German Bahn "Sparpreis": can I use a local train (S-Bahn) instead of ICE?

Question

I'm going by train to Frankfurt airport. Everything is regional trains except for the last leg from Frankfurt Main Station to the airport. This last leg can be done on a local train (S-Bahn, RE) or on a high speed train (ICE). Ironically choosing a high speed train enables "Sparpreis" (saver ticket) which makes the whole ticket substantially cheaper. We are talking half the price here !! (Bizarre pricing, but that's what it is).

"Sparpreis" requires you to take the train as booked ("Zugbindung") for the ICE. Taking a different regional or local trains the same day is fine.

I was considering not taking the ICE since local trains are more convenient and I can hang around Frankfurt downtown a bit (I got plenty of time, if there are no delays).

Question: Can I take the local train? Does not taking the ICE somehow invalidate my fare since the 50% discount is specifically tied to the ICE? If yes, how would Bahn actually know and what would they do?

UPDATE Given the comment I'm trying clarify the question.

Let me describe it the following way: The price to Frankfurt Central is $50. By adding another leg from Central to the airport the total price drops to $25 but ONLY if this extra leg is on an ICE/IC train. I know, this makes absolutely no sense, but that's what is.

The situation is similar to "hidden city ticketing" (or skiplagging) with flights. Often flights from A->B->C are cheaper than just a flight from A->B; even if it's the exact same A->B flight. So customers for A->B just buy A->B->C and simply get off at B. The airlines take a very dim view of this practice and have (on rare occasions) even sued customers over it.

Just as an example: Lufthansa is one of the suing airlines and for air rail tickets they try to enforce this on the Bahn as well. You are not allowed to skip the train portion of a trip. People still do though, since LH has no legally defensible way of proofing whether someone was NOT on a train (unless the passenger does something stupid).

My question: Does Deutsche Bahn has a similar concept to "hidden city ticketing" (as Lufthansa does) and, if yes, do they have any rules and/or enforcement around it?

Answer 1

In this particular case the difference in prices doesn't come from some kind of hidden city ticketing but is a direct result of using regional or long distance trains:

The journey from Frankenberg to Frankfurt uses only regional trains, while the trip to the airport contains one short leg with a long distance train. In Germany, regional trains are planned, ordered and payed by regional transport agencies. Many of them are not operated by Deutsche Bahn but by other companies (the occasional traveler doesn't need to be aware about this, tickets can be bought on bahn.de in most cases. They'll just see trains in different colors and conductors in different uniforms). As a result a trip in regional trains can only be bought for fixed fares (not accounting for special discounts or weekly/monthly tickets).

On the other hand, almost all German long distance trains are operated by Deutsche Bahn as a commercial product. Trips in long distance trains are subject to the pricing made by DB, including Savers and Supersavers tickets. These trips can include rides on regional trains. In that case there will be some compensation paid behind the curtains, but the traveler doesn't need to care about that.

If you compare full fares the prices are as to be expected, the longer trip to the airport costing more. But depending on the date there are additional tickets with quite large discounts available. Obviously there is a disadvantage: You'll be bound to one specific long distance train while the full fares allow you to chose any train of the given category and on the given date. This doesn't apply to regional trains, and therefore not for traveling from Frankenberg to Frankfurt. But there still are limitations on availability and cancellation policies.

There are no issues skipping any leg or part of leg on any ticket in DB trains. If you enter a train at a later stop than planned the only thing you might lose is your seat reservation - transport rules state that it is only valid from the original starting point.

In some rare cases (usually during special promotions) there is also the chance to catch an even cheaper ticket, if your journey consists of long distance trains only, saving DB from paying compensation to the local transport agencies.

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TLDR

can I use a local train (S-Bahn) instead of ICE?

No. Your ticket is only valid on the route and trains listed in the 'über'/'via' field. If a train number is listed, you can't substitute this train with another one.

Does not taking the ICE somehow invalidate my fare since the 50% discount is specifically tied to the ICE?

No.

Does Deutsche Bahn has a similar concept to "hidden city ticketing"

It may happen, but in my experience it's mostly the specific train you select and not the destination that defines the price. Although you might be eligible for some special promotions with one destination but not another.

if yes, do they have any rules and/or enforcement around it?

No, there are no checks if you actually board a train.

Answer 2

The accepted answer is correct, however, note that the so-called Zugbindung (i.e. the rule that forces you to take the exact trains you booked with a Sparpreis or similar ticket), does not apply to regional trains.

So if you have booked a regional train before, after or even in the middle of your connection, you can take any regional train there instead. Zugbindung only applies to high-speed DB trains i.e. IC/ICE.

https://www.bahndampf.de/deutsche-bahn/zugbindung#Welche_Bahntickets_beinhalten_Zugbindung (German)

What you wanted was replacing a ICE with a regional train and IIRC this is indeed different and not possible. Usually it is also not what people want though… 🙃