Thanks for the prompt replies! I'm not unrealisticly thinking the sound would be gone. Our developer was just forced to put a (cheap)soundwall in to get the noise to city code. It's helped somewhat, so I know that even walls can't do a whole lot if they aren't tall enough. I'm just hoping to reduce the hollow echoing between our houses, not eliminate the freeway sound. The path between our houses is parallel to the freeway. I think what happens is the sound hits the side of my house, bounces to his, and then goes back and forth. I should have been more clear, but didn't want too long of a post on my first time. I thought perhaps bamboo would filter/absorb at least a little of the reverberating waves as they travelled between houses. I still may be way off in my thinking! My walkway is about 5' wide and 30' long where I was thinking of putting long, narrow planters along the fence. Wouldn't afternoon breezes help with the leaf rusting sound, since the breezes flow along the walkway? I have some queen palms and am installing a spill fountain in the backyard to help drown out the sound as well. I figure, the more other noises I have, the less freeway noise I will hear. Please don't get me wrong, I LOVE where I live, don't wanna move, just wanna naturally reduce/absorb noise if possible. As far as the good neighbor/leaf drop question, I would guess some (probably varieties with small, dense vegetation) would leave more leaves for my neighbor (and I) to pick up? Thanks for the help. I really do appreciate it.

Since bamboo is hollow, I think you might actually amplify the sound. You might be able to block some sound with something taller and wider, but I don't think you would with only 3-4 ft.--the sound will come around and over. If I was going to try something, it would be larger and the side toward the air conditioner would be something softer than wood...perhaps foam, styrofoam, or acoustical tiles (like on a ceiling). Another possibility is heavy cotton batting (something like that is what our dishwasher is wrapped in, and it is nearly totally silent), but that might be more difficult to use, unless you staple it to plywood or a wooden frame. I realize none of those are pretty, but they could be disguised. To avoid digging, make it something like folding screens or 2 double posts on a stand that whatever material you use could be dropped into. I know that is not a good description, but maybe I can draw a picture of it and attach it. Look on Craigslist for free or cheap materials to experiment with--insulating styrofoam is frequently on there, along with misc. lumber and bricks (at least in our area those items are on there almost every day). I wouldn't put a lot of money into it (unless you have another use for the materials) until I had experimented and thought it would work.

Correction--our property is on the east side of the road. Sounds like my idea of using plants and trees might not work out. We are in a rural setting all wooded with houses on 5 acre tracts. We are leaving about 80 feet of space natural between our house and the road. Would this be enough space to layer plants and trees? Besides the firs there now is mostly salal, huckleberry and lots of moss and old downed trees. None of these plants are dense. I think we are in zone 5. We live north of Lacey about 3 miles from the sound. There is not steady traffic along the road just the occational sound of a car going 50 to 60mph. Thank you for your input!

First thing that comes to mind is dogwood tree, altho they can be fickle and not sure if you are too far south. There is another tree that is supposed to be like the dogwood, I am thinking silverbell???but could be mistaken and not sure if it takes sun or shade. Another choice would be azaleas, they do love the south, and typically do well under pines and like acidity which the pine needles provide some. Azaleas can get pretty big if you let them, and they have the Encore ones now, which I don't have experience with but hear they flower more. Also camellias, which I love, and find easy to grow, as an added bonus they are evergreen and bloom in fall/winter.