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Does your journey to work break the limits of commuting?

No matter how much transport systems improve, the average time we spend commuting stays the same – it’s called Marchetti’s constant.

Nobody likes commuting – and with good reason. A 2014 study that looked at the well-being of commuters in the UK found that people’s happiness and overall sense of satisfaction with their lives decreased with each successive minute of travel.

What’s more, longer commutes correlate with higher blood pressure and obesity. Part of the problem is simply that more time travelling to work means less time for physical activity. But a report this year from the UK’s Royal Society of Public Health also found that commuters consumed 800 more calories a week thanks to extra food eaten in transit. The unpredictability of traffic or public transport also contributes to higher stress. 

Whatever tweaks city planners make to our transport options, the average one-way commute remains roughly 30 minutes

Yet, strangely, one variable seems to remain relatively stable. Wherever we are – and whatever tweaks city planners make to our transport options – the average one-way commute remains roughly 30 minutes. Known as Marchetti’s constant, after Italian physicist Cesare Marchetti, that time seems to be remarkably resilient to change. Only a handful of cities break the rule.

Marchetti’s idea is that people have a daily travel budget of around an hour that they choose to spend in different ways, picking transport options that fill up that time. If we live close to work, we might walk or cycle. If roads or public transport improve, we might move further away. But whether we drive, cycle, walk or take public transport we will spend roughly the same amount of time doing it.

Of course, the number is an average and there are outliers. But since putting forward the idea in 1994, using data that US transportation engineer Yacov Zahavi collected in the 50s and 60s, it has been backed up by several other studies. It also applies over time. A 2013 study comparing average commuting times in the US in 1980 and 2010 found that they had changed little in 30 years, despite enormous improvements to public transport. 

It also seems to apply around the world. In 2014 a team from the Senseable City Lab at the Massachusetts Institute of Technology used mobile phone data to compare commuting times in different countries. Again they found that times remained relatively constant despite people travelling different distances. 

For Marchetti, one hour is the basic limit for the total amount of travel that humans have been willing to put up with each day since the dawn of human society. He speculated that early humans travelling on foot at around 5km/h (3mph) would thus have a territory radius of 2.5km. To test the idea, he looked at the areas associated with individual villages in Greece – territories established over many centuries – and found that they tended to be roughly 5km across, supporting his claim.

If a 30-minute commute is all we will put up with, how big can cities get? 

Marchetti also projected his ideas forward. If a 30-minute commute is all we will put up with, how big can cities get? Big cities with large populations like London and New York – with average commuting times of 46 and 41 minutes, respectively – already seem to be pulling against Marchetti’s proposed limit.

In more densely populated cities, people also rely more on public transport. Our commuting maps below show that 30 minutes on public transport does not get you much further than 10km.  

Does that mean that so-called supercities – merged metropolises with populations in the tens of millions – are unlikely to emerge in the future? For Marchetti it all depends on how good our transport links get: “With Mach 7 airplanes and matching Maglevs, a world city is also possible,” he wrote.

The maps below show the area you can reach using public transport in each city starting from the centre and travelling for 30 minutes. The data comes from Mapnificent.

(Sources: US data from American Community Survey 2011-2015, London data from Transport Statistics Great Britain 2015, Paris data from L'Enquête Globale Transport 2010, Australian data from Australian Bureau of Infrastructure, Transport and Regional Economics 2012.)

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