[TiK]

I experienced that sort of system recently in San Jose with their streetcars. My girlfriend rode it for 4 days straight at least twice a day and never got her tickets checked. I rode it a handful of times as well and never had mine checked either. We both bought tickets every time though.

I think a big factor in having something like this work is to have the people who use it be caring enough to feel that their non-compliance will have a negative impact on the system.