Regulatory Authorities

Federal Standards

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. 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.

Table 1
States adopting California’s clean cars standards
StateLegislationYear AdoptedMY Effective*
New JerseyP.L. 2003, Chapter 26620042009
ConnecticutPublic Act 04-8420042008
WashingtonHouse Bill 139720052009
VermontAmendments to Subchapter XI20052009
New YorkChapter III, Subpart 218-820052009
MaineAmendments to Chapter 12720052009
Rhode IslandAir Pollution Control Regulation No. 3720052009
MassachusettsAmendments to the state’s LEV regulations20052009
OregonDivision 257; OAR 340-256-0220; Division 1220062009
ArizonaExecutive Order 2006-1320062011
PennsylvaniaAmendments to Title 25, Chapters 121 and 12620062008
MarylandSenate Bill 10320072011
Florida†Executive Order 07-1272007
New MexicoExecutive Order 2006-6920072016
* 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:

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.

Table 2
Vehicle weight classifications by the US FHA and US Census Bureau
Gross vehicle weight rating (lbs)Federal Highway AdministrationUS Census Bureau
Vehicle ClassGVWR CategoryVIUS Classes
≤ 6,000Class 1: ≤ 6,000 lbsLight Duty ≤ 10,000 lbsLight Duty ≤ 10,000 lbs
10,000Class 2: 6,001-10,000 lbs
14,000Class 3: 10,001-14,000 lbsMedium Duty 10,001-26,000 lbsMedium Duty 10,001-19,500 lbs
16,000Class 4: 14,001-16,000 lbs
19,500Class 5: 16,001-19,500 lbs
26,000Class 6: 19,501-26,000 lbsLight Heavy Duty 19,501-26,000 lbs
33,000Class 7: 26,001-33,000 lbsHeavy Duty ≥ 26,001 lbsHeavy Duty ≥ 26,001 lbs
> 33,000Class 8: > 33,000 lbs
Table 3
Vehicle weight classifications by the US EPA
Gross vehicle weight rating (lbs)EPA Emissions Classifications
Heavy Duty Vehicles and EnginesLight Duty Vehicles
HD TrucksHD EnginesGeneral trucksPassenger Vehicles
≤ 6,000Light Duty Trucks 1 & 2: ≤ 6,000 lbsLight Light Duty Trucks: ≤ 6,000 lbsLight Duty Trucks ≤ 8,500 lbsLight Duty Vehicles ≤ 8,500 lbs
8,500Light Duty Trucks 3 & 4: 6,001-8,500 lbsHeavy Light Duty Trucks: 6,001-8,500 lbs
10,000Heavy Duty Vehicle 2b: 8,501-10,000 lbsLight Heavy Duty Engines: 8,501-19,500 lbsHeavy Duty Vehicle
Heavy Duty Engine
≥ 8,500 lbs
Medium Duty Passenger Vehicles 8,501-10,000 lbs
14,000Heavy Duty Vehicle 3: 10,001-14,000 lbs
16,000Heavy Duty Vehicle 4: 14,001-16,000 lbs
19,500Heavy Duty Vehicle 5: 16,001-19,500 lbs
26,000Heavy Duty Vehicle 6: 19,501-26,000 lbsMedium Heavy Duty Engines: 19,501-33,000 lbs
33,000Heavy Duty Vehicle 7: 26,001-33,000 lbs
60,000Heavy Duty Vehicle 8a: 33,001-60,000 lbsHeavy Heavy Duty Engines
Urban Bus:
≥ 33,001 lbs
> 60,000Heavy Duty Vehicle 8b: ≥ 60,001 lbs