Flying vs train vs driving: emissions per passenger-kilometre
Per passenger-kilometre, taking the train is typically 5 to 10 times lower in emissions than flying or driving alone. But the honest answer depends on how full the car is and how far you’re going.
Emissions per passenger-kilometre
Approximate DEFRA figures (grams of CO₂e per passenger-km):
| Mode | ~g CO₂e / passenger-km |
|---|---|
| Domestic / short-haul flight | ~150–250 |
| Petrol car, 1 occupant | ~170 |
| Petrol car, 4 occupants | ~45 |
| Long-haul flight (incl. contrails) | ~150–300 |
| Coach / long-distance bus | ~27 |
| National rail (average) | ~35 |
| Electric rail / Eurostar | ~5–15 |
A train beats a solo car drive and a short flight by a wide margin. But a full car (four people) can rival or beat rail, and a packed coach is the lowest-emission long-distance option on the road.
The two caveats that change the answer
- Occupancy. A car’s footprint is shared. One person in a car ≈ 170 g/km; four people ≈ 45 g/km each. Car-pooling is one of the most underrated moves in transport.
- Distance and the flight penalty. Short flights are the worst per kilometre because take-off burns disproportionately, and aviation’s contrails add roughly a second dose of warming on top of the CO₂. For trips where a train exists, the train almost always wins.
The honest framing
The rule of thumb that survives the data: train > full car > coach > empty car > short flight. If you’re choosing between a one-hour flight and a few hours on a train for the same route, the train is usually the lower-carbon choice by a factor of several — and for a solo journey, simply filling the car or taking the coach beats flying. CO2Mate logs each leg with these factors so the comparison is concrete, not a vibe.
Sources: DEFRA UK government conversion factors (per-passenger-km by mode); Our World in Data, “Which form of transport has the smallest carbon footprint?”.