How long is your daily commute? Is it tolerable? Studies on happiness have found that commuting is one of our least favorite activities and research has found that having a longer commute negatively affects our overall happiness.

Marchetti’s Constant

In 1994, Italian physicist Cesare Marchetti formulated a theory based on historical data that people can tolerate about an hour of travel/commuting a day. He found this to be true throughout history. This theory is now known as Marchetti’s Constant.

Marchetti’s Constant posits that ancient humans spent about the same time in daily travel as well as modern office workers. Similarly, workers located in rural areas spend about an hour traveling each day as do residents of large cities. Poor people, rich people, professionals, laborers – in general, will spend up to one hour a day commuting, to his paper here.

Does this theory seem crazy? Not when you consider that humans have to balance the time they spend traveling place-to-place against the amount of time they have available to actually work (produce food/make money) and interact with family and friends. In other words, we have a “time budget” and out of twenty-four hours, we’re generally only willing to spend so long in transit time. That amount is about an hour. While commuting time does vary (we all don’t spend an hour a day commuting), the average time spent commuting in the U.S. is 50 minutes a day (25 minutes each way).

City Size and Commuting Time

Historically, the theory is supported by the size of ancient cities. Marchetti noted that the in walking speed is about 5 km/hr and thus ancient cities typically are only in 2.5km across. “There are no city walls of large, ancient cities (up to 1800), be it Rome or Persepolis, which have a diameter greater than 5km or a 2.5km radius. Even Venice today, still a pedestrian city, has exactly 5km as the maximum dimension of the connected center.” As transportation speeds have increased, so has the size of cities, but the core size of cities reflect the ability to limit travel time to one hour based on current transportation technology.

Very interesting related IFOD on how walking speeds vary with city size: Zipf’s Law , City Size and Walking Speed

Some Interesting Aspects to Marchetti’s Constant

Marchetti’s constant has some very interesting aspects to it.

First, as transportation speeds have increased with technology and infrastructure, humans have generally taken advantage of technological changes by moving farther away. Studies show that as U.S. cities have grown in size, commute times have remained pretty constant at just under a half hour each way. If we end up having hyperloop (super fast) trains, we may just choose to live far away from the city-center rather than shortening our commute.

A study by MIT using cell phone data found that “travel time is largely independent of distance” in various regions studied around the globe. This means “no matter how close people lived to work in these places, they managed to spend about the same time getting there.” According to the MIT researchers, people “adopt their lifestyles (e.g. commute behaviors) in a way so that they spend a reasonable amount of time of their lives commuting.” The MIT study did find that in some countries travel time was longer than an hour a day, but that it was generally constant within the country.

Second, the type of travel matters. Walking, riding a horse, driving a car, or riding a scooter require the active attention of the commuter. Some forms of public transportation allow the commuter to focus on activities other than commuting such as working, reading, watching TV, or talking or texting with friends and family. The ability to engage in productive activities likely increases the amount of tolerable commute time.

Third, the Marchetti Constant provides an interesting perspective on the second order effects of new transportation technology such as motorized scooters and self-driving cars. If self-driving cars will reduce travel times, as they are predicted to do, and if they allow riders to focus on activities other than commuting, which they should, then Marchetti’s constant suggests that self-driving cars will result in more city sprawl. A similar result may occur to the extent that motorized scooters replace walking.

Fourth, what about those of us with shorter commutes? My daily commute is about five minutes. What do I do with my extra 50 minutes a day? According to Geoffrey West, writing in his book Scale, “even if an individual’s daily commute time is less than an hour, then he or she instinctively makes up for it by other activities such as a daily constitutional walk or jog. In support of this Marchetti wryly remarked, ‘Even people in prison for a life sentence, having nothing to do and nowhere to go, walk around for one hour a day, in the open.'” Interesting concept. I do walk or run my dog about 45 minutes each morning.