Introduction

The Tier 2 regulation introduced more stringent numerical emission limits relative to the previous 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 limit.

The Tier 2 emission standards were phased-in from 2004 to 2009. Under the Tier 3 proposal, Tier 2 stadards will be phased-out and replaced by Tier 3 regulations over the period of 2017-2015.

In Tier 2, the applicability of light-duty emission standards has been extended to cover some of the heavier vehicle categories. The Tier 1 standards applied to vehicles up to 8500 lbs GVWR. The Tier 2 standards apply to all vehicles that were covered by Tier 1 and, additionally, to “medium-duty passenger vehicles” (MDPV). The MDPV is a new class of vehicles that are rated between 8,500 and 10,000 lbs GVWR and are used for personal transportation. This category includes primarily larger SUVs and passenger vans. Table 1 outlines and defines the vehicle categories used in the EPA Tier 2 standards. Engines in commercial vehicles above 8500 lbs GVWR, such as cargo vans or light trucks, continue to certify to heavy-duty engine emission standards.

Table 1
Vehicle Categories Used in EPA Tier 2 Standards
Vehicle CategoryAbbreviationRequirements
Light-Duty VehicleLDVmax. 8500 lb GVWR
Light-Duty TruckLDTmax. 8500 lb GVWR,
max. 6000 lb curb weight and
max. 45 ft2 frontal area
Light light-duty truckLLDTmax. 6000 lb GVWR
Light-duty truck 1LDT1max. 3750 lb LVW1
Light-duty truck 2LDT2min. 3750 lb LVW1
Heavy light-duty truckHLDTmin. 6000 lb GVWR
Light-duty truck 3LDT3max. 5750 lb ALVW2
Light-duty truck 4LDT4min. 5750 lb ALVW2
Medium-Duty Passenger VehicleMDPVmax. 10000 lb GVWR3
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. That is, 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) have to use more advanced emission control technologies than vehicles with smaller engines in order to meet the standards.

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. Finally in-use evaluation is used to verify properly maintained vehicles after several years of use.

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

  • Sulfur Levels in Gasoline—The program requires 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 has been 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 QualityDiesel fuel of maximum sulfur level of 15 ppm (known as the ultra low sulfur diesel, ULSD) was made available for highway use beginning in June 2006. The reduction of sulfur content in diesel fuel was legislated by the EPA as a part of the 2007-2010 emission regulation for heavy-duty engines.

Tier 2 Certification Bins

The Tier 2 emission standards are structured into 8 permanent and 3 temporary certification levels of different stringency, called “certification bins”, and an average fleet standard for NOx emissions. Vehicle manufacturers have a choice to certify particular vehicles to any of the available bins. When fully implemented in 2009, the average NOx emissions of the entire light-duty vehicle fleet sold by each manufacturer has to meet the average NOx standard of 0.07 g/mi. The temporary certification bins (bin 9, 10, and an MDPV bin 11) with more relaxed emission limits are available in the phase-in period and expire after the 2008 model year.

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 must still meet the requirements of one of the available bins but have more relaxed fleet average requirements.

The emission standards for all pollutants (certification bins) when tested on the Federal Test Procedure (FTP) are shown in Table 2. Where intermediate useful life exhaust emission standards are applicable, such standards are applicable for five years or 50,000 miles, whichever occurs first. The vehicle “full useful life” period for LDVs and light LDTs has been extended to 120,000 miles or ten years whichever occurs first. For heavy LDTs and MDPVs, it is 11 years or 120,000 miles whichever occurs first. Manufacturers may 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 is 15 years or 150,000 miles, whichever occurs first. For interim non-Tier 2 LDV/LLDTs, the useful life is 10 years or 100,000 miles, whichever occurs first.

Table 2
Tier 2 Emission Standards, FTP 75, g/mi
Bin#Intermediate life (5 years / 50,000 mi)Full useful life
NMOG*CONOxPMHCHONMOG*CONOx†PMHCHO
Temporary Bins
11 MDPVc0.2807.30.90.120.032
10a,b,d,f0.125 (0.160)3.4 (4.4)0.4-0.015 (0.018)0.156 (0.230)4.2 (6.4)0.60.080.018 (0.027)
9a,b,e,f0.075 (0.140)3.40.2-0.0150.090 (0.180)4.20.30.060.018
Permanent Bins
8b0.100 (0.125)3.40.14-0.0150.125 (0.156)4.20.200.020.018
70.0753.40.11-0.0150.0904.20.150.020.018
60.0753.40.08-0.0150.0904.20.100.010.018
50.0753.40.05-0.0150.0904.20.070.010.018
4-----0.0702.10.040.010.011
3-----0.0552.10.030.010.011
2-----0.0102.10.020.010.004
1-----0.0000.00.000.000.000
* 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

a - Bin deleted at end of 2006 model year (2008 for HLDTs)
b - The higher temporary NMOG, CO and HCHO values apply only to HLDTs and MDPVs and expire after 2008
c - An additional temporary bin restricted to MDPVs, expires after model year 2008
d - Optional temporary NMOG standard of 0.195 g/mi (50,000) and 0.280 g/mi (full useful life) applies for qualifying LDT4s and MDPVs only
e - Optional temporary NMOG standard of 0.100 g/mi (50,000) and 0.130 g/mi (full useful life) applies for qualifying LDT2s only
f - 50,000 mile standard optional for diesels certified to bins 9 or 10

It may be noted that bin 5 has a NOx limit of 0.07 g/mi, which is equal to the fleet average NOx standard. 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.

The EPA bins cover California LEV II emission categories, to make certification to the federal and California standards easier for vehicle manufacturers.

Tier 2 Emission Standards Phase-In

The Tier 2 standards are phased-in between 2004 and 2009, as shown in Table 3. For new passenger cars (LDVs) and LLDTs, Tier 2 standards phase-in begins in 2004, with full implementation in the 2007 model year. For HLDTs and MDPVs, the Tier 2 standards are phased in beginning in 2008, with full compliance in 2009.

Up through and including model year 2008, manufacturers must calculate separate fleet average NOx emissions for the portion of their fleet of LDV/LLDT and HLDT/MDPV Tier 2 vehicles being phased-in. Both must 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 must still comply with the full useful life and intermediate useful life FTP exhaust emission standards for one of the available bins listed in Table 2 (i.e., at least bin 10 for LDV/LDTs and bin 11 for MDPVs).

During the period 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) must 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 must meet an interim average standard of 0.20 g/mi NOx (equivalent to bin 8) following the schedule in Table 2. Those vehicles not covered by the phase-in requirements are still subject to the emission standards listed in Table 1 (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, a manufacturer may 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 cannot be used for compliance with phase-in requirements for interim non-Tier 2 MDPVs.

Table 3
Phase-In Percentages for Tier 2 Requirements
Model yearLDV/LLDT
Tier 2a
HLDT/MDPV
Tier 2bInterim Non-Tier 2c
20042525
20055050
20067575
2007100100
200810050100
2009 and subsequent100100
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

Supplemental Exhaust Emission Standards

In addition to meeting the FTP cycle requirements of Table 2, certification of a vehicles requires that it also meet supplemental exhaust emission standards (US06 and SC03 driving cycles). These must 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 must comply with 4000 mile and full useful life SFTP (supplemental federal test procedure) standards. The 4000 mile SFTP standards for NMHC+NOx and CO are outlined in Table 4 and are based on vehicle weight classification only.

Table 4
4000 mile SFTP standards for Tier 2 LDVs and LDTs, g/mi
US06SC03
NMHC+NOxCONMHC+NOxCO
LDV/LDT10.148.00.202.7
LDT20.2510.50.273.5
LDT30.410.50.313.5
LDT40.611.80.444.0

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 - [0.35 × (Tier 1 FTP - Tier 2 FTP)]

For example, an LDT4 certified to bin 10 would have the Tier 2 SFTP standards as shown in Table 5.

Table 5
Example SFTP Standards (LDT4, Bin 10), g/mi
Tier 1 SFTPaTier 1 FTPTier 2 FTPTier 2 SFTP
NMHC+NOx2.090.56+1.53=2.09b0.230+0.6=0.830c1.65
PM0.12d0.120.080.11
CO7.37.36.47.0
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 must meet Tier 2 SFTP requirements. Interim non-Tier 2 HLDTs need only meet 2002 SFTP requirements and interim non-Tier 2 bin 10 LDV/LLDTs can 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 must 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) must not be greater than 1.33 times the applicable FTP NOx standard. This standard is not applicable to MDPVs.

The Tier 2 regulation also contains special in-use standards for:

  • NOx and NMOG emissions that apply to 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.

Table 5 summarizes the different vehicle categories and their testing requirements.

Table 6
Vehicle Categories And Applicable Tests
CategoryFTPSC03US06Cold FTPCertification Short TestIn-UseHwy NOx Std
LDVyesyesyesgasoline onlygasoline onlyyesyes
LDTyesyesyesgasoline onlygasoline onlyyesyes
LLDTyesyesyesgasoline onlygasoline onlyyesyes
LDT1yesyesyesgasoline onlygasoline onlyyesyes
LDT2yesyesyesgasoline onlygasoline onlyyesyes
HLDTyesyesyesgasoline onlygasoline onlyyesyes
LDT3yesyesyesgasoline onlygasoline onlyyesyes
LDT4yesyesyesgasoline onlygasoline onlyyesyes
MDPVyes1nonogasoline only2gasoline only2yesno
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, manufacturer’s must ensure that the complete exhaust system has been designed to facilitate leak-free (i.e. leakage is controlled so as not to lead to the emissions exceeding the limits) assembly, installation and operation for the full useful life of the vehicle. This covers 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 will not permit air to reach the oxygen sensor or catalyst under normal operating conditions.

No crankcase emissions are 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 may generate Tier 2 or interm non-Tier 2 NOx credits or deficits depending on whether its fleet average NOx emissions exceed or are less than the fleet average standard. Credits may be banked for future use or traded to another manufacturer. If a manufacturer has a NOx deficit for a given model year, it must 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 calculates that it has a NOx credit deficit for the 2008 model year, it must 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 NOx credits for LDV/LLDTs and HLDT/MDPVs must be generated, calculated, tracked, averaged, banked, traded, accounted for and reported upon separately from Tier 2 credits. They may not be used to meet the Tier 2 fleet average NOx standard and vise versa. Interim non-Tier 2 NOx credits from HLDT/MDPVs may 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 may obtain NMOG credit for use of direct ozone reducing devices in certifying to the exhaust NMOG standards and for use in complying with the in-use standards. This credit effectively allows 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.