By Christopher Jensen

New York Times News Service

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 the belt so hard that the belt might cause an injury.

If belts with this better technology aren’t available in the back seat, people 55 and older should sit in the front of newer vehicles with those more sophisticated belts, according to the National Highway Traffic Safety Administration.

Researchers say seat belts in most rear seats lack these so-called load limiters, which means they can’t loosen up. So, in a frontal crash, the belt can cause chest, abdominal or spinal injuries, according to a new study by the Insurance Institute for Highway Safety and Children’s Hospital of Philadelphia.

Nevertheless, those rear seat belts — without load limiters or the “pre-tensioners” that tighten for a crash — meet federal safety standards, which are considered a minimum level of protection.

Researchers say improvements are needed because the back is likely to be occupied more often, with people such as older adults who have given up driving or passengers using ride-hailing services like Uber and Lyft. The safety of the back seat could become a bigger focus with autonomous vehicles.

Technically, the back seat did not get more dangerous. The front seats just kept getting safer.

Researchers and the highway safety agency agree that children under 13 should still sit in the back because crashes are complex events and that while improvements are needed, the back seat is still safest for them overall.