Problems posed by the environmental impact of transport are serious, growing and constitute a major challenge to policy makers at all levels. The current array of technological, institutional and planning tools available to deal with these problems are inadequate and need urgently to be upgraded. A key feature of these problems is that they arise from the interaction of human behavioural systems and physical systems. Thus, to improve our understanding of environmental and health problems associated with vehicle emissions, it is necessary to combine data on both travel and traffic behaviour with environmental data. This requires simultaneous data on travel, traffic and environmental variables. There are currently no such integrated databases available in the United Kingdom, and the inability to collect self-consistent traffic, travel and environmental data is a major impediment to the development of the necessary scientific underpinning for effective policy interventions. This paper presents a high level description of a real-time global positioning system based vehicle performance and emissions monitoring system currently under development in the UK, to contribute to the realisation of the data requirements highlighted above.