The closeness of homes to the road is also a factor. The average height needed on Georgia 400 is 15 feet 4 inches. A sound barrier must be solid . A wood fence with cracks and holes is not effective as a sound barrier. A sound barrier also must be continuous to some degree.
Sound barriers are most effective on limited access roads.
They are less effective on roads with numerous entrances to buildings and sub-divisions. To provide the same noise reduction, a wooded lot might need to be 200 feet deep. A 40-foot, landscaped buffer may block sight of a road, but not sound from it. A landscaped buffer is more of a visual barrier than a sound barrier. The state of California uses more attractive barriers.