Reduce emissions of oxides of nitrogen (Nox) from the exhaust of diesel engine motor vehicles, the Selective Catalytic Reduction (SCR) emissions technology is the most acceptance solution. The additive, a 32.5% solution of high-purity urea in demineralised water that is clear, non-toxic and is safe to handle, is dosed into the SCR system at a rate equivalent to 3–5% of diesel consumption. The SCR systems are currently in use throughout Europe, in Japan, Australia, Hong Kong, Taiwan, Korea, New Zealand and Singapore. The United States Environmental Protection Agency's (US EPA) 2010 legislation will limit Nox to levels that will require North American trucks to be equipped with SCR post-2010.
Australia's vehicle emission standards are known as Australian Design Rules (ADRs). Australia has a commitment to harmonise with the vehicle standards developed by the UN Economic Commission for Europe, ADR 80/01 introduced Euro 4 emissions standards for heavy vehicles operating on petrol from 2005 and for heavy vehicles operating on diesel, LPG and NG from 2006. ADR 80/02 (Euro 4) was implemented for heavy vehicles which run on diesel, liquefied petroleum gas or natural gas from January 2007 for new model vehicles and from 29 February 2008 for existing models of vehicle. ADR 80/03 (Euro 5) will be implemented for new model heavy vehicles with a GVM greater than 3.5 tonnes, which run on diesel, liquefied petroleum gas, petrol or natural gas from 2010 and from 2011 for all heavy vehicles.