US: Light-duty: Emissions

Overview

 * Standard type: Conventional pollutant emission limits
 * Regulating body: US Environmental Protection Agency (EPA)
 * Current standard: Tier 2
 * Future standard: Tier 3 standards are currently under development
 * Applicability: Vehicles up to 8,500 lbs GVWR and “medium-duty passenger vehicles” (MDPV) - larger SUVs and passenger vans 8,500-10,000 lbs GVWR

History
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 are currently under development, with proposed rules expected to be released by the end of 2013. The Tier 3 requirements are expected to 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.

Tier 1
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).

 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).

 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 &times; FTP_+ 0.28 &times; US06 + 0.37 &times; SC03. Intermediate life (50,000 mi) standards are shown in parentheses.

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&gt;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. The complete regulatory text is 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.

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.

The emission standards for all pollutants (certification bins) when tested on the FTP75 are shown below.

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.

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.

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 &times; (Tier 1 FTP - Tier 2 FTP)]

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

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&deg;F (-7&deg;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.

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 NOx credits 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
On 3 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. Once the vehicle and fuel provisions are fully implemented, smog-forming volatile organic compounds and nitrogen oxides will be reduced by 80% from current levels, particulate matter will be reduced by 70%, and fuel vapor emissions will be driven to near zero levels. In addition, the medium- and heavy-duty pickup and work van tailpipe standards represent about a 60% reduction in both fleet average NMOG+NOx and per-vehicle PM standards. EPA is also extending the regulatory useful life period during which the standards apply from 120,000 miles to 150,000 miles.

Sulfur in gasoline will be reduced to 10 parts per million on average from 30 ppm today, bringing gasoline fuel requirements in line with those already in place in California, 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, which was comprehensively summarized by the ICCT in 2013. The final rule does make four significant changes from the proposed rule, which are detailed in the ICCT's 2014 policy update:


 * Vehicle emission control cost estimates were cut from $134 per vehicle to $72 per vehicle in model year 2025, and clean fuel cost estimates, fully phased in over all gasoline, were reduced from 0.89 cents per gallon to 0.65 cents per gallon gasoline.


 * 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

Regulatory Documents
Tier 1 legislative text

Tier 2 legislative text

Tier 3 legislative text