Travel behaviour dynamics: a mobility biography study towards change

Doctoral Thesis


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Travel demand management (TDM) strategies continue to receive 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 at the right time. 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. Also important is identifying the period within which commuters are deliberating and seeking information in order to change their mode of transport. Many studies have been conducted, in various contexts, to understand the dynamics of travel behaviour change. Some studies have argued travel behaviour to be rational, thus, an individual engage in active deliberation whenever there is a mode use choice decision problem. These studies suggest variability in travel patterns. Other studies have argued travel behaviour to be habitual in nature and characterised by non-deliberative repetition travel decisions. They argued that deliberate reappraisal of travel choices generally occur when triggered by 'key life course events’ or 'life shocks’. Such habitual behaviour suggests fairly stable travel patterns in a city’s transport network. The process through which the individual goes through in making a mode use change decision when triggered by 'key life course events’ however remain largely unexplored. This study, through the use of a qualitative mobility biography survey, firstly investigated the proposition that commuters in Cape Town engage for long periods of time in non-deliberative habitual mode choice behaviour while exhibiting considerable levels of intra-personal variability. These nondeliberative habitual mode use choice behaviours were posited to change when infrequent key life course events or incidents induce deliberation. Average duration between mode use changes among commuters was found to be about six years, confirming the habitual nature of mode use choice - especially among private vehicle users. Variations were, however, found in other attributes of travel choices such as departure time and route choice. Changes in mode use were observed to be in all directions, with the net change over the long-term being from public to private transport - an indication of 'asymmetric churn’. Key life course events found to cause mode use changes included changes in employment, changes in residential location and car ownership. The study then investigated the process a commuter goes through in making mode use changes when experiencing one of these three major life course events. The time when commuters start to deliberate on mode use change and seek information was investigated. Commuters were found to start deliberating on mode use changes and seek information about thirty and twenty-five days before the life course event occurs respectively and stopped about a day after. Information sought after during deliberation included; operational cost, comfort, travel time, convenience of mode use and safety. Commuters, however thought more about what they would gain by changing mode rather than what they would lose. The study concludes by recommending travel demand management strategies to be targeted at commuters that are about to experience a life course event and not after, as it may be too late. Information aimed at changing mode use choices from private to public transport should lay emphasis on what commuters would gain by changing to public transport rather than what they would lose. Information such as travel cost, travel time, convenience, safety, environmental and health impacts may be included in the design of information packs.