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Train badges — train vs plane

Travelling by train emits on average far less CO₂ than flying — roughly 0.03 kg per passenger-km versus 0.15–0.25 kg for short-haul flights. Aviation accounts for about 2.5% of global CO₂ emissions, and around 4% of human-caused warming once non-CO₂ effects at altitude are included. Read more at Our World in Data ↗.

Every flight deal with a sensible train alternative carries a 1–4 train badge (1 = take the train!, 4 = only for committed train travellers). It shows how strongly the train is worth taking instead of flying, based on how much extra time and money the train costs versus the flight.

1
Train option is cheaper and faster — you should take the train!
2
Take the train if you will accept up to about twice the price for a similar journey time.
3
Take the train if you will accept up to about twice the price and twice the journey time.
4
The train here is long or pricey — for committed train travellers.

How we estimate the CO₂ savings

The CO₂ saved figure on each deal is a preliminary estimate. We take the great-circle (straight-line) distance between the two train stations and apply average emission factors: 0.18 kg CO₂e per passenger-km for flying (plus a fixed takeoff-and-landing premium equivalent to 95 km) and 0.035 kg CO₂e per passenger-km for the train. The difference, doubled for the round trip, is the number we show.

These factors are in line with published averages from the UK government (DEFRA/BEIS) and the European Environment Agency. They are conservative for modern electrified high-speed rail — Eurostar reports around 0.006 kg CO₂e per passenger-km — so the real saving on high-speed routes is likely higher than shown.

CO₂ savings are preliminary estimates and will be refined over time.