France is testing free public transport
The additional bit of information is that often the ticketing systems make up a non trivial fraction of the overall cost of running the transportation network. Often these systems are implemented by large international consortia who funnel money from the public. Take Melbourne for example implementation of their chip card system ran much over budget and was 1.5 billion AUD in the end [1].That doesn't mean making public transport free always makes sense, but it would eliminate some of the large rentseekers from the system.[1] https://en.m.wikipedia.org/wiki/Myki