Sections of Line 15 are just named for the project phasing. Once completed, the Line will be one. Trains departing from Noisy CHamps will pass through the Southern Champigny platforms, run around the whole loop, pass through the Northern Champigny platforms, run the loop again before terminating, again at Champigny Northern platforms and maneuver on a dedicated piece of track before making the trip the other way around. That way, the loop is both complete and has two distinctive temini to regulate traffic. In the worst cases, it could do just one loop from Noisy to Champigny North via Champigny South and the loop just as the Circle Line does in London. Doing two loops is a way to ensure at least half of the trains are going through without forcing a transfer, at worst you just have to wait 3 more minutes.

Thanks for this wonderful video! Just one correction, at the moment going from Charles de Gaulle Airport to Versailles Chateau station requires roughly 1h20 and one transfer, not "2 hours and several transfers". Obviously it is still necessary to pass thought the crowded centre, but the video was exaggerating a little.

Wow