GMC 1999 Sierra 1500 Pickup Owner's Manual page 48

Seats & Safety Belts
AM147008
The lap part of the belt should be low and snug on the hips, just touching
the thighs. In a crash, this applies force to the strong pelvic bones. And
you'd 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.
The safety belt locks only if there's a sudden stop or a crash.
You can be seriously hurt if your shoulder belt is too
loose. In a
crash you would move forward too much, which could increase i
The shoulder belt should fit against your body.
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