VTOL Flying Cars
Technologies in the Film
Although some flying cars are already commercially available, such as the one Terrafugia is developing in Woburn, MA, no flying car exists today that approaches the dexterity and flexibility of control of the DeLorean in Back to the Future II. VTOL stands for "vertical take-off and landing," which describes air vehicles that are capable of getting into the air without runways. Companies such as Terrafugia have built commercial, street-legal flying cars, but these cars require a pilot's license  and a runway to take off, making them much less versatile and likely to reach the public than something like the DeLorean in Back to the Future II.
However, much research is being done in flying cars, and many of us living a technological society have already accepted that flying cars will be an inevitable reality. Flying cars introduce several different controls engineering problems. Keeping the car balanced using, what seems from the movie to be, four different propulsion jets, while the car flies forward can be a very difficult task. The onboard computer would have to keep track of the pitch, roll, and yaw angles of the car using something like a six-axis accelerometer and compensate for any variations introduced to the tilt of the car using the propulsion engines. Much work is being done today just developing machines that can detect the angle-of-attack to approach a landing at a correct angle when gliding as well, such as the autonomous perching glider at MIT . This type of autonomous perching behavior is more relevant to robotic birds and planes today, but would also be relevant to flying cars which need to come to a stop and land very quickly and accurately.
Because of the scale of the task at hand, several individuals and companies are working on such vertical take-off and landing street-legal cars.
Paul Moller has devoted his life to creating flying cars for the public. The latest prototype is called Skycar M400, which costs $950,000 today, can fly at 400 mph in the air, and take off and land vertically . On land, it can run on gasoline, diesel, alcohol, kerosene or propane at about 20mpg. Moller envisions that these cars may one day cost $60,000. 
MACRO Industries is developing a two-seater VTOL flying car that they intend to make commercially available. The company also claims to be developing 5- and 7-seater versions which will fit in normal-sized garages .
Dr. Rali Yoeli at Urban Aeronautics in Israel is conducting research on a rotorless VTOL aerial vehicle.   The design incorporates a unique set of patented thrusters that change angle and direction to propel the car up or forwards.