A roll cage is a safety feature installed in a vehicle used in environments where there is a high danger of rolling, such as race car driving as well as military and police use. Some cars are specifically designed with this feature installed, while others have had this device installed during a retrofit.
The idea behind a roll cage is that if the vehicle rolls, it will protect the occupants. While parts of the vehicle may be damaged or crushed, the cage prevents intrusion into the passenger compartment, creating a safe pocket. In serious accidents, it may not offer enough protection, however, and it is still possible to be severely injured even if the roll cage functions exactly as intended. This safety feature is designed to work with other safety features like crumple zones and seat belts to offer protection in an accident.
In race cars, rolling is a very serious risk, because the vehicles travel at such high speeds that a roll could potentially crush the vehicle. Likewise, vehicles used in police and military work often have high demands placed on them which make a roll cage a good safety consideration. Some luxury cars also have roll cages for safety reasons; in the case of convertibles, a system of bars and supports may be designed to pop up in an accident to protect the occupants of the vehicle if it rolls while the top is down.
In vehicles designed to have a roll cage, the cage is integrated right into the framing of the vehicle. In retrofits, the cage may be installed inside or outside the car, depending on the design. It is important to have it installed by an automotive professional to confirm that it is properly installed, as bad installations can be dangerous. Roll cage kits are available for many vehicles commonly retrofitted with cages, sparing mechanics the need to custom fabricate parts for the purpose of a retrofit.
In addition to a cage, it is also possible to see a roll bar, placed behind the driver's head to offer protection. This feature should not be confused with a sway or stabilization bar which is used to stabilize a vehicle to prevent rolling. Sway bars are also common features on vehicles used at high speeds.