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).
The State of California has the right to adopt its own emission regulations, which are often more stringent than the federal rules. Engine and vehicle emission regulations are adopted by the California Air Resources Board (ARB), 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). States that adopted California Clean Car Standards—including the California LEV II and GHG emission standards—are listed in the following table.
|State||Legislation||Year Adopted||MY Effective*|
|New Jersey||P.L. 2003, Chapter 266||2004||2009|
|Connecticut||Public Act 04-84||2004||2008|
|Washington||House Bill 1397||2005||2009|
|Vermont||Amendments to Subchapter XI||2005||2009|
|New York||Chapter III, Subpart 218-8||2005||2009|
|Maine||Amendments to Chapter 127||2005||2009|
|Rhode Island||Air Pollution Control Regulation No. 37||2005||2009|
|Massachusetts||Amendments to the state’s LEV regulations||2005||2009|
|Oregon||Division 257; OAR 340-256-0220; Division 12||2006||2009|
|Arizona||Executive Order 2006-13||2006||2011|
|Pennsylvania||Amendments to Title 25, Chapters 121 and 126||2006||2008|
|Maryland||Senate Bill 103||2007||2011|
|Florida†||Executive Order 07-127||2007|
|New Mexico||Executive Order 2006-69||2007||2016|
* Generally refers to GHG standards, LEV II standards became effective earlier in some states|
† Pending ratification by the Legislature
Source: Maryland Department of The Environment, 2007
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 Diesel Engines (NSPS)
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 legislation 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.
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. At this time we provide an overview of the following diesel programs:.
Vehicle Weight Classes
Some of the commonly used US vehicle weight classifications are summarized in the following tables.
|Gross vehicle weight rating (lbs)||Federal Highway Administration||US Census Bureau|
|Vehicle Class||GVWR Category||VIUS Classes|
|≤ 6,000||Class 1: ≤ 6,000 lbs||Light Duty ≤ 10,000 lbs||Light Duty ≤ 10,000 lbs|
|10,000||Class 2: 6,001-10,000 lbs|
|14,000||Class 3: 10,001-14,000 lbs||Medium Duty 10,001-26,000 lbs||Medium Duty 10,001-19,500 lbs|
|16,000||Class 4: 14,001-16,000 lbs|
|19,500||Class 5: 16,001-19,500 lbs|
|26,000||Class 6: 19,501-26,000 lbs||Light Heavy Duty 19,501-26,000 lbs|
|33,000||Class 7: 26,001-33,000 lbs||Heavy Duty ≥ 26,001 lbs||Heavy Duty ≥ 26,001 lbs|
|> 33,000||Class 8: > 33,000 lbs|
|Gross vehicle weight rating (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: ≤ 6,000 lbs||Light Light Duty Trucks: ≤ 6,000 lbs||Light Duty Trucks ≤ 8,500 lbs||Light Duty Vehicles ≤ 8,500 lbs|
|8,500||Light Duty Trucks 3 & 4: 6,001-8,500 lbs||Heavy Light Duty Trucks: 6,001-8,500 lbs|
|10,000||Heavy Duty Vehicle 2b: 8,501-10,000 lbs||Light Heavy Duty Engines: 8,501-19,500 lbs||Heavy Duty Vehicle|
Heavy Duty Engine
≥ 8,500 lbs
|Medium Duty Passenger Vehicles 8,501-10,000 lbs|
|14,000||Heavy Duty Vehicle 3: 10,001-14,000 lbs|
|16,000||Heavy Duty Vehicle 4: 14,001-16,000 lbs|
|19,500||Heavy Duty Vehicle 5: 16,001-19,500 lbs|
|26,000||Heavy Duty Vehicle 6: 19,501-26,000 lbs||Medium Heavy Duty Engines: 19,501-33,000 lbs|
|33,000||Heavy Duty Vehicle 7: 26,001-33,000 lbs|
|60,000||Heavy Duty Vehicle 8a: 33,001-60,000 lbs||Heavy Heavy Duty Engines|
≥ 33,001 lbs
|> 60,000||Heavy Duty Vehicle 8b: ≥ 60,001 lbs|