What is Clean Diesel?

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About Clean Diesel


Diesel moves approximately 90 percent of the nation's freight tonnage, and nearly all highway freight trucks are powered by diesel engines.

More than 95 percent of all heavy-duty trucks are diesel-powered as are a majority of medium-duty trucks. Over the last 10 years, emissions from heavy-duty diesel trucks, buses and other vehicles have been reduced by 99 percent for nitrogen oxides (NOx) - an ozone precursor - and 98 percent for particulate emissions. Consider that it would take 60 of these 2010 trucks to equal the same emissions from one pre-1988 truck. A 60-1 ratio!

The new generation of clean diesel vehicles is a growing portion of the total diesel commercial truck population with more than 37 percent of all diesel medium and heavy-duty commercial trucks registered in the United States now equipped with newer technology clean diesel engines - those manufactured in Model Year 2007 or newer that have near zero particulate emissions.

And nearly 22 percent of all diesel trucks in operation are now the newest clean diesel technology (2010 and later model year) that are also near zero emissions in nitrogen oxides.

A new generation of clean diesel technology is fueling those trucks and emissions are going down and fuel savings and greenhouse gas emissions benefits are going up in the nation’s commercial trucking fleet as more truckers invest in new technology clean diesel engines.

Over the past couple of years there has been a lot of speculation about a ‘revolution’ in fuels and technology in the trucking industry. The 2014, year-end U.S. truck vehicles-in-use data shows that 9.1 million are powered by diesel engines, and among the largest trucks, (Class 8) diesel vehicles-in-use accounted for 3.6 million of the overall population. So it appears that the ‘revolution’ is that truckers are choosing new clean diesel truck technology in increasing numbers over all other fuel sources.

In fact, ExxonMobil predicts that not only will diesel surpass gasoline as the number one global transportation fuel by 2020, diesel demand will also account for 70 percent of the growth in demand for all transportation fuels through 2040. ExxonMobil also projects that natural gas will remain only a small share of the global transportation fuel mix, at four percent by 2040, up slightly from today’s one percent range.

Diesel power is the driving force today of goods movement by truck in our economy and diesel will play a central role in efforts to reduce fuel consumption, promote energy security and lower greenhouse gas emissions (GHG) in the years ahead. Diesel also provides a unique technology platform suitable for expanded use of hybrid powertrains and lower-carbon renewable fuels - both strategies for reducing GHG emissions in the future.

Clean Diesel Progress

While continuously making commercial trucks more fuel efficient, diesel engine and truck manufacturers have also been making them dramatically cleaner, a significant accomplishment considering that increased fuel efficiency and lower emissions are near opposite and competing forces in diesel engine design. In fact, diesel vehicles manufactured after 2010 achieve an average five percent improvement in fuel economy resulting in petroleum reduction equivalent to 21 million barrels of crude oil. Additional fuel-saving strategies are being developed to improve efficiency, including further engine refinements, vehicle aerodynamics and expanded use of hybrid technology for some applications.

New diesel vehicles are increasing their penetration in the marketplace because they are more fuel efficient, in part, due to meeting the requirements of Phase 1 of the U.S. EPA/NHTSA Fuel Efficiency standards that went into effect in 2014. The proposed rule establishing a second phase of reductions in CO2 emissions and improvements in fuel efficiency will challenge engine and truck manufacturers to go even further in saving fuel for customers. Manufacturers will continue to work with EPA, NHTSA and the California Air Resources Board toward a final rule that will enable continued progress in investing in new and more fuel efficient vehicles.

In August 2011, U.S. Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration (NHTSA) established a national program to reduce GHG emissions and establish new fuel efficiency standards for commercial vehicles beginning in 2014 through 2018. Because of the sheer magnitude of commercial vehicles operating in the United States, this regulation has the potential to result in significant emissions reduction and energy efficiency gains. The U.S. fleet of trucks consumes about 22 billion gallons of diesel fuel every year. Over the lifetime of the vehicles affected by the new rule, the program is expected to reduce oil consumption by more than 530 million barrels, result in more than $50 billion in net benefits, and reduce carbon dioxide emissions by 270 million metric tons.

Those Phase 1 rules are now implemented beginning with model year 2014. Manufacturers are meeting these targets through continued advancements in engine and aftertreatment technologies along with advanced aerodynamics, transmission, tire and other technologies that improve fuel economy. According to NHTSA, technologies deployed to meet these rules will improve fuel economy for a typical long haul tractor by 20 percent by 2018.  Meanwhile fuel economy among many vocational vehicles will improve by 10 percent and many work trucks by 15 percent by 2018.

On June 22, 2015, EPA and NHTSA announced proposed rules for the second phase of fuel economy and greenhouse gas emissions reduction from the heavy-duty fleet.  These proposed rules would apply beginning in 2021 through 2027 and are anticipated to further reduce carbon emissions by another one billion tons while saving 1.8 billion tons of crude oil. Over the lifetime of the proposed rule, diesel is expected to remain the dominant powertrain and fuel. Technologies envisioned to attain the proposed standards will help further advance diesel's well established fuel efficiency credentials. 

Still yet, Phase 1 and the proposed Phase 2 standards together are estimated to reduce greenhouse gas emissions by 1.2 billion tons by 2027.

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While new engines and vehicles are getting cleaner, technologies to reduce emissions from older vehicles are now widely available. Through the use of retrofit upgrades, older diesel engines can improve their performance and reduce key emissions by up to 90 percent. More information on retrofit technology and ongoing programs can be found in the Forum's Online Retrofit Tool Kit.

For additional information about engine certification standards and government regulations, visit the Engine Manufacturers Association (EMA) website.

Phase 1 Clean Diesel Truck GHG Rule Facts


In May of 2010, President Obama, in a Rose Garden Ceremony, announced a new effort to propose greenhouse gas and fuel efficiency standards for medium and heavy-duty trucks and buses and to begin the process for further standards for light-duty vehicles. Then in August 2011, the U.S. Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration (NHTSA) established a national program to reduce GHG emissions and establish new fuel efficiency standards for commercial trucks and buses beginning in 2014 through 2018.

Why is this final rule important?

It is the first ever regulation of greenhouse gas emissions and fuel efficiency for heavy-duty vehicles. Heavy-duty tractor trailer trucks consume approximately 22 billion gallons of diesel fuel every year, with medium-duty trucks consuming a considerable amount as well. The potential for fuel savings is significant.

What are the medium and heavy-duty trucks subject to this proposed rule?

Why haven't these vehicles been regulated before?

Pursuit of high fuel efficiency has always been a market imperative for this segment. Fuel costs are the first or second highest operating cost of most trucking operations, and the competition for fuel efficiency has always been an integral part of the market.

What is the average fuel efficiency of these vehicles compared to cars?

What are the most important aspects of this final rule for manufacturers?

Which technologies could be incorporated as a result of this rule?


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