It's true that new capacity generates new demand, however I think there are some limits. When the monthly pass pricing became flat, it was way cheaper for peopl

It's true that new capacity generates new demand, however I think there are some limits. When the monthly pass pricing became flat, it was way cheaper for people living far in the suburbs to come to Paris proper. I don't have any numbers, but I don't have the impression that people started coming in in much greater numbers. In the case of Paris, public transit is already insufficient during peak times. I'm sure most people who don't already take it have reasons other than the price, meaning that if it were free there wouldn't be a significant rise in traffic. However, I think that all the money spent on the ticketing system could help improve the general reliability which in turn would help provide more capacity. This would probable incite more people to take public transport which could help the transport authority obtain more funding from the region government. As in Paris the transport authority is already heavily subsidized, I think it would be interesting to have to some numbers on how much tickets bring in vs how much the whole ticketing infrastructure costs.