When fleets seek to track and reduce vehicle emissions, the obvious place to start is tailpipe emissions. But emissions are also associated with extracting, producing, transporting fuel, and generating electricity.

The term “well-to-wheel emissions” represents the bigger emissions picture. In this Fleet 101 article, we'll cover everything you need to know about well-to-wheel emissions!

What Does ‘Well-to-Wheel Emissions’ Mean?   

The term “well-to-wheel emissions” considers all the emissions associated with the complete lifecycle of a fuel, from its production (the “well”) to its use (the “wheel”).

Well-to-wheel emissions can be broken down into two parts:

• Well-to-tank: Emissions that happen between extraction through delivery to a fueling station and transfer to a vehicle or on-site fuel tank.

• Tank-to-wheel: Emissions associated with burning the fuel to power a vehicle (i.e., tailpipe or end-of-lifecycle emissions).

“Well-to-wheel emissions refers to the total emissions produced by a fuel from the point of extraction or generation to the point of use inside a vehicle,” said Chase LeCroy, technical deputy director for Calstart, a national nonprofit focused on accelerating clean transportation. “This encompasses the entirety of emissions to produce and consume that fuel source.” 

Can Well-to-Wheel Emissions Be Calculated?

The short answer is yes. But the better question is, should fleets be responsible for calculating well-to-wheel emissions?

“Well-to-wheel emissions can be calculated and measured, but it’s also useful as a concept for fleets to understand that emissions at the tailpipe are not the only emissions produced by vehicles,” LeCroy said. 

Tim Venghaus, sustainability solutions engineer for PDI Technologies, said whether to calculate well-to-wheel emissions often depends on the fleet size and how far along they are on their sustainability journey. 

“For most fleets, especially smaller ones and companies just starting to measure emissions, this is probably not very important. But as their reporting becomes more sophisticated, they may want to calculate a more holistic representation of their fleet emissions. This includes associated emissions in the drilling, refining, and transportation of fuels,” he said.

Venghaus offers a few caveats about calculating well-to-wheel emissions:

• Other upstream companies, such as oil and gas companies and refineries, are already reporting well-to-tank emissions. “These emissions are outside the fleet operator’s control, meaning they cannot influence decisions to increase efficiency/reduce emissions in the process,” Venghaus explained.

• What fleets can control are tank-to-wheel emissions, which could be lessened by optimizing routes, reducing idling, coaching drivers to fuel-efficient behaviors, buying aerodynamic after-market products, and buying more efficient vehicles. “The tank-to-wheel emissions would be reported as scope 1 emissions for the fleet operator, and scope 3 — specifically category 11 ‘use of sold products’ — by the oil and gas company,” Venghaus added.

Do Well-to-Wheel Emissions Apply to All Vehicle Types?

Although the term suggests that well-to-wheel only applies to vehicles that run on fossil fuels, the concept applies to all vehicle types — but the emissions are calculated differently depending on the energy source.

1. Fossil Fuels

For a fossil fuel like gasoline, well-to-Wheel emissions would encompass emissions generated when it is drilled (at the “well”) up until it is burned inside a vehicle (the “Wheel”), including any emissions generated for refinement and processing in between.

“The amount of well-to-wheel emissions depends on the refining and extraction processes used to produce those fuels. To calculate these values, CARB’s carbon intensity values (the amount of CO2 generated by burning fuel) will consider emissions generated by the production of that fuel source,” LeCroy said.

Venghaus said that well-to-tank emissions might be hard to pin down, and tailpipe emissions are what matter most to fleets.

“The tank-to-wheel portion covers the majority of your vehicle’s footprint. Most fleets would be fine focusing on just this number and comparing that to the electricity emissions for their electric vehicles (EVs),” he said. “However, it is also worth mentioning that aside from carbon and greenhouse gases (GHGs), traditional vehicles emit criteria pollutants that create smog, harm respiratory systems, and have other adverse effects on human health and well-being. EVs and fuel cell vehicles (FCV) do not emit these pollutants and can significantly improve local air quality.”  

2. Zero-Emission Vehicles

While it’s true that EVs and other zero-emission vehicles (ZEVs) don’t have tailpipe emissions, emissions do occur upstream during power generation — essentially, the “well-to-tank” emissions.

“For electric vehicles, this is a simple calculation, multiplying the amount of energy used by the Total Output Emissions Rate (the amount of CO2 generated per MWh of energy generated) for the local grid,” LeCroy explained.  

Venghaus notes that the location where electricity is produced is an integral part of the equation. “The emissions profile will vary based on where the fleet is located as different utilities have different mixes of fuel sources (coal, natural gas, nuclear, renewables, etc.). A company can easily look this up on the EPA eGRID database.”

LeCroy agrees that the fuel sources used to generate electricity must be renewable to make the most significant impact when switching to EVs.

“Swapping all vehicles to electric vehicles is not a one-stop-shop solution to traffic emissions and must occur concurrently with a switch to greener energy sources overall,” he said. “The overall impact on the climate from the electrification of fleets is heavily correlated with the fleet’s location.”

For instance, in states like Washington or California, with electrical grids powered mainly through renewable energy sources, switching to EVs will have a bigger impact than if a fleet is in a state that primarily uses fossil fuels to generate electricity.

“Advocating for a transition to renewable energy is an important cause that will help lower fleets’ well-to-Wheel emissions,” LeCroy said. “It is important to note that in many of these fossil-fuel reliant states (such as New York), the transition to cleaner energy sources has already begun.”

3. Hydrogen

Hydrogen fuel-cell vehicles (FCVs) or fuel-cell electric vehicles (FCEVs) are essentially electric vehicles that store energy in the hydrogen fuel cell instead of batteries.

“The combustion of hydrogen does create emissions but only water, no GHGs or smog-related emissions. So, like an EV, they only have well-to-tank emissions, Venghaus explained. “Hydrogen can produce in various ways, and the dirtiest methods can have a larger carbon footprint than an equivalent gas-powered car. However, using renewable energy, hydrogen produced via electrolysis is a zero-carbon fuel.”

What Are the Key Takeaways for Fleets?

LeCroy said that, although the concept of well-to-wheel emissions is eye-opening, it’s OK for fleets to focus primarily on the “wheel” part of the equation.

“Well-to-wheel emissions are an important concept to keep in mind, but generally not as important to track as closely as tailpipe emissions,” he said. “Since these emissions directly correlate with the amount of energy and fuel burned, fleets should make sure to minimize those emissions.” 

Venghaus noted that understanding well-to-wheel emissions is most important when making vehicle acquisition choices.

“Being aware of this concept should help paint a more inclusive picture of the total impacts of our energy use, which can help inform decisions as we explore potential fuels and vehicles. This is only one consideration to weigh, along with things like performance and duty requirements, fuel availability, vehicle availability, costs, and TCO, etc.,” he said. “The most applicable use of this knowledge is probably looking at your local energy grid to see how big of an impact an EV can have over an internal combustion engine (ICE). In some regions of the country with a high reliance on coal, this will be small to potentially negative. In other regions, with a high renewables ratio, you’ll get a bigger ‘return’ in carbon reductions.”

Although well-to-wheel emissions for EVs can vary, LeCroy suggests fleets should still have urgency in adopting electric vehicles.

“It is still important to move away from fossil fuel-powered vehicles quickly,” he said. “The energy grid is already moving toward greener sources, and the benefits of EVs to local air quality should not be undersold.”

No one has a crystal ball, and the future of propulsion is still far from certain. Right now, the future of clean fleet's might be electric, but today it's propane autogas, biodiesel, ethanol, renewable alternatives, and so much more. 

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