Greg,
The turnpike is well below the golf course. The difference in elevation serves the same purpose as the sound wall.
Tai,
I recall from my landscape studies that distance or solid materials are the only effective barrier against sound. Landscape plantings do not stop sound. However, I think they do provide a mental assistance in blocking out sound - out of sight, out of mind, as it were.
The worst noise offenders are the unusual or unexpected sounds. Colonial in Ft. Worth has the railroad switching going on constantly. You never know when you are going to hear the cars bang together. I was standing on the fourth tee one year during the Colonial NIT when a traffic accident occurred on the adjacent road. Scared the daylights out of me and the golfers.
Overall, if you really look at urban visual distractions, or listen for urban noise distractions, I think you will find that your ear and mind sort of factor those in if you've lived in a city long enough. Your golfers will likely be the same and it won't turn into as big a problem as you think.