Should You Really Be Concerned about Harness and Seat Belt Geometry?
A common question parents ask is whether or not the buckle should be sitting so high on their child after he’s buckled in the carseat. Caregivers may have heard that the buckle should fit low on the hips, like a seat belt, or have seen that the harness fits their child differently than their friend’s child who rides in a different carseat.
The simple answer is that harness geometry differs by manufacturer and may even differ within that manufacturer’s line. The lap portion of the harness may ride higher on your child’s belly in your rear-facing infant seat whereas it sits lower across his thighs when he rides in his convertible seat made by the same manufacturer. Any insert that comes with the carseat will also affect whether the straps cross your child’s thighs or his hips.
The harness may also sit quite differently on a newborn than it does on a larger child because a newborn has skinnier legs. Manufacturers certify their carseats to fit a wide range of weights and all children are proportionally built differently.
The harness also serves several purposes: it restrains a child in a crash, contacts the strongest parts of the body (the bones), spreads out the crash forces over a large part of the body, helps the body ride down crash forces, and protects the head, neck, and spinal cord. The direction the carseat faces plays a role too; a buckle sitting high on a child’s belly plays less of an injury role on a rear-facing carseat because the carseat itself is bearing the brunt of the crash force as are the shoulder straps.
One feature being provided by manufacturers that can greatly change the way the harness sits on your child’s legs is crotch strap length adjustment. Clek’s innovative way of adjusting crotch strap length is to provide two straps of different lengths on one buckle (see pics below). Baby Trend infant seats have adjustable crotch straps and require the buckle latches to be ½”-1″ from the baby’s thighs. Other manufacturers allow the crotch strap to be routed back through the outside slot, which greatly reduces the length and brings the harness down on the thighs.
The one place where harness fit counts is in the shoulder slot height. When your child is rear-facing, the straps must be at or below her shoulders. Why? The majority of crashes are frontal crashes and in all crashes, everything, including your child, will move toward the point of impact. Your rear-facing carseat will dip down and allow your child to slide up the seat. If the harness is positioned above her shoulders, she’ll slide up until she reaches the harness. Then on rebound—after the crash happens and everything that moved toward the impact comes back and settles—your child will slide back down in her seat. That’s a lot of movement and potential for injury, so keeping her down in her seat in the first place is important.
When forward-facing, you want the straps to be at or above her shoulders to hold her back in a crash. The carseat will again move down and toward the front of the vehicle. If the slots used are below her shoulders, possible spinal compression can occur as she’s held down and her shoulders roll forward.
So, for harness use, as long as the shoulder slots are properly positioned, everything else is good (as an end-user, you can’t really redesign where the lap straps are coming out of the carseat anyway). What about belt-positioning boosters and seat belts? Doesn’t using a belt-positioning booster automatically mean proper seat belt positioning?
No.
With boosters, you want the lap portion of the seat belt to fit low on the hips, touching the thighs—and there’s quite a range of what that means. Clothing can get in the way of seeing where the belt actually lies on the lap, so when assessing lap belt fit, it’s good for the child to be wearing snug-fitting clothing. The shoulder belt should be squarely on the shoulder—closer to the neck than the edge of the arm where it may slide off. It should also be noted here that since your child won’t always be wearing snug-fitting clothing, when she’s wearing jeans or other bulky clothing, she should be taught to pull the lap belt snug and low on her hips after buckling.
Younger children tend to have narrow torsos, so getting proper shoulder belt fit on them is more difficult because there’s no room for the seat belt. For a narrow kid like this, it’s better to have the shoulder belt closer to the neck—but not over the throat—so that in a crash, the child can’t slip out of the shoulder belt. Adjusting the headrest up on the booster sets the shoulder belt closer to the neck. The child below shows that she’s too small for a backless booster; she should ideally be in a harnessed seat or at the very least a highback booster so the shoulder belt is positioned better on her. A shoulder belt positioner attached to a backless booster can help too, but not as well as a highback booster. The seat belt is also not adjusted securely on her.
The lap belt portion of the seat belt should be touching or partially laying on the thighs. It can be too far forward on the thighs, which can lead to sliding (submarining) under the seat belt in a crash, and of course, it can sit too high on the soft belly, where injury to internal organs can occur in a crash.
Of course we can’t forget about the big kids who fit into seat belts. How do you know if your child is big enough to fit into a seat belt without needing a booster seat? There’s an easy test, called the 5-Step Test which allows you to tell if your kid still needs a booster.
5-Step Test
- Does the child sit all the way back on the vehicle seat?
- Are his knees bent comfortably at the edge of the vehicle seat?
- Does the seat belt cross the shoulder properly on the center of the collar bone?
- Is the lap belt low, touching the thighs?
- Can the child stay this way for the entire ride?
Vehicle seat belts are designed to fit adult males, not children. It’s not safe for them to sit in one unless it fits them well; they’re at risk for seat belt syndrome, serious head injuries, broken bones, and death. Most kids won’t fit in a seat belt without a booster until around ages 11-12.
Thank you for this great article! I’m having a tough time finding any booster seat to accommodate my 55″ tall, 7-year-old son in my 2015 Honda CRV in California. He outgrew his Graco Nautilus due to his shoulder hitting the seat belt guide. The rear seat belts connect to the car in front of the seats, not behind. When I put my son in any number of backless boosters, the shoulder belt floats in front of him and at the same time is in front of his upper arm instead of his clavicle. When I tried a taller HBB, the seat belt guide prevented the shoulder belt from retracting smoothly. Any suggestions for a booster that might solve this problem? I’m running out of ideas. Thank you!!
Hi Nicole. This is a really tough one and one that I dealt with when my kids were little too. In the past, there used to be boosters where the shoulder belt guides were located in different locations, so there was more choice in the market, but now, they all seem to be oriented the same. Can your son sit in the middle? The shoulder belt coming from behind there is a definite advantage, but I know there may be other passengers you’re not mentioning. Did you try the shoulder belt guide that came with the backless boosters?
Hi Heather. Thank you for your reply! My almost-4-year-old daughter (who’s now at a weight where she can’t use latch) sits in the back too. When we tried squeezing a backless booster in the center, the seat belt holding her harnessed seat in place accidentally unbuckled! I’m nervous about that happening again and not noticing right away. The two seats were so close together (my son’s nesting under hers) in the narrow CRV back seat that my son wanted to put his arm on top of her seat, using it as a high armrest. Unfortunately, the backless booster shoulder belt guide won’t reliably keep the belt on my son’s shoulder when he’s in an outboard seat. It abruptly jumps off the side of his shoulder, toward the door and down, leaving him unprotected. Thank you!
Ah bummer! That’s definitely something you don’t want to ever happen!
I’ve been thinking about different highback boosters that might work and came up with 3 that have the belt guides in different locations. Two are expensive (figures!), but they’re all tall. Two also give you the option of using them backless as well. The Britax Skyline is one that you can use highback or backless: https://amzn.to/3e0ST7g. The Clek Oobr is another you can use highback or backless and the shoulder belt guides are angled much more to the sides: https://fave.co/3k3F4sO (no free returns). And then the Maxi Cosi RodiFix is a fan favorite, lol, but it doesn’t convert to backless: https://amzn.to/2VjoQ4a.
Hopefully one of these options will work for you until he broadens up and is able to use a backless booster in your car.
Hi Heather!
Thank you for the suggestions! Unfortunately, the Britax Skyline wouldn’t allow the seat belt to retract smoothly. I’m looking into the other two. Are either narrow in the back? Many seats are too wide to fit between the protruding wheel well and the buckle.
I’m concerned that my son may never fit in a backless booster in my car because the vehicle headrest is only an inch or two above his ears when in a booster. The shoulder belt fit in a backless booster is worse than when he’s directly on the vehicle seat because the armrest of the booster pulls the shoulder belt forward too far and also down onto his arm. When he’s directly on the vehicle seat, the shoulder belt barely touches his neck and even sits tighter (but not perfect) against his torso. It’s the lap belt and thigh length that he needs the most help with. Are there options out there that might help with the lap belt and seat pan fit without overdoing the shoulder belt adjustment? It doesn’t look comfortable, but I might try a Graco RightGuide.
While brainstorming in the car today I realized that my long-torso 3-year-old’s daughter’s Extend2Fit headrest is fully raised already. I’m going to have an even bigger problem finding seats to fit her until she passes the 5-point test!
Thank you again for all your help!
Nicole
I think the Maxi-Cosi RodiFix might be the one because it doesn’t have any armrests. It’s less boxy than the Clek, so it should be easier to buckle too. It sucks that it’s so expensive 🙁 but it also looks like the vehicle seat backs are curved back so in addition to the seat belts being forward, no kid has a chance of fitting well. What were they thinking?!
I am a mother baby nurse. I feel like the hospital I work for does not do a good job educating new parents on infant car seat safety. None of us are certified so we are told it’s the parent’s responsibility to properly place their infants in the car seat. I feel like we educate them on everything else. But I see so many parents not doing it properly. I would like to know if your photo a love on proper infant safety harness use is available as a printout and how I could get one to present to my hospital for use?
Hi Dianna. It is a problem in some hospitals because they feel the liability of possible misinformation outweighs the possible good. Our photos currently aren’t available for printouts, but we’re happy for you to print them and use them as long as you maintain the logo on them. It’s a good idea and I’ll bring it up the next time we talk.
My almost 5 year-old uses the Evenflo harnessed booster seat in my parents’ car and the bottom straps go completely over his thighs, instead of his hips. Is this as safe? Thanks!
Hi Jennifer. Yes, it’s fine. That’s the way Evenflo designed it to work and they’ve crash tested it.
A related question- why does Britax mak their crotch straps so darn short? I have a Boulevard CT and I love it, except for that…
Alyssa, I’m not sure why they used such a short crotch strap. It took them several years to switch to a longer strap; the ClickTight panel has been reinforced and the strap is longer on newer seats.