Which contactless payment technology was first widely adopted by public transportation systems, fundamentally changing how passengers pay for transit?

The transportation industry has undergone significant technological transformations in payment systems over the past decade. From paper tickets to mobile apps, the way we pay for transit has evolved dramatically. This trivia question focuses on a key retail technology advancement that revolutionized how passengers interact with public transportation systems worldwide. Test your knowledge about this important innovation that changed urban mobility!

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RFID-based smart cards (like London's Oyster card and Hong Kong's Octopus card)
QR code scanning systems (like those used in China's subway systems)
NFC-enabled mobile payment apps (like Apple Pay and Google Pay)
Facial recognition payment systems (like those piloted in some Asian metro systems)