If one is taking a TER or Intercités for a journey entirely inside Île-de-France, can one use an Île-de-France pass such as Navigo, Mobilis, or Ticket Jeunes Weekend valid for the appropriate zones?
Are there TER or Intercités trains which need reservation for travel inside Île-de-France, in second class? If yes, how does one confirm whether a particular train needs reservation before boarding?
Yes you can. All these three tickets can be used on all trains within the Ile-de-France region, including TER and Intercités.
There are some restrictions though:
You are not allowed to use it on trains with compulsory seat reservation, such as TGV trains. Note that reservation is never compulsory, and I think even not possible in TER trains. Regarding the Intercités trains, reservation is compulsory on some of them. This restriction will not bite you as you will not need to travel on them. If you rely on TER and the other operators, you have a very good network at your disposal.
You are not allowed to travel first class.
With "Ticket Jeunes" you are not allowed to access the airports via direct links (RER B, Roissybus, Orlybus, Orlyval), only via the slower local links (e.g. bus 350 at Roissy, RER C at Orly).
None of these passes allows you to use the Orlyval light railway.
You have to be sure that your ticket is indeed valid in the zones you want to travel, for the whole journey. If it isn't, with a Navigo pass, you can purchase a complément de parcours (you need to buy it just before your trip at your origin station). Note that a Navigo monthly or yearly pass (but not a weekly pass) is valid for the whole Île-de-France region on week-ends and public holidays. With Mobilis or Ticket Jeunes Week-end, your pass must be valid for the whole journey.
