Vehicle speed is the most significant factor. If your speed doubles (for example, from 15 mph to
30 mph – 25 km/h to 50 km/h), the energy increases 4 times!
Because the occupants of the vehicle in the above example are not using safety belts, they are not
“attached” to the vehicle. In a frontal collision, they will keep moving at the same speed the vehicle
was moving just before the crash, until something stops them - here, the inside of the passenger
compartment. Because the occupants of the vehicle in the example are not wearing safety belts, their
entire kinetic energy will be absorbed by impact with the wall ⇒ fig. 48.
The same principles apply to people in a vehicle that is in a frontal collision on the highway. Even at
city speeds of 20–30 mph (30–50 km/h), the forces acting on the body can reach one ton (2,000 lbs or
1,000 kg) or more. At greater speeds, these forces are even higher.
Of course, the laws of physics don't apply just to frontal collisions; they determine what happens in all
kinds of accidents and collisions.
What happens to passengers not wearing a safety belt
Fig. 49 The unbelted driver is thrown forward.
Fig. 50 Unbelted passengers in the rear seats are thrown forward on top of the belted driver.
Never rely on airbags alone for protection. Even when they deploy, airbags provide only additional
protection. Airbags are not supposed to deploy in all kinds of accidents. Even if your vehicle is
equipped with airbags, all vehicle occupants, including the driver, must wear safety belts correctly in
order to minimize the risk of severe injury or death in a crash, regardless of whether a seating position
has an airbag or not.
An airbag will deploy only once. Safety belts are always there to offer protection in those accidents in
which airbags are not supposed to deploy or when they have already deployed. Unbelted occupants
can also be thrown out of the vehicle, causing even more severe injuries or death.
It is also important for occupants in the rear seats to wear their safety belts properly since they can be
thrown violently forward through the vehicle in the event of an accident. Unbelted passengers in the
rear seats endanger not only themselves but also the driver and other passengers in the vehicle
⇒ fig. 50.
Safety belts protect
Fig. 51 Belted driver secured by the correctly worn safety belt in the event of a sudden braking maneuver.