Quickest route from CDG to Gare De Lyon Station

Looks like The Direct Bus might be the ticket! Is this relatively new?

http://en.lebusdirect.com/lignes-horaires/ligne-cdg-aeroport-paris-gare-montparnasse.html

It's a new name for Les Cars Air France which has operated that bus route for years.

RER B to RER A is not a Metro trip. It's a minor difference but the RER trains are not the Metro though they have station stops in common. That being said, I am pretty sure that RER A will be out of service in central Paris on July 31st. The fastest way is generally the way that avoids surface traffic, especially if you are traveling during rush hour, so that would be to take RER B to Gare du Nord and change there for RER D. That is actually my preferred RER routing even when RER A is running. The good news is that the RATP website keeps up to date on when trains are out of service so it will offer you a route that will not work on your travel day. That being said, taking the train from CDG to Gare de Lyon is not my preference. I prefer Le Bus Direct because the seats are more comfortable, there is less of a concern about pick pockets, luggage is stowed below the bus and I don't have to think about again until I reach my stop, and I am above ground the entire time thereby not having to look for elevators or escalators when I get to Gare de Lyon.

Thank you JHK for your helpful reply. I really appreciate it!

I knew the difference between the RER and Metro. I'm also aware of pickpockets/thieves on the Metro, but is that true of the RER as well?

Thanks again!

Pickpockets like any place that's crowded and where the tourists are fresh off the plane. The most crowded that I happened to see the RER was going toward the airport in early morning, when there had been a delay. Although it's technically different from Metro, the systems are so integrated within the city center that you'd treat them the same.

The most, or maybe I should say most obvious, pickpockets that I have seen in Paris have been at the Eiffel Tower, the RER B heading to Paris from CDG one morning, and Metro lines 1 and 4. They were so obvious at the Eiffel Tower that my daughter gave me her phone to hold in my cross body bag. A few minutes later she felt a hand was in her pocket. She thought it was a brother looking for her phone and so lightly slapped the hand without looking only to turn around and see a grown man standing behind her. On the RER B the pickpockets are there to take advantage of jet lagged travelers who have not secured their belongings.

"Integrated" means that the ticket you buy at the airport works for both RER and Metro trains (no transfer to the bus, I think.)

I think Le Bus Direct is the way to go on this one, for the reasons stated. It will cost more than RER but will be much easier, and goes right to your destination. Under its previous Les Cars name it gave good service for many years.

I agree about Le Bus Direct. We took it to Montparnasse this Spring before the name change, and during a transport strike, and it was very efficient and comfortable.