STEVE INSKEEP, host:
At some point on this Labor Day, millions of Americans will get in their cars or board a plane, get on a train, get on a bus, and head home from vacation. And when they get home, many of them will say to themselves, you know, that trip home seemed shorter than I expected. The so-called return trip effect is very real and psychologists have been trying to explain it. A new scientific paper suggests a possible answer, as NPR's Joe Palca reports.
JOE PALCA: The return trip effect isn't just limited to travelers here on Earth. Alan Bean was lunar module pilot on Apollo 12.
Mr. ALAN BEAN (Astronaut): Returning from the moon seemed much shorter, but I've always imagined it was because, you know, you're relaxed; you're not in a big hurry.
PALCA: Now, in actual fact, the trip back from the moon was shorter than the trip there - about 12 percent shorter. But Bean says, just like many other people, he's experienced the return trip effect here on earth. As for Bean's explanation, the idea that you're more relaxed, that's one possible answer.
But Niels van de Ven thinks something different is going on. Van de Ven is a psychologist at Tilburg University in the Netherlands. He says the accepted idea is the trip back seems shorter because its more familiar, so people recognize landmarks.
Mr. NIELS VAN DE VEN (Tilburg University Psychology Professor): And that might help to increase the feeling of speed, of how fast you travel.
PALCA: But that didn't seem right to him.
Mr. VAN DE VEN: When I take, for example, an airplane, I also have this feeling and I don't recognize anything on my way, of course. When I look out of the window, I don't see something I recognize.
PALCA: So, van de Ven decided to do some experiments exploring that feeling. One involved people who were riding their bikes to a fair. He asked each person to ride the same route to the fair, but for the ride back, he split people up. One group came back home by the exact same way. For the other group, he mapped out a different course, but one that was the exact same length. If familiarity was the right explanation, only the group traveling home by the same route should feel that the trip home was shorter. But when he did the experiment, he found the route didn't matter. Both groups had the same feeling that the return trip was shorter. Here's what van de Ven thinks is going on.
Mr. VAN DE VEN: Often we see that people are too optimistic when they start to travel.
PALCA: So, when they finish the outbound trip, they feel like it took longer than they expected. That feeling of pessimism carries over to when they're ready to return home.
Mr. VAN DE VEN: So, you start the return journey and you feel, wow, this is going to take a long time.
PALCA: But just as the initial optimism made the trip out feel longer than expected, this pessimism starting out makes the trip home feel shorter.
Mr. MICHAEL ROY (Elizabethtown College Psychology Professor): It's really all about you expectations. What you think coming in.
PALCA: Michael Roy is a psychologist at Elizabethtown College in Pennsylvania. He's a co-author with van de Ven on the article describing this effect in the journal Psychonomic Bulletin and Review. Roy doubts all psychologists will agree with their conclusion about expectation is an important cause of the trip home effect.
Mr. ROY: But it's also - we're not saying that this is the only cause. There are definitely likely other causes as well.
PALCA: In fact, there are psychologists who agree with lunar astronaut Alan Bean, that the trip home seems shorter because there's less pressure to reach the intended target on time. It's true the return home effect is just an illusion, and a better understanding of it might make it go away. But Niels van de Ven says that might not be such a good idea.
Mr. VAN DE VEN: In the end, this return trip effect gives you a positive feeling once you get home. So, I'm not sure whether you want it to go away.
PALCA: Of course, with screaming kids in the back seat or seemingly endless airport delays, no trip home is going to feel all that short.
Joe Palca, NPR News, Washington.