Overview of Amendments to the In‑Use Off‑Road Diesel‑Fueled Fleets Regulation

Image of heavy-duty diesel fueled off-road construction equipment parked at a construction site.

Overview of Amendments to the In‑Use Off‑Road Diesel‑Fueled Fleets Regulation

Background

Off‑road heavy‑duty diesel‑powered vehicles are a diverse group, ranging from small skid steer loaders used in residential landscaping to very large mining trucks, and include dozers, forklifts, cranes, and excavators. The California Air Resources Board (CARB) has regulated in‑use off‑road diesel vehicles since 2008 through the In‑Use Off‑Road Diesel‑Fueled Fleets Regulation (Off‑Road Regulation). The Off‑Road Regulation was subsequently amended twice in 2009, and again in 2010. The Off‑Road Regulation requires fleets to reduce their emissions by retiring older vehicles and replacing the retired vehicles with newer vehicles, repowering older engines, or installing verified diesel emission control strategies in older engines; and by restricting the addition of older vehicles to fleets. CARB recently approved additional amendments to the Off-Road Regulation which are effective October 1, 2023, and described in further detail below.

Need for Amending the Regulation

As seen in the figure shown below, the importance of achieving further oxides of nitrogen (NOx) emissions reductions from the off‑road sector, which includes off‑road equipment subject to the Off-Road Regulation, is only getting more critical as the relative share of on‑road NOx emissions continues to decline due to CARB’s robust on‑road regulatory and incentive policies. The arrow in Figure 1 displays the point at which the emissions from the combined off‑road sector exceed those of on‑road vehicles.

Statewide Emissions of NOx by Mobile Sector The graph shows that on-road emissions start at 2000 tons per day statewide in 2000, but drop by more than 80 percent by 2030. The graph shows off-road equipment, boats and trains at 900 tons per day in 2000, but reduce much more slowly, with around 40 percent reduction in 2030. This leaves off-road sources (including ships and trains) more than double on-road emissions in 2030. The off-road sources surpass on-road in 2019. — Figure 1. Statewide Emissions of NOx by Mobile Source Sector

Off‑road diesel vehicles also emit diesel particulate matter (PM) which has been identified as a toxic air contaminant by CARB and poses a significant public health risk, especially at the local level. Action is needed to reduce diesel PM at a statewide level to reduce the health risk throughout California, especially in communities that experience disproportionate burdens from exposure to toxic air contaminants.

Emission standards for new engines have become progressively cleaner and are divided into increasingly stringent levels (Tiers), starting with Tier 1. Although the population of older vehicles is relatively small - Tiers 0 (or uncontrolled), 1, and 2 only make up one third of the statewide fleet reported to CARB - this small population contributes 60 percent of the NOx and PM emissions in 2022. A single, older Tier 0 off‑road engine has up to 80 times higher emissions per hour compared to a new Tier 4 Final engine. Figure 2 displays the zero‑hour NOx emission factor for engines with a horsepower of 100‑175.

Off-Road Engine Emission Factors (NOx) This graph shows the emission factors of each tier of off-road engine, shown in zero-hour NOx (gram/bhp-hr). Tier 0 has an emission factor of 11.0, Tier 1 is 5.65, Tier 2 is 3.97, Tier 3 is 2.99, Tier 4 initial is 1.87, and Tier 4 final is 0.13. — Figure 2. Off-Road Emission Factors by Tier

Elements of the Amendments

Phase out of the oldest and highest‑emitting off‑road engines from operation in California. The chart below outlines the year, on January 1 of that year, in which the tier phase‑out requirements would begin for each fleet size:

Table 1. Tier and Model Year (MY) Phase‑Out Dates by Fleet Size
Year (January 1)	Large Fleets	Medium Fleets	Small Fleets	Ultra‑Small Fleets
2024	Tier 0/MY 1994 or older on‑road
2026	Tier 1/MY 1999 or older on‑road	Tier 0/MY 1994 or older on‑road
2028	Tier 2/MY 2003 or older on‑road	Tier 1/MY 1999 or older on‑road	Tier 0/MY 1994 or older on‑road	Tier 0/MY 1994 or older on‑road
2030		Tier 2/MY 2003 or older on‑road	Tier 1/MY 1999 or older on‑road	Tier 1/MY 1999 or older on‑road
2032			Tier 2/MY 2003 or older on‑road
2036				Tier 2/MY 2003 or older on‑road

Restrict the addition of vehicles with Tier 3 and 4i engines, which is an expansion of provisions of the Off-Road Regulation that restrict the vehicle‑engine Tier that can be added to a fleet:

Table 2. Compliance Dates for the Restrictions on Adding Vehicles
Year (January 1)	Large Fleets	Medium Fleets	Small Fleets	Ultra‑Small Fleets
2024	Tier 3 Tier 4i/MY 2006 or older on‑road	Tier 3 Tier 4i/MY 2006 or older on‑road	Tier 3	Tier 3
2028			Tier 4i/MY 2006 or older on‑road
2035				Tier 4i/MY 2006 or older on‑road

Starting January 1, 2024, require contracting entities to obtain and retain a fleet’s valid Certificate of Reported Compliance prior to awarding a contract or hiring a fleet;
Starting January 1, 2024, mandate the use of R99 or R100 Renewable Diesel for all fleets, with some limited exceptions;
Provide voluntary compliance flexibility options for fleets that adopt zero‑emission technology; and
Include additional requirements to increase enforceability, provide clarity, and provide additional flexibility for permanent low‑use vehicles.

Benefits of the Amendments

The Amendments are estimated to reduce statewide emissions from off‑road diesel‑fueled vehicles by approximately 31,000 tons of NOx and 2,700 tons of PM beyond the reductions expected from the baseline between 2024‑2038.
The following charts compare the estimated NOx and PM emissions under the baseline and the Amendments and show the year‑by‑year estimated emissions reductions achieved via the Amendments.

This graph shows the projected NOx emissions from off-road diesel vehicles under the Baseline scenario, represented by the dashed blue curve, and the Amendments, represented by the solid orange curve, from 2022 through 2038. The two curves begin together, with about 15300 tons of NOx per year, but diverge starting in 2024. The baseline scenario shows a continued NOx emission decrease that slightly slows around 2030. The Amendments show a quick drop in emissions in the first year, and continues to decrease, keeping a reduction of about 3000 tons of NOx per year compared to the baseline scenario, before beginning to slow in 2028, with the gap in emissions between the two scenarios slowly reduced. By 2038, the NOx emissions under the baseline scenario is projected to be 5300 tons per year, compared to the NOx emissions of 4000 tons under the Amendments. — Figure 3. Statewide NOx Emissions from Off-Road Diesel Vehicles Under the Baseline and Amended Regulation from 2022 to 2038

This graph shows the projected PM emissions from off-road diesel vehicles under the Baseline scenario, represented by the dashed blue curve, and the Amendments, represented by the solid orange curve, from 2022 through 2038. The two curves begin together, with about 830 tons of PM per year, but diverge starting in 2024. The baseline scenario shows a continued PM emission decrease that slightly slows around 2030. The Amendments show a quick drop in emissions in the first year, and continues to decrease, keeping a reduction of about 240 tons of PM per year compared to the baseline scenario, before beginning to slow in 2028, with the gap in emissions between the two scenarios slowly reduced. By 2038, the PM emissions under the baseline scenario is projected to be 220 tons per year, compared to the NOx emissions of 120 tons under the Amendments. — Figure 4. Statewide PM Emissions from Off-Road Diesel Vehicles Under the Baseline and Amended Regulation from 2022 to 2038.

The Amendments are expected to provide additional emissions reductions and associated improvements to air quality that will help protect all communities and would benefit environmental justice communities located in areas with increased exposure to air pollution and toxics from in‑use off‑road diesel vehicles.
Avoids an estimated 570 premature deaths, 82 hospital admissions for cardiovascular illnesses, 98 hospital admissions for respiratory illnesses, 277 emergency room visits, and provides an estimated $5.7 billion in benefits versus $1.9 billion in net costs.

Is Funding Available?

Funding programs are available that offer incentives for cleaner and advanced technology for in‑use off‑road diesel‑fueled vehicles, as well as supporting electric charging or alternative fueling infrastructure. Note that many of these programs are competitive, and some fund a variety of projects other than off‑road diesel equipment. For more information about additional funding opportunities, visit CARB Incentive Programs.

More Information

The rulemaking documents can be found at: https://ww2.arb.ca.gov/rulemaking/2022/off-roaddiesel
For general information about the Off-Road Regulation and to access all reporting forms, visit The Off-Road Zone at www.arb.ca.gov/offroadzone.

California Air Resources Board