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United States 

Environmental Protection 

Agency 

Air and Radiation EPA420-F-98-034 

August 1998 

Office of Mobile Sources 

Regulatory 

Announcement

New Emission Standards for 

Nonroad Diesel Engines 

The U.S. Environmental Protection Agency (EPA) is setting stringent 

new emission standards for diesel engines used in a wide range of 

nonroad construction, agricultural, and industrial equipment and some 

marine applications. This program reduces the recently implemented 

first tier of nonroad engine standards by up to two thirds—a major step 

toward reducing the harmful health effects of ozone and particulate 

matter (PM) nationwide. 

History of Rulemaking 

In recent years, EPA was strongly encouraged by states and others to 

pursue national regulations that would help them address the air quality 

problems in many parts of the country. Prior to issuing a proposal, EPA 

engaged in discussion with state environmental regulators, environmental organizations, engine manufacturers, equipment manufacturers, small 

businesses, and others. One result of this activity was a Statement of 

Principles signed by EPA, engine manufacturers, and the State of California outlining a framework for potential nonroad diesel emission 

standards. 

Overview Of The Final Rule 

The primary feature of this rule is a set of new emission standards for 

mobile nonroad diesel engines of almost all types. Standards for hydrocarbons, oxides of nitrogen (NOx), carbon monoxide, and PM will be 

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implemented in two tiers over ten years 

(1999-2008), with different standards and 

start years for various engine power ratings. By the end of 2001, EPA will reassess 

the feasibility of the standards and will 

propose and adopt appropriate new standards for PM. 

The final rule covers nonroad diesel engines and equipment such as farm tractors, 

bulldozers, and forklifts. The rule does not 

apply to locomotives, marine engines 

above 50 horsepower (hp), underground 

mining equipment, and engines with 

displacements under 50 cubic centimeters 

per cylinder that are typically used in 

model airplanes. Likewise, the new standards do not apply to existing nonroad 

equipment. Only equipment built after the 

start date for an engine category (1999­

2006, depending on the category) is affected by the rule. 

The rulemaking is part of a 3-tiered progression to low emission standards. Each 

tier involves a phase in (by horsepower 

rating) over several years. Tier 1 standards 

were adopted in 1994 for engines over 50 

hp (such as bulldozers) and are phasing in 

from 1996 to 2000. This final rule sets Tier 

1 standards for engines under 50 hp (such 

as lawn tractors), phasing in from 1999 to 

2000. It also phases in more stringent Tier 

2 standards for all engine sizes from 2001 

to 2006, and yet more stringent Tier 3 

standards for engines rated over 50 hp from 

2006 to 2008. The Tier 3 standards that 

will phase in beginning in 2006 are expected to lead to implementation of control 

technologies similar to those that will be 

used by manufacturers of highway heavyduty engines (i.e., trucks and buses) to 

comply with the 2004 highway engine 

standards. 

In addition to the standards, the final rule 

includes related provisions intended to 

ensure compliance with the new standards 

for engines in the field and a program of 

voluntary standards for engines with 

superior emissions performance. 

Health And Environmental 

Benefits 

The new standards will reduce emissions 

from a typical nonroad diesel engine by up 

to two-thirds from the levels of previous 

standards. By meeting these standards, 

manufacturers of new nonroad engines and 

equipment will achieve large reductions in 

the emissions (especially NOx and PM) 

that cause air pollution problems in many 

parts of the country. EPA estimates that by 

2010, NOx emissions will be reduced by 

about a million tons per year, the equivalent of taking 35 million passenger cars off 

the road. 

Ozone causes a range of health problems 

related to breathing, including chest pain, 

coughing, and shortness of breath. PM 

becomes deposited deep in the lungs and 

results in premature death, increased 

emergency room visits, and increased 

respiratory symptoms and disease. In 

addition, ozone, NOx, and PM adversely 

affect the environment in various ways, 

including crop damage, acid rain, and 

reduction in visibility. 

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Flexibility for Industry 

The final rule has several elements that add 

flexibility to how manufacturers comply 

with the standards, reducing the costs of 

compliance without harming the overall 

environmental goals of the rule. For example, the standards are designed to phase 

in over several years with schedules that 

recognize some engines are technologically 

closer to compliance than others (e.g., 

engines similar to highway truck engines). 

Engine manufacturers may also use averaging provisions in choosing their most 

efficient path to compliance. The final rule 

also includes provisions designed to 

smooth the transition by equipment manufacturers as they begin to install the new 

engine designs into existing equipment. 

In addition, since the new standards are 

expected to be adopted by the State of 

California and are consistent with standards being proposed in Europe, manufacturers should be able to use a single engine 

or machine design for all of these markets, 

thus avoiding the added cost of multiple 

versions. 

Assisting the States 

Because the new standards cover a large 

and diverse population of nonroad equipment and are expected to achieve very 

significant, regional-scale emission reductions across the country, implementation of 

this program will be an important part of 

the overall control strategies of numerous 

states and localities grappling with difficult 

air quality problems. 

Cost of the New Program 

The costs of meeting the new emission 

standards are expected to add well under 1 

percent to the purchase price of typical new 

nonroad diesel equipment, although for 

some equipment the standards may cause 

price increases on the order of 2 or 3 

percent. The program is expected to cost 

about $600 per ton of NOx reduced, which 

compares very favorably with other emission control strategies. 

For More Information 

Additional documents on nonroad diesel 

engine standards are available through 

the Assessment and Standards Division 

at asdinfo@epa.gov or (734) 214-4636: 

U.S. Environmental Protection Agency 

Office of Transportation and Air Quality 

Assessment and Standards Division 

2000 Traverwood Road 

Ann Arbor, Michigan 48105 

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