The Insurance Institute for Highway Safety (IIHS) has rolled out new scoring criteria for its updated moderate overlap front crash test.

The move aims to better account for variations in the position of the rear shoulder belt.

A new metric called the chest index will factor in both the position of the shoulder belt on the rear dummy’s chest and chest compression. The belt position is also evaluated on how well the restraints control the motion of the dummy during the crash. The range of shoulder belt positions considered acceptable has also been expanded slightly.

“Most of these changes are part of a planned transition that we informed automakers we’d be making before we launched the updated test a year ago,” said Jessica Jermakian, IIHS vice president of vehicle research.

“The new scoring eliminates an artificial benefit our initial ratings awarded for a high shoulder-belt position. Pressing ahead with a simpler program while we validated the new metric allowed us to start incentivizing vehicle improvements a year earlier.”

Previously published ratings in the updated moderate overlap test, which was launched in 2022, have been adjusted on the Institute’s website in conjunction with this announcement. The ratings of five vehicles improve, and eight receive downgrades.

IIHS launched the updated tests in 2022 after research showed that in newer vehicles the risk of a fatal injury is now higher for belted occupants in the second row than for those in front.

The organization has pointed out, this is not because the second row has become less safe, but because the front seat has become safer due to improved airbags and advanced seat belts that are rarely available in the back.

However, the IIHS said the back seat remains the safest place for children, who can be injured by an inflating front airbag, and the rating does not apply to children secured properly in child safety seats.