When comparing flying vs driving carbon emissions, flying typically produces more CO₂e per passenger for short to medium distances. However, the answer changes significantly depending on distance, number of passengers, and vehicle type. Driving alone in a large SUV on a long route can exceed the emissions of a full economy flight. Driving four people in an efficient car almost always beats flying. There is no single answer — but the data makes the comparison clear.
This is one of the most searched carbon questions — and one of the most misunderstood. The comparison depends on variables most people do not account for. This post works through the numbers for common real-world routes and explains when flying beats driving, when it does not, and what actually determines the outcome.
Flying vs driving carbon emissions: the per-kilometre baseline
The standard comparison unit is grams of CO₂e per passenger kilometre (g CO₂e/km). This normalises for distance and allows a direct comparison between modes. The figures below use UK Government DEFRA emission factors — the most widely cited source for transport comparisons — and apply globally as a reasonable benchmark.
| Transport mode | g CO₂e per passenger km | Notes |
|---|---|---|
| Short-haul flight (economy) | 255 g CO₂e / km | Includes radiative forcing multiplier |
| Long-haul flight (economy) | 195 g CO₂e / km | Lower per km due to cruise efficiency |
| Petrol car — driver only | 170 g CO₂e / km | Average US car at 25 MPG, solo driver |
| Petrol car — 2 passengers | 85 g CO₂e / km | Same car, emissions split between 2 |
| Petrol car — 4 passengers | 43 g CO₂e / km | Same car, emissions split between 4 |
| Electric vehicle (US grid) | 89 g CO₂e / km | 0.34 kWh/mile, eGRID 0.42 kg CO₂/kWh — Decarb methodology |
| Coach / long-distance bus | 27 g CO₂e / km | Lowest-carbon motorised option |
The table shows that a solo petrol car driver (170 g/km) emits less per kilometre than a short-haul flight passenger (255 g/km), but more than a long-haul flight passenger (195 g/km). Add one more passenger to the car and the comparison flips decisively in favour of driving for any distance.
Real route comparisons
Abstract per-kilometre figures become more meaningful when applied to actual journeys. The table below compares estimated emissions for common routes across modes, using ICAO and EPA emission factors.
| Route | Distance | Flight (economy) | Drive solo (25 MPG) | Drive 4 people |
|---|---|---|---|---|
| NYC → Boston | 346 km | 0.22 t CO₂e | 0.059 t CO₂e | 0.015 t CO₂e |
| NYC → Chicago | 1,270 km | 0.28 t CO₂e | 0.22 t CO₂e | 0.054 t CO₂e |
| NYC → Los Angeles | 4,490 km | 0.61 t CO₂e | 0.76 t CO₂e | 0.19 t CO₂e |
| NYC → London | 5,570 km | 0.78 t CO₂e | Not applicable | Not applicable |
The NYC to Chicago route is the most instructive. Flying and driving solo produce similar total emissions for that distance. Add a second passenger to the car and driving wins clearly. For short routes like NYC to Boston, flying is consistently worse regardless of vehicle occupancy — largely because short flights incur the full emissions penalty of take-off and landing without the efficiency gains of long-distance cruising.
Why short flights are disproportionately carbon-intensive
Take-off and landing consume far more fuel per kilometre than cruising. For a very short flight, these two phases account for the majority of total fuel burn. Aviation carbon intensity falls sharply with distance up to around 1,500–2,000 km, then levels off. This means a 300 km flight emits roughly twice as much per passenger kilometre as a 3,000 km flight.
For this reason, replacing short domestic flights with train or car journeys produces the largest per-journey emissions savings. In contrast, replacing a long-haul flight with driving is rarely practical — and over very long distances, a full flight can actually emit less per passenger than a solo petrol car.
The radiative forcing factor
Aviation’s climate impact is not limited to CO₂. Aircraft also emit nitrogen oxides, water vapour, and soot at high altitude, which cause additional warming through contrail formation and ozone effects. This is sometimes called the radiative forcing index (RFI).
Estimates of aviation’s total climate impact — including non-CO₂ effects — range from roughly 1.5 to 4 times the CO₂-only figure, with most peer-reviewed estimates clustering around 1.9–2.0×. The UK Government DEFRA factors used in the tables above already include a radiative forcing multiplier. Some calculators report CO₂-only figures for flights, which substantially understate the total climate impact of flying.
Decarb currently includes CO₂ only for flight emissions, to maintain comparability with ICAO and EPA baselines. Non-CO₂ aviation effects are noted as an exclusion in our methodology. Including a radiative forcing multiplier of 1.9× would roughly double the estimated climate impact of flights in your report. Inclusion is under consideration for a future methodology version.
What about electric vehicles?
An electric vehicle on the US national grid average (0.42 kg CO₂e/kWh) produces approximately 89 g CO₂e per km — roughly half the emissions of a solo petrol car driver, and below short-haul flight levels. On a renewable grid, the figure drops further. Even on the current US grid mix, an EV driver produces substantially fewer emissions than a solo petrol car driver, and less than any flight on a per-kilometre basis.
However, an EV does not eliminate the vehicle manufacturing and battery embodied emissions — roughly 6–12 tons CO₂e for a mid-size EV. Over the lifetime of the vehicle, operational emissions savings outweigh this upfront cost in most scenarios, but embodied emissions matter for a complete lifecycle comparison.
The single biggest variable is car occupancy. A petrol car with four passengers beats a flight on almost every route. A solo petrol car driver loses to a flight on long-haul routes.
If you have the option to share a car, do it. The emissions benefit is larger than switching to a more fuel-efficient vehicle.
Frequently asked questions
What emits more CO₂ — flying or driving?
For a solo traveller, flying typically emits more CO₂e per passenger than driving on short to medium routes. A short-haul economy flight produces around 255 g CO₂e per km, versus 170 g CO₂e per km for a solo petrol car driver. However, adding passengers to a car changes the comparison significantly — four people in a petrol car produces approximately 43 g CO₂e per km, well below any flight.
Is it better to fly or drive for long distances?
For very long distances — cross-country routes of 4,000 km or more — a solo petrol car driver can emit more than a full economy flight, because long-haul flights are more efficient per km than short ones. However, a car with two or more passengers beats flying at almost any distance. An electric vehicle on the current US grid beats flying at all distances.
Why are short flights so carbon-intensive?
Take-off and landing consume far more fuel per kilometre than cruising. On a short flight, these phases account for a high proportion of total fuel burn. Aviation carbon intensity falls steeply with distance up to around 1,500 km, then levels off. A 300 km domestic flight can emit roughly twice as much per passenger kilometre as a 3,000 km flight.
Does flying include non-CO₂ climate effects?
Aviation’s total climate impact is greater than CO₂ alone. Aircraft emit nitrogen oxides, water vapour, and soot at altitude, which cause additional warming through contrail formation. Peer-reviewed estimates suggest aviation’s total warming effect is approximately 1.9–2.0× its CO₂-only impact. Calculators that report CO₂-only figures for flights substantially understate the total climate impact of flying.
How does an electric vehicle compare to flying?
An electric vehicle on the current US grid average produces approximately 89 g CO₂e per km — roughly half a solo petrol car — based on 0.34 kWh/mile and eGRID 2023 grid intensity of 0.42 kg CO₂/kWh. On a renewable electricity tariff, the figure drops to near zero for operational emissions. Over any comparable route, an EV is consistently lower-carbon than flying.
How much do flights contribute to your own footprint?
The Decarb calculator estimates your emissions across flights, transport, energy, food, and more in 3 minutes — free, no account required.
Methodology note
Per-km emission factors: UK Government DEFRA Greenhouse Gas Conversion Factors (2023) — includes radiative forcing for aviation. Route comparison figures: ICAO Carbon Emissions Calculator; US EPA Emissions Factors Hub (2024). EV emission factor: 0.34 kWh/mile × eGRID 2023 national average 0.42 kg CO₂/kWh, consistent with Decarb methodology page. Radiative forcing multiplier range: Lee et al. (2021), Environmental Research Letters; Klöwer et al. (2021), Environmental Research Letters. Aviation efficiency trend: Our World in Data / Bergero et al., Nature Sustainability (2023).
Note on Decarb calculator flight factors: the Decarb calculator uses ICAO per-flight totals (short-haul 0.296 t, medium-haul 0.608 t, long-haul 0.775 t CO₂e per one-way flight) rather than per-km factors. The per-km figures in this post are used for mode comparison purposes only and are not directly comparable to calculator outputs.
Full Decarb methodology including flight emission factor assumptions: decarb.co/methodology
