We now have the sound wall installed and finished it's been up for 1 month and the sound is louder than ever we live very close at where the road was dug out witch they removed thousand of tons of soil to make a banter slope then installed the sound wall. I was told that the sound wall was better there than close to the banter but have a visit to here http://www.rms.nsw.gov.au/documents/projects/planning-principles/urban-design/noise-wall-design-guideline.pdf now RTA say that earth walls are better SA say no RTA say the worst wall material is metal SA don't, Then even removed the timber from inside because Qld said you don't need it. This was told to me by Expressway people. How many has been lied to even the colour we did not get . Cheers 4 now Dave