E Adjei and Prof R Behrens – Centre for Transport Studies, Department of Civil Engineering, University of Cape Town,
Travel demand management (TDM) strategies have received much attention in recent years as a means of managing congestion in cities and promoting more sustainable transport systems. Most TDM measures focus on effecting travel behaviour change amongst commuters. Clearly such measures are likely to have the greatest impact when targeted at commuters most receptive to changing their travel behaviour. The study of commuters in order to understand their travel behaviour patterns, when they are most open to change and what causes them to change, is therefore imperative in drawing up effective TDM strategies.
Many studies have been conducted, in various contexts, to understand the dynamics of travel behaviour change. Some studies have revealed that travel behaviour is habitual in nature and characterised by non-deliberative repetition of travel decisions, and that deliberate reappraisal of travel choices generally only occurs when triggered by ‘key events’ or ‘life shocks’. Such habitual behaviour would suggest fairly stable travel patterns in a city’s transport network, punctuated by occasional disaggregate change stimulated by infrequent events or shocks that alter individual trip decision-making processes. Other studies have revealed that personal travel decisions can be variable, and not as routine as studies revealing habit might suggest. These studies suggest that underlying travel patterns observed in a city’s transport network, that may in aggregated observations appear fairly stable (in terms of system utilisation), are ‘churning’ reciprocal individual changes in travel decisions.
This paper seeks to find evidence for the extent of variability observed in various attributes of travel choice making – departure and arrival times, route choices and mode use choices. In the absence of panel or repeated cross-section data on commuting behaviour in Cape Town, a (n=68) qualitative retrospective survey was administered to examine behavioural dynamics over extended periods of time. The reliability of this survey depends on the ability of respondents to accurately recollect past events. Recall aids in the form of ‘life and commuting history calendars’ were used to enhance the reliability of data. A two week self-completion commuting diary was also employed to gain insight into the day-to-day variability of personal travel decisions.
The paper posits that habitual patterns of behaviour apply more to mode choice and switching, and that intra-personal variability applies more to changes of timing and routing behaviour within a particular mode use domain. The paper concludes with a discussion on the implications of the mobility biography findings for TDM strategy formulation.