1. European Commission. State of the art on alternative fuels transport systems in the European Union; 2015.
2. European Environment Agency. The European environment – state and outlook 2015: synthesis report. Copenhagen; 2015, http://dx.doi.org/10.2800/944899.
3. European Union. Energy, transport and environment indicators. Luxembourg; 2014, http://dx.doi.org/10.2785/56625.
4. European Environment Agency. Air quality in Europe—2014 report. Copenhagen; 2015, http://dx.doi.org/10.2800/92843.
5. PBL Netherlands Environmental Assessment Agency. Trends in global CO2 emissions: 2013 Report. The Hague; 2013.