https://nacfe.org/research/run-on-less/messy-middle/emissions-report/

From Source to Highway:
The Messy Middle Emissions Report

Vehicle emissions are an exceptionally broad and complex subject when it comes to understanding the contribution North American freight movement has on the environment and the people who inhabit it. Emissions are one of the things NACFE tracked during Run on Less – Messy Middle.

From Source to Highway: The Messy Middle Emissions Report looks at transportation emissions including carbon dioxide, methane, nitrogen oxides, sulfur oxides and particulate matter of trucks operating with a variety of powertrains including diesel, natural gas, battery electric and hydrogen fuel cell across various regions in North America Each of these powertrain options has different characteristics from an emissions standpoint.

NACFE’s mission is to help fleets invest in cost saving technologies that improve efficiency and reduce emissions. Taken together the three reports from Run on Less – Messy Middle on operations, total cost of ownership and emissions have brought clarity to long-haul. Using the three reports together should give fleet managers a clear path for making decisions on which efficiency technologies are best suited for their operation.

Fleet Group #1: Diesel

As the North American commercial transportation sector navigates the transition toward a decarbonized future the role of the internal combustion engine remains a subject of intense scrutiny and rigorous innovation. However, using advanced filters and chemical treatments in the exhaust, manufacturers have reduced these pollutants by more than 96%. Soon it will take approximately 100 trucks built to 2027 standards to equal the pollution of just one truck from the 1990s.

The Run on Less – Messy Middle diesel group participants have provided a rebuttal to the notion that the internal combustion engine is obsolete. Through the data provided by Albert Transport, Frito-Lay, MVT, and Schneider, NACFE observed a technology that is mature yet capable of radical improvement. Whether through the aerodynamic rigor of MVT, the biogenic fuel adoption of Frito-Lay, the craftsmanship of Albert Transport, or the balanced approach of Schneider, these fleets demonstrate that the Messy Middle is not a waiting room for the future — it is an active construction site for a cleaner present. 

Fleet Group #2: Natural Gas

Natural gas vehicles, using CNG or liquefied natural gas (LNG), offer a distinct emissions profile defined by the properties of methane. Natural gas is a fuel with the potential to help reduce total GHG emissions with significant advantage in reducing the more immediate and local health effects caused by air pollutants like NOx and PM.

The net CO₂ benefit of a natural gas engine is in the range of 13% to 18% compared to diesel fuel. Natural gas produces approximately 27% less CO₂ per unit of energy on a fuel-comparison basis compared with No. 2 diesel fuel. However, the natural gas engine is less efficient than a diesel, and natural gas must be compressed for storage on the vehicle.

The Cummins X15N (natural gas) represents a paradigm shift from the traditional diesel architecture, despite being part of the same HELM fuel-agnostic platform. While it shares many components below the head gasket with the X15 diesel, its combustion strategy and aftertreatment are fundamentally different.

In the Messy Middle, the natural gas group demonstrated that fleets do not need to wait for a BEV breakthrough to make massive strides in sustainability. The hardware is ready, the fuel is potent, and as these three fleets have proven, the natural gas truck is ready to work.

Fleet Group #3: Battery Electric Vehicles

Tailpipe, or tank-to-wheel, emissions from a BEV in operation are virtually zero. The vehicle propulsion system emits no NOx, PM, or CO₂ during operation, providing immediate air quality benefits in local operating environments. Therefore, discussions about BEV emissions must revolve around the well-to-tank supply of energy to the vehicle batteries.

The data confirms that in 2025, battery-electric trucks are no longer experimental curiosities but rather are capable workhorses. With efficiencies ranging from 1.6 to 1.9 kWh/mile, these vehicles are converting energy into motion at a rate three to four times more efficient than diesel engines. Environmentally, the impact is profound — achieving GHG reductions of 62% to 99% depending on the grid and eliminating local criteria pollutants entirely.

Fleet Group #4: Hydrogen Fuel Cell Vehicles

Hydrogen fuel cell vehicles (FCEV) ideally emit only water vapor and warm air. The chemical reaction taking place inside the fuel cell is remarkably clean compared to an internal combustion engine.

The participants of Run on Less – Messy Middle confirm FCEVs have the potential to successfully navigate today’s Messy Middle. The two FCEV’s in the Run demonstrated when the vehicle technology is paired with a developing fuel supply chain — whether centralized like Pilot’s or modular like OneH2’s — the result has the potential to be a viable, scalable, and zero-emission replacement for the heavy-duty diesel truck. The question is no longer if the technology works, but how fast the infrastructure and vehicles can mature to meet it.

Comparative Analysis: Navigating the Messy Middle

As fleet operators evaluate their options for decarbonization, they are faced with a matrix of choices: clean diesel, fossil diesel, RNG, BEV, and FCEV. Each has a distinct health impact profile when analyzed from a lifecycle perspective.

RNG represents a unique opportunity to decouple heavy-duty trucking from the challenges of diesel. From a criteria pollutant standpoint, modern natural gas engines are inherently cleaner than diesel. The battery-electric truck is the gold standard for local health. With zero tailpipe emissions, a BEV eliminates street-level NOx, PM, and VOCs entirely. FCEVs offer a middle ground. Like BEVs, they have zero tailpipe emissions (emitting only water vapor). Their health impact is entirely determined by the production method of the hydrogen.

Key Findings

The study team identified key findings impacting the transition of the North American heavy-duty trucking industry.

1. Fuel/Energy Origin Outweigh Engine/Powertrain Technology: The carbon footprint of a truck is determined more by the origin of the fuel molecule than the metal of the engine block.
2. Alternative Fuels Achieve Diesel-Like Performance: The era of yesterday’s underpowered alternative energy truck is over.
3. Decarbonization as a Public Health Need: The health impact from freight emissions are large and unevenly distributed. Reducing emissions in populated freight corridors leads to significant reductions in negative health outcomes and healthcare cost expenditures.
4. The Driver Impact: Drivers have as significant an impact on fuel economy and emissions reductions as do the truck technologies.
5. Fleets Should Include Emissions Considerations in their Decisions: As fleets look to the many options available when considering their next truck purchases, it is important to include emissions considerations along with operational and total cost of ownership in decision making.