I wonder if cars with old fashioned mechanical window rollers don't have this issue.

At least a quarter of them could've survived if things still worked like that.

Another important factor to keep in mind is that around a quarter of heatstroke car deaths in children are in those who gained access to vehicles and were unable to leave. Therefore, everyone – not just parents – should keep parked vehicles locked at all times and keep the keys and knobs to them secured. Additionally, children should be warned about the dangers of entering cars on their own and taught how to open rear and front doors as well as trunks and to honk the horn. If children go missing, caregivers should check pools and ponds first, then cars and their trunks.

I wonder if there’s a downward trend after controlling for the most obvious things, like numbers of cars, infants, and hot sunny days.