Travel behaviour change research being conducted at Trinity College Dublin investigating techniques of encouraging sustainable travel in the Greater Dublin Area. Emissions produced from transport in Ireland, like in many other European countries, is a subject of mounting importance. This has sparked some states to employ radical measures to reverse harmful trends in emissions rising. In the European Union, transport alone has been found to account for 25% of all emissions emitted, on average. Furthermore, transport sector emissions in Ireland are projected to increase by 19% from 2013-2020 and 20% between 2020 and 2035. This is driven by an estimated increase in the national car fleet to 2.6 million in 2035, additionally as a result of a 3% growth rate in the economy to 2020 and 2025 (EPA, 2015; ESRI, 2016). These findings have diverted much attention and research funding to projects proposing and simulating methods for mitigating against a rise in emissions in Ireland, as well as promoting sustainability from a bottom-up perspective. Research being conducted at Trinity College Dublin’s Centre of Transport Research is examining the concept of ‘car-shedding’ and the range  of interventions it promotes as a means of encouraging sustainability in transport and ways to encourage sustainable behaviour change. ‘Car-shedding’ is the term given to the collection of measures applied to encourage and incentivise the usage of sustainable transport modes and, as a result, make usage of private vehicles less beneficial or more costly.

Greening Transport project research

The research is being undertaken as part of the Environmental Protection Agency-funded (EPA-funded) 'Greening Transport' project, with the vision of merging the technical evaluation of the emissions of transport (emission modelling), and the improvements in their calculation, with the behavioural changes needed to realise these reductions in emissions. Past attempts to measure the ‘low-hanging fruit’ in terms of emissions reductions from transport have failed to fully merge these two disciplines. The project team, which consists of representatives from industry, government and academia, believes that for the EPA to have a holistic picture of potential emission reductions that are possible in Ireland by 2030 (and beyond), it is vital not to ignore the behavioural constraints in which transport analysis is framed. The aim of this specific research is to apply approaches and concepts from the social sciences, namely behavioural economics and social psychology, in conjunction with transport engineering mechanisms to:
  • Better understand human travel behaviour in the context of transport mode choice, and
  • Investigate the propensity for the population of the Greater Dublin Area (GDA) to car-shed.
In doing so, we aim to provide a range of practical recommendations of how to successfully motivate sustainable travel behaviour change. To do this, the potential demand of alternative modes of transport will be estimated based on survey techniques, willingness to pay calculations and further modelling. The alternative modes that are being considered are: active modes (i.e. walking and cycling), public transport (bus, light and heavy rail), as well as smart modes (i.e. carpooling, car-sharing and on-demand/‘ridesourcing’ services such as Uber or Hailo). Commuter trips (from home to workplace/education) within the study region of the GDA are the focus of this study as congestion has been revealed to be worst when people are commuting between their workplace and home and, in this way, commuting remains the root cause of congestion, which is a growing problem at peak times in the GDA (Malodia and Singla, 2016). The main component of this work comprises of a stated preference experiment, which takes the form of a survey that presents respondents with several hypothetical scenarios incorporating a selection of policy packages. The rationale for this is to estimate the probability of a particular mode being chosen given a choice in a future scenario, and in doing so, the potential for a shift from one mode to another and the percentage share can be determined. The results of this will then be utilised to estimate potential emissions savings with reference to binding EU emissions targets for 2020 and 2030. The stated preference experiment will also be used to quantify the impact of a range of policy instruments to incentivise and encourage usage of more sustainable forms of transport, in addition to incorporating attitudinal questions with the help of certain heuristics in decision making to gather information on personal norms, behavioural control and habit formation (for more information on this: please refer to Tversky and Kahneman, 1974).

Car-shedding interventions

Car-shedding interventions seek to encourage the reassessment of the need to use and/or own a private vehicle and in this way, aim to reduce usage as a result through selling or ceasing ownership of a vehicle by substituting sustainable means of transport. In the Transport Strategy for the GDA 2016-2035, the National Transport Authority of Ireland stated that there will be an investment of over €100 million in sustainable transport measures in the GDA. This research alludes to ways in which such investment should be applied to achieve real behaviour change, and ultimately emissions savings. Interventions such as soft policy measures and market-based instruments have been proposed as the most effective means of achieving sustainable behaviour change, such tools have been similarly termed as Travel Demand Management (TDM) measures. Such measures involve the targeted promotion of public transport, walking, cycling and car-sharing as alternatives to single occupancy private car use. Car-shedding is becoming a growing trend in Ireland and internationally (particularly in the United States of America), as observed in the growing numbers of the younger population (between the ages of 17 and 30) delaying the uptake of driving licences and in such a way delaying ownership of a vehicle to later in life. As illustrated in Figure 1 below, in Ireland, Central Statistics Office figures delineate that from 2009 to 2014, there was a 19.8% fall in the number of people within the 17-29 age cohort holding a full driving license. It is also worth mentioning that during the same period, there was an overall increase of 4.8% in the number of new driving licences being issued. There have been many reasons cited for this trend, such as the rising costs of car ownership (insurance prices being a major deterrent), a growing sense of environmental guilt and health consciousness among younger people, more people delaying marriage and children as well as living longer with parents due to rising rental costs (Wall Street Journal, 2016; National Geographic, 2013; Forbes, 2012). A combination of such motivations lead to trends such as this, yet a growing selection of modern, alternative transport options being becoming available during this period has a large part to play, in addition to driving in some urban areas simply not being a practical form of transport. Those within this age bracket have been termed the ‘early adopters’ of new transport technologies and schemes that take attention away from owing a private auto out rightly and focusing attention of sharing assets and more intelligent means of mobility. These people are the essentially the test bed for innovative ideas such as bike and car-sharing, carpooling apps, on-demand or ‘ridesourcing’ services, which have had a ‘transformative impact on many global cities in enhancing transport accessibility while simultaneously reducing ownership of private vehicles’ (Shaheen & Chan, 2015). [caption id="attachment_34975" align="aligncenter" width="300"]Screen Shot 2017-03-08 at 15.30.00 CLICK TO ENLARGE Source: CSO Ireland Transport Omnibus[/caption]


Research as part of the Greening Transport project seeks to evaluate methods of increasing the propensity of other age groups in the GDA to adopt similar patterns of suppressing and postponing purchase of new vehicles and substituting mobility using other more sustainable options. Ultimately, this research tests a number of policy scenarios which incentivise and encourage use of ‘smart’ modes of transport, in order to spur a shift in the decision-making process of planning travel to a destination, as well as evaluating the most effective and publicly accepted policy action for councillors to take in the Greater Dublin Area. Author: Páraic Carroll, PhD researcher, Centre for Transport Research, Department of Civil, Structural and Environmental Engineering, Trinity College Dublin References: Brog, W., Erl, E., Mense, N. (2002) ‘Individualised Marketing: Changing travel behaviour for a better environment’. OECD Workshop: Environmentally Sustainable Transport, Berlin, pp. 1-21. EPA (2015) ‘Ireland’s Greenhouse Gas Emission Projections, 2014-2035’. Wexford: Environmental Protection Agency. ESRI (2016) ‘Outlook for the Irish Economy’. Dublin: Economic and Social Research Institute. Forbes (2012) ‘Why Generation Y sees no need to get behind the wheel’. Available at: [Accessed on: 29/12/16]. Malodia, S., Singla, H. (2016) A study of carpooling behaviour using a stated preference web survey in selected cities of India, Transportation Planning and Technology, Vol. 39, No. 5, pp. 538-550. National Geographic (2013) ‘US Teenagers are driving much less: 4 Theories About Why’. Available at: [Accessed on: 29/12/16]. Shaheen, S, Chan, N (2015) ‘Mobility and the Shared Economy: Impacts Synopsis. UC Berkeley: Transportation Sustainability Research Center. Tversky, A., Kahneman, D. (1974) Judgement under Uncertainty: Heuristics and Biases, Science, Vol. 185, Issue No. 4157, pp. 1124-1131. Wall Street Journal (2016) ‘Driving is losing its allure for more Americans’. Available at: [Accessed on: 29/12/16].