When I was a kid, Brussels public transport was purely proactive payment. Hop on a bus/tram/subway, scan your card. I didn't ride enough for it to matter, and it was cheap (1 euro per trip), so I didn't game the system but many of my friends just decided it was either going to cost them $500/yr in fines or it would cost them $500/yr in tickets, so they just rode without a ticket.