Regulations ECE R44 03&04 & Regulation R129

By Law, children's car seats have been subjected to accident simulation testing. There are currently two regulations; ECE R44 04 and since 2015 ECE R129.

Under Regulations ECE R44 03 & 04, seats must, amongst other requirements, undergo frontal collision testing at a speed of 50km/h and rear impact collision testing at 30km/h. In Supplement 16 of R44 04 the seat is also subjected to a rollover test. All these tests are undertaken with dummies that represent the weight category of the child approved for the correct weight group of seat. Results of these tests must fall within the requirements of the Regulation.

By Law in the United Kingdom, a child has to be secured with a suitable restraint up until the age of 12 years old or 1.35 metres in height. If travelling elsewhere in Europe including the Republic of Ireland the minimum height is 1.5 metres. The Regulation defines five 'groups', each of which is designed for a particular weight category. As a rule of thumb, if the child is too heavy or tall for one group, it should move up to the next 'group'. We strongly advise parents not to move their child up too quickly as a seat that is too big can be just as ineffective in a car crash as one that is too small.

The different groups and the average age of the child using them are displayed in the graph below. It should be noted that the age is not a criteria but should be seen as a guideline, as it refers to the age and weight of an 'average' child. As a result the weight categories overlap, allowing for added flexibility for those children who do not reflect average trends. This is designed to prevent children from moving up a group too early or too late.

Regulation ECE R129

This Regulation has become known as i-Size, it is an evolving Regulation. Currently, it only regulates infant carriers that may be secured using ISOfix and ISOfix seats only that will accommodate a child to 105cms.

Under Regulation ECE R129 seats must, among other requirements, undergo frontal collisions testing at a speed of 50km/h and rear impact collision testing at 30km/h. The seat is also subjected to a rollover test. All similar to R44 but there is now an additional side impact test requirements. These tests are undertaken with what are known as 'Q' dummies. These dummies enable the measurements of the impact of forces that a child would be subjected to. They also represent the stature (height) of the child and not their weight. Results of these tests must fall within the requirements of the Regulation.

The main aims of Regulation ECE R129:

  • Reduce risks of misuse due to seats being secured by ISOfix
  • It is mandatory to use i-Size regulated seat rear-facing until the child reaches 15 months of age
  • It is considered easier to classify children according to their height and not their weight
  • Seats are subjected to new side-impact testing
  • Improved compatibility: i-Size car seats fit each i-Size seating position in the car
  • A special label indicates the compatibility with each certified vehicle


ISOfix was first introduced by Britax in co-operation with Volkswagen in 1997. It has become an international installation interface for standardised anchorage points between a child's car seat and a vehicle. It minimises installation errors and optimises protection through a rigid connection to the car chassis. The anchorage points are metal loops found between the adult seat back cushion and the bottom cushion (often known as the 'H' point) on the vehicles car seat, where an ISOfix compatible car seat may be attached. The child car seats will have 'extendable arms' which are then connected directly to the metal loops in the vehicle. A very secure attachment.

Some ISOfix child car seats require the use of an additional 'top tether', a strap that is attached to the top of the child car seat for connection to a third metal loop often located at the back of the adult seat, but may be found elsewhere too. Consult the vehicle manual.

ISOfix child restraints are regulated as follows:

Universal - 'Approved' for use in vehicle seating position assessed as compatible with child seats under UN Regulation 16. These seats will typically use a 'top tether'.

Semi-Universal - 'Approved' for use in vehicles that are referenced in a child restraint fitting list. This is sometimes known as the 'application' list showing which car the seat is suitable for.

Restricted - 'Approved' for use in a designated seat position for a particular vehicle type, as indicated by the child restraint manufacturer or the vehicle manufacturer.

Vehicle Specific - 'Approved' for use in specific vehicles or child restraint systems 'built in' to the vehicle. This means seats that have been tested when the whole vehicle underwent testing.

Special Needs - 'Approved' for children who have special or additional needs. It is a child restraint that complies with R44 but can have additional restraining devices to suit the need.

If you are confused by some of the terms used in relation to children's car seats, you are not on your own! Our Jargon Buster page, we hope may help.
ISOfix and i-Size are relatively new terms and may not be familiar to you, so we thought a brief explanation might help.