GMC TopKick 2007 Owner's Manual page 22

In most states and in all Canadian provinces, the
law says to wear safety belts. Here is why:
They work.
You never know if you will be in a crash. If you
do have a crash, you do not know if it will be a
bad one.
A few crashes are mild, and some crashes can
be so serious that even buckled up, a person
would not survive. But most crashes are in
between. In many of them, people who buckle up
can survive and sometimes walk away. Without
belts they could have been badly hurt or killed.
After more than 40 years of safety belts in
vehicles, the facts are clear. In most crashes
buckling up does matter... a lot!
22
Why Safety Belts Work
Q:
Aren't safety belts for kids?
A:
Yes. And they are for adult truckers, and
anyone else who rides in your vehicle.
Here is why: when your vehicle goes, say,
30 mph (50 km/h), so do you and your passengers.