For decades it was a given that the back seat of a car is the safest place in a crash. But that's no longer certain, as advances in seat belt technology up front have been slow to jump to the back seat.

Safety researchers now have new recommendations about what to buy and where to sit, highlighting vehicles whose rear seats have the kind of sophisticated seat belts that have protected front-seat riders for roughly a decade.

Those belts tighten up when sensors detect a crash is imminent. They also can loosen a bit if the occupant is pressing against