A Better Design for Child Seats

The current method of carrying young children (less than 4-6 years old) in cars is to have a special car seat fitted in the back seat. This has several significant problems:

  • It takes significant space in the back seat. The child seat is going to add at least 10cm to the length required in the back seat and often drives the purchase of larger cars (including SUV and 4WD vehicles that are known for being unsafe – especially for children). Having child passengers in a car is a great distraction for the driver, driving a large vehicle increases the difficulty in avoiding accidents – especially when parking.
  • The seat belts of the rear seats are used as part of the mechanism of attaching the child seat to the car. Seat belts are designed to stretch in a crash. It’s recommended that after a crash all seat belts that were used to secure people or objects be replaced as they will have stretched. Seat-belts that don’t stretch will cause more serious injuries. It seems likely to me that a seat belt used to tightly secure a child seat for a long period of time will stretch without a collision. Therefore if an older child is seated where they (or another child) used to have a child-seat then they may be at greater risk in the case of a collision.
  • Child seats should be fitted by specially trained experts if they are to be safe. The majority of seats are not correctly fitted and put children at needless risk (the cost of getting an expert to do the installation is small).

Some car companies are offering child “booster seats” that are an optional attachment to the rear seat (I first noticed this when reviewing the specs of the latest version of the car I drive – the VW Passat [1]). This is a good idea, but it doesn’t go far enough.

The best thing to do would be to provide a selection of back-seat assemblies as factory fitted options which have built-in baby and child seats. The combinations that would be most desired are:

  1. Standard car back-seat for three adults (or two adults for a small car).
  2. A regular seat (for an adult) at the road side of the car combined with a baby (backward facing) seat at the kerb side.
  3. A regular seat (for an adult) at the road side with a young child (forward facing) seat at the kerb side.
  4. A baby seat at the road side with a young child seat at the kerb side.
  5. Two young child seats.

It would be quite possible to have all five of these options available from the factory. Of course there are corner cases that this doesn’t cover such as twins or parents who have two children so close together that they need two baby seats. For those cases option 2 combined with one of the current off-the-shelf baby seats would do. The number of different supported options would need to be kept reasonably small to reduce manufacture cost and to allow a reasonable market for second-hand seats.

One thing to note is that it’s recommended that the first forward-facing seat a child uses is smaller than the later one. Having options for three different built-in baby/child seats (rear-facing and two sizes of forward-facing) would significantly expand the number of combinations (and thus the expense). I suspect that the safety benefits of having an ideal method of securing a forward-facing child seat would compensate for the disadvantage of having it be too large for the child when they are first placed in it.

Another possibility would be to replace the rear seat with a more solid bench with bolt holes for baby and child seats. Securing a child or baby seat to a hard surface with bolts would be a much less technically demanding task than using a seat belt (and thus could be done correctly without expert assistance). Child and baby seats would have to be redesigned for this (I suspect that the safety of them relies on being attached to a soft surface), but after that I expect that safety would improve. For this option the rear seat could bold on to a hard surface that’s suitable for attaching child/baby seats so it would simply be a matter of removing the rear seat and installing the child/baby seat(s). The most common car design in Australia includes a 60/40 split rear seat (meaning that if you have a large item to store in the boot/trunk then you can fold down 40% or 60% of the back of the rear seat to allow the luggage to extend into the passenger compartment). This split could be extended to allow removing the base of the rear seat for 60% or 40% to bolt on child/baby seats.

Once a car model had been designed for replacing the rear seat there would be other options available. For example replacing the rear seat with luggage storage space. While almost all cars allow folding down the backs of the rear seats to store extra luggage the option of removing seats that you don’t need to give even more space is not common at all (I’ve only seen it advertised as a feature in vehicles with 6 or more seats).

I expect that if this idea was implemented it would allow a small car such as a Toyota Corolla to give an equal or greater amount of usable space for children in the rear as a larger vehicle such as a Toyota Camry. While better options for luggage storage would allow people who don’t have children to use a small car while still being able to carry the luggage that they desire. This would allow considerable savings on car purchase prices and fuel use. I expect that a reduction in fuel use world-wide could be achieved by removing the pressure on parents to buy large cars!

The poor support for child seats in cars is really surprising. One of the features that could be introduced is both top and bottom mounts for such seats. There is apparently a standard for this, some (not all) cars support it, but most baby seats apparently don’t. So baby and child seats are secured at the top (to a hook that’s bolted securely to the car frame and which was designed specifically for the purpose) and at the bottom to the seat-belt which was never designed for such things.

It’s a pity that some of the money spent on supposedly protecting children from drugs couldn’t be spent on making cars safer for them. The government is in the best position to force car manufacturers to improve their safety features while parents are in the best position to teach children about the dangers of drugs.

12 comments to A Better Design for Child Seats

  • Mac

    ISOFIX ( fixes most of your concerns… it’s starting to get widespread in EU.

  • Scott

    In the US all cars since 2002 feature LATCH aka ISOFIX, which offers 2 attach points in the crevasse of the seat — generally where it folds over. In my subaru the anchor points are recessed and have plastic over them. Removing this plastic exposes standardized hooks that a car seat can be latched into (push-and-click, etc) and be mounted on the frame of the car. To stop the ability for the seat to ‘roll’ forward an additional anchor point is located on the rear ceiling that a strap is mounted to. What surprises me that the system isn’t generally available in other countries.

  • Just three minor points.

    In the US (Probably most of North America), all cars made after some date, now years in the past, must have hooks down in the seat and up behind the back that a car seat for children attaches to so the seat belt is not used at all (I believe it is called the latch system). The seats attach at two points on the back bottom sides and one point at the top middle.

    Though it is true that the seat belt webbing is likely to stretch/degrade when used to restrain a person/object in an accident, it isn’t a design criteria. I.E. it’s not like a climbing rope that is designed to have elasticity so as not to break your fall suddenly. In fact, our current car has a ‘seat belt pre-tensioner’ that fires a charge that actually puts a great deal of force on the seat belt retracting as much as possible in the event of an accident. This is controlled by the same mechanism that fires the air bag though with a lower threshold for impact speed required to trip it. So it is possible for the pre-tensioner to fire but not the airbag, I believe the set points are in the neighborhood of 20 and 25 mph though it has been some time since I’ve looked in the manual.

    Lastly, professional installation of a car seat (or verifying proper installation of an already placed car seat) in the US is free and as simple as traveling to the local fire department. Fire departments usually have periodic car seat safety drives. Before moving to NJ I was a volunteer fire fighter and there were a few times someone came by the firehouse for help with a new car seat or to see that they had put theirs in right. In fact, when my wife and son were released from the hospital, one of the nurses had to come to the car with us and see that the car seat was the right size/installed properly. This actually was a bit of a pain as my son was premature and thus smaller then normal. Had to go and get an insert so that the seat properly held him,

  • If an alternate back seat were available as a permanent part of the car, would the car have to be crash-tested with all the possible back seat configurations?

  • As states previously Isofix does help. The one problem is that it only has 2 attachment points. Most more serious child seats have another ‘foot’ that rests on the floor so the seat does not swing wildly.

    Recent tests for EuroNcap showed that protection against front and rear collisions have improved a lot, the main weakness now seems to be side-impacts. That and improper use of the child seat of course. The main problem is not only attaching it to the car, but how strange it is to connect up the child.

    To tighten the restraints I had to go into the car and pull with all my force until the space between the child and the belt to the recommended value of ‘one finger’. Of course that was why we only had slight injuries, and the baby none, while the other driver (without a seat belt) had to be reanimated…

  • etbe

    A significant portion of the cars on the road in Australia were manufactured before ISOFIX was released. That gives a strong incentive to manufacturers of child seats to support a single fastening and seat-belt – often without an option for ISOFIX.

    Hopefully in a few years ISOFIX will take over. But at the moment it’s not viable in Australia.
    Michael: If stretch isn’t a design criteria then it should be, see the above URL for the physics. Pre-tensioners are not to stop stretch, rather they are to take up the slack so that the seat-belt will start to slow the passenger as soon as they start moving forward in their seat (keeping them further away from solid things such as the wind-screen and allowing a stretching seat-belt to do more good).

    It’s good that installation is free in the US! I’ll have to advocate a similar program in Australia.

    Don: Good point, however as child seats aren’t sold with a car the combination of child-seat and car that you might purchase would almost certainly never have been crash-tested. Also there are no proper child crash-test-dummies, so any crash-testing has little relevance to children anyway.

    Fred: 4WD and SUV vehicles are unsafe by design, and statistical analysis indicates that people who want to drive them have a lower opinion of their own driving skill than average. It’s not a rash statement, it’s well supported by scientific research. But it would break the flow if I cited references for everything in my posts. I’ll write some future posts about how unsafe 4WD and SUVs are. Sorry if you happen to own one, best to sell it now while the second-hand price is good…

    Peter: Thanks for the detail. Am I correct in assuming that you agree with my claim that a child seat secured by several bolts is the ideal way to solve this problem?

  • Our family has two cars and two child seats. All have LATCH and top tether points. But the documentation for the seats tells us not to use LATCH above a certain child weight, so we have to use the seat belts anyway. The top tether points add a lot of rigidity.

  • Kurt Roeckx

    The reason why your seatbelt webbing should be replaced after an accident is that it’s specially stitched so that a few of the stitches break at a certain force to reduce the force on the passenger. I believe this force is much lower than the force where the webbing starts to have plastic deformation.

    All the webbing I’ve seen stretches a lot. I think at 2500N it was in the order of 5 cm. But we don’t do any tests on the webbing itself. I’ve seen them, but never really took a close look at them.

    On the other hand we did test on the buckle by putting up to 10kN on it, at which points it’s deformed but should still open. I wouldn’t want to use that one again.

    Then you can also have up to 3 pretensioners for a 3 point seatbelt, as most cars have. Those can fire at different points. Those should pull you back in your seat. And I wouldn’t want to that with webbing that didn’t stretch.

  • Searching a little in the site of one of the biggest car seat maker in Europe you’ll find that they also now only sell seats with 3 attachment points: with a foot or a Top Tether.

    Without a third point the seat would rotate in a crash.

    The main aim of this is to fix the child seat directly to the car, so we don’t depend on the seat (designed for an adult) to absorb the crash.

  • etbe

    Writing comments with a bogus email address and selecting email for all comments is annoying (the bounces get to me).

    I’ve deleted all comments by and will delete all other comments that generate such bounces.

    <>: host[] said: 550 <> No such user here (in reply to RCPT TO command)

  • Kurt Roeckx


    I’ve been reading the instruction on URLs you’ve mentioned. What I find weird is that there is no mentioning of the ALR (Automatic Locking Retractor) / KISI (Don’t know how it’s spelled, but I think it’s short for kindersicherheit or something) mechanism that’s some of the retractors have specially for child seats.

    This mechanism is usually activated when you pull out all webbing. When you feed back webbing you will hear a clicking sound, and you can’t pull out any webbing anymore. This can be used to make the webbing tight and stay tight. The mechanism will unlock when you feed enough webbing back.

    You also might want to read:


  • Hi Kurt,

    Few cars seem to have them. My current audi has, our Fiat has not.

    In any case the current Römer Kid Plus just uses the belt.

    Our previous Izi BeSafe was non-isofix, but it actually beat all isofix systems that year. To install it you have to push the seat down into the carseat with your weight (no problem for me), then pull the belt tight. Then you close the two ‘ears’ of the seat and the tention will keep the seat quite stable. Then you pull out a tab below the seat which tightens the belt even more.

    Our first (and second replacement after the crash) was a Dremefa EasyBob (now out of production as the brand got bought by Bébécar) also had to be pushed into the car seat and then the belt had to be clamped by a plastic thing fixing the seat into the car. It proved quite effective.