It is also done to improve the aerodynamics of the car but the interior room is usually compromised. A fast back is a car with a body style whose roofline slopes continuously down at the rears. The word is also used to designate the car itself. Road & Track defines fast back differently (quite distinctively), to quote, "A closed body style, usually a coupe but sometimes a sedan, with a roof sloped gradually in an unbroken line from the windshield to the rear edge of the car. A fastback naturally lends itself to a hatchback configuration and many have it, but not all hatchbacks are fastbacks and vice versa.” Fast back are advantageous for developing aerodynamically better vehicles with a low drag coefficient. One of the related concepts is The Kamm tail. The trend which follows a more steeply raked rear window on traditional three – boxed sedan blurs the difference between a fast back and a notch back design. However, the roof of a true fastback design slopes down continuously to the back usually to the base of the boot at the rear bumper. There is no unique change of angle to a rear deck, however, most four – door cars with steep slopes at the rear windows have less angled trunk lids and even high tails in order to maximize cargo space. The fast back is called a hatchback or a lift back if the rear window of the car is integral to a lid or 'fifth door' (i.e. a hatch) giving access to the trunk area. The late – model Toyota Celica and the Chevrolet Vega are examples of this type. Some small family of cars has switched from fastbacks into lift backs overtime without altering their profile, e.g. Fiat 127, Volkswagen Passat, and Citroën GS.