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Transportation Air Quality Selected Facts and Figures

Emissions Standards

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What Are the Federal Emissions Standards?

The CAA set federal emissions-control standards for all new cars and light trucks sold in the United States. The CAAA established stringent Tier 1 emissions standards, which became effective in 1994. More stringent Tier 2 emissions standards were adopted in 2004. In April 2014, EPA finalized new Tier 3 emissions- control standards.

What Do the New Tier 3 Emissions Standards Do?

Starting in 2017, Tier 3 standards will set new vehicle emissions standards and lower the sulfur content of gasoline, considering the vehicle and its fuel as an integrated system. The new standards reduce both tailpipe and evaporative emissions from passenger cars, light-duty trucks, medium-duty passenger vehicles, and some heavy- duty vehicles.

Estimated Emissions Reductions from the Final Tier 3 Standards

Title: Bar graph showing the estimated NOx, VOC, and CO emissions reductions in 2018 and 2030 from the final Tier 3 standards in annual U.S. short tons X 100,000 - Description: The bar graph shows the amount of estimated emissions reductions from the federal Tier 3 emissions standards for 2018 and 2030, in annual U.S. short tons X 100,000. In 2018, NOx> is just over 2.5, VOC is about 0.5, and CO is a fraction higher than NOx. In 2030, NOx is just over 3, VOC is about 2, and CO is just under 35.

Source: U.S. Environmental Protection Agency, Office of Transportation and Air Quality, EPA Sets Tier 3 Motor Vehicle Emission and Fuel Standards, EPA- 420-F-14-009, March 2014,

What Are the Benefits?

The Tier 3 gasoline sulfur standard will make emissions-control systems more effective for both existing and new vehicles, and will enable more stringent vehicle emissions standards. Removing sulfur allows the vehicle's catalyst to work more efficiently. Lower-sulfur gasoline also facilitates the development of some lower-cost technologies to improve fuel economy and reduce GHG emissions, which reduces gasoline consumption.

What Are the Heavy-Duty Diesel Emissions Standards?

In December 2000, EPA issued the final rule for a two-part strategy to reduce diesel emissions from heavy-duty trucks and buses. This included new diesel-engine standards in model year 2004 for all diesel vehicles over 8,500 pounds. These standards are based on the use of high-efficiency advanced emissions controls.

Estimated Vehicle Emissions Under Heavy-Duty Engine/Fuel Rule (2007–2030)

Title: Line chart showing estimated vehicle emissions from 2007 to 2030 under the 2000 federal heavy-duty engine/fuel rule in thousand short-tons - Description: The line chart shows the estimated emissions of NOx, VOC, and PM-10 after implementation of the 2000 federal heavy-duty engine/fuel rule in thousand short-tons. The NOx> line begins just under 3,000 and decreases steadily to about 400 by 2030. The VOC line begins at about 375 in 2007 and drops to slightly under 350 by 2030. The PM-10 line begins at about 120 and decreases to about 35 by 2030.

Source: U.S. Environmental Protection Agency, Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements, December 2000,

What Are the Fuel Efficiency and GHG Emissions Standards for Heavy-Duty Trucks?

The nation's fleet of medium- and heavy-duty trucks are required to meet fuel efficiency and GHG emissions standards for three categories of medium- and heavy-duty trucks:

In 2015, EPA and the National Highway Traffic Safety Administration (NHTSA) issued a notice of proposed rulemaking (NPRM) to establish a comprehensive Phase 2 Heavy Duty National Program that will reduce GHG emissions and fuel consumption for new on-road heavy duty vehicles. This program would phase in over the long- term, beginning in the 2018 model year and culminating in standards for model year 2027.

Source: U.S. Environmental Protection Agency, Office of Transportation and Air Quality, Paving the Way toward Cleaner, More Efficient Trucks, EPA-420-F-11-032, August 2011,

U.S. Environmental Protection Agency, Cutting Carbon Pollution, Improving Fuel Efficiency, Saving Money, and Supporting Innovation for Trucks, EPA-420-F-15-900, June 2015,

What Are the Non-Road Vehicle Emissions Standards?

Non-road diesel engines include excavators and other construction equipment, farm tractors and other agricultural equipment, heavy forklifts, airport ground service equipment, and utility equipment such as generators, pumps, and compressors. Non-road diesel engines are subject to a set of tiered emissions standards. Tier 1 through 4 standards are currently in effect, having been implemented in steps since 1998. The regulations have been phased in for newly manufactured engines in different years depending on the power output of the engine. Each tier represents a progression to more stringent regulations.

Tier 4 standards were implemented from 2008 to 2015 and call for stricter limits on NOx and PM (about a 90 percent reduction in emissions). EPA also has mandated the use of lower sulfur diesel fuel to enable more advanced pollution control on these engines. Since 2010, ultra-low sulfur diesel fuel is required, containing only 15 ppm of sulfur. Engine manufacturers must produce new engines with advanced emissions control technologies similar to those expected for highway trucks and buses. Exhaust emissions from these engines will decrease by more than 90 percent.

In 2008, EPA adopted more stringent emissions standards and mandated the application of idle-emission controls on newly manufactured and remanufactured locomotives. The idle reduction technology automatically shuts locomotives down if they are left idling unnecessarily. While such devices cannot eliminate all idling, they can reduce most unnecessary idling.

What Effects Do the Standards Have on Pollutants?

These standards removed 99 percent of the sulfur in diesel fuel by 2010, resulting in dramatic reductions in soot from all diesel engines.

The Non-road Diesel Rule complements the Clean Diesel Truck and Bus Rule. The new standards were estimated to result in reductions of pollution equivalent to having some 2 million fewer trucks on the road.

Sources: U.S. Environmental Protection Agency,

U.S. Environmental Protection Agency, Clean Air Nonroad Diesel Rule-Regulatory Announcement, Publication No. EPA420-F-04-032, May 2004,

U.S. Environmental Protection Agency, Clean Diesel Programs-Facts and Figures, Publication No. EPA 420-F-04-040, May 2004,

U.S. Environmental Protection Agency, Control of Emissions from Idling Locomotives, December 2013,

Updated: 5/3/2016
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