In Vienna, where there is not a single automated check for public transport tickets (annual passes are analog plastic cards, one-way tickets are paper), there is consistently a less than ~2% fraud rate. So over 98% of users have a valid ticket at any time.

The City of Vienna has concluded that the cost of building such checkpoints combined with the reduced quality of service and the destruction of the city image could never be worth it. I wonder how other cities justify this without implicitly calling their denizens morally inferior to ours.