Over a period of hundred years New York subway commuters have used tokens, followed by MetroCards and now smart cards are being used to pay the fare. Tokens evolved at a snail's pace and then they were replaced by bright yellow credit card sized MetroCard and in order to make things better Metropolitan Transportation Authority or MTA in association with MasterCard and Citi has launched the New York City Subway Trial in spring 2006. This pilot is meant to find out whether a contactless payment system which uses RFID is a quicker way of riders to make through turnstiles to their trains.

These cards offer convenience but you would have to wait in a queue in order to purchase MetroCards. The trial as of now is only open to Citi customers. Riders are required to touch their cards on the trial symbol located on the card readers rather than swipe cards which they used to do earlier.

As per MTA's web site:

At least one payment reader was installed in every station along the Lexington Avenue Line from 138th St. Stations, Bronx, through Borough Hall, Brooklyn, and one payment reader was installed at every subway entrance area in Grand Central and Union Square.

Even though trials look fine but it's still early to say whether MTA would persist with the idea or not