Wiktionary
n. (context automotive English) A set of steel or similar bars used in a racing car designed to protect the driver (or driver and co-driver) if the car rolls over or in involved in some kind of crash. (The roof of an ordinary car is not normally strong enough to survive the car rolling.)
Wikipedia
A roll cage is a specially engineered and constructed frame built in (or sometimes around, in which case it is known as an exo cage) the passenger compartment of a vehicle to protect its occupants from being injured in an accident, particularly in the event of a roll-over.
Usage examples of "roll cage".
The riders sat inside a roll cage, an array of steel bars forming a barrier around the men, affording them tremendous protection from being clubbed or having an enemy leap on the bikes.
The front bench was open except for a roll cage mounting an automatic impeller, but the back was enclosed.
Lower by a bit, too small of wheels and tires, but the thing did have a roll cage, two seats, and a steering wheel.
The terminal mounted on his roll cage ate the rectangle and spit it out again.
Daniel wondered if they were sturdy enough to act as a roll cage, though as the car'd be over water on most of this patrol it probably didn't matter.