Researchers Shinichi Watanabe, Katsufumi Sato, Paul J. Ponganis recently published an article (see here) on “Activity Time Budget during Foraging Trips of Emperor Penguins.” Other articles have been published on the daily time budgets of different animals (see for example here). The question then is, if animals have time budgets, do humans have them as well?
In transportation studies there is a theory of constant travel time budgets; but there are also articles which both support it and which are against it.
What it is
People throughout the world tend to spend about the same amount of time on travel, averaging about 1.2 hours per day (Schafer, 2000). After all, there are only so many hours in a day, part of which is devoted to sleep, work and other personal activities. As a result, people tend to adapt their lives to their accessibility. For example, when a person first obtains a bicycle or automobile, they don’t usually simply travel faster to the same destinations, they usually spend about the same amount of time traveling to more distant destinations. Conversely, if your accessibility improves, for example, if several stores open near your home, you may visit them more frequently than if shopping trips require several miles of travel. As a result, travel time budgets tend to remain constant as mobility and land use accessibility change.
The concept is expressed by Marchetti’s constant. The Wikipedia page on this says “Even since Neolithic times, people have kept the time at which they travel per day the same, even though the distance may increase”. The same Wikipedia page refers to the work of Yakov Zahavi, who “also noticed that “people seem to have a constant ‘travel time budget’.
Other articles in favour of the concept of Travel Time Budgets
Thomas Longden (ref. 724 / 2012) says that Schafer and Victor (2000) noted that time use surveys and travel surveys tend to show travel budgets are approximately 1.1 hrs per person per day.
David Metz (ref. 725/ 2008) says “…. in the long run average travel time is conserved, implying that travellers take the benefit of improvements in the form of additional access to more distant destinations made possible by higher speeds”.
Arnulf Grübler (ref. 325 / 1990) in a very detailed work, says “Empirical evidence suggests that the time devoted by an individual (on average) to transportation appears to be close to an anthropological constant: it ranges from around 1 to 1.5 hours per day, both in rural-agricultural and in urban-industrial societies.”
Articles against the concept of Travel Time Budgets
Frank Milthorpe (ref. 723 / 2007) concludes
Analysis of the Sydney travel surveys have shown that there has been an increase in the average daily travel times in the period 1981 to 2005. This result is consistent with findings from North America and some European countries and in contrast to the findings in Great Britain.
Whilst the analysis and reporting of mean travel time is a convenient measure (….) it masks the considerable variation between individuals. We also suspect that there is considerable variation in the travel times of an individual on a day to day basis (and) from the analysis undertaken there is variation in the daily travel times between genders and age-groups.
Van Wee et al (ref.722 / 2002) say that “recent research suggests that during the past decades the average travel time of the Dutch population has increased”.
Mokhtarian and Chen (ref. 706 / 2003) conclude that
At the aggregate level, travel expenditures initially appear to have some stability (but also) At the disaggregate level, there is a high degree of variation in both travel time and money expenditures (Kirby, 1981). Even proponents of a constant travel time budget acknowledge this variation, which appears in aggregate studies as well. For example, Zahavi and Talvitie (1980, p. 18), after asserting “the inescapable conclusion that travel time and money budgets exist”, express the “belief that travel time and money budgets are not constant, but they are functions of several variables”
The overall conclusion we draw from these studies, then, is that the claim of the definitive existence of constant travel time and money budgets in time and space is not supported.
Maybe transportation studies researchers should team up with zoologists and other experts on animal behaviour to establish a basic concept of human behaviour patterns. At the moment my own feeling is still that there is substance to the idea of travel time budgets – which is one reason why I suspect that cost benefits from travel time savings are not real.
On this point the recent IBRD / World Bank publication by Robert Cervero (ref. 730 / 2011) is worth reading. For example the abstract includes this text:
“This paper challenges the widespread and often indiscriminant use of travel-time savings as a principal metric of economic benefits for evaluating urban transport projects. Time-budget theory and empirical evidence reveals that the benefits of a widened road or extended rail line often get expressed by more and longer trips to larger numbers of destinations and not by less time spent traveling”.
The photograph is from wikipedia / Stan Shebs (link)
325 – Grübler, Arnold “The rise and fall of infrastructures”, Physica-Verlag Heidelberg, 1990
706 – Mokhtarian and Chen, “TTB or Not TTB, that is the Question: A Review and Analysis of the Empirical Literature onTravel Time (and Money) Budgets” Paper submitted to Transportation Research, USA 2003
722 – Van Wee, Rietveld, Meurs, “A constant travel time budget? In search for explanation for an increase in average speed”, University of Amsterdam 2002
723 – Milthorpe, Frank , “Consistency in Daily Travel Time – An Empirical Assessment from Sydney Travel Surveys”, 30th Australasian Transport Research Forum, 2007
724 – Longden, Thomas , “Constant Travel Budgets and Kilometres: the impact of deviations on energy use and climate policy”, Fondazione Eni Enrico Mattei, 2012
725 – Metz, David “The myth of travel time saving”, Transport Reviews, Vol. 28, No. 3, 321–336, May 2008
730 – Cervero, Robert, “Beyond travel time savings”, IBRD / World Bank, Washington USA 2011