Rail is consistently lower-emission than flying the same route, yet travellers keep booking short flights. The reason is that the comparison people make is time, and time depends on distance in a specific way.
The emissions comparison is not close
Trains carry many passengers per unit of energy, avoid the fuel-intensive climb entirely and, where electrified, draw power from a grid that is progressively decarbonising.
Aviation has no equivalent trajectory, because its fuel must be carried and burned aboard and the alternatives to kerosene remain scarce.
Even diesel rail generally compares well against a short flight, because the per-passenger energy required to move a train is far lower.
Door to door is the only fair time measure
A short flight might show an hour of flying time against five hours by rail, which is the comparison booking sites present.
Adding travel to an out-of-town airport, check-in, security, boarding, taxiing and the journey from the arrival airport into the city typically adds three to four hours.
Rail stations sit in city centres and boarding takes minutes, so the rail journey's advertised duration is close to its real one.
The competitive band is real and measurable
Rail generally wins door to door up to around three or four hours of travel time on a fast line, which is why airlines withdraw from those routes once high-speed rail opens.
Beyond roughly five hours the balance tips, and beyond eight it tips decisively unless the traveller values an overnight service.
Sleeper trains extend the band considerably, because the journey occupies hours that would have been spent in accommodation anyway.
Booking friction is the practical obstacle
Cross-border rail is often sold by national operators with separate systems, so a journey crossing three countries may require three bookings.
Prices can also rise steeply close to departure, which is the opposite of the pattern many travellers expect from budget flights.
Booking early and, where possible, buying a through ticket that protects connections removes most of the difficulty, though it requires more planning than a flight search.
What rail changes about a trip
Arriving in a city centre removes the transfer at both ends, and the time on board is usable in a way that airport time is not.
Baggage rules are looser, which reduces the pressure toward the very light packing that flying encourages.
The main constraint remains geography. Where no line exists, or where a border has no through service, the choice is not available regardless of the arithmetic.