Ben Schiller:

Driving around U.S. cities, it may not seem like there are fewer cars on the road. Many places are as congested as ever. But a new study suggests that it could be a lot worse. Changing attitudes about owning a vehicle and the rise of sharing services like Zipcar have indeed reduced the number of cars on the road from what otherwise would’ve occurred.
 AlixPartners, a consultancy that has automotive clients, interviewed 1,000 licensed drivers in 10 U.S. metro markets to understand what’s motivating people to use car-sharing services and what effect that’s having on vehicle sales. It estimates there are already 500,000 fewer vehicles on the road because of sharing’s popularity, and that lost sales will only increase. By 2020, it expects 4 million people will be sharing cars, and that there will be 1.2 million fewer cars.