United States
- Regulatory Authorities
- Regulated Engines and Vehicles
- Emission Measurement Procedures
- Vehicle Weight Classes
- Auxiliary Emission Control Devices and Defeat Devices
Regulatory Authorities
Federal Standards. US federal emission standards for engines and vehicles, including emission standards for greenhouse gas (GHG) emissions, are established by the US Environmental Protection Agency (EPA). The EPA authority to regulate engine emissions—and the air quality in general—is based on the Clean Air Act (CAA), most recently amended in 1990.
Fuel economy standards are developed by the National Highway Traffic Safety Administration (NHTSA), an agency within the US Department of Transportation (DOT).
The development of engine emission standards occurs according to the procedures of the US rulemaking process. New regulations are first published as proposed rules. Following a period of public discussion, the new rule is finalized and signed into law. New regulatory proposals and regulations are published in the Federal Register. Consolidated regulations become a part of the Code of Federal Regulations (CFR).
California Standards. The State of California has the right to adopt its own emission regulations, which are often more stringent than the federal rules [5374]. Engine and vehicle emission regulations are adopted by the California Air Resources Board (CARB), a regulatory body within the California EPA.
California is the only state vested with the authority to develop its own emission regulations. Other states have a choice to either implement the federal emission standards, or else to adopt California requirements (CAA section 177).
Regulated Engines and Vehicles
Emission Standards for New Engines and Vehicles
The following categories of new engines and/or vehicles are subject to emission standards in the USA:
- Cars and Light Trucks: Tier 1 | Tier 2 | Tier 3 | California
- Heavy-Duty Truck and Bus Engines
- Mobile Nonroad Diesel Engines
- Railway Locomotives
- Marine Engines
- Small spark ignited (SSI) engines (≤ 19 kW)
- Large spark ignited (LSI) engines (> 19 kW)
- Stationary Engines: SI NSPS | CI NSPS | NESHAP
GHG & Fuel Economy
Fuel economy in new light-duty vehicles has been regulated since the 1970’s by CAFE standards administered by the National Highway Traffic Safety Administration (NHTSA), an agency within the Department of Transportation (DOT).
The first greenhouse gas regulations for motor vehicles were adopted in 2002 in California. At the federal level, GHG emission standards and harmonized CAFE regulations for light-duty vehicles were adopted in joint regulatory actions by the EPA and the NHSTA in 2010 and 2012. GHG/fuel economy regulation for heavy-duty trucks was adopted in 2011.
In California, zero-emission vehicle (ZEV) sales requirements are also applicable to manufacturers of light-duty as well as heavy-duty vehicles.
On-Board Diagnostics (OBD)
On-Board Diagnostic requirements—California and federal—apply to light-duty vehicles, as well as to increasing number of categories of heavy-duty engines. OBD regulations ensure compliance with emission standards by setting requirements to monitor selected emission system components (e.g., catalytic converters) or in-use emission levels, and to alert the driver/operator—such as by a dashboard-mounted malfunction indicator light—when a problem is detected.
In-Use Engine Regulations
In addition to new engine emission regulations, there is a growing number of programs—mandatory or incentive-based—to reduce emissions from in-use diesel engines. These initiatives are being implemented by all levels of government: federal, state, and local. We provide an overview of the following diesel programs:
Emission Measurement Procedures
Historically, the EPA has published emission test procedures along with emission standards in the relevant section of the Code of Federal Regulations (CFR). For example, heavy-duty engine test procedures were included in 40 CFR § 86 Subpart N [6243]. In 2002, the EPA initiated another approach for engine certification. Engine emission test procedures would be found in 40 CFR § 1065 [4010]. Engine test procedures affecting large spark-ignition engines and recreational vehicles where first incorporated into § 1065 in 2002 [6244] followed by nonroad Tier 4 engines in 2004 [2786], 2010 and later on road heavy-duty engines in 2005 [6245] and Tier 3 and 4 locomotive and marine engines in 2008 [3562]. This approach also affected the test fuels used to measure emissions as their properties are specified in the emission measurement procedure. Part 1065 specifies common test fuels used for the applications using these test procedures.
A similar approach occurred for vehicle emission test procedures. In 2011, the EPA established 40 CRF § 1066, initially to measure GHG emissions under the heavy-duty Phase 1 rule [2324]. In 2014, this was expanded to include criteria pollutants for vehicles at or below 14,000 lbs GVWR with the Tier 3 rule [2999]. In 2015, the Tier 3 rule was amended to require that all MY 2022 and later light- and heavy-duty vehicles, except motorcycles, previously subject to § 86 testing to use § 1066 procedures [6252]. It also applies to heavy-duty vehicles subject to the Phase 2 rule [2918]. Part 1066 references large portions of 40 CFR § 1065 to align test specifications that apply equally to engine-based and vehicle-based testing, such as CVS and analyzer specifications, calibrations, test fuels, calculations, and definitions of many terms.
While California emission test procedures generally follow those of the EPA, they are not always identical. California introduces changes to the relevant sections of the CFR and issues them as California Test Procedures. California test procedures relevant to heavy-duty engines include:
- California Exhaust Emission Standards and Test Procedures For 1985 Through 2003 Model Heavy Duty Diesel Engines And Vehicles [6246],
- California Exhaust Emission Standards and Test Procedures for 2004 and Subsequent Model Heavy‑Duty Diesel Engines and Vehicles [5726] and
- California Interim Certification Procedures for 2004 and Subsequent Model Hybrid-Electric and Other Hybrid Vehicles in the Urban Bus and Heavy‑Duty Vehicle Classes [6247].
California test procedures relevant to vehicles include [6253]:
- California 2015 and Subsequent Model Criteria Pollutant Exhaust Emission Standards and Test Procedures and 2017 and Subsequent Model Greenhouse Gas Exhaust Emission Standards and Test Procedures for Passenger Cars, Light Duty Trucks, and Medium Duty Vehicles (LEV III) [6254] and
- California 2026 and Subsequent Model Year Criteria Pollutant Emission Standards and Test Procedures for Passenger Cars, Light-Duty Trucks, and Medium-Duty Vehicles (LEV IV) [6255].
Vehicle Weight Classes
Some of the commonly used US vehicle weight classifications based on the gross vehicle weight rating (GVWR) are summarized in the following tables.
| GVWR (lbs) | Federal Highway Administration | US Census Bureau | |
|---|---|---|---|
| Vehicle Class | GVWR Category | VIUS Classes | |
| ≤ 6,000 | Class 1 | Light Duty ≤ 10,000 lbs | Light Duty ≤ 10,000 lbs |
| 6,001-10,000 | Class 2 | ||
| 10,001-14,000 | Class 3 | Medium Duty 10,001-26,000 lbs | Medium Duty 10,001-19,500 lbs |
| 14,001-16,000 | Class 4 | ||
| 16,001-19,500 | Class 5 | ||
| 19,501-26,000 | Class 6 | Light Heavy Duty 19,501-26,000 lbs | |
| 26,001-33,000 | Class 7 | Heavy Duty ≥ 26,001 lbs | Heavy Duty ≥ 26,001 lbs |
| > 33,000 | Class 8 | ||
| GVWR (lbs) | EPA Emissions Classifications | |||
|---|---|---|---|---|
| Heavy Duty Vehicles and Engines | Light Duty Vehicles | |||
| HD Trucks | HD Engines | General Trucks | Passenger Vehicles | |
| ≤ 6,000 | Light Duty Trucks 1 & 2 | Light Light Duty Trucks ≤ 6,000 lbs | Light Duty Trucks ≤ 8,500 lbs | Light Duty Vehicles (LDV) ≤ 8,500 lbs |
| 6,001-8,500 | Light Duty Trucks 3 & 4 | Heavy Light Duty Trucks 6,001-8,500 lbs | ||
| 8,501-10,000 | Heavy Duty Vehicle 2b | Light Heavy Duty Engines 8,501-19,500 lbs | Heavy Duty Vehicle Heavy Duty Engine ≥ 8,500 lbs | Medium Duty Passenger Vehicles (MDPV) 8,501-10,000 lbs |
| 10,001-14,000 | Heavy Duty Vehicle 3 | |||
| 14,001-16,000 | Heavy Duty Vehicle 4 | |||
| 16,001-19,500 | Heavy Duty Vehicle 5 | |||
| 19,501-26,000 | Heavy Duty Vehicle 6 | Medium Heavy Duty Engines 19,501-33,000 lbs | ||
| 26,001-33,000 | Heavy Duty Vehicle 7 | |||
| 33,001-60,000 | Heavy Duty Vehicle 8a | Heavy Heavy Duty Engines Urban Bus ≥ 33,001 lbs | ||
| > 60,000 | Heavy Duty Vehicle 8b | |||
California. For light-duty vehicles, the classifications used by CARB are harmonized with those by the US EPA. Heavy-duty vehicles, on the other hand, are defined in California as those having GVWR of above 14,000 lbs (for MY 1995 and later). The corresponding California classes of diesel engines used in heavy-duty vehicles are:
- Light heavy-duty diesel engines: 14,000 lbs ≤ LHDDE ≤ 19,500 lbs
- Medium heavy-duty diesel engines: 19,500 lbs ≤ MHDDE ≤ 33,000 lbs
- Heavy heavy-duty diesel engines: HHDDE > 33,000 lbs
In addition, California regulations often use a medium-duty vehicle (MDV) designation, in reference to various low-GVWR sub-categories of heavy-duty vehicles. The MDV definition was changed on several occasions. In most MY 2000 and newer applications, MDVs have been defined as vehicles of 8,500 lbs < GVWR ≤ 14,000 lbs. Diesel powered MDVs can be emission certified under either chassis or engine dynamometer procedure. The engines used in these vehicles are referred to as medium-duty engines (MDE).
Auxiliary Emission Control Devices and Defeat Devices
Under some operating conditions, components of the emission control system can be shut-off or deactivated. This is usually done for reasons including: ensuring engine start-up, protection of the vehicle against damage or accident and preventing the unwanted shut-down of emergency vehicles or equipment. Deactivating components of the emission control system is carried out using what is called an Auxiliary Emission Control Device (AECD). EPA regulations define an AECD as:
any element of design which senses temperature, vehicle speed, engine RPM, transmission gear, manifold vacuum, or any other parameter for the purpose of activating, modulating, delaying, or deactivating the operation of any part of the emission control system.
The EPA definition for emission control system covers all components that are used to control emissions including: aftertreatment devices, engine modifications, sensors, actuators, EGR system and so on.
A defeat device is an AECD that reduces the effectiveness of the emission control system under conditions which may reasonably be expected to be encountered in normal vehicle operation and use. Defeat devices are prohibited. In order for manufacturers to certify their vehicles and engines, during the application for certification, they must submit a list of AECDs, justify their use, explain how they work and demonstrate that the AECDs are not defeat devices.
While there are some differences, the definitions of AECD, emission control system and defeat device as well their approval is relatively consistent for light-, medium- and heavy-duty vehicles and engines as well as nonroad engines.