Reducing emissions from diesel engines is one of the most important air quality challenges facing the country. Building on the successes of EPA's regulatory and voluntary efforts to reduce emissions from diesel engines, EPA has created the National Clean Diesel Campaign (NCDC). The Campaign will work aggressively to reduce the pollution emitted from diesel engines across the country through the implementation of varied control strategies and the aggressive involvement of national, state, and local partners.

NCDC participants are committed to reducing diesel emissions and finding innovative ways to protect human health and the environment. To fully address the challenges of reducing diesel emissions the NCDC is using a multi-pronged approach:

- Commitment to the successful implementation of the 2007 Highway Engine Rule and the Clean Air Nonroad Diesel Rule.
- Developing new emissions standards for locomotive and marine diesel engines.
- Promoting the reduction of emissions for existing diesel engines through cost-effective and innovative strategies, including use of cleaner fuels, retrofitting and repairing existing fleets, idling reduction among others.

Clean ultra-low sulfur diesel fuel will be required for use in highway diesel engines starting in 2006. Lower sulfur diesel fuel for nonroad diesel engines will be required in 2007, followed by ultra-low sulfur fuel for these machines in 2010, and for locomotives and marine engines in 2012. Low sulfur diesel fuel is already available in some areas of the country.

Besides reducing emissions from the existing diesel fleet, these clean fuels will enable the use of advanced aftertreatment technologies on new engines. Technologies like particulate traps, capable of emission reductions of 90% and more, will be required under new standards set to begin phasing into the highway sector in 2007, and into the nonroad sector in 2011. These programs will yield enormous long-term benefits for public health and the environment. By 2030, when the engine fleet has been fully turned over, PM and NOx will be reduced by 250,000 tons/year and 4 million tons/year, respectively. This will result in annual benefits of over $150 billion, at a cost of approximately $7 billion.

A number of regional partnerships are also working on reducing diesel emissions, including the West Coast Diesel Emissions Reductions Collaborative, the Midwest Clean Diesel Initiative, Greater Boston Breathes Better (GB3), and the Northeast Diesel Collaborative (NEDC).