Aims

There are three conventions that we wish to challenge in light, particularly, of the opportunities that the information age is providing to undertake activities while travelling:

1. Travel time is unproductive 'lost' time:
When undertaking a journey in order to participate in an activity at an alternative location, an individual 'invests' time. Transport scheme appraisal in the UK has, since the 1960s, been based on an assumption that time spent travelling during the course of the working day is unproductive wasted time and therefore a loss to the economy. Time spent travelling at other times (including commuting) is costed according to an individual's willingness to trade time for money. Accordingly, travel time savings have usually been the principal financial benefit of a scheme - these have generally been taken to account for over 80 per cent of road scheme benefits [7]. This interpretation of the value of travel time has significantly shaped the current UK transport system [8].

2. Levels of mobility are constrained by a travel time budget:
There is historical global evidence to suggest that, at the aggregate level, "people spend somewhat more than one hour per day travelling, on average (travel time budget), despite widely differing transportation infrastructures, geographies, cultures, and per capita income levels" [9]. In other words, the time that individuals in society set aside for mobility seems finite, limited and broadly fixed, regardless of variations in many other factors. The travel time budget dictates that as the means of travel become faster, distance travelled will increase, or, conversely, that the need or desire to travel further will be accompanied by a requirement to develop faster modes of travel. If travel speeds have an upper limit, it follows that aggregate mobility levels (as measured by passenger kilometres) will also have an upper limit (although whether its distribution between members of a given society remains the same over time is less certain).

3. Travel time and activity time are discrete:
Applied travel demand modelling has traditionally followed a trip-based approach. More than 20 years ago an alternative approach became the subject of research. This is known as the activity-based approach because it is based on the idea that travel demand arises, or is derived, from the desire or need to participate in activities. "The development of the activity-based approach to travel demand analysis is characterized by a desire to understand the phenomenon of urban travel, not merely to develop predictive models that appear to produce acceptable forecasts" [10]. The activity-based approach holds the prospect of more realistic representation of patterns of travel in time and space. Nevertheless, this still treats travel time and activity time as separate albeit with assumed interdependencies.

Research Questions >

References

[7] IHT (1997). Transport in the Urban Environment. The Institution of Highways and Transportation.
[8] See Vigar, G. (2002) The Politics of Mobility. London: Spon
[9] Schafer, A. (1998). The Global Demand for Motorized Mobility. Transportation Research A, 32(6), 455-477.
[10] Pas, E.I. (1996). Recent Advances in Activity-Based Travel Demand Modelling. Proc. Activity-Based Travel Forecasting Conference, USDOT.