: Where did all those hitchhikers go?
Ryssdal: Oh, I know the answer to that. When my mother cautioned me against hitchhiking when I was a kid, she said almost literally, 'I will kill you with my bare hands before I let you hitchhike.' Truly.
Dubner: Because it's too dangerous, right?
Dubner: Well that's what my Freakonomics co-author Steve Levitt thinks to some degree. The fear that an axe murderer out there creates the perception that this thing is a very dangerous thing to do. And in the hands of an alarmist media, even a few violent incidents can go a really long way.
Steve Levitt: If even anybody thought there were homicidal maniacs who were killing hitchhikers or hitchhikers killing people to pick them up, then certainly that would have the kind of chilling effect on a market that very few things could have.
Ryssdal: So, I mean there are some homicidal maniacs, but there must be some rational explanation for why people aren't hitchhiking. Right?
Dubner: In fact, the explanation we've come up is good, old-fashioned supply and demand. I talked to a transportation consultant named Alan Pisarsk, who says the demand for hitchhiking fell as more people learned how to drive, especially as more women got driver's licenses starting in the 1970s.
Alan Pisarsk: If you look at the distributions today, men and women in terms of drivers licensing is almost identical and almost ubiquitous. It's in the 92-93 percentile.
And probably more important, car ownership has just gone through the roof. And cars last longer, too. So Kai, what do you think the average lifespan of a car was 40 years ago?
Ryssdal: Uh, forty years ago? I'm going to say 12.36 years.
Dubner: That's a great guess, but five years. Here's Pisarski again.
Pisarski: Back in the '60s, cars did not last all that long. Today, the average age of a vehicle in America is north of nine years. I came down to the studio in a 14-year-old car.
Ryssdal: Yeah, just went over 150,000 miles on the Ryssdal family minivan. So yeah.
Dubner: There you go. A hundred used to be a big milestone, right? Now we do it routinely. Now there are other reasons why hitchhiking has died off: The growth of the interstate system really changed the way we get around, airline deregulation, which lowered airline ticket prices.
Ryssdal: But hit me with the why I care thing here, Dubner. I mean, other than the curiosity of seeing hitchhikers on the road in Tahoe.
Dubner: Well, I'll tell you this. If you care even a little bit about transportation, about cost and congestion and accident risk, carbon emissions, all of that, you've got to be depressed to learn the following thing -- about 80 percent of all passenger-vehicle capacity in this country goes unused.
Ryssdal: Wow. That's crazy.
Dubner: Eighty percent. We are driving around with seats without people in them. So Kai, next time you're out tooling around in your minivan, I want you to forget your mother's warning and pick up a couple of strangers, all right?
Ryssdal: OK. So first of all, I can't do that because it's not safe because my mother told me it wasn't. And also, my mother's listening to this, so there's no way.
Dubner: Your only valid excuse is if you've got your mother in the backseat, then you've got a valid excuse. Otherwise, pick up the hitchhikers.
Ryssdal: Stephen Dubner, FreakonmicsRadio.com, see ya.
Dubner: My pleasure.
Ryssdal: It's true. I'm going to hear from my mother about this. I promise you.