There is growing concern about the health and environmental impact of road transport on air quality. EU Air Quality Directives (in particular Directive 2008/50/EC on ambient air quality and cleaner air for Europe) require since 2005 limits for particulate matter (PM10) as these limits are s still being exceeded in a large number of cities. Directive 2008/50/EC foresees limits for smaller particulates and in 2010, limits for nitrogen-dioxide (NO2) also became binding. As a result, cities are urgently seeking more effective and efficient means of reducing air pollution. Transport is one of the most complicated and politically sensitive sectors for achieving these reductions, and yet is particularly important to those cities suffering from high particulate and NOx pollution. Although information on the impacts of many single new ‘clean’ technologies is available, the real-life results in combination with sustainable urban transport programmes can be quite different.