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Is a 5-point harness safer than a booster seat and seat belt for an older child?

This is a myth I’ve personally wanted to confirm/bust for quite some time, so I decided it was time to do the research and try to find a definitive answer. It seems to be a common question from a lot of parents and there has not been one final declaration either way, so today we’ll take a look at the evidence and try to come to a consensus. No promises that we’ll find a real answer though.

Myth: 5-point harnesses are always safer than a 3-point seat belt for older kids.

So right off the bat, I want to make a few points- by “always” in the myth, I mean for neurotypical, booster age (let’s say age 5 and up) children and adults. It’s clear that 5-point harnesses are safer for children who cannot sit in the proper position for an entire car ride, but for adults and mature children, we need to look at the evidence to see if there’s an advantage either way.

Transport Canada - Integrated harness and booster NCAP test

Photo Credit: Transport Canada

First, let’s look at the studies that have compared properly fitting seat belts (meaning in a booster for kids age 5 and up) and 5-point harnesses in similar crash circumstances:

That’s right, there aren’t any. Zip, zilch, zero. So that will make this a bit more challenging.

There are a number of studies that compare children in 5-point harnesses to seat belts alone and a number that compare children in belt positioning boosters to seat belts alone, and even one Canadian study that compared boosters with a 5-point harnessed seat but with a dummy that was heavier than the weight limit of the harness. But none that compare children in 5-point harnesses to children in belt-positioning boosters for older kids.  One study did show a modest benefit of a 5-point harness over boosters for 3-year olds, but showed much smaller benefits for 4-year olds and concluded, “The results for any type of injury support the recommendation for graduation at 4 years or about 40 pounds in general, although it may be the case that more severe injuries are better prevented by CRS (Child Restraint System with harness) even at 4 years old.”

So despite the past research, we don’t have any firm evidence to tell us whether older kids (5+) are safer in boosters vs. forward-facing 5-point harnesses. I’m sure it will be no surprise that in the studies that exist, both 5-point harnesses and high back belt-positioning boosters both reduce the risk of injuries to children as compared to seat belts alone. But that doesn’t help us here.

So we’ll take a step back and look at the established pros and cons of each restraint type.

5-point Harness (forward-facing):

-Pro: When used correctly they almost completely eliminate the risk of ejection in all types of crashes.
-Pro: They disperse the crash forces over more areas of the body, which equals less force in each area.
-Pro: They keep a child optimally positioned throughout a car ride, even when asleep.
-Pro: They have a tether that reduces forward head excursion (as compared with non-use of tether).
-Con: The seat must be installed properly with less than one inch of movement with top tether for best practice.
-Con: The harness must be appropriately tightened (to pass the pinch test), otherwise child will experience greater head excursion increasing the chances that the head will strike something inside the vehicle.
-Con: The harness has a weight limit and a height limit
-Con: In holding the body against the seat, the neck may incur increased forces in a frontal crash.

Belt-Positioning Booster with 3-point Lap/Shoulder Belt:

SK300 in booster mode - great belt fit-Pro: Seat belt retracts on its own (ideally), so there’s less risk of it being too loose (in appropriate riders).
-Pro: No complicated installation process.
-Pro: No weight limit on seat belts.
-Pro: Backless boosters will have less head excursion in frontal crashes simply because the head is starting off in a more rearward position initially.
-Pro: A lap/shoulder seatbelt allows the neck and spine to move together more easily (compared to 5-pt harness)
-Con: Kids can move out of optimal position easily and frequently, especially while sleeping.
-Con: Some seats don’t have LATCH to hold them in place while loading or unoccupied
-Con: More variables involved (as compared to properly installed 5-pt harness) that cannot be accounted for pre-crash. E.g., what point in the crash sequence the retractor locks. Does the child “roll out” of the shoulder belt during the crash?
-Con: Seatbelts provide fewer points of restraint with the body, which may mean greater chance of head excursion, ejection and submarining under the lap belt in severe crashes. Especially a concern in far side impacts, rollovers and multi-impact crashes.

Well. That didn’t really help much, now did it?

forward-facing crash testWe unquestionably need more investigation on head/neck forces in 5-point harnesses versus 3-pt seat belt. When a body is harnessed into a seat, the only real free movement comes above and below the harness- so we see the neck snap forward (why rear facing is recommended for younger kids) and the arms and legs go flying forward. It’s a lot of pressure on the neck, which isn’t ideal for children before their spine is fully ossified (converted from cartilage to bone).

In a seatbelt, there is more rotational movement of the body around the shoulder belt, which may, theoretically, reduce the forces acting on the head and neck because the spine is also moving. What we don’t know is if it’s a meaningful decrease in neck forces or if this theory even pans out in real life, especially for older kids. And, even if there is a meanfuling decrease in neck forces in a 3-pt seat belt, is it significant enough to offset an increased risk of ejection or partial ejection in a booster – especially in side impacts and rollovers?

So, I realize this is anticlimactic, but:
BUSTED, PLAUSIBLE OR CONFIRMED?

Ummmmm, PLAUSIBLE?

Harness, Highback booster, backless booster

There’s no real answer here, which is as frustrating for me as it is for you, I can assure you. I think the big takeaways are:

1) Children who cannot sit properly in a seatbelt through an entire car ride (even when asleep) NEED to be in a 5-point harness, even if we find out that seat belts are better in some ways.
2) Proper use of both 5-point harnessed seats and belt-positioning boosters greatly reduce the risk of injury in a crash.
3) We need someone to really study this.

I promise to update when/if more information becomes available. In the meantime, I’d love to hear what other people have found when researching this themselves.