[dominicr]

The size of population and complexity of the system is only one small factor. You still have to organise about the same level of transport system regardelss of where the money comes from. Ridership doesn't increase massively with these schemes, what tends to happen is that the people who use the service just use it more.

In Tallin apparently some of the funding needed came from an increase in municipal taxes. You have to be registered as living in or around Tallin to get the free transport, and a lot of people updated their registration to addresses in Tallin. As a result tax income moved to Tallin (but at a loss to other places).

So a large factor in the cost effectiveness of a free transport policy is the amount that the transport system is subsudied and the ratio of that amount to the budget. In places where the transpost system is mostly funded by taxes (most places in the world, especially Europe & the US) it's easier to introduce as there's less of an impact on the budget.

The benefits & beneficiaries of this policy aren't clear and easy to define as they vary place to place. There's a lot of thinking that it's better to provide free or cheap transport for those who earn less and have to make long public transport journies to work as they're priced out of living in cities.