Marchetti’s Wall

One of the most fascinating random facts appears to be how the outer limits of cities are determined. In ancient times, it was a defendable region often served by a fortified castle on the high ground. As towns began to spread without reference to defensibility, one of the most significant factors was commuting time: “Marchetti's Constant is a term for the average amount of time spent traveling each day, which is approximately one and a half hours. Developed by Venetian physicist Cesare Marchetti, it posits that although forms of urban planning and transport may change, and although some live in villages and others in cities, people gradually adjust their lives to their conditions (including location of their homes relative to their workplace) such that the average travel time stays approximately constant. Even since Neolithic times, people have kept the time at which they travel per day the same, even though the distance may increase.” Wikipedia.

As transportation systems got better, through subways, busses and cars, the edge of cities could expand accordingly, but Marchetti found that there was an overwhelming resistance from commuters to the extent that their commute went beyond an hour in each direction, hence the “wall” in the above title. We don’t have enough statistical information to see if these assumptions apply in the hyper-growth cities in Asia, but we are seeing definite changes in Austral-Asia, North America and Europe, and the depletion of the world’s petroleum resources and expensive fossil fuel are placing increasing pressures on commuters… and hence on the growth potential of many cities. The July 5^th FastCompany.com notes: “Even oil companies admit that we are reaching peak oil--the point when the maximum rate of petroleum production is reached and begins to go into an unstoppable decline. But one thing would, at least somewhat, mitigate that problem. We may have also reached peak car usage in our major cities.

A study… from the Curtin University Sustainability Policy Institute says that many cities--including Vienna, Zurich, Atlanta, Los Angeles, and Houston--have already seen a decline in car usage between 1995 and 2005. Driving rates in the U.S. did, however, rise in 2010 by 0.7%...” There has been an increase in city center growth and a decline in the value of homes in outlying suburbs (even beyond the current collapse of home prices), a trend that seems to tell us much about future urban growth. As many European cities close off sections of major city centers and charge drivers high prices to drive into the main sections of towns, the pressure to live closer to work is rising rapidly, placing even more downward vectors on suburban homes. Indeed, the notion of cities rising up more than they grow sideways appears to be an unstoppable trend.

I’m Peter Dekom, and learning about why we actually do things can be damned interesting sometimes.