I installed a roof rack on my car recently, it's always full of bugs. The car itself is almost bug free.

It's possible that modern aerodynamic cars are better at avoiding bugs than old cars, although I don't know if this explains the whole difference.

I concur with this. I drove an RV for a period - possibly the least aerodynamic vehicle around. It was a losing battle to keep it remotely clean of bugs. Now driving in the same areas in a normal vehicle, it is a practically non existent problem.

I think it does. I don't remember the bugs being nearly so bad back in the 1960s and 1970s as they are now where I live, but I never have to clean off the windshield of my car. When I was a youth we would fight for the privilege of squeegeeing the windshield at every gas fill-up. Now, it's hard to go out without drawing a cloud and even the dog wants to stay inside in the summer.

I suspect automobile aerodynamics play a bigger role in the windscreen index reduction than ecological destruction does.

I'm sure aerodynamics play a part, but insect population decline is a very real issue. You (and your dog) may think you have a "bug problem" where you live, but the wider picture is grim.

https://www.nhm.ac.uk/discover/news/2019/february/the-world-... https://www.pnas.org/doi/10.1073/pnas.2023989118