Emission factors
Summary
Emission factors are standardized coefficients that convert activity data (like kilometers driven, liters of fuel consumed, tonne-kilometers moved, or kWh used) into estimated emissions of greenhouse gases or air pollutants. In road transport they enable consistent, comparable carbon accounting by linking specific vehicles, fuels, operating conditions, and geographical contexts to emissions, and can be defined on a tank-to-wheel (tailpipe only) or well-to-wheel (including upstream fuel or electricity production) basis.
What Are Emission Factors?
Emission factors are standardized coefficients that estimate how much greenhouse gas (GHG) or air pollution is emitted per unit of activity—such as per mile driven, per gallon of fuel consumed, or per ton-mile transported. In road transportation, emission factors convert operational data into emissions so carriers, shippers, and platforms can quantify and report their environmental impact in a consistent way.
In the U.S., emission factors are commonly aligned with methodologies from the EPA, EPA SmartWay, the GHG Protocol, and—where relevant to fuel pathways—California’s CARB (California Air Resources Board).
How Emission Factors Work
At a basic level, emission factors link an activity (distance, fuel use, payload) to emissions for pollutants such as CO₂, CH₄, and N₂O—often expressed as CO₂e (carbon dioxide equivalent). These factors come from measurements, laboratory testing, and modeled data published by recognized bodies such as the EPA and GHG Protocol.
For trucking and van operations, emission factors may be defined:
Per vehicle-mile (g CO₂e/mile), by vehicle and fuel type
Per unit of fuel (kg CO₂e/gallon or MJ), covering both combustion and upstream production
Per ton-mile (g CO₂e/ton-mile), incorporating loading and backhauls
A key methodological choice is Tank-to-Wheel (TTW) versus Well-to-Wheel (WTW):
TTW includes tailpipe emissions only (aligned with many EPA tailpipe standards).
WTW adds upstream emissions from fuel production. U.S. organizations often reference GHG Protocol guidance or CARB lifecycle assessments (e.g., CA-GREET) for upstream accounting.
Your choice should match the reporting framework used (e.g., GHG Protocol, customer requirements, SmartWay reporting).
Applying Emission Factors in Road Transportation
In logistics workflows, emission factors are applied to activity data to calculate emissions for routes, lanes, and customers. Factors vary based on:
Vehicle type (van, straight truck, tractor-trailer) and emissions standard
Energy source (diesel, biodiesel blends, CNG/LNG, renewable diesel/HVO, electricity)
Driving conditions and geography (urban/regional/highway; electricity grid mix)
Load factor and utilization (affecting per–ton-mile results)
In the U.S. market, the EPA SmartWay program provides freight intensity metrics, emission estimates, and benchmarking that complement emission-factor-based reporting.
When high-quality fuel consumption data is available, fuel-based factors tend to be the most accurate. Distance-based factors are useful when only mileage is known, and weight-based factors support multimodal comparisons and customer allocation. A transport management system such as the Dashdoc TMS can automate per-shipment CO₂ calculations, ensure consistent boundaries, and centralize factor sources.
Examples
Distance-based example
A diesel 18-ton truck travels 200 km with a WTW factor of 750 g CO₂e/km.
Emissions = 200 × 0.75 = 150 kg CO₂e.Fuel-based example
A tractor-trailer uses 100 liters of diesel. With a WTW factor of 3.2 kg CO₂e/liter:
Emissions = 100 × 3.2 = 320 kg CO₂e.Ton-mile example
A 10-ton payload moves 500 km with a WTW factor of 90 g CO₂e/tkm.
Total tkm = 10 × 500 = 5,000.
Emissions = 5,000 × 0.09 = 450 kg CO₂e.
Tip: Electric delivery vans use electricity-based emission factors (g CO₂e/kWh). In the U.S., grid emissions should ideally use region-specific factors (e.g., EPA eGRID). CARB also publishes lifecycle emission factors for electricity used in California.
If you prefer starting from fuel consumption and costs, you can estimate usage with the Dashdoc fuel surcharge calculator, then apply the correct emission factor.
Key Benefits
Consistency and comparability: Standardized factors ensure comparable emissions reporting across fleets, lanes, and years.
Scalability: Apply the same methodology across shipments, customers, or your full network.
Decision support: Compare fuels, vehicles, and routes to guide decarbonization strategies—such as aerodynamics, driver coaching, electrification, or switching fuels—and evaluate cost-versus-carbon trade-offs using tools like Dashdoc’s freight rate calculator.
Compliance readiness: Align with U.S. expectations via EPA, SmartWay, GHG Protocol, and—where required—CARB clean-fuel and lifecycle accounting frameworks.
Transparency: Clear documentation of factor sources, boundaries (TTW/WTW), pollutants, and reference years.
What to Define for Any Emission Factor
Boundary: TTW vs. WTW; pollutants included (CO₂, CH₄, N₂O, CO₂e).
Unit: g/mile, kg/gallon, g/ton-mile, or g/kWh.
Vehicle & energy context: Vehicle class, engine standard, fuel or electricity source.
Geography & year: U.S. nationwide or region-specific EPA/CARB pathways; match factor year to your activity data.
Data quality: Source credibility, methodology alignment (GHG Protocol, EPA), and real-world relevance.
Industry Context
Emission factors underpin carbon accounting in U.S. road freight, supporting customer CO₂ reporting, Scope 1 and Scope 3 disclosures, RFPs, sustainability commitments, and carbon surcharges. Shippers use them to compare carriers and modes; carriers use them to baseline performance, track improvements, and validate lower-carbon services.
In the U.S., EPA SmartWay is the most widely recognized voluntary program for freight emissions benchmarking. CARB drives some of the country’s strictest fuel-pathway and vehicle-emission rules, particularly relevant for fleets operating in California. The GHG Protocol remains the global standard for organizational and value-chain emissions accounting.
Accurate emission factors also support network design, consolidation decisions, and investment cases for renewable diesel, LNG, or electric trucks. For practical tools that rely on distance and fuel consumption inputs, explore the Dashdoc Toolbox.
Conclusion
Emission factors convert everyday transport activity into credible emissions data. Selecting the right boundaries, units, and level of detail—and using current, geography-appropriate, and vehicle-specific values—enables accurate reporting and better decarbonization decisions across the U.S. road transportation sector.
FAQ on Emission Factors
Emission factors are coefficients that estimate emissions per unit of activity, such as g CO2e per km, kg CO2e per liter of fuel, g CO2e per tonne‑kilometer, or g CO2e per kWh. They translate operational data (distance, fuel use, payload, electricity) into greenhouse gas outputs and can be reported as tank‑to‑wheel (TTW) or well‑to‑wheel (WTW).
TTW covers only tailpipe emissions during vehicle operation. WTW includes TTW plus upstream emissions from extracting, producing, and delivering the energy (fuel or electricity). WTW is higher for most fuels and depends on country- or supplier-specific pathways and grid mixes.
Decide boundary (TTW or WTW). 2) Match the unit to your best data (fuel-, distance-, tkm-, or kWh-based). 3) Specify vehicle class, standard, and energy type. 4) Use geography- and year-appropriate datasets. 5) Prefer recognized sources and document assumptions for transparency.
Use distance-based factors when reliable mileage is available but fuel or payload data is missing. Ensure they match vehicle category, standard, duty cycle (urban/regional/highway), and geography. Note they are less precise than fuel-based factors for combustion vehicles.
Use electricity intensity factors in g CO2e/kWh from credible sources (e.g., national grid inventories, supplier guarantees of origin, IEA, EPA eGRID). Include charging losses and distinguish TTW (often zero) from WTW, which reflects the grid mix and time/location of charging.