I’ve seen two things that give any data on how many people in Budapest use public transit without paying for it:

About 6 weeks ago, I saw ticket control for the first time outside the metro. Of about 50 people on board, all but about 3 had tickets or passes (or at least moved by the ticket controllers slowly enough that the ticket inspectors’d’ve had to be incompetent, not just rare, to miss them) and the other three sidled or hurried away uncaught, so 6% is probably a reasonable estimate of the fraction of rides stolen from the public transit. Just one sample, but if the rate’s even a bit above that, it’s pretty good, since paying is almost entirely a matter of honor.

Today, I finally saw someone caught for the first time. Good to know that there’s some enforcement left in the system, even if it’s poorly designed. (A tip for fare scheme designers: the expected cost of the fines for not buying a ticket should be clearly more than the cost of a ticket, or at least not clearly much less.)