We have seen a remarkable number of cases in which seat belted occupants are somehow either partially ejected or completely thrown from a vehicle during a rollover despite the fact that they were wearing their seat belts. The evidence points to a startling conclusion: seatbelts are not reliably remaining locked during the course of a rollover.
In some ways this isn’t surprising. The lock mechanisms in most
American cars are designed principally for non-rollover accidents. They
are often simple designs. One is just a small marble-sized steel ball
in a small plastic “dish.” Accident forces cause the ball
to move up on to the edge of the dish rather than the bottom, where the
ball pushes a small plastic bar into the seat belt retractor teeth, locking
it up. During a rollover the ball can roll back into the base of the dish,
unlocking the retractor and, if tension is released and then reapplied
to the seat belt, causing belt webbing to pay out. This can happen, for
instance, when a rolling vehicle lands on its wheels forcing the ball
back to the bottom of the dish and releasing belt tension momentarily.
The occupant’s body then moves downward or to the side pulling out
webbing while the retractor is unlocked and introducing slack.
Fortunately, this does not happen most of the time in rollovers. However,
when it does happen the consequences are grave. Nobody should be left
without effective restraint during a rollover. In rollover accidents as
long as you stay in the car and the car doesn’t crush on you, you
stand a very good chance of surviving without serious permanent injury.
When you are ejected or partially ejected, such as when a head sticks
far outside the window opening, the risk of serious injury and death skyrocket.
Fortunately the fix is simple and cheap. Most European seat belts have
a second, backup method for locking the retractor, called the web sensing
device. This device, which costs less than fifty cents, locks the belt
any time the webbing pulls out rapidly. You can check your car to see
if you have one. If you pull the seat belt webbing out very fast, does
it lock up even when the car is sitting still? If so, you have a web sensing feature.
Our auto makers are already using this feature in the cars they sell to
their European customers. American customers deserve the same protection.