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Why Retrofit?

Diesel retrofits offer a number of benefits over other emissions reduction strategies, including cost effectiveness and immediate, significant reductions.

Meeting the Challenge

While the environmental performance of diesel engines is constantly improving, new emissions standards only apply to new engines. However, because diesel is truly the workhorse of the American economy - with engines often lasting hundreds of thousands of miles or running for hundreds of thousands of hours - a sizable fleet of equipment manufactured over two to three decades ago is still in operation. Fortunately, many of the same advances used to improve new engines can be applied to this existing fleet.

The term “retrofit” covers many technologies and activities to reduce emissions from older engines, vehicles and equipment and has typically been defined broadly. While the term is frequently used as a label describing various exhaust emissions control devices such as the diesel oxidation catalysts and particulate filters, it can also encompass a broader range of options to reduce emissions, including re-powering, rebuilding and in some instances replacing existing equipment.

Rebuild: Engines face normal wear and tear and need to be rebuilt to operate efficiently returning to the manufacturer's original specifications. During the course of a rebuild, equipment owners may choose to install new engine components that improve both the fuel economy and emissions profile. In fact, U.S. Environmental Protection Agency (EPA) rules outline emission requirements on rebuilt engines to insure emissions reductions.

Refuel: Since 2008, the use of Ultra Low Sulfur Diesel fuel (ULSD) has been mandated in the U.S. The use of ULSD greatly reduces sulfur dioxide, a key component in smog, and also allows for the operation of other emission control technologies.

Repower: Replacing an older engine with a new diesel engine that meets the most current EPA emissions criteria will greatly reduce emissions.

Replace: In certain instances, the most cost effective strategy to reduce emissions may be to replace the vehicle or equipment.

Retrofit: The installation of various emission control technologies may also improve emissions from older diesel engines. The mandated use of ULSD has paved the way for many emission control technologies to reduce criteria pollutant emissions from older diesel engines.

Immediate Significant Reductions

Over the past decade, major advances in diesel technologies have resulted in the development of cleaner diesel engines, fuels and retrofit devices that can be installed on vehicles and equipment to reduce in-use emissions by –up to 85 percent, depending on the technology and the characteristics of the vehicle or equipment.

In nearly all cases, the emission reductions are immediate. Planners don't need to wait to see if the reductions actually materialize by monitoring travel behavior - as can be required with many control measures. Diesel retrofit strategies can be particularly important in metropolitan areas where high volumes of heavy-duty trucks are prevalent and/or where major construction projects are underway for long periods of time.

Flexible and Voluntary Programs 
A number of voluntary approaches to diesel emission reductions have proved successful throughout the United States that, in contrast to regulatory measures, are less onerous and cumbersome than compliance with regulatory measures. The types of equipment and vehicles retrofit under these programs can include: heavy-duty trucks, forklifts, bucket loaders, tractors, wheel loaders, refuse trucks, transit and school buses and others.

Lack of Infrastructure Requirements 
In contrast to many alternative fuel measures, diesel retrofit strategies do not require installation of special infrastructure. Ultra-low sulfur diesel fuel is now available nationwide. Another advantage to diesel retrofits is the ability to easily and quickly install. 

Diesel Retrofit Technologies

Particulate filters are capable of capturing up to 95 percent of particulate matter, or soot. According to the Manufacturers of Emission Controls Association, over 100,000 diesel particulate filters have been sold nationwide since 2001 helping to improve emissions on older and new diesel vehicles and equipment.

Exhaust gas recirculation (EGR) recirculates a portion of engine exhaust back into the engine diluting the oxygen content of the fuel-air mixture. EGR technology significantly reduces both NOx and Particulate Matter.

Selective Catalyst Reduction (SCR) is an advanced active emissions control technology system that injects a liquid-reductant agent, known as Diesel Exhaust Fluid (DEF) through a special catalyst into the exhaust stream of a diesel engine. The DEF sets off a chemical reaction that converts nitrogen oxides into nitrogen, water and tiny amounts of carbon dioxide (CO2), natural components of the air we breathe, which is then expelled through the vehicle tailpipe.

Read more about SCR

Diesel Oxidation Catalysts (DOC) are similar to converters installed on light-duty vehicles. Exhaust travels through a honeycomb like structure that attracts fine particles. Diesel oxidation catalysts are capable of eliminating Particulate Matter by 20-50 percent. The U.S. EPA estimates that almost 20,000 DOC have been installed on older vehicles and equipment since 2008 making this technology one of the more popular and cost effective retrofit options.

Read more about retrofit technologies, including installation costs, on the EPA's website. 

Diesel Retrofit Toolkit

America needs diesel engines and cleaner air; advanced clean diesel technology offers both. Diesel power drives the economy by building our nation's infrastructure of roads and bridges, taking crops from the fields to food on the table, and providing vital transportation of people and goods in the most efficient and cost effective manner possible.

No other technology can match diesel's unique combination of energy efficiency, sheer power, reliability and durability across so many sectors of the economy. In all applications, diesel technology has experienced continuous improvement with increasing performance, lower fuel consumption and lower emissions, making today's technology much cleaner and more efficient than what was available even a few years ago.

The future looks even cleaner. Industry's continued improvements are leading to a new generation of clean diesel vehicles and equipment that will virtually eliminate regulated emissions in both on- and off-road applications. This new clean diesel technology will not only be available in new vehicles and equipment, but can be applied to existing engines, thereby multiplying its benefits. The nation's goals for accelerated improvements in air quality have led regulators to identify the modernizing and upgrading of existing diesel engines as one of the most cost-effective options for achieving emissions reductions.

The modernizing and upgrading of older diesel vehicles through one of retrofit's "five Rs" can help achieve significant, cost effective reduction of criteria pollutants including particulate matter (PM), commonly known as soot, and oxides of nitrogen.

Financial Resources

While the air quality benefits of diesel retrofit are strong, the economic benefits are less clear. Large operators may capture the good will and economic value of good corporate citizenship more readily than small operators that face few direct economic or market pressures related to their environmental performance. The federal government provides a significant source of funding for diesel retrofit programs through several programs including: the Congestion Mitigation and Air Quality (CMAQ) Improvement Program, the Diesel Emissions Reduction Act¸ and the Environmental Quality Incentives Program (EQIP). Additionally, many states and localities provide retrofit assistance as well.

Federal Programs

State Programs

In addition to federal financial assistance programs for diesel retrofits, many states also provide financial assistance to help the owners of diesel equipment purchase retrofit technologies. Below is a listing of a few of those programs. If you are an equipment owner seeking financial assistance for retrofit technologies, please contact your state department of environment or air quality. 

Local Programs

Many localities and public authorities also provide financial assistance to owners of specific types of diesel equipment to purchase retrofit technologies or new equipment. Below is a listing of a few local programs.

Many large seaports around the country adopted requirements prohibiting older diesel powered trucks from entering maritime facilities. Port authorities provide resources in order to help truck owners purchase newer trucks or retrofit equipment. Below is a digest of requirements:


The U.S. Environmental Protection Agency has developed a new mapping feature to promote local environmental awareness called MyEnvironment, which you can use below. MyEnvironment provides users with a cross-section of environmental information including data on air, water, energy, and much more.


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