How transport emissions are calculated
Personal vehicle emissions depend on three inputs: miles driven per year, fuel type, and vehicle efficiency. The EPA’s emission factor for petrol combustion is approximately 8.89 kg CO₂ per gallon of petrol consumed. For a car achieving 28 miles per gallon — the approximate US fleet average according to the US Department of Transportation (2023) — that produces 0.317 kg CO₂e per mile driven. At 12,000 miles per year, the estimated annual footprint from that vehicle is approximately 3.8 tons CO₂e.
Electric vehicles produce zero direct emissions at the tailpipe but carry indirect emissions from the electricity used to charge them. The US DOE Alternative Fuels Data Center (2024) estimates an average EV produces approximately 0.06 kg CO₂e per mile on the national grid average of 0.37 kg CO₂e/kWh (eGRID 2023). At 12,000 miles per year, that is approximately 0.72 tons CO₂e — a reduction of roughly 3 tons CO₂e compared to the petrol equivalent. In states with cleaner grids such as California, Washington, or New York, the EV figure drops further.
| Vehicle type | kg CO₂e / mile | 12,000 miles / year | Source |
|---|---|---|---|
| Petrol car (28 MPG) | 0.317 | 3.80 tons CO₂e | EPA 2024 |
| Petrol car (20 MPG — SUV/truck) | 0.445 | 5.34 tons CO₂e | EPA 2024 |
| EV (US national grid avg) | 0.060 | 0.72 tons CO₂e | DOE AFDC / eGRID 2023 |
| EV (California grid) | 0.025 | 0.30 tons CO₂e | eGRID 2023 CAMX |
| Public transit (bus, national avg) | 0.089 | 1.07 tons CO₂e | EPA 2024 |
The commute: where most driving emissions accumulate
The average American commutes 27.6 minutes each way, covering approximately 16 miles round trip, according to the US Census Bureau’s 2023 American Community Survey. For a five-day commuter driving a 28 MPG petrol car, that is approximately 4,160 commute miles per year — producing around 1.32 tons CO₂e from commuting alone, at an annual fuel cost of approximately $530 at current petrol prices.
Two remote working days per week eliminates 40% of those commute miles without any capital expenditure. For the driver above, that saves approximately 0.53 tons CO₂e per year and approximately $212 in fuel costs annually — with no vehicle change required. This is a Green Reward: the saving is immediate, costs nothing, and the financial return is positive from day one.
Remote working — Green Reward calculation
2 remote days/week · 16-mile round trip · 28 MPG petrol car · $3.50/gallon
Annual saving: ~0.53 tons CO₂e · ~$212 in fuel
Payback period: immediate. Zero upfront cost. Source: US Census Bureau (2023), EPA (2024).
EV vs petrol: the full cost comparison
Switching to an EV at the natural end of a vehicle’s life — not prematurely — is one of the highest single-action transport reductions available. The US DOE estimates average fuel cost savings of $800–1,200 per year when switching from petrol to electric, depending on local electricity and petrol prices. At 12,000 miles per year, the emissions saving on the national grid average runs at approximately 3.1 tons CO₂e annually — equivalent to eliminating the entire transport footprint of a below-average driver.
One important caveat: replacing a functioning petrol vehicle early to buy an EV is not automatically a net emissions saving. Manufacturing a new vehicle produces approximately 8–10 tons CO₂e in embodied emissions, according to the IEA’s Global EV Outlook (2023). For a vehicle switch to break even on lifecycle emissions, the EV needs to be driven for several years on a grid with average or better carbon intensity. The correct timing is vehicle replacement, not early disposal.
Reduction actions ranked by impact
Switch to an EV at next vehicle replacement. Estimated saving: 2.5–3.5 tons CO₂e/year on the national grid average. Financial saving: $800–1,200/year in fuel costs. The Inflation Reduction Act (2022) provides a federal tax credit of up to $7,500 for new EVs meeting income and vehicle price requirements.
Add two remote working days per week. Estimated saving: 0.4–0.8 tons CO₂e/year depending on commute distance and vehicle. Financial saving: $150–400/year in fuel. Zero upfront cost.
Switch short car trips to walking, cycling, or transit. Trips under 3 miles account for approximately 50% of all US car trips by count, according to the National Household Travel Survey (2022), but a disproportionately high share of per-mile emissions due to cold engine starts. Replacing half of these trips reduces annual transport emissions by an estimated 0.2–0.5 tons CO₂e.
Choose a smaller or more efficient petrol car at next replacement. Moving from 20 MPG to 35 MPG at the same annual mileage reduces transport emissions by approximately 2.2 tons CO₂e/year and saves approximately $750/year in fuel. This applies for drivers not yet ready to switch to electric.
Frequently asked questions
What is the carbon footprint of driving a car?
A petrol car achieving 28 MPG (the approximate US fleet average) produces approximately 0.317 kg CO₂e per mile, according to EPA emission factors (2024). At 12,000 miles per year, that is approximately 3.8 tons CO₂e annually. Higher-emission vehicles — trucks and SUVs averaging 20 MPG — produce approximately 5.3 tons CO₂e at the same mileage. Actual figures vary with driving style, load, and road conditions; these are fleet-average estimates.
Are electric vehicles actually lower carbon than petrol cars?
Yes, on the US national grid average, and more so on cleaner regional grids. The US DOE estimates an EV produces approximately 0.06 kg CO₂e per mile on the national average grid — roughly 80% lower than a 28 MPG petrol car. On California’s grid the figure drops to approximately 0.025 kg CO₂e per mile. The manufacturing emissions of an EV are higher than for a petrol car, but operational savings recover that difference within 2–4 years of typical driving, according to the IEA’s Global EV Outlook (2023).
How much does working from home reduce transport emissions?
Each remote working day eliminates one round-trip commute. For the average American commuting 16 miles round trip in a 28 MPG petrol car, one remote day per week saves approximately 0.26 tons CO₂e per year. Two days per week saves approximately 0.53 tons CO₂e. The saving scales with commute distance and vehicle efficiency — a longer commute or less efficient vehicle produces proportionally larger savings per remote day.
Should I replace my petrol car with an EV now to reduce emissions?
Only if you were already planning to replace the vehicle. Manufacturing a new EV produces approximately 8–10 tons CO₂e in embodied emissions, according to the IEA Global EV Outlook (2023). Scrapping a functional petrol car early to buy an EV incurs those manufacturing emissions immediately and may not achieve net lifecycle savings for several years. The correct approach is to run your current vehicle to its natural end of life, then replace it with an EV. In the meantime, reducing miles driven and adding remote working days are the most cost-effective near-term transport reductions.
Is public transport lower carbon than driving alone?
Generally yes for bus and rail, depending on occupancy. The EPA (2024) estimates national average bus emissions at approximately 0.089 kg CO₂e per passenger mile — lower than a solo petrol car driver but higher than a fully occupied vehicle. Rail averages approximately 0.041 kg CO₂e per passenger mile nationally. The comparison changes with occupancy: a petrol car with four passengers produces approximately 0.079 kg CO₂e per person per mile — comparable to the bus average. Solo driving is consistently the highest per-person emissions option for ground transport.
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Sources
- US EPA, Emissions Factors for Greenhouse Gas Inventories. Washington DC: EPA, 2024.
- US EPA eGRID 2023, national and regional grid emission factors.
- US DOE Alternative Fuels Data Center, Electric Vehicle Benefits and Considerations. afdc.energy.gov, 2024.
- IEA, Global EV Outlook 2023. Paris: International Energy Agency, 2023.
- US Census Bureau, American Community Survey — Commuting Characteristics. census.gov, 2023.
- US Department of Transportation, Average Fuel Economy of US Light Duty Vehicles. bts.gov, 2023.
- Federal Highway Administration, National Household Travel Survey 2022. fhwa.dot.gov, 2022.
- US Congress, Inflation Reduction Act of 2022, Section 30D EV tax credit.
