To catch the future of payment schemes, go underground. Beneath the streets of the nation's capital, more than 60 percent of peak-time riders on the Metro (Washington, DC's subway network) have switched from magnetic-stripe tickets to "smart cards" embedded with memory chips and radio transponders. Riders can load as much as $200 into their SmarTrip cards at a kiosk or over the Internet. Antennae built into subway turnstiles pick up radio signals from the cards and convert them into streams of bits that denote the embarkation point and subtract money from the card's memory. Similar systems are being planned for other U.S. cities, and next year London will adopt these newfangled fare cards for its famous double-decker buses and massive Underground subway network.

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