Child Passenger Safety Week is September 17-23, 2017. Sadly, car seat manufacturers are doing a major disservice to child safety by their pursuit, marketing, and manufacture of heavier and heavier seats.
Research has shown that impacts with other objects in a crash is the most common cause of injury to children in car seats. Impact with other objects is more likely with a heavier seat than a lighter seat. The following equation, derived from Newton’s second law, proves this fact:
x=(m Δv)/(Δt k)
where x is excursion (car seat and child movement)
m is seat mass
Δv is change in velocity for the crash
Δt is the time a restraining force is applied to seat
k is a vehicle and installation specific constant
This equation shows that excursion (car seat and child movement) increases as the car seat and child weight increases. Extensive car seat testing and development experience validates this equation. Unfortunately, some major manufacturers ignore Newton’s laws and actually advertise the fact that their seats are heavy.
Many factors go into car seat performance during a real life collision. All car seats sold in the United States are required to meet federal standards for acceleration, excursion and other factors in a frontal impact. However, federal test standards and methods are woefully outdated. They are not a reliable indicator of real life performance in modern automobiles. There are no federal standards or test methods for side impacts.
So how should one select a car seat? Consumers should certainly consider the weight of the seat before purchase. Manufacturers often produce an entire line of seats out of the same basic molds and tooling. This means that an economy seat will often share the same underpinnings as the premium seat, with minor or secondary features serving as the only differentiating characteristics between seats. Features such as cup holders, arm rests, head rest variations, additional cushions, etc make for good selling points and help to justify a higher price. However, these features also add additional weight which can compromises consumer safety by increasing child and seat movement during a frontal impact. In the absence of independent test data the lightest seat often has the best performing excursion.