The Batmobile (or the Tumbler as it is called in this newest incarnation) is actually a real car, or more accurately several different cars that were built specifically as prototypes for the movie. No CGI here, not even the flames ejected from the rocket engine. All of the scenes with the Batmobile that we see in The Dark Knight were filmed using these prototypes. When the Batmobile is racing along city streets, that’s one of the “race versions” which were constructed around a stripped out NASCAR race car at a cost of about $250,000 each. These are high performance vehicles capable of accelerating to 60 mph in 5 seconds. They are each equipped with special suspension systems similar to those found in Baja racing trucks, and in order to help the car negotiate high speed turns, each rear wheel is equipped with extra brakes that can be activated separately with hand levers. Engaging the supplemental brakes on only one side provides a greater net torque on the car and a tighter turning radius compared to normal braking.
The prototype is also outfitted with a rugged steel frame, which, with the aid of the suspension, allows the car to execute 30-foot jumps without crumpling on impact. And it attains a top speed over 100 mph. There is also a much less outfitted “opening version” that they use to film Batman getting in and out of the vehicle. The “jet version” is one of the race versions outfitted with propane tanks that ignite for scenes involving rocket thrust, and there is even a miniature version which they film jumping ravines and other obstacles. However, the scene in Batman Begins where he jumps through the waterfall was actually filmed using the "race version." It really can jump!