Traffic law obligates the use of a child restraint system until they are taller than 135cms. From then on they can use the seatbelts or carry on using their restraining system. The DGT is preparing a new regulation that would prohibit children from occupying the front seat (or only when the other seats are occupied by children too); this is only a modification to the law and is not yet approved.
Doubt can arise when for example a child measures 140cms: must they use the seatbelt or continue to use a child seat? The answer depends on how well adjusted the seatbelt is. For a seatbelt to offer protection it must be properly adjusted across the hips and never across the tummy, the upper strap must pass over the middle of the collarbone and never across the neck. If the seatbelt ends up across the tummy of the neck then continue to use a booster seat helping with lateral protection too.
Thinking about everything that has been said up to now, although it is legal to travel without using a child seat for those over 135cms at MAPFRE FOUNDATION we recommend that as a general rule you continue to use a CRS until the child reaches 150cms, even if over 12 years of age. It is also important not to exceed the permitted weight for a child seat. (For a booster seat from group III, 36 kilos). Exceeding the age limit for a child seat does not reduce the effectiveness of the child seat but does increase the safety of our child.