Although the American historian and sociologist Lewis Mumford attributed the acute observation to the British mathematician and philosopher Bertrand Russell as early as 1934, it was the Italian physicist Cesare Marchetti, in his 1994 paper Anthropological Invariants in Travel Behaviour, who formulated the principle that today bears his name (although Marchetti himself attributes the finding to the Israeli transport analyst and engineer Yacov Zahavi). Be that as it may, this principle states that the average time a person spends each day commuting between home and work is one hour, or half an hour each way. This average commuting time in one direction, or “Marchetti’s constant“, is the same in cities before 1800 as it is today in modern cities.
According to data provided by the publication Quartz (taken from Marchetti’s article), before 1800, when people walked to work, the average diameter of European cities (including Rome, Venice and Berlin) was 5 km. If we take into account that most people cover a distance of 1.6 to 3.2 km when walking for 30 min, we can conclude that the time needed to walk the radius of these cities was quite close to Marchetti’s constant. Again, according to recent available data, the average commuting time in the United States is currently 27.6 min, 26.2 min in Canada or 29.5 min in the United Kingdom; in Europe, the average is 25 min, whilst in China (2015 data), the national average was 27 min,; on the other hand, in a Middle Eastern country like Dubai (as there is no overall data), the average travel time is 39.32 min (we should not forget that these data are averages, which implies some variability and, in any case, only show trends).
While Marchetti attributes the curious fact in his article to “the unity of travel instincts around the world, regardless of culture, race and religion”, other analysts attribute it to issues of consumption and economy of time. In any case, Marchetti’s constant explains the natural way in which urbanism and cities develop. Its validity, at least during the last two centuries, is explained by the fact that when a new means of transport appears that reduces travel time for its inhabitants, cities typically expand up to the limit at which this time becomes longer than 30 minutes. So, for example, trams and subways first allowed people to live in one neighbourhood and work in another. Subsequently, commuter trains, or cars and motorways, gradually increased the distance between suburban dwellings and city workplaces. And always, up to the limit of about 30 minutes each way.
As we can see, the Marchetti constant is a function of the efficiency (or speed) of the available means of transport, and the radius of the cities. We can therefore express mathematically (for purely playful and illustrative purposes), the principle underlying the so-called Marchetti constant (kM), as a function (f) of the radius of the city, or distance that people have to travel from their home to their workplace (r), and of the speed of travel that the means of transport available to them allow (v):
kM = f (r/v)
Today, with the rise of telecommuting and the resulting lack of commuting, the evolution of urban planning could take a different path. At the moment, according to recent studies, remote working has led to a shift in demand for real estate from dense inner-city business districts to less dense suburban neighbourhoods and rural areas. Sure that you, like us, are no stranger to news reports of the growing exodus towards villages thanks to teleworking. It will be interesting to follow developments.
