Today's car seats can be installed with a seat belt or the LATCH system. Many parents want an extra measure of security when it comes to their baby's protection on the road, which leads some parents to install their baby's car seat with both a vehicle seat belt and the LATCH system. It's easy to see why some parents believe that if one strap holding the car seat into the car is good, two straps holding it into the car must be better.
Using two installation methods doesn't necessarily add an extra layer of protection, though.
Why You Can't Use the Seat Belt and LATCH
Car seats are designed to handle crash forces in specific ways. While we know, thanks to federally mandated crash testing, that baby's car seat will withstand crash forces when installed with the seat belt, or with the LATCH system, we do not know if the same car seat will withstand crash forces when both systems are used at the same time. Putting two installation belts through the same belt path could put stress on the car seat shell from two different angles during a crash, causing breakage. Using two installation belts could also concentrate more crash force on a small area of the car seat, which could cause it to move or fail in ways we can't easily predict.
The rule of thumb to follow with installation is to never use your baby's car seat in a way that was not intended by the manufacturer.
When you install the car seat using methods not outlined in the instruction manual, you are, in essence, using your child as the crash test dummy. We cannot be sure of what will happen when car seats are used in ways that have not been crash tested and approved. Read your car seat instructions and your vehicle owner's manual to find out how your car seat can be installed.
If you cannot get the car seat installed tightly using either the vehicle seat belt or the LATCH system, find a certified child passenger safety technician or a car seat inspection station by visiting Safe Kids USA.
Which Installation Method Is Best?
You should choose the installation method that allows you to get the best fit in your vehicle. The car seat is installed correctly when you can't move it more than an inch in any direction when you grab the car seat at the belt path and when the car seat is at the proper angle, such as when rear-facing.
It's also important to note that the lower anchors of the LATCH system have a weight limit. That means if you're using the LATCH system to install your child's car seat, you will need to switch to a seat belt installation once your child reaches the weight limit. The lower anchor weight limit is now listed on the car seat labels and in the instruction manual, so you need to look for the spot where the manufacturer tells you to switch to the seat belt method. It's best to learn both installation methods right from the start so you're prepared for any vehicle switches, too.
Car seat safety information can change very quickly. While it's correct right now to say that you should only use the seat belt or LATCH to install your car seat, a manufacturer could decide tomorrow to allow using both.
If that happens, it will be clearly stated in the instruction manual. That type of change also would mean the manufacturer had crash tested their car seats with that type of installation, and it was found to perform adequately in a crash. As with anything car-seat-related, you should always read that instruction manual, even if you think you're very familiar with the car seat model. Some updates may be made that apply to newer versions of the same car seat.
Heather Corley is a certified Child Passenger Safety Technician-Instructor.