Buick 2010 Lucerne Owner's Manual page 64

3. Be sure that the belt is not twisted and it lies flat.
The elastic cord must be under the belt and the
guide on top.
2-32
WARNING:
{
A safety belt that is not properly worn may not
provide the protection needed in a crash. The
person wearing the belt could be seriously injured.
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.