[dragonwriter]

> There are other traffic differences as well. We can't tie all of it just to the car seat. Even with car seats (and other measures not in MX), it's still a leading cause in the US.

In the US, the absolute number (not just the rates) of child deaths as vehicle passengers have dropped almost monotically since 1989, to less than half by 2019 what they were in 1989.

> the article thinks 90% of the issues would be covered at age 4,

details vary by state, but beyond age 4, most states only require boosters (to deal with shoulder belt height) which do not have the bulk or other issues of safety seats, not actual safety seats. (In some states, this is actually earlier than age 4.) So, while abandoning rules isn't going to have much benefit on fertility, if the burden of safety seats is the source of the problem you are trying to address.