Question Evidence / research about FF harness safety

Hi, I'm in New Zealand and my oldest boy is almost 5. He is currently FF in a Safety 1st Complete Air 65, and is happy harnessed. He has almost outgrown that seat by height (he is 114kg and 115cm tall, long torso, headrest / harness at highest setting with not much room to grow).

I have always heard 'keep them harnessed as long as possible' and believed it was safer than moving to a booster with seatbelt, so had planned to buy a high backed booster seat that could harness and then progress to seatbelt (probably a Radian).

But, I contacted Hakan at carseat.se about RF our baby (just turned one), and he mentioned that in Sweden after children turn from RF at age 4 or so, they go straight into a high backed booster with seatbelt, and that in Sweden harnessing at that age is not considered safer than the seatbelt and could be considered less safe, and harnessed boosters are not even available.

Can anyone point me to research or evidence about the safety benefits of harnessing FF beyond age say 4.5 or 5? If it is safer, I will buy a harnessed booster. If there isn't any benefit harnessing at age 5+, I'll get a good quality high backed booster for use with the seatbelt.

Thank you, Sarah

There's no evidence either way, after age 4/40 lbs, assuming the child can sit properly the whole time. If he's outgrown the CA by height, the only thing that would buy you much more time would be a Britax Frontier anyway. If you can teach him to sit still, then I would booster him.

What Stelvis said...no real evidence for that age. Since you're in NZ, I'd get a nice, beefy booster from Europe.

There isn't any conclusive evidence that a properly used booster is more or less safe than a properly used harnessed car seat at that age. The key here in both cases is "properly used."

Backing up for a minute, should you choose a harnessed booster, the Radian would not be the best choice for your situation. The harness isn't any taller than the Complete Air, and as a booster it will be outgrown not long after the harness is outgrown. What other options do you have available down there? Do you have Britax Frontiers?

I'm no expert in the metric system, but can you double-check your son's weight? Is that a typo? According to my little conversion widget 114 kg is about the size of a large adult man.

Most boosters in the US anyway have a starting weight of 40 lbs, which is about 18 kg. A few boosters here start at 30 lbs, or about 14 kg, but whether it's advisable to use a booster for a child that light is a matter of debate.

If your child is over 18 kg and will sit up properly in a booster, won't play with the seat belt, won't squirm or lean out, and won't fall out of place when sleeping, then a booster is a safe an appropriate choice. If your child isn't ready for that responsibility, and that varies a lot from one child to the next, then you would be best off continuing to harness a while longer.

One of the reasons it's so hard to get data on which one is safer is that in the US about 80% of harnessed car seats (and a fair number of boosters for that matter) are not used correctly. It's hard to tease out numbers with an assumption that the harnessed seat is correctly installed, adjusted, and buckled, because it's so rare that this is the case. It appears that for children who are old enough and big enough to use boosters that both types of seats offer approximately equal crash protection - but would a harness offer more protection if it were actually used correctly? We simply don't know.

It's also hard to compare US data with Swedish data because in Europe they simply don't have harnessed car seats for bigger kids like we do in the US. So over there, for kids over 18 kg, the only options are a few Swedish rear facing seats or a booster. There's simply nothing else to compare for older kids.

I see we don't know "for certain" type of answers to this question a lot, but I'm wondering- what would an educated guess be from a CPST about harness vs booster as to which is safer (assuming appropriate usage/maturity)? Not necessarily based on hard research done between the two, but based on all that you know otherwise about car seat safety?

Hi Sarah, welcome! It sounds like the previous posters have given you great advice. If he is over 18kg, and a relatively calm/compliant child, I would feel comfortable with a sturdy high-backed booster. If your '114kg' means 14kg, though, I would probably get a Frontier, if they are available, and keep him harnessed for a while longer.

Carseat Mama, that's an excellent question. I think if you asked ten different CPSTs, you'd likely get a half-dozen different answers, lol.

Brigala, I know, is a big fan of extended harnessing. There are others who are comfortable putting kids into boosters at 4.5 or 5. I personally skirt the line of not wanting to make that decision, so I rear-face as long as possible to try to skirt past the grey zone. I personally like to see them harnessed until around kindergarten age, and move them into boosters around 5.5/6. I tend to subscribe lightly to the Swedish 'neck loading' theory, but I do also subscribe to the 'American kids can't sit properly at 4' theory, lol.

Clear as mud? Honestly, it depends on the individual child and the individual situation. As long as your older child is properly harnessed -or- sits properly in a booster, they are quite safe, safer than most kids out there on the road today.

carseatmama007 said:

I see we don't know "for certain" type of answers to this question a lot, but I'm wondering- what would an educated guess be from a CPST about harness vs booster as to which is safer (assuming appropriate usage/maturity)? Not necessarily based on hard research done between the two, but based on all that you know otherwise about car seat safety?

Click to expand...

I think they're equally safe assuming appropriate usage/maturity, but I'm more conservative on "maturity" than many other similarly-educated and experienced CPSTs. I know there are a *small* number of exceptions, and that's tricky because all parents believe their kids are exceptional, but I think very few children are truly ready for full-time booster use much before age 5.5-6.

Carrie_R said:

Clear as mud? Honestly, it depends on the individual child and the individual situation. As long as your older child is properly harnessed -or- sits properly in a booster, they are quite safe, safer than most kids out there on the road today.

Click to expand...

I TOTALLY agree with this (and pretty much everything else Carrie said.) One of my cousins, now 8, was perfect in a booster at 4.5yo (uh, they had her in one from age 2, so that might be why.) Her little brother, 5yo, is all over the place even in a harness, so I dread the day when his eldest sister and I have to make the decision to shell out $$$ for a Frontier or booster him a bit before 6 (when he'll outgrow the Maestro.) So, it completely depends on the child. I'm hanging out in the middle for DD til she's older...it's hard to say right now if she'll be fine to booster train at 4.5 or closer to 6.

I will say that I don't subscribe to the "harness til humanely possible" (meaning 8-10yo) approach if the child typically-developing. Partly because of the controversy surrounding neck loads and top tether limits, and partly because they've gotta learn how to ride without a harness at some point. Now, if someone provides evidence that it really is safer, I certainly have an open mind!

Purely my opinion, of course, and I concur with whomever said you'll get 10 different opinions. It just boils down to- depends on the kid/car/situation.

Yay another kiwi


You cant buy frontiers here unless you illegally import one and I'm pretty sure the safety 1st is one of the tallest on the market so if he has outgrow it then you don't really have much choice but to put him in a booster.

Baby on the move have a good selection of boosters, we bought a Graco Logico for our son who is about the same height as yours and he is on the tallest setting. After that we have 2 Sunshine kids Montereys

My son rear faced until he was 4 and then went into a harnessed seat in my car until he was 5. On his 5th birthday he moved into a booster, we also used boosters in everyone else's car once he turned 4, he did fantastically well (but he is a rule follower anyway).

My DS is doing really great part-time in a booster at almost 5. Like, really great. So it is very child dependent.

It is true that I'm a fan of "extended harnessing." I don't believe that neck loading is a safety concern. However, I also think that for a child over 40 lbs who is over 4 years old (probably at least 5 for most kids) and can be trusted to use the booster correctly is also well protected in a booster. And I get that it's all a matter of opinion and there are arguments on every side of the debate.

And since I have a big kid who will most likely be too big for anything except a Frontier by age 4 or 4.5, and whose activity/maturity level compared to other kids her age is such that I suspect she's not going to be on the early side of the "mature enough" group. So I will most likely never get to be challenged on the "Do I harness to age 8?" or "Do I put her in a booster when she seems mature enough?" question. I'll be lucky if she's ready to booster at age 6 when I project she'll outgrow the Frontier's harness. :/

Thank you so much for the considered responses.

So sorry about the weight typo, proof that I shouldn't be on carseat forums late at night!

M is just *19kg*, and 114cm tall. He will be 5 at the beginning of November, he is tall for his age and very lean.

He is a very responsible kid, a rule follower (and a rule reminder, and a rule imposer on others!). I'm confident he would behave well in a booster, and I would certainly make sure I buckled him in myself etc.

Thank you for the warning about the harness height in the Radian - I'm so glad I over-think everything and hadn't just bought two of them [one for each car] as I originally planned to!

As far as I was aware from all my looking, our only extended harnessing options in NZ are the Radian or the Evenflo SecureKid. I took him to our local BabyontheMove to try both, and the SecureKid didn't look to be a good fit for him - he sits cross-legged a lot and the SecureKid has large moulded cup holders that would have stopped him from crossing his legs. [Now I'm wondering if there are safety issues with sitting cross-legged in a carseat?!]

It seems like a good quality high backed booster will be fine for us at his age, stage, and personality. I will post separately about choosing a booster - I have registered now, as KiwiMummy. I also need to ask for some advice about my littlest boy who has just turned 1

Thank you again for your help

It sounds like the booster is your best bet given his height.

Do you happen to recall how much growing room he had between the tops of his shoulders and the top harness position? How much room does he have in the Complete Air? I'm just curious, mostly, although it may influence booster recommendations as well.

My first thought is that it might make sense to pass down the Complete Air in a rear-facing position for your 1 y.o.. That is, if you can get a good rear-facing installation with it. That seat can be challenging in some cars.

Brigala - I hope you didn't think I was calling you out up there... my intention was just to provide contrast about CPSTs. (I just couldn't recall who was comfortable with boostering on the early side!) I very much respect your opinions on cps-related matters and sincerely hope it came off as I intended!!

My twins moved to boosters at 5.5 and 6. I have to say, I'm insanely jealous of everybody's rule following youngsters. Even now at 6yrs 2mo, my boys still need semi-regular reminders.

The twin who moved to a booster at 6 is the exception, IMO, to the 40lbs rule. He's the kind of kid 30lbs ratings were designed for. He is just 35lbs, and I don't expect him to hit 40lbs until he's 8. But I did make him wait until he was 6 before he got to move to a booster f/t.

No offense taken, Carrie.

I moved my daughter to a booster at 7 and now at 7 1/2 still needs reminders. I learned my lesson and now let my 5 yo sit boostered for short trips. I was of the mindset, "harness til junior high!" and she was plenty big enough to have booster trained a few years ago. She's pretty responsible and follows the rules but I still Think she doesn't sit as well in her HBB booster as my son will by that age. Just my 2 cents.