The TERM 2013 report by the European Environmental Agency (which can be downloaded at http://www.eea.europa.eu/publications/term-2013) analyses the effects on environment of the transport policies, considering the targets, the EU has established to reduce greenhouse gas emissions.
These targets are linked to policies set to promote public transportation and non-motorised mobility. It seems that emissions linked to mobility are smaller than the targets established for each year, a positive outcome; but overall emissions are still 25% over the 1990 levels used for targets. Urban pollution problems caused by nitrogen dioxide are relevant and growing due to the expansion of the share of diesel vehicles in the overall fleet.
The report confirms that the cities in which public transportation and non-motorised modes are strong have less pollution and produce less greenhouse gases.