Seat Belt Operating Principle

Only properly fastened seat belts provide protection.

If force applied to the occupant's body exceeds a certain level, occupants of the vehicle may be injured.

When the vehicle decelerates rapidly, a large force is applied to the occupant's body. This force is significantly reduced if forward movement of the body is slowed. Therefore, the main objective in protecting an occupant from injury in a collision is to maximize the time and distance over which the body's forward movement is stopped.

Consider a person running at 25 km/h who collides with a concrete wall. Consider a second person running at 25 km/h who collides with a concrete wall covered by a deformable padding 90 cm thick.

In the first case, the person may suffer serious injury or even death.

In the second case, the person is unlikely to be injured. Why? In the first case, the body strikes a non-yielding concrete surface and stops instantly. All of the energy built up while running is absorbed by the body rather than by the rigid concrete surface.

In the second example, the body has the same kinetic energy as in the first example. However, in this case the body moves forward into the padding, which provides additional time and distance to stop the body, as the padding absorbs the running person's energy by deforming.

When the vehicle collides with a concrete wall at 50 km/h, the front bumper stops instantly, but the passenger compartment decelerates more slowly as the front structural components of the vehicle deform. A person wearing a seat belt remains in place and is protected by the "padding" provided by the deformation of the front of the vehicle and the stretching of the seat belts.

The body of a belted occupant decelerates from 50 km/h to zero over a distance of 90 to 120 cm. In addition, a belted occupant remains in place, so contact with hard parts of the vehicle is avoided when the airbags deploy in a frontal collision. An unbelted occupant has no such protection. The unbelted occupant is not restrained in the vehicle, so the body continues to move forward at 50 km/h, the speed before the collision, until it strikes a hard object at approximately 50 km/h and stops instantly. Therefore, even when the airbags deploy in a frontal collision, an unbelted front passenger faces a considerably higher risk of serious injury or death than a properly belted passenger. (See section "SUPPLEMENTAL RESTRAINT SYSTEM")

SEAT BELTS PROVIDE PROTECTION

Vehicle crash statistics show that drivers and passengers wearing their seat belts properly are at lower risk of injury and have a higher chance of surviving a crash. For this reason, the laws in most countries require the use of seat belts when operating a vehicle.

SEAT BELT USE

All front and rear seats are equipped with three-point seat belts. The seat belts for the front seats and the outboard rear seats are retracted and locked by an inertia reel mechanism. In the normal fastened position, a three-point seat belt does not require length adjustment and allows freedom of movement at a constant vehicle speed.

In the event of a sudden or sharp stop, or high acceleration or deceleration, the seat belt locks automatically to hold the occupant's body in place.

To use all the protection features of the seat belt, it must be properly fastened and the occupant must sit in the correct position in accordance with the following requirements:

• The seat back must be in the upright position (not reclined, to prevent "submarining" or sliding under the seat belt and injuring vulnerable parts of the body in a collision).
• The occupant must sit upright (not slouched, so that the lap and shoulder portions of the belt provide maximum restraint and minimize injury to soft and vulnerable parts of the body in a collision.)
• The latch plate must be fully inserted into the buckle until it clicks (an unfastened seat belt provides no protection; pull on the belt to check that it is securely latched).
• The lap portion of the seat belt must pass low across and fit snugly over the hip bones (not over the abdomen, where belt tension may cause serious injury in a collision - THIS IS ESPECIALLY IMPORTANT FOR PREGNANT WOMEN).
• The shoulder portion of the seat belt must pass over the shoulder nearest the door and across the chest (not under the arm, behind the neck, over the shoulder farthest from the door, or behind the back. The belt must not be loose, to prevent excessive forward movement of the body and injury in a collision).
• Knees in the "straight ahead" position (so that the driver's knee bolsters in a collision prevent "submarining" under the seat belt).
• Individual seat belt (a seat belt is designed for one person; using one seat belt for several people may cause injury in a collision).
• Child in a child seat (in a collision, very high forces occur, so an adult cannot hold a child who is restrained together with them by one belt).
• Driver and all passengers must be belted (unbelted occupants can be injured themselves and injure other occupants of the vehicle, since their position is not restrained in a collision).
• Seat belts must not be twisted (twisted seat belts cannot move freely and do not provide proper restraint; instead of distributing the load evenly, they can dig into the body, increasing the risk of injury or death).
• Lock the doors (in a collision, unlocked doors increase the risk of injury or death from external impact or ejection from the vehicle).
• Perform periodic checks (while driving, periodically check that the lap portion of the seat belt rests on the hips and does not ride up onto the waist, and that the shoulder portion passes across the middle of the shoulder and chest. A correct belt position allows the skeletal system to absorb the belt load on the shoulders and hips, while an incorrect position may cause injury to the neck or abdominal organs.)
• No hard or breakable objects may be placed between the seat belt and the body (objects such as ballpoint pens, glasses, etc. in pockets or on clothing may cause serious injury in a collision).

If the seat belt passes over the armrest (if equipped), the lap portion of the belt will press on the abdomen rather than the hip bones in a collision.
• Make sure the seat belts pass under the armrests.

Failure to observe this requirement may result in injury or even death in a collision.