Modern cars are built to withstand all types of crashes, including rollovers, but it doesn't mean they're perfect.
Ford thinks it has a better solution for rollover protection. It was recently granted a patent for an external roof rack-mounted airbag system. Instead of a traditional airbag, which is inside the vehicle, these airbags drape over the side of the vehicle to help cushion the blow of a rollover.
No, they cannot be detached and used as flotation devices. This isn't a Boeing 737.
US Patent and Trademark OfficeThe airbags will be stored inside the rack attached to the vehicle's roof. When the airbags expand and drape over the side of the vehicle, they may be held in place by elastic tethers. While traditional airbags inflate and deflate within fractions of a second, these ones will likely stay inflated for longer, as a vehicle may roll several times before coming to a stop.
While it would require a car to have a roof rack, a great number of models these days come with some sort of built-in solution along these lines, especially in higher trims. And it wouldn't be beyond the realm of imagination to envision cars that carry roof racks specifically to include these airbags.
It may sound strange, but it's not the first external airbag. Volvo has what it calls a "pedestrian airbag," which inflates across the windshield, cushioning the blow for a pedestrian who rolls up the vehicle's hood after a collision.