| dc.description.abstract | This doctoral research examines the behavioural response of commuters within the Greater Dublin Area (GDA), Ireland, to a range of policy incentives devised to encourage travellers to make greater usage of sustainable travel modes for work and education trips. Several policy measures were evaluated using discrete choice and four stage modelling techniques, to identify a means of stimulating a shift from single occupancy vehicle (SOV) use to alternative modes such as walking, cycling, public transport and more sustainable use of the private car, namely carpooling and car-sharing. Such policy tools were utilised to increase potential levels of car-shedding behaviour in the GDA by increasing the likelihood of sustainable mode choice, through making alternative modes more time and cost efficient, safer and ultimately more convenient to use when commuting than private cars. The research presented in this thesis coins the term of car-shedding, which is defined as the incidence of a reduction in private car trips, by means of encouraging the reassessment of the need to utilise a private car for certain trip purposes (Carroll, et al., 2017). In this way, the potential of reducing utility of private vehicles through shedding of single occupancy vehicle trips in exchange for more sustainable means of transport is stimulated exclusively through the incentivisation of alternative modes rather than disincentivising private car use.
A stated preference survey (SP) was employed as the instrument for gathering mode choices and socio-demographic data of a sample of commuters in the GDA, based on a number of hypothetically designed choice scenarios incorporating policy incentives. In this experiment respondents were asked to make a trade-off between the trip characteristics of three modes, one of which being a private car or status quo option (i.e. bus, rail and car). The SP results from this survey were then fed into a multinomial logit (MNL) model to generate likelihood estimates of certain modes being chosen given the introduction of particular policy measures. In addition to this, a range of behavioural indicators were elicited from analysing the output of market elasticities and simulation models from discrete choice modelling. Notable results generated from this analysis determined that policy incentives offering tangible time and cost savings in particular, led to the greatest shift towards sustainable modes across the attributes modelled. The findings showed that reductions in the modal share of SOVs of up to 8% in a Do Maximum scenario could be achieved if policies are put in place to reduce the time and cost attributes of commuting to work by alternative modes. Furthermore, in relation to sustainable car use, a 1% change in the convenience, time and cost attributes yielded a direct elasticity or increase in the probability of carpooling and car-sharing being chosen, of up to 0.34%, suggesting that the carpool and car-share modes may be relatively elastic to such trip characteristic changes.
Extensive four stage modelling work was subsequently conducted using National Transport Authority s (NTA) Regional Modelling System (RMS) to represent the policy changes explored in the SP experiment in order to produce real life estimates of trip making behaviour. Changes to model parameters in the mode choice and trip assignment stages of the Eastern Regional Model (ERM) (covering the Greater Dublin Area) were made to account for improvements made to infrastructure, frequency, time and cost attributes of various modes included in the model. The changes were made based on Do Nothing/ Base , Do Something , and Do Maximum scenarios, which were designed based on attribute level values from the SP survey. The outputs generated from these model scenarios determined that pedestrians in the GDA were more sensitive to parameter changes made in ERM than the other modes tested. This was highlighted in the active modes and the optimal car-shedding model results, where walking experienced the largest and, in some cases, the only increase in mode share as a result of the policy implementation. In addition to this, daily CO2, NOx and PM2.5 emission reductions were estimated from changes recorded in vehicle kilometres travelled of private cars. The associated monetary savings from these reductions were similarly estimated, which determined that up to 5,705 from CO2 reductions, up to 5,499.94 from NOx reductions and up to 9,010 from PM2.5 reductions, could be saved from daily commute trips.
Overall, the results produced in this thesis research suggest that policy incentives alone, leading to tangible improvements to commuters time and cost trip characteristics can act as effective mechanisms in encouraging car-shedding behaviour or a sustainable mode shift in the GDA. The empirical results explored in this thesis supports this hypothesis which may present valuable guidance and recommendations for policymakers that are pursuing methods of reducing the environmental consequences of emissions from transport in Ireland as a matter of urgency. | en |
