[Stu from NYC]

Originally Posted by Boston-Sean

This explains it:

On Highway Noise Barriers, the Science Is Mixed. Are There Alternatives?

Wow thank you for sharing. Many years ago my college physics class taught me that sound does not travel in straight lines but waves and totally forgot.

So the fed govt is actually the cause of having these walls all over the highways. Sure would not want one in my backyard rather an eyesore.