Buick 2005 Rainier Owner's Manual page 28

The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash this
applies force to the strong pelvic bones. And you would
be less likely to slide under the lap belt. If you slid
under it, the belt would apply force at your abdomen.
This could cause serious or even fatal injuries. The
shoulder belt should go over the shoulder and across
the chest. These parts of the body are best able to take
belt restraining forces.
1-22
CAUTION:
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You can be seriously hurt if your shoulder belt
is too loose. In a crash, you would move
forward too much, which could increase injury.
The shoulder belt should fit against your body.