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Comment by ColinWright | Hacker News Reader

Some of these violations are common and ubiquitous. It's been well-known for decades that the UK train fares are not a metric, for a time even failing all three properties:

* Splitting tickets at an intermediate station sometimes reduced the total fare, so p(A,B)+p(B,C)<p(A,C);

* Reverse journeys are not always the same price, so p(A,B)!=p(B,A); and

* For a time it was necessary to purchase a platform ticket to enter the station proper, so p(A,A)!=0.

Even now I save thousands of pounds a year by finding optimal split ticket journeys, some of which take (partial) advantage of advance fare discounts.

So I'm not surprised, and no longer think of common sense as something to be expected from fare structures.

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It may be more risky to try this with splitting your flights into individually booked segments.

Say, for example, I book a flight from ZRH to PRG with a stopover in VIE (which is usually cheaper than the ZRH VIE segement alone and backs the assertion of the paper up nicely, but I digress).

The legal connection minimum time in VIE is 30 minutes and Austrian Airlines will happily sell me a ticket with 35 minutes time to connect.

If the ZRH VIE flight is delayed and I miss my connection it's their responsibilty to resolve the issue. Potentially putting me up into a hotel overnight and even compensating me for a delayed arrival. EU rules are pretty strict here.

If I book the segments seperately it's my responsibilty and if I miss the connection due to delays I'm shit out of luck and the airline has no obligation or responsibility towards me.

I realize that the UK train network is very different than the scenario described and I appreciate that big savings can be made by planning ahead. I just don't think that this necessarily applies for flight ticketing.

Note that I'm not argueing that big savings can't be made by hidden city - or nested booking strategies. But those come with another bundle of potential problems.

Yes, that is indeed a downside, plus if you have hold luggage you have to consider the extra time to get it out of the first plane and checking it in to the second one which might well not be possible if the transfer time is as little as 30 minutes.

But assuming you have margin for that and since we are comparing the two same flights, we can assume that our loss is also the airliner loss, hence they will make everything they can to make the transfer work for the people that bought a single fare.

Therefore I see the difference in price as insurance against something that the airliner themselves have an incentive to avoid. Additionally to the risk, as with any insurance, I also consider the cost of the worst case scenario.

Most of the time my decision is not to pay the "insurance", unless time is critical and missing the connection means more than hotel + extra flight.

I've always found it interesting how round trips in one direction cost different than round trips in the other. I.E. p(A,B,A) != p(B,A,B). For example, I booked a trip October 2nd to Oct 17th from Singapore to San Francisco.

On United,

  $1170 - SFO UA 869,UA 895 -> SING UA 896, UA 862-> SFO
  $1690 - SING UA 896, UA 862 -> SFO UA 875, UA 7991 -> SING

I guess it makes sense that travel in one direction on certain days might be more significant than the other, But I find the $500 difference (almost 50% increase) to be pretty impressive.

I waited a few days, and re-ticketed again, and the price dropped from $1690 to $1463 - so that's also odd.

That's quite common within Europe, where a ticket from Warsaw to Zurich can be significantly cheaper than into the other direction.

In this case it makes a modicum of sense. Chalk it up to differences in purchasing power.

  I waited a few days, and re-ticketed again, and the price dropped from $1690 to $1463 - so that's also odd.

Not really. Airline pricing is very much based on mathematical models. When the system determines that the flight won't be sold for $1690 it lowers the price.

The trick is to fill every seat on the plane as expensively as possible, but not to leave any empty seats. Check out this article for details https://en.wikipedia.org/wiki/Yield_management .

In principle: There is no product going stale faster than an empty seat on a plane after the doors close.

Their goal is to maximize income, not fill seats. If it was the last flight they'd ever fly, you'd expect the price of an empty seat to converge to zero (or well, the cost of the fuel to lift a person and their baggage above the clouds) as the gates close, but you also have to keep the price expectation high for the customers silently haggling with the online ticketing system for a better price.

OT: it drives me crazy that yield management is not applied to events. If you have only sold half the tickets for your concert, reduce the remaining tickets. hn, do something!

If they did yield management properly at events which tend to sell out they'd also be able to capture ticket scalpers' potential profits rather than attempting overly elaborate ID schemes to prevent ticket resale. Not sure that many people would be thankful for higher ticket prices, but some of them might prefer that rather than having to buy tickets within an hour of them going on sale via a booking platform that struggles to cope with the traffic spike.

I used to work for a ticketing company. I know some Major League Baseball teams were making efforts at "dynamic pricing" which was basically yield management. Some ticket brokers do this as well.

> where a ticket from Warsaw to Zurich can be significantly cheaper than into the other direction. In this case it makes a modicum of sense. Chalk it up to differences in purchasing power.

Not just that. Everyone wants to be in Greece in August, not many people want to be in London.

Unless they're staying the whole month or the period is bracketed by major discontinuities, it isn't clear how that preference is relevant. A round trip is at least two flights. Why should the order of them matter?

Demand.

It's pretty easy to imagine that demand could be quite different. For example, flying to San Francisco before the Super Bowl is going to be much more expensive than flying out of SF.

In the summer there is a daily direct flight from Hamburg to Whitehorse in the Yukon to cater to all the tourists pouring in. They flood to the Yukon in last spring, and leave again in the fall. The flight is somewhere around $$800 one way, $1500 return.

If you fly the reverse time of that i.e. Yukon->Hanburg in late spring and then Hamburg->Yukon in the fall, you can do return for ~$300 - because the planes are almost empty.

There's not really any good reason to expect arrival costs to be the same as departure costs for a given location. For instance, it takes much longer to board a plane than disembark, which means there's a comparative premium on leaving from less efficient airports. So even if it weren't about maximizing price, you'd expect different costs for different directions.

I believe airline ticket prices are often based seat demand and availability. SFO is United's west coast hub, so it could be that they are routing most trans-pacific flights through there and demand for seats is higher as a result.

Most airlines run giant data analysis operations on schedule (date and time) passenger utilization and anything else they can collect to derive an optimal pricing strategy.

Most fares are updated once per day and these days even intraday is possible. Most everyone uses SABRE, Amadeus and one other as their reservation backends which have various limitations (Spirit is an example that doesn't but it's very rare and theirs sucks). There are also a ton of caches everywhere to speed up the process which affects latency and increases stale pricing. It's sometimes very chaotic as to what everyone will see.

Also keep in mind that A->B and B->A and A->C->B, etc all have a different optimal pricing structure which is why you get so many odd prices. None of the reservation systems can consider every possibility either, they often have to short circuit a search or it would take forever so you can get variations depending on when/where/from what you look for these fares. Dallas to Austin is pretty trivial to search but small airport in Texas to small airport in China is ridiculously complex as there are trillions of combos.

Landing slots at airports have different fees. If you the A is a very expensive airport (e.g. Heathrow) the price of flying from and to A can be higher than the reverse.

The 2nd and 3rd there are not economically unreasonable, and the 3rd isn't metric-violating.

The 2nd would make sense if the net demand to go one way is greater than the other (think about moving trucks going from Detroit to San Francisco and vice versa).

The 3rd is the charge to go from outside the platform to inside it, not to stay in the same place. Whatever criticism you might make of the practice, the two A's are not the same.

Edit: And, FWIW, in case anyone hasn't heard the explanation, the "hidden city ticketing" in the first case exists when a provider with A-B routes and B-C routes wants to compete with a direct A-C provider and has to make the sum of the two legs (which takes more time) cost less than the direct, since it's necessarily less convenient, requiring them to vigorously scout for people who get off at B.

How do you find the optimal split?

Start by deciding on acceptable routes. Here's a graphic of a recent journey I computed:

http://www.solipsys.co.uk/images/Route_HOO_HWY.png

Choose your date and time window for travel.

Then for every leg, download possible times and prices. Finally, simple search for the optimal combination.

You don't have contact details in your profile, but if you email me I can send you more details. I'm extremely busy just now, but if we establish contact I can send you relevant things in slow time. Let me know.

http://www.moneysavingexpert.com/split-cheap-train-tickets/

My experience is that the results from that site are very, very poor. My simplistic home-brew system regularly beats it by 30% or more.

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