I'm looking at tickets for a Montparnasse to St. Malo train trip. The only itineraries that fit my schedules are one-stops in Rennes, with a 10 minute transfer to go on to St. Malo. I see other times where there are no transfer trains, and other trains with 25 minutes to transfer, just not during my window. Is a train transfer from the Paris train to a different one to St. Malo very risky? If we're late arriving, would we be able to use our thru-tickets for a later train to St. Malo?

It depends on the train and dates. It should be enough time. If the second train is a TER, you can get on another TER but not any other type. Also, there are certain dates when those TERs on that route require reservations,also, so date matters. I think that's the case in the summer or maybe until end Sept, not sure.

Valid connections are displayed on SNCF connect (and other vendors) and sold with a single transaction/"ticket". Is it the case for the trip you allude to?

Rouelan: Yes, it is one ticket, but comes up with a notice/warning that the transfer time is only 10 minutes, hence the questions.

Christina: I just verified, the Rennes-St. Malo leg of the ticket gives a TER train. Will I be prompted during purchase about the reservation requirement you mention, or is that just part of the ticketing process? Secondarily, how would one find the status of later TER trains and a reservation requirement? I'm anticipating either the end of September or Early October of next year, but want to pin down transfers, etc. so I can properly get accomodations.

Thanks to both of you for your questions.

It says on the SNCF schedule if it requires reservations. I just checked on TERs from Rennes to St Malo and it is aspprently only if you want to carry on a bicycle. It says this

La réservation vélo est obligatoire du 1ermai au 1erseptembre 2024 sur les trains TER BreizhGo.

So that shouldn't be a problem end of September no matter waht. I was on a TER once some years ago in the south that was only good for a certain time also, I think it said so on the ticket.

The SNCF website shows train schedules, that's what I use. But in the station, you look at the board and it shows you the trains scheduled and if they are TERs or not. Some will be TGVs or INOUI, most likely. You could have a very long wait For example, this Friday there is a TGV at 1:30 and 3:30 but a TER at 11:35, 12:35, 1:35 pm, then 16:07 and 16:35 (weird, probably because it's a Friday) and 17:35.

If you are planning the one that would require the 1:35 pm departure as that's with a 10 min corespondence, you'll have to wait until at least 4 pm probably. There are several in the evening, also, of course. IF you are planning the early one that is more like a 10:29 departure, you have the 1:35 pm possibility. l don't know why that would be your only possibility, there is a direct train at 7:07 am that is only a half hour earlier. I can understand not wanting the one that takes four hours but you have to realize the reason is that there is a 1:10 transfer time (the 8:43 to 12:32 one). So obviously you would be better off doing that than having to wait around until 4 pm.

YOur call, I'd probably do either the 7 am one or the 8:43 one and not stress about it either way.

I'm debating just staying in Paris on the first night and catching the first no transfer train at 7:07 am to avoid any issues. We will be spending our last week in Paris so I was hoping to spend as much time in Brittany as possible, but the first day isn't productive anyway, and getting off the train at 10:00 is about the time DW gets up on the first full day after the flights anyway, so I can drag her to the train early and she can sleep on it for the couple of hours to St. Malo.

Thanks.

Then, it is not a problem unless you have serious mobility issues (hence the warning for short connect). If the train for St Malo is not on the same platform, you will have to go upstairs / short walk / downstairs for your train. It will take max 5 mns. If the Paris train is slightly delayed, it is likely that the train for St Malo will also be delayed to wait for connecting pax. If you however are to misconnect, conductors aboard the Paris train will advise you what to do.
Some info on misconnect
https://www.sncf-voyageurs.com/en/contact-us/in-case-of-delay/billet-direct/
What I dont know is if you have to go to a tkt counter in Rennes to reaccommodate you on the next train if it is a TGV. If it is a TER, just hop on this train, there are no reservations on such trains.

Transfers out in the regional stations are super easy because they are not very big -- often six or eight tracks at the most. Once you have made a transfer in such a station, you will find that even 10 minutes can seem long because you would like the other train to be there, but you still have to wait for it even though you were huffing and puffing to catch it;