After seat belts were introduced, the number of motor vehicle related deaths dropped rapidly. At first lap belts were the only game in town. Then came shoulder belts and finally airbags. You would think that seat belt use would be universal. Yet there are still many of us who either forget about seat belts, are too much in a rush to take the microsecond it would take to secure the belt, are too high or drunk or just plain stupid.
On long trips it is all too tempting to slide that shoulder belt away and just rely on the lap belt. Why not? After all, you won’t fly through the window and what could happen? Well, there were good reasons why auto manufacturers long ago discontinued lap belts in favor of the lap/shoulder belt combination. Because of physics-and believe me no one is immune from physics- rapid deceleration can lead to major injuries.
With just a lap belt in place your chest will accelerate and then decelerate much faster the rest of your body. What results is a huge amount of pressure on your lower back. This can cause a fracture. Sometimes the fractured bone can injure the spinal cord and lead to paralysis of the lower extremities.
And that’s not all. Increased pressure on the belly can result in injuries to your pancreas and bowel. This kind of injuries might be missed, even with CT scans. A tip off that you might have some serious internal issues is the presence of the so called seat belt sign. This is an abrasion over your belly and (if your shoulder belt was fastened) over your chest as well.
Yes, serious injuries can occur despite lap and seat belt use. Still, currently the best way to survive an accident other than avoiding the accident in the first place, is to use both the lap and shoulder belts at all times.