Buick 2000 Regal Owner's Manual page 25

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'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 if there's a sudden stop or crash, or
if you pull the belt very quickly out of the retractor.
Shoulder Belt Height Adjuster
Before you begin to drive, move the shoulder belt
adjuster to the height that is right for you.
To move it down, squeeze the release lever and the
shoulder belt guide as shown and move the height
adjuster to the desired position. You can move the
adjuster up just by pushing up on the shoulder belt
guide. After you move the adjuster to where you want it,
try to move it down without squeezing the release lever
to make sure it has locked into position.
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