The STREAM study inventories the current environmental impact of all modes of freight and passenger transport and provides forecasts for 2010 and 2020, making due allowance for the influence of progressive emissions standards, specific technological innovations and alternative fuels. This makes STREAM an extremely comprehensive, up-to-date and accessible database of transport emissions. The main focus of the study is on emissions of the greenhouse gas CO2 and air pollutants like particulates and oxides of nitrogen and sulphur. What emerges from the data is that there is no such thing as ’the cleanest’ mode of transport. The scale level of the trip or transport movement is an important factor in performance, often even more so than the mode of transport as such. Logistical factors like occupancy and loading factors are also key. Technology likewise has a major influence. A new vehicle is thus four to ten times cleaner than one dating from the early 1990s. For rail and (inland) shipping, too, there are technologies available with which considerable reductions in air pollutant emissions can be achieved. As yet, technology is having far less influence on fuel consumption. With a hybrid drive, for example, only 20% fuel savings can be achieved and this technology only makes sense in urban traffic, with a lot of ‘start/stop’ driving. For a series of well-defined market segments the report also compares emis-sions per unit performance based on average vehicle technology (as reflected in average age, for example) and average occupancy rate. The study was carried out by CE Delft for the Dutch Environment ministry, VROM, and the Transport ministry’s Institute for Transport Policy Analysis, KIM.