ParisByTrain.com

[MCH]

I'm taking the RER B to RER E (Gard du Nord)to Haussman St. Lazare exit. My question is
1.) Once I arrive at Haussman St. Lazare how do I get to Gare St. Lazare. (I would appreciate specifics like go up/down escalators, turn right etc.) I will likely have one large and one carryon wheeled suitcases.

I am then traveling from Gare St. Lazare to Caen. My flight arrives at 9:40am at CDG and I hope to make the 12:10 train. My questions are
2) If I buy the ticket ahead of time can I exchange it for the next train if I don't make the 12:10pm train and have to take the next train at 1:45pm ?
3) Should I buy or not buy the ticket ahead of time?
4) it is a Tuesday arrival will I be able to make the 12:10 train arriving at CDG at 9:40am probably at Terminal 1.
5) What terminal does American Airlines land in?

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