Cashless Public Transportation

The London government is looking at eliminating the acceptance of cash for all of its public transportation systems. If the pilot work out it will be used as a model for other cities throughout Europe.
With a lot of European governments looking at ways to eliminate where cash is accepted it will be interesting to see what happens in the US as chip and pin cards come to the marketplace over the next few years. Do you think that cash will start to get phased out of being accepted within the US?