Surprisingly, the sound barriers along the interstates today are partially a product of the entertainment history of Los Angeles. As far back as the '40s, the Hollywood Bowl investigated putting up a wall to shield itself from highway noise. Also, the clamor from freeways running near movie studio lots were such a concern that the Association of Motion Picture Producers worked with the Department of Public Works to conduct studies on the problem in the '50s.
It took until 1968 for the California Department of Public Works to build its first sound-mitigating barrier, but construction started booming in the '70s. According to the report as of 2010, 2,748 linear miles of these walls ran along US roads.
The piece also investigates how the walls are actually designed and the challenge of keeping them anonymous but not too boring. Even if the idea of reading about sound barriers seems dull to you, the report also includes some great vintage imagery of America's roads and the chance to build your own highway wall out of paper. Check it out on Medium.