Marchetti's Constant

Marchetti's Constant is a term for the average amount of time spent travelling 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.

Activist, consultant and author Peter Newman often makes reference to Marchetti's Constant in his arguments for sustainable urban planning and transport.

A related concept is that of Yakov Zahavi, who also noticed that people seem to have a constant 'travel time budget'. Zahavi's work is cited by David Metz in his book 'The Limits to Travel' (2008) published by Earthscan, London p. 8. Metz refers to the travel time budget as 'a stable daily amount of time that people make available for travel' (ibid). Metz cites data of average travel time in Britain drawn from the British National Travel Survey in support of Marchetti's and Zahavi's conclusions. This work casts doubt on the contention that investment in infrastructure saves travel time. Instead it appears from Metz's figures that people invest travel time saved in travelling a longer distance. The point is also made in a 2009 paper by Yves Crozet: 'Economic Development and the Role of Travel time: The key concept of accessibility' published in Commissioned Papers for the 4th International Future Urban Transport Conference of the Volvo Research and Educational Foundations, Gothenburg, Sweden, April 19-21 2009.

From http://en.wikipedia.org/