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Our child is ready to switch from a five-point harness child car seat to a car booster seat, and we looked at a couple of models in a store. We saw one model that has clips on it to clip into the anchors that the five-point harness uses.

Is there any point to this? The difference is that a five-point harness replaces the regular seat belts and must be strongly connected to the car's frame. A booster seat just holds the seat belt in a safe position on the child's body. I don't think there's any tension between the car and the booster seat in a crash, so why would it need to be anchored?

Has anyone seen any reliable information on this feature?

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    Actually, it sounds pretty handy to me, ours is always shifting when my daughter gets in and out of the car and so it doesn't remain in the best position to line up the belt the way it should. I have to keep a close eye on her getting in and out so the seat is in the right position even though she is otherwise old enough to handle the whole routine, belt herself etc.
    – balanced mama
    Commented Nov 19, 2012 at 1:40
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    Normally, unoccupied boosters should be stowed in the trunk/cargo area. See your manual. An unoccupied--but latched--booster prevents it form becoming a projectile in an accident.
    – Byran Zaugg
    Commented Feb 24, 2015 at 0:18
  • I thought it might be, but I wasn't sure if the difference between "Is there any purpose for..." and "Is there a safety benefit to..." was insignificant enough.
    – user11394
    Commented Feb 24, 2015 at 18:14

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Imagine what happens in a frontal crash - an unanchored object will continue forwards at the speed it was travelling (say 70mph if we are talking about a UK motorway).

So with the seatbelt holding the child, if the car came to an instant halt, the booster would effectively hit the child at 70mph in the back of the knees. (Yes I know this is a huge simplification, but it shows the principle)

With the booster anchored as well, it will decelerate at the same rate as the child, so this impact will not occur.

Boosters are pretty light, but as kinetic energy is 1/2 x Mass x (Velocity squared) anything you can do to reduce that v-squared really helps.

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    I guess it depends on the booster, but the ones our kids had, the seatbelt when under the arm-rests of the booster so the belt anchored both the child and the seat.
    – DA01
    Commented Oct 22, 2012 at 16:00
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    No, the child and the booster are traveling at roughly the same speed (70mph). The belt stops the child, the child stops the booster. For the boosters weight, it's force is going to be insignificant, compared to the force exerted by the child on the belt. Your child--and other passengers--are more likely to be injured by a loose toy in the car or a booster which is unoccupied (see my answer).
    – Byran Zaugg
    Commented Feb 24, 2015 at 0:19
  • Try firing even a light booster seat at you at 70mph. You'll rapidly realise it is not insignificant, and it pushes the child into the belt.
    – Rory Alsop ♦
    Commented Feb 24, 2015 at 6:45
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Anchors for booster seats are only for convenience, not for safety.

In actuality, the LATCH system, as mandated in US vehicles from 2002 onward, supports a total combined weight of both child and seat of no more than 65 pounds. I found this information on Consumer Reports.

Depending on the weight of your car seat or booster seat, this may mean the LATCH system only supports children weighing anywhere from 32-50 pounds. In these cases, it's necessarily safer to use the seat belts to secure the seat, rather than the LATCH system.

The reason LATCH was developed was not because it is inherently safer, but because it's inherently easier to secure the seats properly.

Securing seats properly with the seat belt straps is more difficult, so more care must be taken in doing so. However, seat belts do not have the surprisingly low maximum supported weight that LATCH systems do. Seat belts are designed to safely secure adult passengers of various weights. For most five-point harness seats, it's also possible to secure them with the seat belt, instead of the anchors.

Booster seats that only use the seat belt to secure the child, and don't secure the seat, gain no additional safety benefit from the LATCH system. It's there mainly for convenience: the child can get in the seat themselves without it shifting and it doesn't become "free" when not in use. Children in this types of seats are more likely to outgrow or already by over the weight limits of LATCH systems.

As Byran answered, if the booster seat is not in use, it should be anchored with the LATCH system or stored in a safe area, in order to prevent it from becoming a hazard during a car accident.

Answer adapted from another answer of mine.

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  • This looks like a duplicate question that you actually have a good answer for from January - can you merge the additional information from your answer into there (see the above question link to the dup)?
    – Joe
    Commented Feb 24, 2015 at 16:00
  • @Joe Sure, done.
    – user11394
    Commented Feb 24, 2015 at 18:12

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