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The magic one-hour travel limit

Following somewhat from the discussion on slow transit and travel times, I coincidentally happened to read a paper today that sheds some light onto the ‘magic one hour limit’. This idea that people are willing to travel up to an hour each way to work is more or less considered a fact in transport planning literature, but why is this so, and has it always been that way?

The paper I read was entitled “Anthropological Invariants in Travel Behaviour”, written by an anthropologist named Marchetti almost two decades ago. Marchetti claims that travel patterns are determined by basic animal instincts, innate behaviours of survival and prosperity-seeking that have remained constant across aeons of technological development.

According to him there are two competing instincts that influence travel behaviours: the first is the instinct for territorial animals such as humans to strive to increase their territory. This in order to maximise access to resources and expand the powerbase, a strategy that promotes long term survival and prosperity. The second instinct is the drive to limit exposure to hostile forces and remain within easy reach of a defensible ‘nest’ such as a cave, or in modern terms, a house. This strategy promotes short term survival and the maintenance of existing resources.

So what does this mean? Well according to Marchetti the trade off between these two instincts results in people feeling the need to travel on a daily basis, but not wanting to stray more than one hour travel time from home. So there we have it: commuting an hour each day to hunt, gather or otherwise work for a living is a basic survival instinct we’ve had since we were cavemen.

This concept suggests that settlements will naturally spread up to one hours travel across, much more than that and our animal instincts fall out of balance. People can typically walk around 5km per hour across good terrain, so back in the days when travel was almost exclusively by foot functional cities could only be approximately 5km across. Marchetti claims this is exactly how big they got, apparently ancient walled cities were almost all 5km across while the core of the modern day walking city of Venice is the same size. With the introduction of horse travel, railways, cars and then airplanes, the distance one can travel in an hour has successively increased. With the car and motorways people can live their lives in a city a hundred kilometres across, as we see in Auckland and other places today. For people that commute via air shuttle or high speed rail, their ‘home town’ becomes three or four hundred kilometres across. Indeed the Paris commuter belt now extends from the Belgian border half way to the Pyrenees thanks to the TGV network.

One interesting thing to consider is that when travel distance increases linearly, the area accessible increases exponentially. For example, the 5km wide one-hour-walking city covers around 20km2 (about the area from Ponsonby to Parnell) the 100km wide one-hour-driving city covers 7,800km2 (about the size of the greater Auckland region) while the 300km wide one-hour-by-high-speed-rail city could cover a staggering 70,600km2 (about the size of Ireland!).

The one-hour city by foot…                                                                                          and by car.

This leads to the question, do we need to live our day to day lives over such a great distance, what are the pros and cons of having such a great area within one hours’ travel?

The arguments against are much the same as the arguments against sprawl. Things like the waste of energy and resources spent travelling such great distances, the huge expense on infrastructure and the consumption of natural environments or productive rural land for urban uses. The arguments for are largely from the economic sector, suggestions that a city covering a larger area can have a much larger population as part of the single economic unit. This give people greater access to jobs and services, while conversely businesses have a wider pool of labour from which to select the most appropriate staff. Furthermore there are economies of scale to be had with large cities giving them a competitive edge in the global marketplace, and wider cities mean more people without super cramped conditions.

Marchetti raises the prospect that once 500km/h+ maglev technologies are deployed in regular usage conurbations will become immense, with places like the Tokyo-Osaka corridor functioning as a single city of over 100 million people. The prospects of a city that size are both terrifying and amazing at the same time.

7 comments to The magic one-hour travel limit

  • I was recently looking at a map of 1870s Auckland and it’s boundary almost exactly matched the limits of the first green circle you’ve drawn there…

  • David

    Surely you don’t need to be able to get right across the city in an hour, just far enough so that you can meet anyone who lives in the city. That would suggest that the radius of a walking city is 5km, not the diameter as you are suggesting here. If you can go an hour from home, then your walking range is described by a circle with house at the centre and a radius of 5km and area of about 75km2. Also, as speeds increase, the area of the city increases quadratically not exponentially (quadratically means x^2, exponentially means 2^x). end pedantry.

  • I’d suggest it is part of the instinct, you have to be able to get to any part of your “territory” to defend it or take advantage of opportunities within 1 hour…

  • Al

    Excellent discussion. I think there is some validity in this principle and its assumptions, as well as lessons for us. Of course the critical element now for cities is that the 1 hour circle is shrinking! Just because we can notionally drive at 100km/h doesn’t meant the hour circle should be 100km out. As more people live in this notional circle, the speed we can all achieve goes down, and consequently the circle reduces in size. Auckland is experiencing this. It would be interesting to draw a “1 hour” ring based on current travel times.
    The problem for cities then becomes trying to maintain the “hour” for those who once had this privelige and expect to maintain it. Thus the arguement for more roads – not necessarily to reduce travel time, but to maintain (or more accurately “restore”) their 1 hour travel. But of course we know that that is impossible. Ultimately we cannot keep building roads to maintain this travel time – there is a finite limit to the size of roads through existing cities. So we then look for alternatives to maintain the hour – e.g. trains / trams / busways. But places will explore these only when they realise they cannot widen the roads any further e.g. North Shore busway. Unfortunately it seems that rather than jumping to obvious solutions, we have to wait until we have explored all the road widening possible first! and of course the situation is complicated in dispersed polycentric cities like Auckland where many people’s journeys are not to the CBD. So they still maybe within an hour of their destination.

  • Nick R

    Jeremy, no surprises there. In the 1870s walking was the only way to get around Auckland so the (uni-centric) urban area would be constrained to a reasonable walk time away from the sole location of employment at the wharves/downtown.

    Thanks for the clarification in terms David, I’m not much of a mathmatician!
    On the topic of whether it should be a 5km radius or a 5km diameter, the issue is perhaps a little confusing and one I was a bit puzzled over myself.
    It was Marchetti’s suggestion that one should use the diameter (or rather twice the radius), as people need to get out and back to the ‘nest’ within the hour, which also translates to being able to get anywhere in the city within an hour. However with commutes people seem happy to go one hour each way, perhaps because we see the workplace as a second nest?

    Why the ‘magic’ time limit is one hour and not some other length of time isn’t really discussed, except for the suggestion that one hour is the sweet spot between the two opposing instincts.

    Good point about the shrinking real travel times Al, I guess this is just further evidence that transport improvements (particularly freeways) tend not to actually save people travel time but rather allow them to travel further in the same amount of time.

  • There’s an interesting book by highly regarded UK transport academic David Metz on this topic.

  • Al

    “I guess this is just further evidence that transport improvements (particularly freeways) tend not to actually save people travel time but rather allow them to travel further in the same amount of time.”
    …..or maybe to allow MORE people to travel the SAME distance in the SAME time (as they have been used to). But this cannot continue and fails to tackle the underlying problem.

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