Do Mysterious Forces Dictate Our Travel Patterns?

Sure, studying transportation is important if you need to find the best route to the hardware store. But you might be surprised to know that transportation study might have other uses, like enlightening you about the most profound philosophical mysteries of the universe. For example, transportation might just tell us some surprising things about the degree to which we truly have free will.

We think we decide when, where, and how we journey, but despite our illusion of control it?s quite possible that we are in the grip of mysterious forces that dictate our travel patterns. Are we marionettes with travel pulling the strings?

A. Schafer and D.G. Victor published a paper in which they examined dozens of studies on how much time people spend traveling. The settings for these studies were quite different?including African villages and cities in communist Eastern Europe, as well as modern Latin American, Asian, Western European and American locales?but overall, travel times were surprisingly similar.

Virtually every study found that its region?s residents travel, on average, between about 45 minutes and 1.5 hours per day. The average for all regions was about 1.1 hours. Given that the technological endowments, political systems, cultures, religions, incomes, transportation systems and land use patterns of these places are quite different, the regularity in daily travel times might be viewed as pretty noteworthy.

Based on this it is tempting to speculate that there is some sort of innate Travel Time Budget (TTB) built into human beings. The TTB theory holds that the time we spend traveling is relatively fixed, leaving us with strikingly little ultimate control, appearances to the contrary.

Going even further, Yacov Zahavi (a pioneer of the TTB theory) and like-minded scholars maintain that people across times and cultures tend to spend a constant fraction of their money, as well as their time, on transportation. Schafer and Victor assembled data on the percentage of their expenditures that people from a range of rich-world societies devote to travel. Excluding the odd case of Japan (which featured an atypical amount of high-speed public transport, plus high price levels for other goods), the data points cluster pretty tightly in the range of 8 to 15 percent, again despite very different national situations. Score another point for determinism over free will.

Proponents of the TTB theory admit some factors do cause travel time and money budgets to vary. For example, residents of big cities spend more time traveling than others, and those with cars devote a larger share of their incomes to travel than those without them (hence the low expenditure rates for the developing countries). Still, though, proponents of TTB maintain that regularities in expenditures of both travel time and money outweigh the differences.

As when Einstein determined that the speed of light is fixed, which leads to the rest of nature having to resort to some bizarre tricks, fixing total travel time leads to odd fluctuations in other aspects of the transportation equation.

For example, what happens when those African villagers eventually buy cars and can make a journey to the market in only minutes when it used to take hours? According to TTB proponents, they do not apply the time savings to other activities, but instead devote them to other types of travel. More mobility leads to more frequent trips, and, especially, to trips that are longer in physical distance. Thus, those who acquire an auto may make a grocery shopping trip to a distant supermarket or warehouse club instead of to the neighborhood market on the corner.

What might account for stable transportation budgets? Well, for one, until we start colonizing other planets there are only 24 hours in the day. Take out time for all of the essential activities like sleeping, eating, working, grooming, child rearing, shopping for essentials, etc., and the residual which one can devote to travel obviously has an upper bound. Still, this does not explain the hypothesized lower bound, which is considerably more mysterious.

Cesare Marchetti has theorized that the travel time budget is the product of evolutionary pressures stretching far back into our pre-agriculture past. He sees the desire to travel as part and parcel of an instinct to expand our territory, with all of the tasty roots, berries and wooly mammoths that were the lives? ambitions of our distant ancestors.

However, territorial expansion was not without its costs; travel involved danger from god knows what crazy predators might be stalking out there, plus those pesky headhunters on the other side of the river. Also, travel is simply hard work. In addition, Marchetti maintains that man balanced wanderlust with a cave instinct; the urge to turn into a couch potato apparently far predated the invention of the couch or the discovery of the potato.

So Mother Nature is held to have settled on a rough balance between home and away, and to have programmed us with a primal travel urge to maximize our survival and the survival of those who are in one way or another responsible for the propagation of our genes.

Why is TTB important? In addition to its sheer freakworthiness, it might have considerable practical import. Schafer and Victor believe future travel patterns can be extrapolated using the TTB law.

So in all this is a great theory, which has but a single minor drawback: it might not be true. A favorite scholar of mine, Patricia L. Mokhtarian, and her colleague Cynthia Chen have carefully reviewed the evidence on the TTB. Their findings soon.


This fit nicely with the theory that early homonids evolved bipedalism because it gave them the advantage of being able to walk long distances at a steady pace without expending much energy. It wouldn't be much advantage to homebodies (cavebodies?)

Jeff Smith

My job used to be about a five minute drive from my house, which seemed like an incredible time-saver. But as soon as I got home from work, I'd go for an hour-long run or a bike ride. I own a treadmill, but I never use it, even when it's sub-zero outside, I'd still rather run around outdoors. For whatever reason, I feel stifled unless I spend about an hour each day out and about. This article shows that there's nothing unique about me.


Is there any practice someone *won't* try to claim is innate, or any unit of behavior so small that someone *won't* strive to attribute to a special "mental module"? So now there's some sort of "organ," even if only a conceptual organ, inside the human body that makes us travel at least 45 minutes each day? This hypothesized TTB has no evidence except the phenomenon it was invented expressly to explain.


It'd be informative to know how much divergence there is in the travel time numbers. If it was indeed something innate in humans, you'd expect most people to cluster close to the 1.5 hour TTB number. If it was merely an effect of statistics, you'd expect to see large numbers of homebodies who travel very little, and others who spend much time travelling.

Also, I have to wonder, what exactly counts as travel? Say I decide to spend a day hiking in the mountains: I might spend maybe an hour driving to & from the trailhead for 8 hours walking. Is that 8 hours part of my travel time budget, or my recreation/exercise budget? Or even simpler: in warmer seasons, I frequently ride a loop of about 20 miles, starting from home & returning. Exercise or travel?

Sujit Datta

Others have recently used cell phone data to map out human mobility patterns (see and, for example). Trajectories seem to be surprisingly predictable and surprisingly invariable from person to person, suggesting that there is indeed something intrinsic to our mobility patterns.

Michael Radosevich

It probably goes way back to our origins as hunters and gatherers. In hunter-gatherer societies, two hours was about the maximum time anyone would "work" in one day. If an area was so bereft of food and necessities that more than two hours were needed to obtain what was needed, the tribe would migrate to a richer area.

If you adjust for time spent munching berries or frolicking while hunting and gathering, the TTB would probably be the same for our ancestors as it is for us today.

The TTB - if spent walking - also approximates the exercise we need to maintain good health, which most physiologists place at about 45 minutes.


Why would a rational actor travel more than they need to after gaining some efficiency, unless they were unable to meet all of their needs before? I used to ride the bus and light rail for an hour each way to work. I recently moved to within 1/4 mile of a light rail station, and my commute has been reduced to 25 minutes each way. I must say that I am perfectly content spending the extra time with my wife and kids, and have no subconcious desire to hop in the car for no reason when I get home.

The duration of a trip is decided by the distance between the departure and destination points, the mode chosen for travel, the speed which is applied to that mode, and several exogenous factors like traffic and weather. The purpose of the trip, however, is much more difficult to put into a model, and usually has something to do with a percieved benefit from the trip. If a person has basically everything that he needs, how can we assume that he will automatically need more once he can obtain his necessities in less time? Wouldn't there be a threshold based on the amount of trips that he was putting off before because of time constraints?



Seems a variant of Parkinson's expands to fill the time available for its completion. More seriously, you will find the study of the variance more interesting than the mean; particularly at the lower (segmented) quintiles.


So, if technology permits people to do something else productive while traveling (like working on a laptop while riding a commuter train), do our brains count it as travel time or not?

I have a hypothesis that small children have a smaller travel budget than adults, and their brains have a hard time dealing with exceeding that limit, which is generally reached about 15 minutes into a typical road trip.


Re #5: "Others have recently used cell phone data to map out human mobility patterns..."

The full articles are paywalled, alas. However, I'd point out the perhaps obvious: they're not mapping the mobility patterns of humans, but of the subset who are cell phone owners. And even that subset is only measured during periods when they're carrying their cell phones.

Joshua Northey

I bike to work every day and the total time each day for my commute is about .9-1.4 hours (the wind makes a huge difference as it is MN and I am bundled up).



Thank you for defining "hypothesis". It is, indeed, an idea trying to explain the phenomenon of consistent travel times. Now it's on to find evidence to prove or disprove it. That's how science works.


I've been curious as to the answer to this for a while. If a woman keeps her last name when she is married, is she more or less likely to become divorced? Intuitively, I feel that a couple with the same last name would have a stronger bond. However, I have no empirical evidence to support this view.