A person's understanding what happens in an automobile collision may help him to appreciate the value of seat belts. When, for example, a car collides with a solid barrier at 30 miles (48 kilometres) per hour, actually there are two collisions: (1) The car's collision, in which the automobile hits the barrier, buckles and then comes to a stop in about one tenth of a second, and (2) the "human collision," in which a person's body is hurled with crushing impact against some part of the car's interior. During the one tenth of a second in which the car is coming to a standstill, a person's body continues to move at a speed of 30 miles per hour. Hence, when the body strikes glass or metal, serious injury or death usually results because the body absorbs most of the impact.
Likewise, in a 30-mile-per-hour crash, the car's front end yields perhaps two feet (.6 meter) on impact as it is crushed and bent. However, when a person collides with the dashboard or windshield, he usually stops over a much shorter distance, perhaps one to two inches (2.5 to 5 centimetres). This difference in stopping distance means that an individual will stop much more abruptly than the automobile. So, to allow the body to come to a more gradual stop, thus greatly reducing impact forces on it, all the car's stopping distance must be utilized. This is accomplished by the seat belt. By holding the individual in his seat, the belt makes him a part of the car. The effect of a seat belt can be understood by comparing the results from falling on soft ground with those from falling the same distance on concrete. The soft ground yields, perhaps a couple of inches, providing a greater stopping distance and reducing the force of the impact. The unyielding concrete stops a person much more abruptly, resulting in greater impact and, therefore, greater injury. Like the soft ground that yields, the seat belt gives a person an additional 2 feet (.6 meter) in which to stop. The force of the impact, now considerably reduced, is borne by the hips and shoulders, and these parts of the body can best withstand the force.
Likewise, in a 30-mile-per-hour crash, the car's front end yields perhaps two feet (.6 meter) on impact as it is crushed and bent. However, when a person collides with the dashboard or windshield, he usually stops over a much shorter distance, perhaps one to two inches (2.5 to 5 centimetres). This difference in stopping distance means that an individual will stop much more abruptly than the automobile. So, to allow the body to come to a more gradual stop, thus greatly reducing impact forces on it, all the car's stopping distance must be utilized. This is accomplished by the seat belt. By holding the individual in his seat, the belt makes him a part of the car. The effect of a seat belt can be understood by comparing the results from falling on soft ground with those from falling the same distance on concrete. The soft ground yields, perhaps a couple of inches, providing a greater stopping distance and reducing the force of the impact. The unyielding concrete stops a person much more abruptly, resulting in greater impact and, therefore, greater injury. Like the soft ground that yields, the seat belt gives a person an additional 2 feet (.6 meter) in which to stop. The force of the impact, now considerably reduced, is borne by the hips and shoulders, and these parts of the body can best withstand the force.