For years I’ve come across complaints that the rear side window of this or that car doesn’t go all the way down. Often people assume the reason for this is safety, to prevent children from falling out of a moving car.

Well, that’s not the reason, at least not the primary reason. Especially in this age of mandatory car seats, when children are no longer standing unrestrained on the rear seat as the car goes down the road. (Yes, this was done when I was a child, along with throwing a bunch of children unrestrained into the “way back” of station wagons.)

So, why don’t rear windows usually go all the way down? Because there’s not enough space in the door for them to go down into. Look at the outline of the rear door. Almost all of the time the rear wheel opening cuts well into the lower rear corner of the door. So, at its rear edge, the door isn’t very tall. If the rear window is a single piece of glass running the entire length of the door, it will only go down part of the way before running into the lower edge of the door.

One solution: split the rear window, so that the retractable front piece of glass can retract farther, and maybe even all the way, into the door. This clutters up the design, so designers resist doing it. Often when this approach is used the split isn’t far enough forward to enable the glass to retract all the way, just more of the way than it could otherwise.

Child safety likely remains an additional factor. Not actual child safety, given today’s restraints, but perceived child safety. After using this excuse for partially retractable windows for decades, manufacturers must now work with this “fact” they created.