i'm also guilty of having suki loose in the car. i don't drive with my windows down, so at least this particular tragedy probably won't happen.
i haven't tried crating, but it just makes me nervous - if i were to get rear-ended, she'd be squooshed. i guess i could try the crate in the back seat sometime. not sure if she'd better or worse. she's not very fond of the car - she doesn't whine or freak out, but you can tell she's not very comfortable. she seems to be on high alert.
We only open the windows a tiny bit, never enough for Tillo to even stick his head/muzzle out. And I don't like crates in the car either. I prefer a car harnass. Tillo actually has a harnass for the car.. I'm just too lazy to put it on him. Tillo likes to switch places from the sun.. out of the sun.. just how hot he gets.. and that's not possible if tied to one place. But that's probably not a very good reason to leave him loose.. 😉