by the year 2030 and estimated 1,200,000,000 cars will already be built.
In the developing world there will be an accelerated increase in car population(some studies predict by over 2 million)-increase between 1995 and 2020.

in terms of traffic:
to achieve a constant level of congestion 3 to 4 percent of all passenger vehicles on the road would have to become carpool vehicles. To accomplish the same effect through public transportation, existing transit systems would need to increase in size by one third.
todays flying cars: Curtiss Autoplane, Arrowbile, Airphibian, ConvAirCar, Avrocar