Definitions
Definitions of the following common terms in the 2025 Transportation ATB are presented below:
Vehicles
Vehicle Terms
Vehicle cost and emissions depend in part on fuel characteristics. Some powertrains use more than one fuel because of blending of liquid fuels or multiple fueling options for plug-in hybrid electric vehicles.
Operating costs and emissions depend in part on the mix of electricity generation sources that are used. The grid mix alternatives that are available in the ATB are described on the Electricity page.
Vehicles are classified by powertrain, the energy source, energy conversion device, and propulsion system. Some powertrains include additional detail, such as range, hybrid configuration, and turbocharging.
The primary fuel menu can be used to select which fuel a vehicle will use. This allows display of costs and emissions for that vehicle using the selected fuel.
For battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell electric vehicles (FCEVs), vehicle ranges are specified because they are an important determinant of modeled vehicle prices. Interactive charts for each of these vehicle powertrain types include a vehicle range filter. Vehicle ranges correspond to those used in the underlying sources cited. As technologies and markets develop, the ranges studied in these references may shift. For assumptions about vehicle ranges in the ATB, see the Vehicle Range Assumptions page.
The ATB displays vehicle data in two vehicle weight categories: 1) light-duty vehicles and 2) medium- and heavy-duty vehicles. Each vehicle weight category is subdivided further by vehicle size class.
A representative sample of body types and size classes is included in the ATB. Definitions and data on other body types and size classes can be found in Islam et al. (2023). For the list of vehicle size classes in the ATB, see the Vehicle Size Class Assumptions page.
The assumed vehicle life in years by vehicle size class is on the Levelized Cost of Driving Assumptions page.
Vehicle Powertrains
Battery electric vehicles use a battery pack to store the electrical energy that powers the motor. The batteries are charged by plugging the vehicle into an electric power source (DOE, 2024). For additional background, see the Alternative Fuels Data Center's All-Electric Vehicles webpage. For assumptions about BEVs in the ATB, see the Battery Electric Vehicle Assumptions page.
Diesel internal combustion vehicles have a compression-ignited injection system. In a combustion chamber, the engine piston plug compresses the injected diesel fuel, raising the temperatures until ignition occurs (DOE, 2024). For additional background, see the Alternative Fuels Data Center's How Do Diesel Vehicles Work? webpage. For assumptions about diesel internal combustion engine vehicles in the ATB, see the Diesel Internal Combustion Engine Vehicle page.
Fuel cell electric vehicles use fuel cells for energy conversion, which are more efficient than internal combustion engines. FCEVs use hydrogen as the power source, convert the hydrogen to electricity, and emit water vapor and warm air with no other tailpipe emissions. FCEVs and the supporting hydrogen fueling infrastructure are in an early deployment stage (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Fuel Cell Electric Vehicles webpage. For assumptions about FCEVs in the ATB, see the Fuel Cell Electric Vehicle Assumptions page.
Gasoline hybrid electric vehicles use both an internal combustion engine that uses gasoline and an electric motor (or motors). Electrical energy for the motors is stored as chemical energy in batteries. They have high fuel economy and low tailpipe emissions, with power and range comparable to those of conventional vehicles (DOE, 2024). For additional information, see the Alternative Fuels Data Center's Hybrid Electric Vehicles webpage. For assumptions about gasoline hybrid electric vehicles in the ATB, see the Gasoline Hybrid Electric Vehicle page.
Gasoline internal combustion engine vehicles typically use a spark-ignited internal combustion engine. In a combustion chamber, injected fuel is combined with air. The mixture of air and fuel ignites from a spark from the spark plug (DOE, 2024). For additional background, see the Alternative Fuels Data Center's How Do Gasoline Cars Work? webpage. For assumptions about gasoline internal combustion engine vehicles in the ATB, see the Gasoline Internal Combustion Engine Vehicle page.
Light-duty natural gas internal combustion engine vehicles are typically dedicated natural gas or bifuel vehicles that use either natural gas or gasoline. The acceleration, horsepower, and cruise speed of natural gas vehicles and similar models of conventional vehicles are comparable, but natural gas vehicles generally have a shorter driving range because natural gas has a lower energy density (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Natural Gas Vehicles webpage. For assumptions about natural gas internal combustion engine vehicles in the ATB, see the Natural Gas Internal Combustion Engine Vehicle page.
Plug-in hybrid electric vehicles use both an electric motor and an internal combustion engine. Batteries power the motor; gasoline, diesel, or another fuel powers the engine or other propulsion source. Operating costs and fuel use are lower than those for conventional vehicles because electricity from the grid is less expensive (see assumptions about electricity costs) and electric motors are very efficient. Greenhouse gas (GHG) emissions from PHEVs may also be lower, depending on the electricity source (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Plug-In Hybrid Electric Vehicles webpage.
Fuels
Biodiesel is a renewable and biodegradable fuel that comprises fatty acid methyl esters and is manufactured from vegetable oils, animal fats, or used cooking oil (recycled restaurant grease) to specifications listed in ASTM D6751 (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Biodiesel Fuel Basics webpage. Note renewable diesel is a different fuel.
Biomass is defined in the Bioenergy Technologies Office Multi-Year Program Plan (DOE, 2023), p. vii, as follows: "Biomass is a renewable carbon resource with potential for wide application across industries." "Renewable carbon resources are carbon-based resources that are regularly regenerated, either via photosynthesis (e.g., plants and algae) or through regular generation of carbon-based waste (e.g., the nonrecycled portion of municipal solid waste, biosolids, sludges, plastics, and CO2 and industrial waste gases)." See also ./biomass_assumptions.
Blendstock for oxygenate blending comprises liquid hydrocarbon components intended for blending with oxygenates (EIA, 2019a). Conventional blendstock for oxygenate blending (CBOB) is blended with oxygenates to produce finished conventional motor gasoline, and reformulated BOB (RBOB) is blended with oxygenates to produce finished reformulated motor gasoline, which is reformulated to reduce emissions.
See the Blendstock for Oxygenate Blending page.
Conventional E10 is a low-level blend comprising 10% ethanol and 90% gasoline by volume (DOE, 2024). For additional information, see the U.S. Energy Information Administration's (EIA's) Gasoline Explained webpage.
Conventional E15 is a blend comprising 10.5% to 15% ethanol and gasoline by volume (DOE, 2024), with the balance comprising CBOB. The Transportation ATB assumes ethanol content of 15% by volume.
Conventional jet fuel (aviation fuel) is refined from petroleum. This product fuels aviation aircraft engines, and it may comprise kerosene-type aviation fuel (the predominant type) and naphtha-type aviation fuel (EIA, 2019b).
Heavy fuel oil is a residual oil, meaning it has a lower boiling point and remains liquid at the boiling point of more volatile distillate or diesel petroleum products. Heavy fuel oil corresponds to fuel oil number 6 and may be blended with lighter products to form fuel oil number 4 or 5 (Kelechava, 2021). It is used in marine applications. Related terms include residual fuel oil and bunker fuel.
Ultra-low-sulfur diesel is a product of petroleum refining that comprises distillates or blends of distillates with residual oil used in motor vehicles (EIA, 2019b). For additional information, see EIA's Diesel Fuel Explained webpage.
Conventional marine diesel is fuel supplied to ships and boats. It primarily comprises residual and distillate fuel oil (EIA, 2019b).
Electricity is produced from energy sources such as wind and solar energy, hydropower, nuclear energy, stored hydrogen, oil, coal, and natural gas. It is defined as an alternative fuel by the Energy Policy Act of 1992 (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Electricity Basics webpage. For the electricity price and emission assumptions in the ATB, including grid mix options, see the Electricity page.
Ethanol is a renewable fuel. Made from biomass (i.e., a variety of plant materials), ethanol is used in 98% of U.S. gasoline. Typically, gasoline comprises E10 (10% ethanol, 90% blendstock for oxygenate blending (BOB)) (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Ethanol Fuel Basics webpage. For the ethanol price and emission assumptions in the ATB, see the Ethanol page.
High-blend ethanol fuel contains 51% to 83% ethanol by volume. The blend level of ethanol is selected based on air quality regulations and depends on location and season. This blend level meets ASTM 5798 specifications and is used in flexible-fuel vehicles (DOE, 2024). This fuel is often called "E85." For additional background, see the Alternative Fuels Data Center's E85 Flex Fuel Specification webpage. The Transportation ATB assumes ethanol content of 83%.
Hydrogen is an alternative fuel that can be produced from a variety of resources. Government—including the U.S. Department of Energy Hydrogen and Fuel Cells Technology Office—and industry are engaged in research and development (R&D) to improve production and distribution and reduce emissions and costs for hydrogen use in fuel cell electric vehicles (DOE, 2024). For information about hydrogen production pathways, see the National Renewable Energy Laboratory's Hydrogen Analysis Production Case Studies. For the hydrogen price and emission assumptions in the ATB, see the Hydrogen page.
Light-duty natural gas internal combustion engine vehicles are typically dedicated natural gas or bifuel vehicles that use either natural gas or gasoline. The acceleration, horsepower, and cruise speed of natural gas vehicles and similar models of conventional vehicles are comparable, but natural gas vehicles generally have a shorter driving range because natural gas has a lower energy density (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Natural Gas Vehicles webpage. For the natural gas price and emission assumptions in the ATB, see the Natural Gas page.
Reformulated gasoline is a gasoline blend that results in lower emissions of nitrogen oxides (NOx; see NOx emissions), volatile organic compounds, and toxic pollutants than conventional gasoline when burned (U.S. Environmental Protection Agency [EPA]: "Gasoline Standards: Reformulated Gasoline"). Reformulated E10 contains 10% ethanol by volume, with the balance comprising Reformulated Blendstock for Oxygenate Blending (BOB). In contrast, conventional E10 gasoline contains 10% ethanol by volume, with the balance comprising Conventional Blendstock for Oxygenate Blending.
Reformulated gasoline is a gasoline blend that results in lower emissions of NOx (see NOx emissions), volatile organic compounds, and toxic pollutants than conventional gasoline when burned (EPA: "Gasoline Standards: Reformulated Gasoline"). Reformulated E15 contains 10.5%–15.0% ethanol by volume, with the balance comprising RBOB (DOE, 2024). The Transportation ATB assumes an ethanol content of 15% by volume.
Renewable diesel is a drop-in replacement for diesel typically produced from biomass sources. It is chemically the same as petroleum diesel and meets the ASTM D975. As a drop-in fuel, it can be used in all existing infrastructure and engines intended for petroleum diesel. It is also called "green" diesel (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Renewable Diesel webpage. Note biodiesel is a different fuel.
Synthetic aviation fuel (SAF) is the term used throughout the ATB, but other sources may also refer to sustainable aviation fuel, alternative jet fuel, alternative aviation fuel, "biojet," aviation biofuel, or renewable jet fuel. Up to specified blending limits that vary by pathway, it can be used directly in airplanes that use regular, petroleum-based aviation fuel. Specifications for SAF include ASTM D7566 and ASTM D1655, as described in the Alternative Fuels Data Center (DOE, 2024). For additional background, see the Alternative Fuels Data Center's Sustainable Aviation Fuel webpage. For additional information about the definition of SAF, see the Synthetic Aviation Fuel Assumptions page.
Scenarios
Vehicle Scenarios
Vehicle scenarios in the Transportation ATB incorporate assumptions on both the level of technology advancement achieved in each powertrain (e.g., lightweighting and engine efficiency) and the projected costs for the assumed technologies through 2050. Assumptions for assigning values in the Advanced and Mid trajectories reflect the project teams' judgment. Given the rapid pace of technology improvement and market advancement, the assumptions here may not reflect the most recent trends. As data become available, ATB data are updated to reflect updated cost and performance trajectories.
When comparing across scenarios, technology advances include changes that may reduce costs or may increase costs while improving performance, which implies costs do not always decline between less-advanced and more-advanced scenarios. However, although technology advancements that improve performance may increase vehicle cost, they may also result in a lower levelized cost of driving (LCOD) because of potential fuel savings.
In the ATB Conservative trajectory, technology cost and performance improve from Base Year levels at rates based on the Annual Energy Outlook. The ATB Conservative trajectory accounts for trade-offs between vehicle efficiency and performance modeled in the Annual Energy Outlook (EIA, 2025). We note some inconsistencies may exist between the assumed ATB Base Year vehicle attributes compared to those in the Annual Energy Outlook; the use of relative year-over-year changes is intended to minimize the impact of these discrepancies, but differences could impact the expected level of improvement.
For most vehicle types, this case is available instead of the Constant Trajectory, starting with the 2025 Transportation ATB update, which was used in prior updates.
The Mid trajectory is based on "estimates of expected original equipment manufacturer (OEM) improvements based on business-as-usual regulatory and market environments" as defined in the low case from (Islam et al., 2023). These technology improvements are used to improve fuel efficiency, reduce component sizing requirements, or both. This is in contrast to the ATB Conservative trajectory, which improves both efficiency and performance.
In the Advanced trajectory, technology advances occur with breakthroughs, increased public and private R&D investment, and other market conditions that lead to significantly improved cost and performance levels—but the technologies do not necessarily reach their full technical potential. Vehicle technologies advance substantially and achieve high performance, low cost, or both. Attaining this level of cost improvement is assumed to be very uncertain.
In the ATB Constant trajectory, technology cost and performance from the Base Year are shown through 2050, without further advancement in R&D or markets. This cost level is extended through 2050 for reference only; it does not imply frozen costs and performance are anticipated and should not be confused with a business-as-usual or baseline scenario. Starting with the 2025 Transportation ATB update, the Constant trajectory has been discontinued for most vehicle types. (Exceptions are refuse and vocational vehicles.)
Fuel Scenarios
In the Current Market scenario, fuel price and emissions data are shown for fuels that are commercially available; the exact source, timing, averaging, and other details are described in the references. Current Market fuel prices are primarily based on data from EIA. Current Market fuel prices include taxes but may differ from observed retail prices because of market volatility and local market conditions. See specific notes and references on the fuels pages for specific dates and averaging methods.
In this scenario, fuel metrics are based on techno-economic modeling of the current technology at current market production volume of the specific fuel pathway as specified in the notes and references on the fuels pages. This scenario may be used for fuels that lack a robust, national, commercial market. Modeled costs or costs plus a fixed return on investment may differ from observed market prices.
In this scenario, fuel metrics are based on techno-economic modeling of the current technology at high market production volume of the specific fuel pathway. Timing of this scenario depends on when high production volume is achieved.
In this scenario, fuel metrics are based on a future technological state modeled at low market production volume of the specific fuel pathway, as might be the case for a pioneer plant. We do not assess the potential for competitiveness of future modeled fuels.
In this scenario, fuel metrics are based on a future technological state, based on engineering-economic modeling at high market production volume of the specific fuel pathway, often called "nth plant." Timing of this scenario depends on when high production volume of the specific fuel pathway is achieved. We do not assess the potential for competitiveness of future modeled fuels.
Select subsets of fuels are shown on the vehicle charts for the Transportation ATB and include three fuel pathways:
- Baseline fuels are meant to best represent current fuels available for each powertrain today. Because of the variability of current hydrogen prices, current modeled costs are used as the baseline fuel instead of current market costs for hydrogen for fuel cell electric vehicles.
- The Lowest Cost fuels correspond to the fuel pathways with the lowest cost of those included in the ATB for each powertrain.
- The Lowest CO2e Emissions fuels correspond to the fuel pathways with the lowest CO2e emissions of those included in the ATB for each powertrain. For a tabular summary, see the Lowest CO2e Emissions Fuel Assumptions page.
Policy Representation in the ATB
Many provisions and tax credits, including those in the Inflation Reduction Act of 2022 (IRA), affect the cost of clean energy and transportation. Most current data and modeling in the ATB do not explicitly include the provisions in the IRA (or other policy). See this link for further discussion of policy assumptions. 🗨
Metrics
This version of the Transportation ATB generally adopts 2024 as the Base Year. This is aligned with one of our major references: EIA's 2025 Annual Energy Outlook (EIA, 2025).
All costs are converted to 2024 dollars using the gross domestic product implicit price deflator (FRED and U.S. Bureau of Economic Analysis, 2025).
The ATB includes empirical fuels data (labeled "current market"), modeled fuels and vehicle prices that represent historical years that have been validated against contemporary empirical data ("current modeled"), and model results that represent projected values for future years ("future modeled"). All these categories are generally described as "data" and are distinguished by their labels.
The parameter list for vehicles in Tableau figures includes battery cost ($ and $/kilowatt-hour [kWh]), capital cost ($/mile [mi]), charge depleting electricity consumption (watt-hour [Wh]/mi), CO2e emissions (grams/gasoline gallon equivalent [g/gge]), charge sustaining electricity consumption (mi/gge), discounted lifetime vehicle miles traveled (mi), discounted maintenance and repair cost ($/mi), fuel cell cost ($/kilowatt [kW]), fuel CO2e emissions (g/gge), fuel cost ($/mi), fuel economy ($/gge), fuel price ($/gge), hydrogen storage tank cost ($/kgH2), levelized cost of driving ($/mi), pack energy (kWh), PHEV utility factor, range (mi), and vehicle cost ($).
Vehicle Metrics
For the Transportation ATB, fuel economy is tank-to-wheels fuel economy, reported in miles per gasoline gallon equivalent, and it represents how efficiently a vehicle converts fuel during operation (Elgowainy et al., 2016). For light-duty vehicles, fuel economy values represent adjusted, on-road estimates, based on a harmonic average of 55% city (Urban Dynamometer Driving Schedule cycle) and 45% highway (Highway Fuel Economy Test cycle) driving for all vehicle powertrains. For medium- and heavy-duty vehicles, fuel economy values represent a harmonically weighted average of the ARB, EPA55, and EPA65 medium-duty/heavy-duty vehicle test cycles, and test cycle weights for each vehicle class are from (Burnham et al., 2021) and (Islam et al., 2023). (The ARB test cycle is developed by the California Air Resources Board; the EPA test cycles are developed by the U.S. Environmental Protection Agency.) Note adjusted, real-world modeled estimates may vary from actual realized fuel economy because of differences in testing drive cycles compared to real-world driving conditions (e.g., fraction of city vs. highway driving; assumed driving speeds).
As noted in the definition for the ATB Conservative trajectory, Base r values used for all scenarios are based on (Islam et al., 2023) with the above assumptions for fuel economy, whereas projections in the ATB Conservative trajectory reflect year-over-year changes from the 2025 Annual Energy Outlook (EIA, 2025). Some inconsistencies may exist between (Islam et al., 2023) and (EIA, 2025) in the assumed mix of vehicle types within a given class, with associated potential for inconsistencies in projected vehicle characteristics.
For details about fuel economy assumptions for plug-in hybrid electric vehicles, see the Fuel Economy Assumptions page.
Modeled vehicle price represents an estimated cost to the consumer to purchase a new vehicle, based on modeling that includes manufacturing costs and profit. Changes in modeled vehicle price over time and between scenarios primarily reflect changes in vehicle design (e.g., adoption of technologies to improve fuel economy; component sizing requirements) and changes in component-level manufacturing costs. Costs are based on manufacturing production volume of vehicles by powertrain category.
The ATB Conservative trajectory is based on the EIA 2025 Annual Energy Outlook (EIA, 2025), which estimates light-duty vehicle prices based on actual manufacturer's suggested retail price, for both Base Year and projections. Changes in vehicle prices reflect technology adoption (including consideration of regulatory compliance), technology/powertrain learning, and changes in retail price markups.
The trajectory of modeled vehicle prices in the ATB Mid trajectory and Advanced trajectory are based on vehicle modeling in (Islam et al., 2023), which assumes a retail price equivalent factor of 1.5 for light-duty vehicles and 1.2 for medium- and heavy-duty vehicles to estimate retail prices based on manufacturing costs. These estimates may not reflect actual retail price trajectories, which may differ because of external market drivers not included in the ATB (e.g., automotive market supply and demand imbalances, original equipment manufacturer regulatory compliance and pricing strategies, taxes, and dealer incentives).
Government incentives, subsidies, or tax credits are not included in modeled vehicle price.
Production volume is the quantity of a good that is produced. In the ATB, we consider annual vehicle production, production of components that are shared across vehicles, and annual fuel production. Notably, FCEVs are assumed to be produced at low volumes; see the definition for fuel cell electric vehicles. For fuels, we specify high or low volume of production of the specific fuel pathway; see Fuel Scenarios. For additional details on production volume and its applications in the ATB, see the Production Volume Assumptions page.
The levelized cost of driving is an indicator of the cost of driving a vehicle on a per-mile basis. As defined and calculated in the Transportation ATB, LCOD includes initial costs for the vehicle, fuel costs, maintenance and repair costs, and, if applicable, residential charger equipment and installation. It does not include any other costs, such as insurance, registration, tolls, or driving labor. LCOD here assumes a typical first and single owner over an assumed vehicle life and does not consider depreciation and resale value. Note changes in the presented LCOD over time are attributable only to vehicle technology changes because fuel costs for a specified pathway are held constant over time in the ATB. Note this assumption is distinct from the consideration of fuel prices in underlying vehicle modeling; for example, the projected vehicle attributes in the ATB Conservative trajectory—based on modeling in the 2025 Annual Energy Outlook (EIA, 2025)—reflect changes to vehicle configurations in response to changing fuel prices. For additional information on the interpretation and calculation of LCOD, see the Levelized Cost of Driving Assumptions page.
Fuel Metrics
Diesel gallon equivalent (dge) is the volume of fuel that contains the same amount of energy as a gallon of diesel. We use a value of 128,450 British thermal units (Btu), which is the amount of energy in a gallon of U.S. conventional diesel on a lower heating value basis from R&D GREET 2023.
This cost is a calculated estimate of what the cost of a fuel might be with either current or future technology at either low or high production volume of the specific fuel pathway. On-road fuel costs include distribution and taxes; blendstock costs do not. For biofuels, changes in the market for biomass feedstocks can cause market prices at any given time to differ from the biofuels market prices noted in the ATB. See Key Assumptions on the fuels pages and references for details.
The fuel price represents the market or retail price at which commercial fuels are sold. Taxes are included for all fuels currently taxed. This means the price shown for a single fuel pathway may differ by fuel types or application because of different tax and distribution costs. See notes and references on each fuels page for details.
Gasoline gallon equivalent is the volume of fuel that contains the same amount of energy as a gallon of gasoline. We use a value of 116,090 Btu, which is the amount of energy in a gallon of gasoline blendstock on a lower heating value basis from R&D GREET 2023.
The lower heating value is the amount of energy released per unit of fuel that is burned, not including the heat of vaporization of the water contained in the fuel. The lower heating values from the R&D GREET model are used for gge conversions. Values in Btu/gal or Btu/kWh are shown next.
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The following values are used for taxes and distribution costs of gasoline and diesel fuel for all scenarios. Values are based on EIA's 2025 Annual Energy Outlook (EIA, 2025), where taxes include federal, state, local, and energy taxes. In the Annual Energy Outlook, taxes are based on average values of the most recently available federal and state taxes; an additional 1% of the retail price is added to reflect local taxes (EIA, 2022).
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Miles per gasoline gallon equivalent (gge).
Additional Fuel Metrics
The following fuel metrics are available from the BETO Techno-Economic Analysis Database.
This revenue is the value derived from the sale of products other than fuel.
This is the investment in the durable physical plant for fuel production.
This is the cost associated with labor and overhead for operating the fuel production facility.
This is the cost of feedstock at the throat of the reactor once a mature supply industry has been established.
This is the cost of expendable inputs needed for fuel production.
The fuel price, which is synonymous with the minimum fuel selling price, is the price at which fuels are sold at the plant gate. It does not include distribution costs or taxes.
This is the value derived from the sale of electricity coproduced with fuel.
This is the volume of feedstock that can be processed per unit of time.
This is the sum of the yield of each valued product from the fuel production process.
Emissions Metrics
Emissions for CO2e, NOx , SOx, and PM10 are estimated for well-to-tank and well-to-wheels portions of the fuel life cycles, not including emissions associated with vehicle production. The Transportation ATB reports only absolute values of physical emissions and does not account for the social cost of carbon or other associated impacts. Note the changes over time are attributable only to vehicle technology changes; emissions associated with fuels are held constant at the values for the selected fuel.
CO2e is the carbon dioxide equivalent of GHG emissions. The Transportation ATB considers GHG emissions from CO2, CH4, and NOx, consistent with R&D GREET. The global warming potentials are also based on R&D GREET model default values, which are based on the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (IPCC, 2022). R&D GREET model defaults do not include effects on soil organic carbon. Values (from defaults) for induced land use change are used when the biomass resource is corn or soybeans but not for feedstocks from wastes. ILUC estimates included in R&D GREET are based on the GTAP-BIO model. There are other potential sources and ranges of ILUC estimates based on various modeling approaches, some of which are compared in (U.S. EPA, 2023).
NOx are nitrogen oxides.
SOx are sulfur oxides.
PM is particulate matter. In the Transportation ATB, we report PM2.5 and PM10, which comprises particles that have aerodynamic diameters of less than 2.5 and 10 microns, respectively. These metrics are reported in R&D GREET model results.
Tank-to-wheels emissions are emissions from fuel consumption during the operation phase of the vehicle (Elgowainy et al., 2016).
Well-to-tank emissions include emissions from fuel production at the primary source of energy (feedstock) to its delivery to the vehicle's energy storage system (e.g., fuel tank or battery) (Elgowainy et al., 2016).
These are emissions from both the well to the tank and the tank to the wake (which includes fuel consumption during operation of an aircraft).
These are emissions from both the well to the tank and the tank to the wheels. Well-to-wheels emissions are presented in different units depending on the data shown.
For fuels, we present the well-to-wheels emissions in grams per metric million Btu (on lower heating value basis). This represents the emissions associated with each unit of energy used onboard the vehicle; it does not incorporate vehicle fuel economy. This methodology is consistent with the Renewable Fuel Standards (RFS2), which evaluate fuels on a gram per unit energy basis (EPA, 2015); (EPA, 2010).
For vehicles, we present the well-to-wheels emissions in g/mi, which incorporates both the fuel emissions and the vehicle fuel economy. This methodology is consistent with regulations that consider potential fuel economy improvements of advanced powertrains, such as California's Low Carbon Fuel Standard (California Air Resources Board, 2019).
Transportation Metrics
Passenger-mile is a unit used to indicate 1 mile traveled by one passenger.
Seat-mile is a unit used to indicate 1 mile traveled by one seat, typically on a commercial aviation flight or public transportation mode. This is calculated by multiplying the number of miles an airplane or other vehicle travels by the available number of seats on that vehicle.
Vehicle-mile is a unit used to indicate 1 mile traveled by one vehicle.
References
The following references are specific to this page; for all references in this ATB, see References.