Free weekend travel on Paris Metro & RER system.

We just returned home from a great trip to Paris. On our last day (March 21), all of the Paris Metro system (including connections to the RER) were free.

In an effort to reduce the air pollution in Paris, the government imposed weekend restrictions on driving (no even numbered license plates) and opened up the Metro for free travel for all. We did not see any signs in the Metro station (none in English at least) and only learned about the free Metro travel AFTER we bought out Metro tickets to Orly airport. Upon learning of the free Metro, we then noticed the open gates into the station platform areas. The Orlyval train still required a ticket from the RER B - Antony station (included in the unnecessary tickets that we bought).