> At University of Michigan Transportation Research Institute, we
> researched the practice of switching seat belts to the locking mode when
> used with boosters as part of the development of an updated version of
> the UMTRI document on best practices in child passenger safety (coming
> soon.) When speaking with several vehicle manufacturers, most were
> against the practice of locking seatbelt with boosters because seatbelts
> are designed to allow the torso to rotate past vertical in a frontal
> crash, which acts to prevent submarining below the lap part of the belt
> when there's no crotch strap. When we have tested boosters with the 6YO
> and 10YO dummies, they definitely generate sufficient belt loads to
> activate the locking mechanism in a severe crash. I suspect that some
> of the reports of nonlocking belts may be from a combination of low
> occupant mass and low crash severity.
> The suggestion to lock the seatbelt with boosters to deal with wiggly
> out-of-position kids arose years ago when there weren't higher weight
> harness products available. These would be the best choice if a child
> can't sit properly in a booster seat. Since one of the key curriculum
> directives is to follow the manufacturers' directions, if the
> manufacturers don't tell you to lock the seatbelt with a booster, CPST's
> shouldn't be suggesting it as an option for parents.
>
> Kathy Klinich
> University of Michigan Transportation Research Institute