Can a wall of dirt block more highway noise than a concrete barrier? Sound barriers line highways everywhere, but their materials vary widely. You place digital decibel meters at measured distances behind four barrier types. You test concrete walls and wood fences. You also test earth berms and rows of trees. You record readings every 30 seconds for 10 minutes at each site. The earth berm reduced noise the most at every distance. Concrete came second. The wood fence blocked less, and trees barely reduced noise at all.