But even if cutting prices is within Paris only it will probably affect suburb-Paris traffic, because it changes the cost of a trip to Paris, possibly now cheaper than driving. The article is light on details, but it looks like these measures are taken by the city of Paris with the aim to reduce the traffic within the city.
https://parismap360.com/carte/image/en/paris-rer-map.jpg
But even if cutting prices is within Paris only it will probably affect suburb-Paris traffic, because it changes the cost of a trip to Paris, possibly now cheaper than driving. The article is light on details, but it looks like these measures are taken by the city of Paris with the aim to reduce the traffic within the city.