Regulatory Authorities
Federal emission standards for engines and vehicles 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, most recently amended in 1990.
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.
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 | 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
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.
GHG & Fuel Economy
At the federal level, fuel economy in new light-duty vehicles is regulated by CAFE standards. There are no federal CO2 and/or greenhouse gas (GHG) emission standards.
In California, GHG emission regulations were adopted from light-duty vehicles, but are being challenged in court by the automotive industry.
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:.