The use of private cars is responsible for a large amount of the world’s CO2 emissions and the amount of pollution produced by the aviation industry is also growing at an alarming rate. Thus, it is important to understand the factors that can lead to pro-environmental behaviours (PEB), such as choosing more environmentally friendly options for air and car travel. I explored whether the Theory of Planned Behaviour (TPB) variables of environmental attitudes, subjective norms, and perceived behavioural control (PBC) predicted individuals’ willingness to change their travel behaviour. A sample of 327 participants from New Zealand and the United States of America completed an online questionnaire measuring TPB variables for low-, medium- and high-cost behaviours which were defined as short, medium, and long trips by both car and plane. I hypothesised that, in line with the A-B-C model, the TBP variables would be most predictive of intentions to reduce the environmental impact of medium-cost behaviours, rather than low- or high-cost behaviours. Attitudes, subjective norms, and PBC almost always significantly predicted behavioural intention for the NZ sample, whilst only subjective norms and PBC were significant predictors for the USA sample, however, there was no support for the low-cost hypothesis or A-B-C model. Findings may influence and inform interventions and policy aimed at behavioural change in different contexts and that it may be beneficial for interventions to be tailored to specific populations based upon the strength of correlating variables.