Using EU funding, the 'Carbon aware travel choices in the climate-friendly world of tomorrow' (CATCH) project developed an information system to encourage both the European public and decision makers to reduce the carbon dioxide (CO2) emissions produced by transport in cities. CATCH brought together representatives from global cities and organisations working in the transport sector. The first step was to assess how people react to information on climate change and different approaches to changing behaviour towards more sustainable transport options. The project team then developed a series of knowledge-based tools. These included an information system giving examples of successful sustainable urban transport systems and data on greenhouse gas (GHG) emissions in different regions. Users can navigate through the information with interactive and motivational visual tools that help them appreciate the effects of carbon from different transport choices. Using the CATCH tools enables comparisons to be made of the situation in different cities and the effects of possible policy measures. Partners from four European countries and Brazil and China worked together on the two-year project which ended in 2012.