Best way to travel from Orly to CDG

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Hopefully others have more insight, but:

1) Chatelet-les-Halles is huge and getting lost is not out of the question
2) The bus is subject to traffic delays, and you don't say what time of day/day of
week you'd be doing this

So for my money, I would take OrlyVal to Antony and then RER B all the way to CDG.

I would take line 14 at Orly to Châtelet and take the RER B from there to CDG.

When I fly into Orly, I take the Orly Val into town. From town I take the RER to CDG. I've never done both at one time, but it is one option for getting from one to the other using public transportation. It should be cheaper and, maybe, faster than a taxi.

At this point there's no best, but there are three good ones.

Orly-Val to RER B in Anthony is 16euro. Pro-you are in one of the first stops and have a choice of seats. Con-because this is a branch of the south end of the line, you have 10-15 minutes between RER B trains going to CDG.

Line 14 Metro to RER B changing at Chatelet. Pro: the 14 line is not far from the RER B in this large station. Line 14 is new, clean. Con- you are getting on the RER at a point where fewer seats will be available. Price ? (probably the 16 euro day pass)

Orly-bus directly to Denfert Rochereau changing to the RER B--easy change outside at street level into the Denfert station. You are catching the RER B at a station in the southern end of the city. Con-a bit slower and could hit traffic jams. Pro-you are in daylight in a seat, looking at the suburbs and the city. Price ?

Always get into a RER B that has Aéroport marked as a station on the lit panel on the platform. As the RER B line exits the city, it has different branches. Be sure you get into a train that goes to CDG. IMO, some trains stop at many stations outside Paris, while others are more direct, stopping at fewer. The difference in time isn't a deal-breaker for me, just a bit boring.

I would attempt this using métro 14, Châtelet, RER B (to CDG, not Mitry/Claye departing from the same platform). The MTA fare from ORY is 10.30€. The IDF Mobilité definition of an MTA fare is from airport origin (CDG/ORY) to any métro/RER station. The MTA fare is relatively new and, to my knowledge, only available in the electronic format meaning it needs to be loaded onto a Navigo Easy card (2€), or properly configured smartphone.

All the material referencing the ticket MTA is available online, now we just need someone with the practical experience, verifying that it works as described for travel from ORY to CDG (and visa versa).

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