Bloomberg News
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In many instances, mass transit systems have proven to be catalysts for adoption of new payment technology, starting with the genesis of contactless cards for access to buses and trains in Hong Kong and Japan in the late 1990s. Hong Kong's Octopus Card is one of the earliest examples of how transit networks can expand beyond their initial purpose to become a more versatile payment vehicle for retail use.

Since then, many metropolitan areas have moved from traditional cash and tokens for fare to faster and more user friendly digital alternatives. However, there is still a long way to go — and legacy systems die hard.