The projections are based on a summary of two Frost and Sullivan reports (N748-18) Car-sharing: a Sustainable and Innovative Personal Transport Solution with Great Potential and Huge Opportunities and (M4FA-18) Sustainable and Innovative Personal Transport Solutions – Strategic Analysis of Carsharing Market in Europe, says that carsharing membership in North America rose by 117% between 2007 and 2009 and the growth at that rate is expected to continue over the next 5 to 10 years. This leads to the estimate of 4.4 million members in North America and 5.5 million in Europe by 2016.
(It seems somewhat counterintuitive to me that Europe would have more carsharing members than the US but I haven't seen the report yet to understand the rationale.)
This report follows on Zipcar's press release from June 2009 predicting worldwide market size for carsharing at 37 million members.
Nevertheless, even if only a fraction of these gains occur, carsharing has a very bright future ahead. The marketing departments and street teams better get to work!