US: Light-duty: Emissions


U.S. Tier 3 standards phase in from 2017–2025 and apply to vehicles up to 14,000 lbs gross vehicle weight. Once fully phased-in, Tier 3 tailpipe PM and NOx+NMOG emission limits for light- and medium-duty passenger vehicles are the most stringent in the world

Standard type
Conventional pollutant emission limits

Regulating Body
US Environmental Protection Agency (EPA)

Current Standard
Tier 3

Vehicles up to 8,500 lbs GVWR and “medium-duty passenger vehicles” (MDPV) – larger SUVs and passenger vans 8,500-10,000 lbs GVWR. Tier 3 extends coverage to Class 2b and 3 heavy-duty vehicles up to 14,000 lbs GVWR. See vehicle definitions.


The United States has historically had the world’s most stringent vehicle tailpipe conventional pollutant emission standards. The first nationwide US light duty vehicle emission standards were implemented in 1968, and subsequently reviewed every couple of years. New standards were referred to by the effective model year of the regulation from 1968 to 1987. Federal legislation in 1981 established new emission standards, retroactively known as “Tier 0,” beginning in 1987. The Clean Air Act Amendments (CAAA) of 1990 subsequently defined two new tiers of standards for light-duty vehicles:

  • Tier 1 standards, which were published as a final rule on June 5, 1991, were phased-in progressively between 1994 and 1997.
  • Tier 2 standards, which were adopted on December 21, 1999, were phased-in from 2004 to 2009, and currently apply to vehicles up to 8,500 lbs GVWR and “medium-duty passenger vehicles” (MDPV) – larger SUVs and passenger vans 8,500-10,000 lbs GVWR.

Additional milestones include:

  • Cold CO (20F) standards were adopted in 1992 and phased-in on the same schedule as Tier 1.
  • To further control air toxic emissions, 20F HC standards were added in 2007.
  • SFTP standards (US06 and SC03) were adopted in 1996 and were phased in from 2000 through 2004.
  • Standardized OBD II requirements were required on all vehicles in 1996.

Tier 3 standards were finalized in March 2014. The Tier 3 requirements will phase in from 2017 to 2025.

One of the defining features of US standards – as opposed to European standards – is that they are “fuel neutral,” meaning that all vehicles are subject to the same emission limits, regardless of the fuel used.

The National Low Emission Vehicle (NLEV) Program, a voluntary program during the transition between Tier 1 and Tier 2, was established through an agreement between the Northeastern states and auto manufacturers. Beginning in the Northeast with model year 1999 vehicles, and nationally with model year 2001, new cars and light light-duty trucks (LLDT) had to meet tailpipe standards that were more stringent than EPA could legally mandate during the transition from Tier 1 to Tier 2. However, after the NLEV program was agreed upon, these standards were enforceable in the same manner as any other federal new motor vehicle program.

Technical Standards

The Tier 1 final rule was published on June 5, 1991, and phased-in progressively between 1994 and 1997. Tier 1 was in effect until 1999 for passenger vehicles and LLDT, and until 2004 for heavy light-duty trucks (HLDT). Tier 1 also regulates evaporative emissions; these requirements are summarized on the EPA’s website. Vehicle Categories Tier 1 standards applied to all new light-duty vehicles (LDV), such as passenger cars, light-duty trucks, sport utility vehicles (SUV), minivans and pick-up trucks. The LDV category included all vehicles less than 8500 lb gross vehicle weight rating, GVWR (i.e., vehicle weight plus rated cargo capacity). LDVs were further divided into the following sub-categories:

  • Passenger cars
  • Light light-duty trucks (LLDT), below 6000 lbs GVWR
  • Heavy light-duty trucks (HLDT), above 6000 lbs GVWR

FTP-based Emission Standards Tier 1 emission standards are summarized below. Car and light truck emissions are measured over the Federal Test Procedure (FTP).

EPA Tier 1 Emission Standards for Passenger Cars and Light-Duty Trucks, FTP 75, g/mi
Category 50,000 miles/5 years 100,000 miles/10 years1
THC NMHC CO NOx† diesel NOx gasoline PM‡ THC NMHC CO NOx† diesel NOx gasoline PM‡
Passenger cars 0.41 0.25 3.4 1.0 0.4 0.08 0.31 4.2 1.25 0.6 0.10
LLDT, LVW <3,750 lbs 0.25 3.4 1.0 0.4 0.08 0.80 0.31 4.2 1.25 0.6 0.10
LLDT, LVW >3,750 lbs 0.32 4.4 0.7 0.08 0.80 0.40 5.5 0.97 0.97 0.10
HLDT, ALVW <5,750 lbs 0.32 4.4 0.7 0.80 0.46 6.4 0.98 0.98 0.10
HLDT, ALVW > 5,750 lbs 0.39 5.0 1.1 0.80 0.56 7.3 1.53 1.53 0.12
Notes:1 – Useful life 120,000 miles/11 years for all HLDT standards and for THC standards for LDT † – More relaxed NOx limits for diesels applicable to vehicles through 2003 model year ‡ – PM standards applicable to diesel vehicles only Abbreviations: LVW – loaded vehicle weight (curb weight + 300 lbs) ALVW – adjusted LVW (the numerical average of the curb weight and the GVWR) LLDT – light light-duty truck (below 6,000 lbs GVWR) HLDT – heavy light-duty truck (above 6,000 lbs GVWR)

Updated Limit Values: SFTP Emission Standards In addition to the FTP75 test, a Supplemental Federal Test Procedure (SFTP) was phased-in between 2000 and 2004. The SFTP includes additional test cycles to measure emissions during aggressive highway driving (US06 cycle), and also to measure urban driving emissions while the vehicle’s air conditioning system is operating (SC03). Tier 1 SFTP standards, which applied to NMHC+NOx and CO emissions, are summarized below. The NMHC+NOx standards are weighted, while CO standards are standalone for US06 and SC03 with an option for weighted standard. Weighting for NMHC+NOx and optional weighting for CO is: SFTP = 0.35 × FTP_+ 0.28 × US06 + 0.37 × SC03. Intermediate life (50,000 mi) standards are shown in parentheses.

EPA Tier 1 SFTP Standards
Category* NMHC+NOx, g/mi CO, g/mi
Weighted US06 SC03 Weighted
Passenger cars & LLDT, LVW <3,750 lbs 0.91/2.07† (0.65/1.48†) 11.1 (9.0) 3.7 (3.0) 4.2 (3.4)
LLDT, LVW >3,750 lbs 1.37 (1.02) 14.6 (11.6) 4.9 (3.9) 5.5 (4.4)
HLDT, ALVW <5,750 lbs 1.44 (1.02) 16.9 (11.6) 5.6 (3.9) 6.4 (4.4)
HLDT, ALVW >5,750 lbs 2.09 (1.49) 19.3 (13.2) 6.4 (4.4) 7.3 (5.0)
Notes: * See note in the above table for abbreviations † The more relaxed value is for diesel fueled vehicles

In 1999, as part of a voluntary agreement with auto manufacturers, the National Light Emission Vehicle (NLEV) Program replaced Tier 1 as the standard for passenger vehicles and LLDTs during the transition to Tier 2 standards. NLEV (National Low Emission Vehicle) Program The NLEV program for passenger vehicles and light light duty trucks was in effect during the interim between Tier 1 and Tier 2 and was an agreement with northeastern states and auto manufacturers. For more information, see the NLEV Official Legislation. The NLEV program harmonized federal and California motor vehicle standards (CA LEV I) and provided emission reductions that were equivalent to the California Low Emission Vehicle program. The program was phased-in through schedules that required car manufacturers to certify a percentage of their vehicle fleets to increasingly cleaner standards (TLEV, LEV, ULEV). The NLEV program extended only to lighter vehicles and did not include the Heavy LDT (HLDT, GVWR>6,000 lbs) vehicle category.

Tier 2

In December 1999, EPA announced an update to the Tier 1 standard. Tier 2 regulates light-duty vehicle conventional pollutant emissions in the United States. The Tier 2 regulation introduced more stringent numerical emission limits, relative to Tier 1 requirements, and a number of additional changes that made the standards more stringent for larger vehicles. Under the Tier 2 regulation, the same emission standards apply to all vehicle weight categories, i.e., cars, minivans, light-duty trucks, and SUVs have the same emission limits. Evaporative emissions requirements for Tier 2 are summarized on the EPA’s website. The complete regulatory text is also available on EPA’s Tier 2 website.

Vehicle Categories

In Tier 2, the applicability of light-duty emission standards has been extended to cover some heavier vehicle categories. The Tier 1 standards applied to vehicles up to 8,500 lbs GVWR. The Tier 2 standards apply to all vehicles that were covered by Tier 1 and, additionally, to MDPVs. The MDPV is a new class of vehicles rated 8,500-10,000 lbs GVWR and used for personal transportation. This category includes primarily larger SUVs and passenger vans. The table below outlines and defines the vehicle categories used in the EPA Tier 2 standards. Engines in commercial vehicles above 8,500 lbs GVWR, such as cargo vans or light trucks, continue to certify to heavy-duty engine emission standards.

Vehicle Categories Used in EPA Tier 2 Standards
Vehicle Category Abbreviation Requirements
Light-Duty Vehicle LDV max. 8500 lb GVWR
Light-Duty Truck LDT max. 8500 lb GVWR, max. 6000 lb curb weight and max. 45 ft2 frontal area
Light light-duty truck LLDT max. 6000 lb GVWR
Light-duty truck 1 LDT1 max. 3750 lb LVW1
Light-duty truck 2 LDT2 min. 3750 lb LVW1
Heavy light-duty truck HLDT min. 6000 lb GVWR
Light-duty truck 3 LDT3 max. 5750 lb ALVW2
Light-duty truck 4 LDT4 min. 5750 lb ALVW2
Medium-Duty Passenger Vehicle MDPV max. 10000 lb GVWR3
Notes: 1 – LVW (loaded vehicle weight) = curb weight + 300 lb 2 – ALVW (adjusted loaded vehicle weight) = average of GVWR and curb weight 3 – Manufacturers may alternatively certify engines for diesel fueled MDPVs through the heavy-duty diesel engine regulations

The same emission limits apply to all vehicles regardless of the fuel they use – vehicles fueled by gasoline, diesel, or alternative fuels all must meet the same standards. Since light-duty emission standards are expressed in grams of pollutants per mile, vehicles with large engines (such light trucks or SUVs) must use more advanced emission control technologies than vehicles with smaller engines in order to meet the standards.

Limit Values: Tier 2 Certification Bins

Manufacturers must certify that each vehicle will not exceed the pollution limits for the selected bin. Manufacturers may choose from the range of bins, as long as all vehicles they sell each model year fall below a certain average emission limit.1 The emission standards for all pollutants (certification bins) when tested on the FTP75 are shown below.

Tier 2 Emission Standards, FTP 75, g/mi
Bin# Intermediate life (5 years / 50,000 mi) Full useful life
Temporary Bins
11a,c 0.195 5 0.6 0.12 0.022 0.280 7.3 0.9 0.12 0.032
10a,b,d,f 0.125 (0.160) 3.4 (4.4) 0.4 0.08 0.015 (0.018) 0.156 (0.230) 4.2 (6.4) 0.6 0.08 0.018 (0.027)
9a,b,e 0.075 (0.140) 3.4 0.2 0.06 0.015 0.090 (0.180) 4.2 0.3 0.06 0.018
Permanent Bins
8b,g 0.100 (0.125) 3.4 0.14 0.02 0.015 0.125 (0.156) 4.2 0.20 0.02 0.018
7 0.075 3.4 0.11 0.02 0.015 0.090 4.2 0.15 0.02 0.018
6 0.075 3.4 0.08 0.01 0.015 0.090 4.2 0.10 0.01 0.018
5 0.075 3.4 0.05 0.01 0.015 0.090 4.2 0.07 0.01 0.018
4 0.070 2.1 0.04 0.01 0.011
3 0.055 2.1 0.03 0.01 0.011
2 0.010 2.1 0.02 0.01 0.004
1 0.000 0.0 0.00 0.00 0.000
Notes: * for diesel fueled vehicle, NMOG (non-methane organic gases) means NMHC (non-methane hydrocarbons) † average manufacturer fleet NOx standard is 0.07 g/mi for Tier 2 vehicles ‡ Intermediate life standards are optional for vehicles certified to a useful life of 150,000 miles a. This bin deleted at end of 2006 model year (end of 2008 model year for HLDTs and MDPVs ). b. Higher NMOG, CO and HCHO values apply for HLDTs and MDPVs only. c. This bin is only for MDPVs. d. Optional NMOG standard (0.195 g/mi for intermediate life, 0.280 for full life) applies for qualifying LDT4s and qualifying MDPVs only. e. Optional NMOG standard (0.100 g/mi for intermediate life, 0.130 for full life) applies for qualifying LDT2s only. f. Intermediate life standards of this bin are optional for diesels. g. Higher NMOG standard deleted at end of 2008 model year.

Bins 8b-11 were phased out between 2006 and 2008. By 2008, all vehicles must fall into any Bin from 1-8a. Each vehicle manufacturer must have a fleet average equivalent to NOx emissions defined in Bin 5, which correlates to an average NOx level of 0.07 g/mi. Therefore, NOx emissions from vehicles certified to bins higher than Bin 5 must be offset by selling a sufficient number of vehicles certified to bins lower than Bin 5. Where intermediate useful life exhaust emission standards are applicable, such standards are applicable for five years or 50,000 miles, whichever occurs first. Tier 2 vehicles are those meeting the requirements of one of the available bins and that are used to meet the requirement that a percentage of the fleet have average NOx emissions of 0.07 g/mile. During the phase-in period, the rest of the fleet not used to comply with the 0.07 g/mile NOx average are referred to as interim non-Tier 2 vehicles. They were still required to meet the requirements of one of the available bins but had more relaxed fleet average requirements. The EPA bins cover California LEV II emission categories, to make certification for both federal and California standards easier for vehicle manufacturers. However, EPA Tier 2 fleet average requirements were for NOx. This is different from the California LEV II standards, which use Non Methane Organic Gase (NMOG) emissions for their fleet average requirements.

Tier 2 Emission Standards Phase-In

The Tier 2 standards were phased-in between 2004 and 2009, as shown below. For new passenger cars (LDVs) and LLDTs, Tier 2 began phasing in in 2004, with full implementation in MY 2007. For HLDTs and MDPVs, Tier 2 standards began phase-in in 2008, with full compliance in 2009. Up to and including model year 2008, manufacturers were required to calculate separate fleet average NOx emissions for the portion of their fleet of LDV/LLDT and HLDT/MDPV Tier 2 vehicles. Both were required to comply with the 0.07 g/mile standard (equivalent to bin 5) for the required phase-in percentage for that year. During the phase-in period, vehicles not used to meet the Tier 2 FTP phase-in requirements were still required to comply with the full useful life and intermediate useful life FTP exhaust emission standards for one of the available bins (i.e., at least bin 10 for LDV/LDTs and bin 11 for MDPVs). For 2004-2007, all passenger cars (LDVs) and LLDTs not certified to the primary Tier 2 standards (i.e., the 0.07 g/mile fleet average NOx) were required to meet an interim average standard of 0.30 g/mi NOx, equivalent to bin 9 and the NLEV standards for LDVs. During the period 2004-2008, HLDTs and MDPVs not certified to the final Tier 2 were required to meet an interim average standard of 0.20 g/mi NOx(equivalent to bin 8). Those vehicles not covered by the phase-in requirements were still subject to emission standards (i.e., bin 10, 0.6 g/mi NOx for HLDTs and bin 11, 0.9 g/mi NOx for MDPVs). Through model year 2007, manufacturers were able to opt to certify diesel engines for MDPVs through the heavy-duty diesel engine requirements instead of the entire vehicle through the light-duty regulations. These vehicles could not be used for compliance with phase-in requirements for interim non-Tier 2 MDPVs.

Phase-In Percentages for Tier 2 Requirements
Model year LDV/LLDT Tier 2a HLDT/MDPV
Tier 2b Interim Non-Tier 2c
2004 25 25
2005 50 50
2006 75 75
2007 100 100
2008 100 50 100
2009 and subsequent 100 100
Notes: a – Percentage of LDV/LLDTs that must meet Tier 2 requirements b – Percentage of HLDT/MDPVs that must meet Tier 2 requirements c – Percentage of non-Tier 2 HLDT/MDPVs that must meet interim non-Tier 2 fleet average NOx requirements

Useful life

The vehicle full useful life period for LDVs and light LDTs was extended to 120,000 miles or ten years whichever occurs first. For heavy LDTs and MDPVs, it was 11 years or 120,000 miles whichever occurred first. Manufacturers could elect to optionally certify to the Tier 2 exhaust emission standards for 150,000 miles to gain NOx credits or to opt out of intermediate life standards. In such cases, useful life was 15 years or 150,000 miles, whichever occurred first. For interim non-Tier 2 LDV/LLDTs, the useful life was 10 years or 100,000 miles, whichever occurred first.

Fuel Quality

The Tier 2 regulation introduced new requirements for fuel quality. Cleaner fuels were required by advanced emission aftertreatment devices (e.g., catalysts and particulate filters) that were necessary to meet the emission regulations.

  • Sulfur Levels in Gasoline—The program required that most refiners and importers meet a corporate average gasoline sulfur standard of 120 ppm and a cap of 300 ppm beginning in 2004. Since 2006, the average standard was reduced to 30 ppm with an 80 ppm sulfur cap. Temporary, less stringent standards applied to some small refiners through 2007. In addition, temporary, less stringent standards applied to a limited geographic area in the western USA for the 2004-2006 period.
  • Diesel Fuel Quality—Diesel fuel of maximum sulfur level of 15 ppm (known as ultra low sulfur diesel, ULSD) was made available for highway use beginning in June 2006. The reduction of sulfur content in diesel fuel was regulated by the EPA as a part of the 2007-2010 emission regulation for heavy-duty engines.

New Vehicle Testing and Certification

The EPA Tier 2 program uses a three-tiered compliance strategy. Pre-production evaluation is used to certify vehicles prior to sale. A production evaluation is used on the assembly line for early evaluation of production vehicles. Compliance and enforcement programs ensure in-use emissions are controlled for the useful life of the vehicle.

Supplemental Exhaust Emission Standards

In addition to meeting the FTP cycle requirements, certification of vehicles depended on compliance supplemental exhaust emission standards (US06 and SC03 driving cycles). Supplemental exhaust emission standards were required to be met by LDV and LDTs but not MDPVs, alternative fueled LDV/LDTs, or flexible fueled LDV/LDTs when operated on a fuel other than gasoline or diesel. With some exceptions, manufacturers are required to comply with 4,000 mile and full useful life SFTP (supplemental federal test procedure) standards. The Tier 2 SFTP standards were simply the Tier 1 SFTP standards combined with the NLEV SFTP requirements. The SFTP standards were not increased in stringency for Tier 2. The 4,000 mile SFTP standards for NMHC+NOx and CO are outlined below and are based on vehicle weight classification only.

4000 mile SFTP standards for Tier 2 LDVs and LDTs, g/mi
US06 SC03
LDV/LDT1 0.14 8.0 0.20 2.7
LDT2 0.25 10.5 0.27 3.5
LDT3 0.4 10.5 0.31 3.5
LDT4 0.6 11.8 0.44 4.0

Full useful life Tier 2 SFTP standards for NMHC+NOx, PM and CO are based on both vehicle weight classification and the certification bin applicable to that vehicle. They are equal to the Tier 1 SFTP standards minus 35% of the difference between the Tier 1 and Tier 2 FTP standards:

SFTP Standard = Tier 1 SFTP – 2

For example, an LDT4 certified to bin 10 would have the Tier 2 SFTP standards as shown below.

Example SFTP Standards (LDT4, Bin 10), g/mi
Tier 1 SFTPa Tier 1 FTP Tier 2 FTP Tier 2 SFTP
NMHC+NOx 2.09 0.56+1.53=2.09b 0.230+0.6=0.830c 1.65
PM 0.12d 0.12 0.08 0.11
CO 7.3 7.3 6.4 7.0
a – Available from 40 CFR 86.1811-04 b – Sum of NOx and NMHC standards c – Sum of NOx and NMOG standards d – Tier 1 FTP standard

Full useful life SFTP compliance is determined by weighting the emission test results as follows:

0.35(FTP) + 0.28(US06) + 0.37(SC03)

and comparing the result with the calculated SFTP standard. With the exception of HLDTs and bin 10 LDV/LLDTs, interim non-Tier 2 vehicles are required to meet Tier 2 SFTP requirements. Interim non-Tier 2 HLDTs need only have met 2002 SFTP requirements. Interim non-Tier 2 bin 10 LDV/LLDTs could meet Tier 1 SFTP requirements. SFTP standards for PM are not applicable to interim non-Tier 2 LDV/Ts. Gasoline fueled LDV/Ts and MDPVs are required to also meet cold temperature limits—measured on the FTP cycle at 20°F (-7°C)—for CO and certification short test limits for raw CO and HC concentrations that do not apply to diesels. The maximum projected NOx emissions measured on the federal Highway Fuel Economy Test (HWFET) cannot be greater than 1.33 times the applicable FTP NOx standard. This standard is not applicable to MDPVs.

Compliance and Enforcement

In-use evaluation is used to verify properly maintained vehicles after several years of use. The Tier 2 regulation also contains special in-use standards for:

  • NOx and NMOG emissions that apply to bin 5, 4, 3 and 2 LDV/LLDTs produced up through the 2008 model year and HLDT/MDPVs produced up through the 2010 model year
  • NOx and PM emissions for diesel vehicles certified to bin 10,High altitude NOx emissions for 2007-2009 model year diesel vehicles certified to bins 7 and 8

The table below summarizes the different vehicle categories and their testing requirements.

Vehicle Categories And Applicable Tests
Category FTP SC03 US06 Cold FTP Certification Short Test In-Use Hwy NOx Std
LDV, LLDT, LDT1-4, HLDT yes yes yes gasoline only gasoline only yes yes
MDPV yes1 no no gasoline only2 gasoline only2 yes no
1 – Manufacturers may alternatively certify engines for diesel fueled MDPVs through the heavy-duty diesel engine regulations 2 – Does not apply to interim Tier 2 vehicles

Other Provisions

  • For Tier 2 and interim non-Tier 2 vehicles beginning with the 2004 model year, manufacturers were required to ensure that the complete exhaust system had been designed to facilitate leak-free (i.e. leakage is controlled so as not to lead to the emission exceeding the limits) assembly, installation and operation for the full useful life of the vehicle. This covered all components from the engine block manifold gasket surface to a point sufficiently past the last catalyst and oxygen sensor in the system to assure that leaks beyond that point would not permit air to reach the oxygen sensor or catalyst under normal operating conditions.
  • No crankcase emissions were allowed to be discharged into the ambient atmosphere from any 2001 and later model year vehicles certified to these standards.
  • NOx Credits and Deficits. A manufacturer could generate Tier 2 or interm non-Tier 2 NOx credits or deficits depending on whether its fleet average NOx emissions exceed or were less than the fleet average standard. Credits could be banked for future use or traded to another manufacturer. If a manufacturer had a NOx deficit for a given model year, it was required to obtain sufficient credits from vehicles produced by itself or another manufacturer no later than three years after the year of the deficit. For example, if a manufacturer calculated that it had a NOx credit deficit for the 2008 model year, it was required to obtain sufficient NOx credits to offset that deficit from its own production or that of other manufacturers’ 2011 or earlier model year vehicles. Interim non-Tier 2 NOxcredits for LDV/LLDTs and HLDT/MDPVs were required to be generated, calculated, tracked, averaged, banked, traded, accounted for and reported upon separately from Tier 2 credits. They could not be used to meet the Tier 2 fleet average NOx standard and vise versa. Interim non-Tier 2 NOx credits from HLDT/MDPVs could not be used to meet the fleet average NOx standard for interim non-Tier 2 LDV/LLDTs, and vise versa.
  • Direct Ozone Reducing Devices. A manufacturer could obtain NMOG credit for use of direct ozone reducing devices in certifying the exhaust NMOG standards and for use in complying with in-use standards. The credit effectively allowed the manufacturer to increase the exhaust NMOG emission standards by the amount of the applicable credit. For example, if the applicable NMOG credit was 0.01 g/mi, and the vehicle was being certified in Bin 5, exhaust NMOG emissions must be no greater than 0.10 g/mi, as opposed to the normal NMOG certification standard of 0.09 g/mi for Bin 5.

Tier 3

In March 2014, U.S. EPA finalized new emission standards for vehicles and fuels, commonly referred to as Tier 3 emission standards. The standards, to be phased in from MY 2017 and fully implemented by MY 2025, will reduce both tailpipe and evaporative emissions from passenger cars, light-duty trucks, medium-duty passenger vehicles and some heavy-duty vehicles. Chassis-based emission requirements were extended to Class 2B and 3 work trucks (up to 14,000 lbs.), covering some vehicles that had formerly been included under heavy-duty emissions standards. Once fully implemented, the vehicle and fuel standards will reduce allowable emissions of volatile organic compounds and nitrogen oxides by 80%, and particulate matter by 70%, with additional reductions in allowable fuel vapor emissions. The medium- and heavy-duty pickup and work van tailpipe standards represent about a 60% reduction in fleet average NMOG+NOx and per-vehicle PM standards. The useful life period is also extended under the Tier 3 program to match California’s LEV III requirements. Under Tier 3 requirements, the vehicles must meet standards over the full useful life of 150,000 miles or 15 years. Due to legislative limitations under the Clean Air Act, EPA provided an option to comply with NMOG+NOx requirements over 120,000-mile / 10-year useful life, as under the Tier 2, provided that they certify vehicles to proportionally lower NMOG+NOx standards (85% of the 150,000-mile limits provided). Sulfur in gasoline will be reduced to 10 parts per million on average from 30 ppm, bringing gasoline fuel requirements in line with those already in place in Europe, Japan, and South Korea (although these countries have a 10 ppm cap rather than a 10 ppm average, as adopted by EPA). Changes to the fuel used for certification were also adopted, reflecting the widespread use of 10% ethanol blends in commercial gasoline. The requirements of the final rule remain largely the same as in the EPA’s April 2013 Notice of Proposed Regulation. The final rule does make four significant changes from the proposed rule:

  • Reduced the regulatory cost estimates: vehicle emission control cost estimates were cut from $134 per vehicle to $72 per vehicle in model year 2025; and full-phased in cost estimates for gasoline standards were reduced from 0.89 cents per gallon to 0.65 cents per gallon.
  • Adopted more stringent standards for Supplemental FTP (SFTP) particulate emissions
  • Changed certification fuel ethanol requirements from 15% to 10%
  • Provided fuel refineries more flexibility in phasing in sulfur reduction

The ICCT provides a detailed overview of both the original proposal and the significant changes in the final rule.

Limit Values and Phase-In for Light- and Medium-Duty Vehicles

The following sections summarize the provisions in the final rule as found in ICCT’s 2014 policy update. The Federal Test Procedure (FTP) standards cover the primary pollutants of concern — NMOG, NOx and PM — as well as carbon monoxide (CO) and formaldehyde (HCHO). The use of the combined NMOG+NOx standard is a significant change with respect to the Tier 2 program, which uses a NOx fleet-average standard. The FTP NMOG+NOx standards are fleet average standards. The manufacturer must certify each of its vehicles to a per-vehicle “bin” standard and sales-weight these values to calculate its fleet-average NMOG+NOx emissions for each model year. Each Tier 3 bin has a NMOG+NOx standard, as well as CO and HCHO standards. These vehicle emission limits apply equally to gasoline, diesel, and alternative-fueled vehicles. As with the Tier 2 program, the proposed standards would apply to all light-duty vehicles (LDVs) and light-duty trucks (LDTs) below 8,500 lbs maximum Gross Vehicle Weight Rating (GVWR), and medium-duty passenger vehicles (MDPVs) (8,500 to 10,000 lbs GVWR). The following table shows the phase-in schedule for light-duty cars and trucks and medium-duty passenger vehicles.

Phase-in for LDV, LDT, and MDPV Fleet Average FTP NMOG+NOx Standards [mg/mi]
Test Cycle Vehicle Class Tier 2 Tier 3 (Model Year)
2016a 2017b 2018 2019 2020 2021 2022 2023 2024 2025 and later
FTP LDV/LDT1c 160 86 79 72 65 58 51 44 37 30
FTP LDT2,3,4 and MDPV 160 101 92 83 74 65 56 47 38 30
a 120,000 mile useful life for Tier 2 b Starting with MY2018 for vehicles with GVWR >6,000 lbs c Tier 3 standards apply for a 150,000 mile useful life. Manufacturers could choose to certify all of their LDVs and LDT1s to a useful life of 120,000 miles. If any of these families are certified to the shorter useful life, a proportionally lower numerical fleet-average standard would apply, calculated by multiplying the respective 150,000 mile standard by 0.85 and rounding to the nearest mg.

In addition to FTP standards, Tier 3 includes NMOG+NOx and PM standards measured on the Supplemental FTP (SFTP). SFTP standards for NMOG and NOx are based upon two additional test cycles: the US06 is designed to simulate higher speeds and higher acceleration rates (and thus higher loads) and the SC03 simulates air conditioning operation at 95°F with full simulated sunload. SFTP NMOG+NOx standards are based upon a weighted composite value of emissions on the FTP, US06 and the SC03 (0.35 x FTP + 0.28 x US06 + 0.37 x SC03), as is done for the Tier 2 SFTP standards. The SFTP NMOG+NOx standards are fleet average standards, with the standards phased in as described in the following table. CO standards are 4200 mg/mile for all years.

Phase-in for Tier 3 LDV and MDPV Composite Fleet Average SFTP NMOG+NOx Standards [mg/mi]
Test cycle Pollutant Model year
2017 2018 2019 2020 2021 2022 2023 2024 2025+
SFTP NMOG + NOx 103a 97 90 83 77 70 63 57 50
SFTP CO 4200a
a Starting with MY2018 for vehicles with GVWR >6,000 lbs

Particulate matter (PM) standards are the same for each year and apply to each vehicle separately, with a phase-in period based on sales percentages used instead of a fleet average. The FTP PM standard for LDV and MDPV is 3 mg/mile, with a separate in-use FTP PM standard of 6 mg/mi during the phase in period. PM standards were also established for the US06 cycle, with 10 mg/mile for 2017 and 2018 and 6 mg/mile for all subsequent years, also with interim in-use standards for 2019 to 2023. Note that the US06 PM standards are one of the few changes from the proposed rule. The phase-in sales percentages are listed in the following table.

Phase-in for LDV, LDT, and MDPV Per-Vehicle PM Standards
Test cycle Variable Model year
2017a 2018 2019 2020 2021 2022 2023 2024
 % of US sales 20% 20% 40% 70% 100%
FTP Certification, mg/mile 3
In-Use, mg/mile 6 3
US06 Certification, mg/mile 10 6
In-Use, mg/mile 10 6
a Starting with MY2018 for vehicles with GVWR >6,000 lbs

Limit Values and Phase-In for Class 2b and 3 Heavy-Duty Vehicles

Tier 3 standards also extend the weight range of the vehicles subject to the standard. Tier 2 standards were limited to vehicles up to 10,000 lbs. Tier 3 standards regulate Class 2b and 3 work trucks (up to 14,000 lbs.) that had formerly been included under heavy-duty emissions standards. These vehicles are typically full size pickup trucks and work vans that are certified as complete vehicles on a chassis dynamometer and report emissions on a grams per mile basis. Current regulations allow for choosing between chassis or engine certification, with most manufacturers choosing the former. Tier 3 standards now fully incorporate these complete vehicles and require emissions to be decreased over time. Incomplete HDVs below 10,000 lbs GVWR will continue the current chassis vs. engine certification practice. The standards levels for both Class 2b and Class 3 HDVs are significantly higher than those for light-duty trucks due to marked differences in vehicle size, capability, and testing load condition. The bin structure and standards levels are consistent with those in the LEV III program. The HDV bin structure is presented below. The standard uses interim bins that are a carryover of previous standards. Interim bins do not include SFTP requirements, longer useful life requirements, or requirements to conduct exhaust emissions testing with the new gasoline test fuel.

Bin Structure of Tier 3 FTP Standards for HDVs [mg/mi]
NMOG+NOx NMOG NOx PM CO Formaldehyde
Class 2b (8,501-10,000 lbs GVWR)
Bin 395 (interim) 195 200 8 6.4 6
Bin 340 140 200 8 6.4 6
Bin 250 250 8 6.4 6
Bin 200 200 8 4.2 6
Bin 170 170 8 4.2 6
Bin 150 150 8 3.2 6
Bin 0 0 0 0 0
Class 3 (10,001-14,000 lbs GVWR)
Bin 630 (interim) 230 400 10 7.3 6
Bin 570 (interim) 170 400 10 7.3 6
Bin 400 400 10 7.3 6
Bin 270 270 10 4.2 6
Bin 230 230 10 4.2 6
Bin 200 200 10 3.7 6
Bin 0 0 0 0 0

Following the LDV bin structure, the rule applies HDV fleet average standards that change over time. The tightening of fleet average standards will shift the fleet mix from higher to lower bins over time. These standards are consistent with those in the LEV III program in MY2018 and later. Manufacturers are permitted to average the two fleet classes using credits.

Tier 3 HDV Fleet Average FTP NMOG+NOx Standards [mg/mi]
Voluntary Required program
Model Year 2016 2017 2018 2019 2020 2021 2022 and later
Class 2ba 333 310 278 253 228 203 178
Class 3b 548 508 451 400 349 298 247
a Complete trucks between 8,501 and 10,000 GVWR b Complete trucks between 10,001 and 14,000 GVWR

PM standards of 8 mg/mi and 10 mg/mi will be applied to Class 2b and Class 3 HDVs, respectively, phasing in as an increasing percentage of a manufacturer’s sales each year. EPA will use the same phase-in schedule as for the light-duty sector during model years 2018-2019-2020-2021: 20-40-70-100 percent, respectively. In addition, EPA provides a more flexible but equivalent alternative PM phase-in option that allows manufacturers that over-comply in early years to carry-over these benefits to meet phase-in requirements for later years. Tier 3 includes the first-ever SFTP standards for HDVs. As for light-duty vehicles, the SFTP compliance is based on a weighted composite of measured emissions over the FTP cycle, the SC03 cycle, and an aggressive driving cycle. This aggressive driving cycle is tailored to various HDV sub-categories: the US06 cycle for most HDVs, the highway portion of the US06 cycle for low power-to-weight Class 2b HDVs, and the LA-92 (or “Unified”) cycle for Class 3 HDVs. The SFTP standards are the same as those adopted for California LEV III vehicles, and will apply to NMOG+NOx, PM, and CO emissions.

Tier 3 SFTP Standards for HDVs [mg/mi]
Class 2b with horsepower (hp)/GWVR less than or equal to 0.024 hp/lba
FTP Bins 200, 250, 340 550 7 22
FTP Bins 150, 170 350 7 12
Class 2b
FTP Bins 200, 250, 340 800 10 22
FTP Bins 150, 170 450 10 12
Class 3
FTP Bins 270, 400, 570 550 7 6
FTP Bins 200, 230 350 7 4
a These standards apply for vehicles optionally tested using emissions from only the highway portion of the US06 cycle.

Evaporative Standards

Evaporative standards are designed to eliminate hydrocarbon emissions from fuel evaporation. Tier 3 evaporative standards will reduce evaporative emissions by about 50%. They apply to all gasoline light-duty and heavy-duty vehicles and encompass new evaporative limits, new bleed testing requirements, leak test, and on-board-diagnostics requirements. These requirements will be phased-in over a six model year period. Phase-in requirements for 2017 model year apply only to 40% of the combined fleet of LDVs, LDT1s and LDT2s; after that the sales percentage requirements, for all LDVs, LDTs, MDPVs and heavy-duty gasoline vehicles (HDGVs), are 60 percent for model years (MYs) 2018 and 2019, 80 percent for MYs 2020 and 2021, and 100 percent for MYs 2022 and later. The phase-in of both the bleed and leak tests are linked to the phase-in of the “zero” evaporative standards. When a vehicle certifies to the primary evaporative standards based upon the phase-in schedule, that vehicle will then also need to meet the bleed and leak tests. The standards allow manufacturers to generate credits through early certifications (before the 2017 MY) and to demonstrate compliance using averaging concepts. There will be no credit trading between evaporative classes. EPA is not proposing any changes to the existing light-duty running loss or refueling emission standards, with the exception of the certification test fuel requirement.

Tier 3 Evaporative Standards
Vehicle Class Highest Diurnal + Hot Soak Level, g/test (over both 2-day and 3-day SHED diurnal tests)
LDV, LDT1 0.300
LDT2 0.400
LDT3, LDT4, MDPV 0.500
HDGVs 0.600

Canister Bleed Emission test Tier 3 includes a new testing requirement referred to as the bleed emission test procedure to help ensure fuel vapor emissions are virtually eliminated. Under this requirement, manufacturers are required to measure diurnal emissions over the 2-day diurnal test procedure from just the fuel tank and the evaporative emission canister and comply with a 0.020 gram per test (g/test) standard for all LDVs, LDTs, and MDPVs, without averaging. The corresponding canister bleed test standard for HDGVs would be 0.030 g/test. These standards would be phased in over a period of six model years between MY 2017 and MY 2022, with the leak test phasing in beginning in 2018.

On-Board Diagnostics Systems (OBD)

Current EPA regulations allow manufacturers to certify On-Board Diagnostic (OBD) systems with CARB and to accept CARB OBD certifications. Tier 3 upgrades EPA’s requirements to be consistent with the latest CARB regulations. EPA has also made specific additions to enhance the implementation of the leak emission standard. EPA has adopted the current CARB OBD regulations effective for the 2017 MY. New leak standard and test procedure to control fuel vapor leaks The ODB system of current vehicles has the capability to check leaks in the vehicle’s evaporative emission control system. These systems employ either positive or negative pressure leak detection pumps or operate based on natural vacuum for negative pressure leak detection. EPA’s test is based on a similar concept of placing the system under a slight positive pressure (from an external source), measuring the flow needed to maintain that pressure in the fuel/evaporative control system, and converting that flow rate to an equivalent orifice diameter. This standard will prohibit leaks with a cumulative equivalent diameter of 0.02 inches or greater. This will help ensure vehicles maintain near zero fuel vapor emissions over their full useful life. New LDV, LDT, MDPV, and HDGVs less than or equal to 14,000 lbs. GVWR meeting the Tier 3 evaporative emission regulations will also be required to meet the leak emission standard beginning in the 2018 model year.


The rule provides vehicle manufacturers lead time and compliance flexibilities to minimize the regulatory burden. For example, early compliance and production of ultra-low emitting vehicles will result in manufacturer credits. Also, the requirements are almost completely harmonized with the California Air Resources Board (CARB) Low Emission Vehicle (LEV III) program, allowing automakers to sell the same vehicles in all 50 states.

Fuel Requirements

The rule requires a reduction in sulfur content in gasoline, from the current 30-ppm average to 10-ppm average, effective January 1, 2017. The sulfur limits at the refinery gate and downstream are unchanged from Tier 2, with maximum of:

  • 80 ppm for the refinery gate
  • 95 ppm for downstream

The rule also requires that oxygenates, such as denatured fuel ethanol, are compatible with the Tier 3 sulfur requirements.

Tier 2 and Tier 3 Gasoline Sulfur Standards
Standard Refinery annual average standard Refinery gate per gallon cap Downstream per gallon cap
Tier 2 30 ppm 80 ppm 95 ppm
Tier 3 10 ppma 80 ppm 95 ppm
a Effective Jan 1st, 2017 for most refiners and January 1st, 2020 for eligible small refiners and small volume refineries

The final rule provides certain flexibilities for refiners:

  • Simplifies and adds flexibility to the Averaging, Banking, and Trading program.
  • Allows Tier 2 sulfur credits from as early as 2012 to be used for Tier 3 compliance.
  • Delays compliance deadline for small refineries that process 75,000 bbl/day or less crude oil, to January 1, 2020.
  • Allows hardship provisions and temporary waivers for unforeseen circumstances.

Certification Fuel

EPA and CARB are updating and harmonizing requirements for the fuel used for certification testing. Changes include using fuel with 10% ethanol, reduction of octane specs to match regular-grade gasoline, and changes in distillation temperatures, aromatics, olefins, sulfur content, and benzene specifications to better match today’s in-use fuel and to be consistent with the updated gasoline sulfur and benzene requirements.

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