Lots of dribbling fountains.
At this point I could fill a book on what I have discovered.
Here, it seems towels are better than the materials you would normally think of:
Berms are amazing.
Conifer trees will carry sound over berms.
I would like to ask that you do an experiment and post it here. Look into pink noise. Get a recording of pink noise and play it over a large speaker pointed at a 45 degree angle above the road. Sorta halfway between pointing it at the cars and pointing is straight up. Try several different volume levels and post your results here.