The global population is very mobile; many of us use planes, trains, ships, and cars to travel, while goods are transported vast distances by a semi-truck, plane, or train. The transportation sector is the single greatest source of greenhouse gas emissions (GHG) in the United States, making up 29 percent of all carbon emissions.

With 58%of all transportation sources and 17% of all U.S. output, passenger vehicles and trucks are the major contributors to GHG emissions in the transportation sector. When you are an agency owning a fleet, it is very important that you meet the fleet-average emission standards and greenhouse gas emission standards with certification bins. But how do you know if your fleet meets these crucial emissions standards?

EPA Emission Standards

The maximum amount of a certain pollutant that can be released into the atmosphere from a single source, whether mobile or stationary, is set by emission standards. The United States Environmental Protection Agency (EPA) has provided these standards which are applicable to all on- and off-road engines. Based on the clean air act (CAA), which was recently revised in 1990, EPA is empowered to control engine emissions and air quality in general in the United States.

There are limitations on the amount of certain gaseous, vapor, and particulate pollutants that can be emitted from any term process as well as from specific processes. There are three categories for engine categories, including a tier system. Each tier (Tier 1, Tier 2, Tier 3) refers to a different emission certification standard, as per the EPA and CAA.

Light-Duty Vehicles

The Light-Duty Vehicles (LDV) category includes all gasoline vehicles of less than 8500 lb gross loaded vehicle weight rating. Under the LDV category are passenger cars, light-duty trucks, sport utility vehicles (SUV), minivans, medium-duty passenger vehicles, and pick-up trucks, and they all release greenhouse gases (GHG) and smog-forming pollutants from their tailpipes.

Your agency’s fleet or all the complete vehicles it produces in a given model year must adhere to a set of yearly non-methane organic gases (NMOG) + nitrogen oxide (NOx) average. Until model year (MY) 2025, the fleet average cap decreased yearly. The regulation’s ultimate goal is represented by the indicated fleet average (MY 2025). Every year, a specific proportion of an operator’s fleet must comply with the mandated PM pollution standard term (0.003 g/mi); this proportion rises every year until it reaches 100 percent in MY 2021.

Heavy-Duty Vehicles

In the federal jurisdiction, heavy-duty vehicles are those with a gross loaded vehicle weight rating (GVWR) of more than 8,500 lbs, and more than 14,000 lbs in California by truck fleets (MY 1995 and later). Light heavy-duty diesel engines (LHDDE), medium heavy-duty diesel engines (MHDDE), and heavy-duty engines are the different service classes for diesel engines used in heavy-duty vehicles according to GVWR (HHDDE).

The current US federal evaporative emission standards for heavy-duty engines were phased in over the period of 2007-2010 where the following standards apply:

    • Smoke Opacity—Smoke opacity limits of 20% / 15% / 50% at acceleration/lug/peak modes, respectively, have been applicable since 1974.
    • Idle CO Standard—An idle CO emission standard of 0.5% applies to compression-ignition engines fueled by diesel fuel since 1988, by methanol since 1990, and by natural gas and LPG since 1994.
    • Idle NOx Standard—In California, idling NOx emission standards have been applicable since 2007.

Additionally, in the MY 2024 to 2027 and after, manufacturers must provide diesel engines emission certification to a NOx idling emission threshold of 10 g/hr and 5 g/hr, respectively. Diagnostic devices, technology systems, and programs may be installed in place of meeting the exhaust emission standards in heavy-duty low emission vehicles that adhere to the fuel standards.

fleet trucks in parking lot

Penalties for Excess Emissions

If the average CO2 emissions of a manufacturer’s fleet exceed its specific emission target in a given term, the manufacturer has to pay – for each of its vehicles newly registered in that year – an excess emissions premium of 40 CFR § 77.6 – for excess emissions of sulfur dioxide, carbon dioxide, nitrogen oxides that go above fuel fleet emission standards.

While it may be true that a large percentage of emissions from transportation comes from light-duty vehicles, that does not mean that truck fleets and service fleet vehicles are not significant contributors to these emissions. Although their impacts on carbon emissions are minuscule at best, there are still numbers involved with them as well.

Light-duty trucks and medium-duty vehicles were the largest sources of carbon monoxide emissions in transportation at 60%. Medium- and heavy-duty trucks were the second-largest source of evaporative emissions in transportation at 23% (this does not include heavy-duty diesel vehicles).


California has the right to independently establish its own regulations for vehicle emissions. California has set its own rules to reduce the levels of pollution in its state and has regulated the emission standards of certain vehicle classes.

This is because there is an exemption within California’s emission regulations that allows vehicle manufacturers who wish to continue selling their products in California to adhere to another standard than the one we set for them. Once EPA sets standards for a specific kind of engine category, it is up to manufacturers how they comply with these standards, within the specified time frames of an implementation program that corresponds with manufacture.

Changing Emissions Regulations

Using less fuel and having more electric vehicles results in fewer emissions, which helps to keep the air cleaner. The EPA’s Tier 4 standards, which are a part of this movement, significantly lower the allowable levels of exhaust emissions from diesel engines. These reduced emissions standards must be met by all newly produced diesel engines.

The laws governing car smog tests are handled at the state and local levels, while the EPA regulations deal with emissions on a nationwide level. Smog testing is not required in all states, and depending on the type of vehicle, some jurisdictions only require emissions testing at specific intervals (typically every two years).

Technology to Meet Changing Standards

Changing evaporative emission standards and the EPA’s Tier 4 regulations for diesel engines have changed the game for work truck fleets. Operators within the industry must know their obligations to the environment and invest in technology like heavy-duty low-emission vehicles, diagnostic scan tools, zero-emission vehicles, and electric vehicles that will help reduce idle times, lower maintenance costs, and increase fleet productivity.

The great news is that in terms of smog-related emissions, semi-trucks and other commercial trucking vehicles have improved fuel efficiency over the last 70 years. Engines have gone from 4 to 5 mpg up to 7 to 8 mpg. In some cases where fleets have been conscious about purchasing fuel-efficient vehicles, they’ve witnessed an average of 10 mpg. That may not seem like a lot, but over time, this can dramatically reduce your fleet’s carbon emissions, especially as regulations continue to evolve.

And as these stringent regulations continue to evolve, all-in-one innovative technologies and programs can help fleets stay ahead of the curve — substantially decreasing truck engine idling, reducing carbon monoxide emissions (and maintenance needs), extending chassis life, and saving money!

Make Sure Your Fleet Meets Emission Standards. Call Triad Diagnostic Solutions Today!

Request complete details of any of our commercial, off-highway, or material handling kits or schedule a demo with one of our technicians. This is especially useful if you’re experiencing issues with a commercial truck, automotive, or material handling equipment.