Furthermore, the study forecasts that by 2021 car sharing could replace an additional 1.2 million purchases of new vehicles.
"Our study suggests that Americans' willingness to avoid vehicle purchases due to growing car-sharing options is higher than many have thought," said Mark Wakefield, managing director at AlixPartners and leader of the firm's Automotive Practice in North America.
Wakefield believes the growing popularity of car sharing companies is a trend auto makers cannot afford to dismiss.
(Read more: Gen Y holding back on buying cars)
Car sharing in cities accelerating
Unlike many previous studies about the popularity of car sharing, the Alix Partners study specifically looked at how quickly these programs are impacting auto purchases in ten cities.
The study suggests that one car-sharing fleet vehicle displaces 32 vehicles that would have otherwise been purchased.