Why are air fares often cheaper than train tickets?

“You wrote that economic forces have made planes more affordable than trains,” writes John Hall. “How?”

After a trip around the Balkans earlier this month, I mused that a plane can be cheaper than a train for many journeys. “Previous generations of backpackers would never have dreamed of flying the 300 miles between Sofia and Athens,” I wrote.

I had booked a few days in advance and found a flight between the Bulgarian and Greek capitals for €15 (£13) on Ryanair.

Now, a lot of stories that claim to show how planes are far cheaper than trains turn out to be tosh. Typically they compare a book-ahead air fare with an on-the-day (or “walk-up”) rail ticket. In the case of that Sofia to Athens trip, the overall train fare for a journey via Thessaloniki (and, for the time being, a brief bus ride across the Bulgarian-Greek border) is a little over €60.

The fare is fixed, irrespective of how far ahead you book. I paid a quarter of that with a few days’ planning, but buying that Ryanair flight just a day before travel typically costs €100.

The reason for the really cheap €15 deal I found is because the Irish airline is “load factor active, yield passive”. In other words, Ryanair will cut fares to whatever level is necessary to fill its planes, which it does with alacrity; only an average of 5 per cent of seats are empty. I imagine those trains between Sofia and Athens struggle to fill half their seats with fare-paying passengers.

The costs per-seat-mile of operating a plane may be significantly higher than for trains, but if enough bottoms are filling those seats the advantage starts to move to the airline.

Next, the basic air fare is really just the start of negotiations, which is why Ryanair is prepared to sell at any price to lure passengers onboard. The airline believes that skinflints like me who will jump through every hoop necessary to get the lowest fare are rare. Most passengers will pay to select a seat, check in a bag or buy priority boarding. And some will be tempted with scratchcards.

These ancillaries are a critical part of Ryanair’s revenues. And while train operators are just as keen as airlines to sell ambitiously priced food and drink, they can’t extract revenue from much else.

(One exception is the high-speed/low-cost operator Ouigo of France; this French Railways subsidiary emulates the budget airline model with the use of “secondary” stations such as Marne-la-Vallée outside Paris, strict baggage limits and even a €2 charge for a charge; seats with power sockets cost extra.)

On the other hand, purchase and maintenance costs for aircraft are far higher that for trains. You don’t get 80-year-old planes carrying commercial passengers in the UK, yet rolling stock built eight decades ago is still going strong on the Island Line of the Isle of Wight.

But rail infrastructure is a huge fixed cost which has to be paid for by the passengers and freight users (or subsidised by the state), even if only a handful of trains run every day.

While air infrastructure isn’t cheap, airlines can buy just the space and time they need at an airport, and pay the going rate for air-traffic control charges. Since their assets are entirely mobile, the route network can change overnight with no significant penalty. Try doing that with a rail network.

Airline pilots generally get paid more handsomely than train drivers, and there are always at least two of them on the flight deck. But because planes are so fast compared with trains, those salaries per mile are a lot lower. And while trains typically change crew at each international frontier, planes (thankfully) do not.

Budget airlines have slashed costs, to the benefit of carriers and passengers. When I bought my Ryanair ticket, the process took about a minute and involved no human contact. But buying a train ticket often requires queueing up for usually a lot longer than a minute to ask a man or a woman, often in a hat, for a token for travel.

So much about rail travel is still analogue. The industry will eventually drag itself out of the 19th century and narrow the air advantage, but it will prove a long haul. Dampening the appeal of air may require draconian government or international action to limit the environmental impacts of passengers by increasing the cost through taxation. But until then, there will be plenty of takers for the €15 fast track to Athens.