Earlier quoted context omitted.
How many bugs are on your car's windshield/grille, versus 20 years ago?
How much more aerodynamic is your car now versus then?
By 2015, the bugs has drastically diminished enough for me to remark upon it before coming across any studies. The confounding factor here though is that the county I was in had a lot of development in it over that time. My routes stayed mostly the same (meaning both ‘where I drove’ and ‘how many buildings were along them’) but I can’t discount the expansion of the surrounding sprawl as a big factor.
Even after I moved to a neighboring more-rural county though, with a longer commute to the same workplace, I did not really see an increase.