Mother showing how to properly adjust the car seat harness on baby.

A significant contributing factor to child deaths in vehicle crashes is that most child car seats are improperly installed, federal regulators say.

A study from the National Highway Traffic Safety Administration (NHTSA) found that an estimated 46 percent of car seats include at least one error that could reduce the protection of the car seat in a crash.

Many parents may not realize just how dangerous a partially buckled or loose harness can be for their child. “Improper harnessing increases the child’s risk of injury or even ejection from their car seat in the event of a crash,” says Jennifer Stockburger, director of operations at CR’s Auto Test Center.

These harnessing mistakes can be avoided. CR’s car seat safety experts detail six crucial mistakes that are made and offer strategies on how to avoid them.

Parents and caregivers continue to improperly harness children into their car seats, according to research and a consumer-engagement study conducted by Consumer Reports. Many of the participants in CR's study revealed the struggles and confusion they have experienced.

Their disclosures include detrimental errors, such as:

  • Not re-adjusting the harness straps as their child grew; that can increase how much a child's body can move during a crash.
  • Allowing one side of the harness strap to be looser than the other, which means the crash forces are distributed unevenly to a child’s body.
  • Sometimes leaving the harness unbuckled, which leaves children without the protection they need.
More on Car Seats

“The straps in my car seat are wacky, with one side always tighter than the other,” one mother told CR. “If my child is wearing bulky clothing, one side gets so tight that I leave that strap unbuckled. But if I loosen the tight strap, it makes the other strap too loose.”

CR has heard repeatedly that proper car seat installation and harnessing can feel intimidating at times for parents and caregivers.

“About once a week the strap gets twisted within the clip that hooks into the crotch buckle,” another mom explained about her child’s car seat. “Then the clip is in the wrong direction and won’t work with the buckle, and the whole thing just becomes a pain in the butt.”

Why Proper Harnessing Is Important

  • A tight harness secures a child to the car seat and limits the transfer of crash forces to that child.
  • A secure harness reduces a child’s risk of being ejected from the seat.
  • A correctly positioned, tight harness reduces a child’s movement during a crash, limiting the potential that she will wind up outside the protection of the car seat shell, or that she will come into contact with something else inside the vehicle.
  • The harness spreads the forces of the crash evenly over the stronger, bony parts of the child’s body, specifically the shoulders and hips. This also helps to control the movement of the child’s head during a crash.

“Ultimately, proper harnessing ensures that your child is reaping the full benefits of both the car seat and the vehicle’s crash management features,” says Emily Thomas, Ph.D., Consumer Reports' auto safety engineer.

Know Your Way Around a Car Seat

Even if parents have a general idea of how the harness should fit on their children, there are finer points that many parents don’t know. CR’s car seat experts have identified six common harnessing mistakes and have strategies on how to tackle them.  

Problem No. 1: Loose harness

Why it’s unsafe: If a harness is too loose, the child could move outside of the protection of the car seat’s shell and possibly be ejected from the seat in a crash.

Pro tip: First, remove the harness slack at the child’s hips by pushing down on the crotch buckle and pull up on the straps in the torso area. Slide the chest clip as far down as possible, then use the harness adjuster strap at the front of the shell to tighten the harness—pull on the strap to tighten. The harness is tight enough when you can’t pinch any webbing between your fingers at the child’s shoulder. Last, position the chest clip at the child’s armpit level.

Problem No. 2: Harness straps that have never been adjusted

Why it’s unsafe: Many parents think harness straps are a set-it-and-forget-it item, but they need to adjust the harness height as children grow. It is not only dangerous to have poorly adjusted straps but also can make it difficult to get the child in and out of the seat over time. If the strap height is incorrect, it can increase the amount a child's body is allowed to move in a crash.

Pro tip: In a rear-facing seat, the harness height should be at or slightly below the shoulders. In a forward-facing seat, the harness height should be at or slightly above the shoulders.

There are two main types of harness systems: Those that can be adjusted externally and the re-thread type.

The externally adjustable harness straps are often the easiest to use. The harness can be adjusted by using a handle at the top of the seat, and it eliminates the need for parents to uninstall the seat.

Seats with a re-thread harness have to be removed from a car in order for parents to adjust the harness’s height. These harness straps may need to be individually threaded into a slot in the seat to fit properly. Once parents are familiar with the process, it will be easy to make adjustments as their child grows.

Some harnesses have multiple loops behind the seat and adjustments to extend or shorten their length, depending on the child’s size or which harness slot you’re using. Remember to always double-check the car seat owner’s manual for proper instructions on when and how to make these important adjustments. 

Problem No. 3: Uneven harness straps

Why it’s unsafe: Forces from a crash won’t be evenly distributed across the child’s body, increasing the injury risk to the side of the body that absorbs more of the force.

Pro tip: Loosen the harness completely, by pushing down on the harness release button, then pull the shoulder strap on the uneven side until the straps are even again. It’s important to do this while keeping one hand under both straps to help gauge the evenness between the two straps.

Problem No. 4: Crotch buckle left undone

Why it’s unsafe: This could allow the child to slide down and “submarine” out of his car seat in a crash. This means that crash forces will hit hardest on the weaker portions of the child’s body. There have also been cases of strangulation from children who have squirmed their way down in the seat and gotten their neck caught on the chest clip.

Pro tip: Always make sure both the crotch buckle and the chest clip are secured. If you find that you don’t have enough slack in the harness to be able to reach the crotch buckle, loosen the harness by pushing down on the harness release button. This releases the tension so that you can pull on the harness to loosen it. To tighten most seats, simply pull on the harness adjuster strap.  

Problem No. 5: Twisted straps

Why it’s unsafe: These may bind in the locking mechanisms, giving parents a false sense that the harness is tight when it’s not. Because a twisted strap is narrower than a flat strap, it also puts more force over a smaller area, which would amplify the impact of the crash forces.

Pro tip: All straps should lie flat and even. If the strap twists while parents are re-threading the harness, undo the harness and re-thread it again. Use the trick demonstrated here for untwisting a strap through a buckle or chest clip. 

First, fold the twisted strap into a triangle. Next, while keeping the triangle completely flat, slide the triangle entirely through the buckle. Last, see whether the strap has been untwisted and can be buckled properly. 

Problem No. 6: Incorrect chest-clip position

Why it’s unsafe: The chest clip is less about restraining the child and more about making sure the shoulder straps are correctly positioned. If the clip is positioned too high, there may be a risk that the clip could bruise or otherwise injure the child’s throat or neck. If the chest clip is too low on the child’s belly, it can apply too much force to the soft parts of the abdomen. A low chest clip also widens the space between the harness straps and increases the likelihood of the straps falling off of the child’s shoulders, leaving the child at risk of being ejected from the seat.

Pro tip: The chest clip should always be at armpit level. 

When shopping for your next car seat, look for a seat with an externally adjustable harness or one with an easy-to-access harness-adjusting mechanism at the front of the car seat, rather than behind it.