to reduce car trips for commute to achieve the minimum recommended physical activity levels of 30 minutes per day. Other intervention studies using TTM aim to encourage sustainable behaviour. By reducing single occupied motor vehicle and replacing them with so called sustainable transport (public transport, car pooling, biking or walking), greenhouse gas emissions can be reduced considerably. A reduction in the number of cars on our roads solves other problems such as congestion, traffic noise and traffic accidents. By combining health and environment related purposes, the message becomes stronger. Additionally, by emphasising personal health, physical activity or even direct economic impact, people see a direct result from their changed behaviour, while saving the environment is a more general and effects are not directly noticeable. Different outcome measures were used to assess the effectiveness of the intervention. Health-centred intervention studies measured BMI, weight, waist circumference as well as general health. However, only one of three found a significant change in general health, while BMI and other measures had no effect. Measures that are associated with both health and sustainability were more common. Effects were reported as number of car trips, distance travelled, main mode share etc. Results varied due to greatly differing approaches. In general, car use could be reduced between 6% and 55%, while use of the alternative mode (walking, biking and/or public transport) increased between 11% and 150%. These results indicate a shift to action or maintenance stage, some researchers investigated attitude shifts such as the willingness to change. Attitudes towards using alternative modes improved with approximately 20% to 70%. Many of the intervention studies did not clearly differentiate between the five stages, but categorised participants in pre-action and action stage. This approach makes it difficult to assess the effects per stage. Also, interventions included different processes of change; in many cases these processes are not matched to the recommended stage. It highlights the need to develop a standardised approach for travel intervention design. Identifying and assessing which processes are most effective in the context of travel behaviour change should be a priority in the future in order to secure the role of TTM in travel behaviour research. Criticisms The TTM has been called "arguably the dominant model of health behaviour change, having received unprecedented research attention, yet it has simultaneously attracted criticism". Depending on the field of application (e.g. smoking cessation, substance abuse, condom use, diabetes treatment, obesity