2003 Chevrolet Impala Owner's Manual - Page 23

5. To make the lap part tight, pull down on the buckle end of the belt as you pull up on the shoulder belt. 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 outof the retractor.