Key Emissions Regulations You Need to Be Aware of in 2026

2026 is shaping up to be a big one for heavy-duty diesel operators. At both the federal and state levels, emissions regulations are being tightened, and now more than ever, remaining compliant has never been so important. These changes are set to impact us all when it comes to the maintenance, repairs, and upgrades of our vehicles. 

Here you will find everything you need to know about the new federal emissions mandates and those of our home state, Illinois, as well as how to prepare for them.

Federal Emissions Regulations Coming in 2026

EPA Phase 2 Greenhouse Gas (GHG) Emissions Standards: Final Step Hits

The EPA’s Phase 2 GHG standards, finalized in 2016, roll out the final tier of requirements for heavy-duty trucks, trailers, and buses starting with model year 2027. This is the final step in this policy and is expected to come into effect in mid-2026.

These rules target CO₂ emissions, fuel efficiency, and overall system integration.

Key requirements:

• Advanced aerodynamic technologies
  
  
• Low rolling resistance tires
  
  
• Automatic engine shutdown systems
  
  
• More efficient powertrains and transmission controls

Who it affects: Class 2b through Class 8 vehicles (vocational trucks, buses, and tractors)

EPA 2027 Heavy-Duty NOx Rule (Part of Clean Trucks Plan)

Though it’s labeled as a 2027 rule, this one hits the streets in mid-to-late 2026. It’s the first big move under the EPA’s Clean Trucks Plan, targeting deep cuts in nitrogen oxide (NOx) emissions.

It’s so big that this new ruling aims to cut NOx limits by 80–90% compared to current standards.

What it includes:

• Tougher limits on engine-out NOx
  
  
• Extended emissions warranties (from ~435,000 mi to ~800,000 mi on some trucks)
  
  
• New DEF quality sensors and DPF regeneration monitoring
  
  
• Major changes to tampering detection and ECM enforcement

Illinois-Specific Emissions Rules (Chicago and Statewide)

Illinois Adopts the Advanced Clean Trucks (ACT) Rule

Illinois adopted California’s ACT rule in July 2023, committing the state to a timeline to electrify and reduce emissions from medium- and heavy-duty trucks. Although these rules begin with fleet reporting in 2024, the impact becomes much more visible in 2026 as model-year requirements and compliance expectations expand.

The ACT rule doesn’t ban diesel, but it does force manufacturers to sell a certain percentage of zero-emission trucks (ZETs) in Illinois.

How it impacts fleets:

• May see limited diesel options for some truck classes
  
  
• More electric and hybrid offerings from OEMs in the region
  
  
• Increased regulatory pressure on diesel fleet renewal

Illinois Diesel Emissions Reduction Act (DERA) and I-M Clean Air Act

While not new, Illinois’ participation in the Diesel Emissions Reduction Act (DERA) and its own Illinois-Metropolitan (I-M) Clean Air Act will affect many diesel fleets as enforcement tightens in 2026.

Key rules to know:

• Mandatory vehicle emissions testing in designated counties (including Cook County)
  
  
• Incentives and grants to retrofit or replace older diesel engines
  
  
• Penalties for operating non-compliant trucks in inspection zones

How to Prepare Your Diesel Fleet for 2026

These new rules aren’t just theoretical—they’ll show up in your maintenance costs, parts availability, and compliance paperwork. Here's how to stay ahead:

1. Audit Your Fleet’s Emissions Systems

Check if your EGR, DPF, and SCR systems are functioning optimally. Faulty sensors or clogged filters can trigger compliance failures fast.

2. Stay Current with ECM Updates

With tighter EPA rules, manufacturers are rolling out software updates that affect DEF dosing, idle limits, and emission monitoring. Failing to address these updates can mean falling out of compliance.

3. Prioritize Preventive Maintenance

Don’t wait for forced regeneration or DEF errors. Create a PM schedule that proactively handles aftertreatment maintenance, especially as systems become more sensitive.

4. Start Exploring ZEV Options

Illinois fleets may soon be required to add zero-emission vehicles (ZEVs) to stay compliant under the ACT rule. Look into grants and pilot programs early to reduce upfront costs.

In Summary

Whether you're running a bus depot in downtown Chicago or hauling freight across I-80, 2026 brings a regulatory wave that demands your attention. Between federal limits on GHG and NOx and Illinois’ aggressive move toward clean trucks, there's no room for guesswork. Stay compliant, stay ahead, and most of all, stay running.

Don’t get sidelined by emissions compliance. Get a professional aftertreatment systems inspection, have your software updated, and lock in your PM schedule now, because 2026 is just around the corner, and you can’t afford to be on the wrong side of emissions regulations.