Every year they seem to be adding more and more electric bikes in the CitiBike fleet. One day, in the not-to-distant future they'll all be electric. That's how much we humans are addicted to energy (not fossil fuels -- but energy). That's the problem with going green, no one really wants to do it, if it means they have to give a little.
BTW, bikes are so popular in NYC (and other large cities), because it's such a pain to drive and find parking. Much easier to get around on a bike and cheaper. Yet, people believe they're being green when they do it. It'd be far more greener if we didn't demand electric bikes.