Question
QUESTION: The side of our house is located on a busy street on top a  sloping hill (with about a 5' rise) So far we have a 3' retaining wall next to the city sidewalk followed by a 15' span of mixed evergreens and lilacs, followed by a 6' wooden fence. We still hear noise very clearly. Any other ideas on how to buffer the road noise. We have roughly 20' to the house left which is landscaped with perennials. Zone 4 Thanks

ANSWER: I was thinking about this question over the weekend.  Unfortunately, there is not much that can be done. You've done the first three steps -

Distance from the source of the noise, physical barriers, and use of evergreens...sometimes there is "relief" by lowering yourself to the offending noise (as in a sunken courtyard - in effect using the earth as a sound blocking device)

The other two are; create a "white noise" with a flowing fountain of some sort.  Gurgling water can "mask" the offending sound, but not eliminate it.  

And finally, increase the wood barrier to something more substantive - a *SOLID* brick or cinder block wall. And wrap it around the ends...don't just end it at the property corner, but turn it back into the property, if possible.

It is the vibration more than the noise that always bothered me, when I was living at a noisy intersection in Los Angeles.  

As you've probably noticed, it increases at night, too!!  It has to do with that "white noise" principle.  Less stuff humming or whirring at night, as compared to the daytime hours.

You may also look into triple-pane windows.

~M


---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply. I had thought about a waterfall, but trying to come up with ideas to accommodate a flat yard and still look natural with only about 10 feet seemed complicated and expensive. Any ideas for sources for inspiration. Also, would it help to mask noise by stacking cinder block between our hedge of lilacs and wooden fence (which is about a foot)? How high would we need to go to make a difference? Thanks for all the input.

Answer
To make a difference, the wall would have to be fairly large - here is a link to a "Garden Wall" detail that is pretty straight-forward (scroll to the bottom & click on the "Garden Wall" PDF link).  

http://www.slocounty.ca.gov/planning/building/Building_details_info/bldcons.htm

I'd say at least 4 feet, if not 6 feet tall.

As far as a waterfall, boy....I'd google it and see what you come up with & Yes, it ain't cheep or easy.

~M