TGV ticket price appreciation as departure date approaches

Question

I want to know the mechanics of how the SNCF increases their TGV fares as the departure date for a certain TGV trip approaches (or the train is getting fully booked).

That question may be too broad for the stack exchange format, so let me focus on the following well-delimited question which is inspired by what I read on this TA forum:

Are the fares for flexible tickets (is that TGV pro or TGV leisure?) for a given TGV journey fixed in time? Second: is -at any point in time- the price for a regular ticket lower than the one for the flexible ticket?

Feel free however to digress on other aspects of the mechanics behind TGV ticket appreciation if you have useful and relevant information.

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As secondary additional information: I myself want to use the TGV from Nantes or Angers (I don't know yet which one) to Brussels somewhere during the weekend of 5-7 september 2018. I guess that's a local low-season for tourism and train occuations.

Answer 1

Generally speaking, TGV fares work more-or-less like airfares. Historically, the SNCF based their first booking system for what they call “prix de marché” (that's Socrate in 1993, before that fares were in most cases based on a fixed rate per kilometer) on systems used in the aviation industry. What that means is that the fare is not based only on time-to-departure but on the concept of “buckets”. Once a bucket is full, you have to book in the next available (more expensive) bucket. If a train is relatively full, the cheapest available fare can increase early on. If a train is relatively empty, cheaper fares will be available longer.

Concretely, on a given day, early morning (less popular) trains can be cheaper than trains leaving later in the day (i.e. further away in time). Similarly, trains on Sunday evening (weekend return) can be more expensive than trains around Saturday night (useless for weekend trips). And fares in different classes (flexible tickets or first class tickets for example) are not directly correlated (e.g. if second-class inflexible tickets get more expensive, first-class tickets might still be cheap). And sometimes you can luck out and get a super-cheap fare a week or two before departure.

That's not the only factor, the SNCF also advertises special “Prem's” fare that have to be booked more than three months before departure and I cannot rule out that some fares are never available a day or so before departure but other than that the bucket model matches my observations pretty well. Flight tickets: buy two weeks before even during holiday seasons? explains how it works for airline fares.