I hate these 'free transit' comparsions. New York can't afford to complete second ave subway and many other extentions and service upgrades. Finishing those upgrades would do far more than free transit. Sure there need to be programs for the poor, but the vast majority of riders are not poor and don't need fare savings near as much as more service. Even the poor: many live in places with poor transit service and would be helped more if New York spent money on service - they could save a lot paying full fare and getting rid of the car if only the service was good enough.
the above in New York which has good for US service, other cities even more so.