The carbon footprint per mile driven in the US depends primarily on one variable: fuel efficiency. A standard 25 MPG gasoline car emits approximately 0.36 kg CO₂ per mile, using the EPA’s standardised emission factor of 8.89 kg CO₂ per gallon of gasoline burned. Everything else flows from that relationship.
How the calculation works
For gasoline vehicles, the formula is straightforward:
kg CO₂ per mile = 8.89 ÷ MPG
At different fuel economy levels:
| Vehicle type | Fuel economy | kg CO₂ per mile | Annual CO₂ (12,000 miles) |
|---|---|---|---|
| Hybrid | 45 MPG | 0.20 | 2.4 tCO₂e |
| Standard sedan | 25 MPG | 0.36 | 4.3 tCO₂e |
| Large SUV / truck | 17 MPG | 0.53 | 6.4 tCO₂e |
| Electric vehicle (US grid avg) | — | 0.14 | 1.7 tCO₂e |
These figures represent direct tailpipe emissions only. Vehicle manufacturing, battery production, and oil extraction are excluded — consistent with Decarb’s operational boundary across all categories.
What 12,000 miles per year actually means
The US average driver covers approximately 12,000 miles per year. In a standard 25 MPG sedan, that produces:
0.36 × 12,000 = 4,320 kg CO₂ per year — 4.3 tCO₂e annually
That is roughly 30% of the average American footprint from driving alone. For many households, ground transport is the largest single operational emission source.
The nonlinear nature of the relationship matters here. Improving from 15 MPG to 25 MPG reduces emissions by 0.24 kg per mile. Improving from 35 MPG to 45 MPG reduces emissions by only 0.06 kg per mile. The largest gains come at the lower end of the efficiency range.
Electric vehicles: emissions shift, not disappear
For EVs, tailpipe emissions drop to zero but electricity generation emissions take their place. At the US grid average:
0.34 kWh per mile × 0.42 kg CO₂/kWh = 0.14 kg CO₂ per mile
That is roughly 60% lower than a standard sedan on the same journey. However, the figure varies significantly by state. In states with cleaner grids — California, New York, the Pacific Northwest — EV emissions can fall below 0.05 kg per mile. In coal-heavy regions, they can exceed 0.20 kg per mile.
Grid intensity is therefore as important as vehicle efficiency for EV drivers.
Occupancy changes everything
A solo driver in a 25 MPG sedan emits 0.36 kg CO₂ per mile. Two people sharing that car each emit 0.18 kg per mile — equivalent to a hybrid. Three people drops it to 0.12 kg per mile, below the EV average.
Occupancy is the most underestimated variable in personal transport emissions. A carpool is often more impactful than a vehicle upgrade.
How driving compares to flying
The NYC → LA route is a useful benchmark. Driving solo in a 25 MPG car covers approximately 2,790 miles one way, producing roughly 1.0 tCO₂e — and 2.0 tCO₂e round trip. The equivalent economy class flight produces 0.608 tCO₂e round trip, making solo driving approximately 3.3× more carbon-intensive than flying on this route.
With two passengers in the car, per-person emissions drop to approximately 0.5 tCO₂e one way. With three, driving becomes the lower-carbon option per person compared to flying.
What Decarb includes and excludes
For transparency, driving emissions in Decarb calculations cover:
Included: tailpipe CO₂ for gasoline vehicles, electricity generation emissions for EVs.
Excluded: vehicle manufacturing, battery production, road infrastructure, oil extraction and refining.
Under the GHG Protocol framework, gasoline driving is treated as a Scope 1 equivalent and EV driving as Scope 2 equivalent.
What to do with this
Driving emissions respond to three levers in order of typical impact: occupancy, fuel efficiency, and fuel type. If you drive regularly and drive alone, the highest-impact action is often not switching vehicles — it is sharing the journey.
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