In past years, researchers have suggested that it has to do with the way our bodies experience and measure time as it passes, or the way we remember the trips we take after the fact, or perhaps a bit of both. On Wednesday, a team in Japan released a new report in the journal PLOS ONE detailing the latest effort to solve the mystery. This group's take? That the return trip effect is created by travelers' memories of their journeys — and those memories alone.

What causes this so-called “return trip effect”? You might guess that it has something to do with knowing the route — on the way back, you see landmarks that help you better gauge when you’re close to your destination. Well, you’d be wrong! According to this study, the return trip effect (which makes the return trip seem 17-22% shorter on average!) is seen even when people take different routes on the outward and return trips.

Although changing expectations may play a role in the Return Trip Effect for unfamiliar destinations, when traveling on familiar roads these data suggest that lower levels of conscious engagement with driving is the likely reason for the subjective experience of shorter return trips.

Three studies confirm the existence of the return trip effect: The return trip often seems shorter than the initial trip, even though the distance traveled and the actual time spent traveling are identical. A pretest shows that people indeed experience a return trip effect regularly, and the effect was found on a bus trip (Study 1), a bicycle trip (Study 2), and when participants watched a video of someone else traveling (Study 3). The return trip effect also existed when another, equidistant route was taken on the return trip, showing that it is not familiarity with the route that causes this effect. Rather, it seems that a violation of expectations causes this effect.