Future emissions standards in the US and California for heavy-duty vehicles

Future emissions standards in the US and California for heavy-duty vehicles
08 December 2021

In November 2018, the US EPA (Environmental Protection Agency) first announced an initiative aimed at revising emissions standards for heavy-duty vehicles. According to the EPA, heavy-duty vehicles are a large contributor to NOX emissions and they account for 32% of NOX emissions from all mobile sources. Current emissions standards for heavy-duty diesel vehicles in the US have been in place since model year 2010; the current emissions limit for NOX is 0.20 g/bhph and for PM is 0.01 g/bhph. The EPA is currently reviewing heavy-duty vehicles emissions standards with the aim of reducing emissions and improving air quality.

This initiative will see the preparation of a new regulation that will include revised NOX emissions limits for heavy-duty trucks and engines; in January 2020, the EPA issued an Advanced Notice of Proposed Rule.  The publication of this document is the first step towards the draft regulation containing updated emissions requirements for heavy-duty vehicles in the US. In August 2021, the EPA announced the Clean Trucks Plan; a new document was published which confirms the EPA’s plans to revise emissions standards for heavy-duty vehicles, with a particular focus on lowering NOX emissions. Updated emissions standards are due to be published by the end of 2022.

In this post, we take a look at the future emissions standards in the US and California and at the optional programme California is already following to reduce NOX emissions from heavy-duty vehicles.
What developments for heavy-duty emissions standards have been announced?
The current work on developing new emissions standards aims to make sure that emissions reductions occur in the real world in all types of truck operation - the updated legislation will establish new, more stringent emissions standards for NOX and other pollutants for heavy-duty engines. The November 2018 announcement followed on from a response in December 2016, when over 20 state and local government agencies sent petitions to the EPA, requesting a revision of the NOX emissions standards for heavy-duty vehicles. The Advanced Notice of Proposed Rule identifies the need, in particular, to further reduce NOX emissions from heavy-duty vehicles at a federal level to improve air quality. The EPA examined several topics in the Advanced Notice with regards to the reduction of emissions and possible improvements in the certification procedure; these include the following:

  • Potential improvement for hybrid and other advanced technology vehicle certification
  • Lower emissions limits and possible changes to the test cycles used to determine emissions
  • Expansion of the in-use requirements to capture nearly all real-world operation (similar to the in-use programme in the EU).
  • The increase of mileage-based useful life values to be more reflective of real-world usage.

One of the key focus areas of the new standards will be the reduction of NOX emissions during trucks operation under low-load conditions, as reported in the August 2021 update. Manufacturers will be given sufficient lead time to meet new requirements; the new regulation is expected to be finalised by the end of 2022, with the new standards coming into effect from model year 2027. The EPA also announced that it will revise the Phase 2 GHG (greenhouse gas) emissions standards, possible updates to these requirements could come into effect starting from model year 2027 as well.

Further updates and explanation of US heavy-duty vehicle emissions legislation and CO2 emissions standards can be discovered by subscribing to EMLEG.

What is the status in California?
CARB, the California Air Resources Board, which regulates emissions requirements in California, developed options for voluntary low NOX certification from model year 2015. The low NOX voluntary programme allows certification to three levels of NOX emissions, the lowest being 0.02 g/bhph, which corresponds to a 90% reduction on the current mandatory limit. In 2019, several gas engines were certified to the optional low NOX standards.

In June 2020, CARB approved the Advanced Clean Trucks regulation which requires heavy-duty vehicle manufacturers to sell an increasing proportion of zero-emissions (ZEV) and near-zero emissions vehicles (NZEV) in California, starting from the model year 2024. The final approval to the regulation was issued in March 2021; these new requirements are based on a system of deficits and credits, where credits are generated when a manufacturer sells ZEVs and NZEVs which fulfil specific requirements. Each manufacturer will have to achieve enough credits to offset the deficits, for every model year. The Advanced Clean Truck Regulation is part of an holistic approach to accelerate large-scale reduction of emissions.

CARB published a proposal for updated heavy-duty standards and test procedures named the Heavy-Duty Omnibus Regulation in June 2020. The updated standards for California will cover both diesel and gasoline engines/vehicles and will apply from model year 2024; California is set to implement updated standards for heavy duty vehicles three years before the new federal standards are likely to come into effect. One of the many aspects of the new regulation is the introduction of lower NOx limits in two stages: from 2024 and then from 2027. Heavy-duty diesel vehicles of model year 2027 and after will have to comply with a NOX limit of 0.02 g/bhph, which is the same value required by the current most stringent optional low NOX certification. These new standards will also require compliance with emissions limits on a new low-load tests cycle. The CARB new standards were prepared in their final form in October 2021; you can keep up to date with developments in California’s heavy-duty vehicle regulations by subscribing to EMLEG.

Within EMLEG, you can find details of the EPA and CARB proposed and final emissions standards as well as all updates or developments in the standards; details and explanation of emissions standards for all heavy-duty vehicles in over 50 countries are included. In addition to heavy-duty vehicles regulation information, you’ll also discover details of regulations for other market sectors including light-duty vehicles, motorcycles, non-road engines and more.
New details are added into EMLEG as they are published, which provides an easy way to keep track of and understand emissions standards by country and market sector. Discover more about EMLEG and request a demo.