This paper details an experimental investigation into the effect of harness mounting height, relative to the occupant’s shoulders, on the performance of forward facing child restraints in frontal impacts. Child restraints typically feature a range of mounting slots for locating the restraint harness in the seat back. There had been speculation that, in frontal crashes, excessively low harness mountings could lead to an increased risk of spinal injuries.

The experiments conducted for this project showed that, when compared to results for harness slot positions at shoulder level, lumbar compressive forces were significantly larger for harness slot heights below the dummy’s shoulders. However, these lower mounting positions produced lower head and neck loads. In all cases, higher mounting positions better limited the dummy’s head excursion. All tests were performed twice, and repeatability between identical tests was better than that typically quoted for such experiments.

This project establishes a link between the restraint harness mounting height and the level of protection offered to the occupant’s spine, head and neck. It recommends that a mounting height at the level of the child’s shoulders offers the best overall protection in a frontal impact. It also recommends that the Australian Standard AS 1754-1991 should be amended, to increase the minimum height of mounting slots. These recommendations may need to be modified in the future as a result of further research in child biomechanics.