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What happens if the seat belt is fastened incorrectly?

¿Qué ocurre si el cinturón de seguridad está mal colocado?


Not using the safety belt or not using it correctly can jeopardize the safety of all vehicle occupants, especially the youngest ones. First of all, we must bear in mind the importance of not changing to a seat belt too soon. Why? The child's body is not yet sufficiently prepared and the seat belt is not properly adjusted, i.e. the child is not tall enough for the belt to adjust correctly. Therefore, as the child grows older, he or she shold only use a booster seat (preferably with a backrest). Its main purpose is to 'lift' the child so that the belt provides the correct protection.  Here we address the consequences of not using a booster seat when needed.

Bear in mind we shouldn't stop using child restraint systems  too soon, which often happens, as indicated in the report 'Car booster seats: Until when should they be used?' by Fundación MAPFRE

Until when should a child use a booster seat? Although many countries only require the use of a child restraint system up to a height of 135 cm, the ideal height as of which the child can use a seat belt is 150 cm. In general terms, at this point the belt will adjust properly. 

How do we know if the belt if correctly adjusted?  

  • The diagonal strap should cover the collar bone, over the shoulder and across the chest. 
  • The lap belt should be as low as possible over the hips.


In addition to the difficulty of finding a child restraint system that can be installed with a two-point belt, this type of belt is much less effective in protecting its occupant. However, when it comes to children, the three-point belt should not be fitted to a child without a child restraint system. The main reason is that the diagonal belt can cause irreversible damage to the child, i.e. the belt is too close to the neck and can cause serious consequences. 

Therefore, if the child is less than 150 cm tall, a three-point belt should only be used with a booster or booster seat. 


A study recently presented by Marta Anglès, from Applus IDIADA, and Farid Bendjellal, from Britax, under the name 'Safer Transport of children in buses and coaches (STCBC) during the meeting organized by the German entity TUV: ‘Protection of children in cars’, reveals that a two-point belt is much less safe than a three-point belt. To this end, they refer to different crash tests. 

Among the conclusions we found that a two-point belt only restricts the weight above the legs of the manikin used in the test, and there was no restriction to the torso area. This means that in the event of an impact the torso has a lifting movement that ends with the dummy's head in contact with the seat. In addition, there is a risk of the occupant's ejection. 

When the dummy being used is equivalent to a larger child, they observe that the dummy's legs collide with the backrest of the front seat. The head may even impact against the seat.


The aforementioned work carried out by Fundación MAPFRE shows the consequences of a child of approximately 6 years of age traveling in the seat using the seat belt but without a booster seat. This crash test shows that the belt presses on the child's neck area and can cause serious injuries to this area. It was also observed that the test dummy slid forward, making the seat belt exert pressure on its abdomen which could cause the submarining effect.

We can also find the opposite situation. The upper band is too far from the shoulder, towards the arm. In this case, the torso is not correctly restrained and the risk of the head impacting against a part of the car increases.


Remember that the belt must never be twisted, folded or loose, as this would prevent it from serving its purpose: to protect in the event of an accident or an impact. If the belt is twisted, it will not correctly sustain the weight of the body and could also cause cuts or burns. If it's loose it can lead to the dreaded submarine effect.

Whether the belt is installed with a child restraint system (here we discuss what happens if you travel with a poorly installed child seat) or directly on the child or adult, the belt must be correctly positioned.

In fact, a crash test conducted by Fundación MAPFRE demonstrates, among other things, the consequences of wearing a loose seat belt:


We may also find that the child fastens his/her seat belt but places his/her arms over it. The effect is similar to wearing a two-point belt. 
This video shows that the result can be fatal. The child's head crashes against the seat itself or its legs due to the inertia. Also noteworthy is the pressure on the abdomen. 
Finally, if the time has come to use a belt, never use clips or bulky garments such as coats. Of course, neither should cushions or pillows be used for comfort, since, as previously mentioned, this can cause the body to slide under, known as the submarine effect. 
The seat belt is one of the safety elements that has saved the most lives, but a child should only use it at the right time. Never too soon or incorrectly. The child's safety is at stake. 
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