So long as fuel is reasonably priced, planes can take more people farther, faster it is simple economics. Trains are still preferable for local trips and even some medium range trips, but to go all the way across Europe by train would be terribly expensive compared to taking a cheap flight.
That doesn't really answer the question. What about planes is cheaper? For simple economics to apply, they have to do something cheaper than trains, and it's not obvious what that is. As far as I know, for example, trains are significantly more fuel efficient per passenger-mile.
There are several reasons why flying can be so cheap in Europe:
1. The discount airlines have become masters at turnaround times. When the planes are sitting at the gate, they're not making money. They slashed these as much as they could.
2. They only fly one model of airplane (typically either the 373 or a320) to simplify maintenance.
3. Most major airports in Europe are privatised. One of the effects of this is that they've become giant malls that want to get people through them, so landing fees have steadily gone down (there are edge cases where the airports pay the airlines to go to them, but those are rather rare exceptions).
4. Some airlines (more specifically Ryanair) fly to cheaper/more outlier airports. If you take a Ryanair flight to Paris, you're landing in Beauvais Airport, which is almost halfway to the english channel. You'll then have to take a bus. When in europe, I usually prefer Easyjet for the reason that though they're more expensive, you're landing at an airport with decent transit to the city you're visiting.
5. There's no frills at all. If you're just flying with no luggage, you won't believe how cheap it can be (I flew from madrid to london for 25 euros). But the fills aren't cheap. Checked baggage is more than the cost of the flight, food is a rip off, etc.
Also, trains in europe are still often state-owned (not the case everywhere, I know), so they're forced to run uneconomical lines for political purposes, etc.
> (there are edge cases where the airports pay the airlines to go to them, but those are rather rare exceptions).
Thing may have changed since a few things happened meanwhile, but a couple of years ago Ryanair got about 100 Million EUR [1] (sorry, link in Italian) from various Italian airports. Verona airport used to pay up to 24 EUR per passenger to low cost companies.
My understanding is that some airports have been opened for political reasons even when there was no real need, so they are "forced" to make such agreements in order to guarantee a decent amount of passengers.
I'm wondering if this happens also elsewhere in Europe.
> 1. The discount airlines have become masters at turnaround times. When the planes are sitting at the gate, they're not making money. They slashed these as much as they could.
As a european who moved to the US recently, this was mind boggeling the first time I boarded a plane in the US. I arrived at the airport expecting a typical 10 minute boarding time, but kept getting more surprised at how inefficient they managed to make boarding a plane as time passed. Just the time spend waiting in the plane at the gate before they let you get out seems to be longer in some cases than the typical turnaround time for euro flights.
Not having to maintain thousands of miles of rail seems like a big cost savings right up front. Trains should have lower fuel costs, but fuel really isn't that expensive in the grand scheme of things. People are also willing to give up some creature comforts if the trip is short which helps airlines. Trains also have a lower throughput of passengers compared to employee hours, so salary costs per passenger are higher.
The simple economics is in passenger volume. A plane can carry more people, to more destinations within Europe, several times a day.
Your statement that "As far as I know, for example, trains are significantly more fuel efficient per passenger-mile" definitely has some merit, but... trains are only more fuel efficient per passenger if they are as full as planes. An Airbus with 180 passengers might beat a train in per passenger miles if the train is not loaded.
Considering that, trains definitely are cheaper for highly utilized routes (commuting routes, for example), but for a leisurely trip across Europe, an Airbus packed to the gils could be cheaper.
Planes most likely benefit from the economies of scale, simply for the huge number of riders they service in comparison with trains for longer stretches.
The complicated area of railroad tracks probably doesn't help either. Someone is paying for them and the maintenance is frequent judging by the business my friends working on the railroads get.
