The top release clasps are no safer. Also when installed next to eachother, the seatbelts can prove very dangerous. Just the other day I saw this happen when my mother in law put a
booster next to an installed carseat. The carseats are allowed up to 1 inch of movement and as she went around a turn at 10 miles an hour, the carseat moved slightly and the button on the seatbelt was pushed just right. (Normally we would always use the 5-point harness on the 65lb weight limit seat but we lost our second locking clip and were on our way to get one. Without a locking clip, we decided using the seatbelt would be safer).
- 5-point harnesses are made differently than a standard seatbelt. Think of all the accidents on the news and how many babies deploy from the car, still safely attached to their carseat, but not the car itself.
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LATCH and seatbelts still have a failure rate, carseat or not. The true benefit of using a carseat is that, in the event of an accident, the child stays securely buckled to a safe object, protecting their head, neck and back from injury.
- With Kyle David Miller's situation, you are correct that it was the belt that failed, but many accidents involve children too small for the seatbelt (which was designed for a 4'11" petite woman), slipping out of the single shoulder belt and being injured this way. Same goes with a 3-point harness or a 3-point harness with a bar in front.
The truth of the matter is that 5-point harnesses are designed and built to be safer and all of us would be safer in them, but the babies and children, with their bodies still growing need them the most.