Much discussion has taken place in Auto/Oil-I, Auto/Oil-II and many other forums on how to achieve air quality targets in a scientific and cost-effective way. The basis is sound science, starting with a thorough understanding of the adverse health effects of air pollution and the establishment of robust air quality standards. Reliable modelling of future air quality—taking account of already agreed abatement measures—can then identify the remaining gaps and the pollutants to be addressed. With this approach, the possible ways of solving the problems can be determined by combining available measures in an optimum manner. Auto/Oil-I has been a good example of how to achieve the scientific basis for defining measures to meet air quality targets. Road transport has been the major area of possible improvements and engine/vehicle emission standards and fuel qualities were subsequently defined. With regard to fuel quality, the conclusions were based on an emissions test programme studying advanced engine technology and fuel properties. The programme not only showed the importance of vehicle technology and fuel quality on their own, but also demonstrated the importance of their interactions. A major outcome for current and future debate on both engine technology and fuel quality was that fuels and vehicle technology need to be developed together as a single system.