Advice from Bay Area landscape experts: highway noise reduction

bishakha_bSeptember 16, 2012

Hi All,

What plantings would you put to lessen highway noise? We have a long boundary with 280 behind us. Some people have suggested redwoods - mass plantings of 30 gallon ones, to be thinned out in ~ 10 years. Is that the right choice? Are there others?

How big will the redwoods grow? What would be an average life-expectancy? Would their roots cause problems with the foundations of the house?

Any suggestions for sound reduction would be much appreciated.



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Sorry to be the bearer of bad news, bluesv, but trees aren't going to help. It is a common misconception that plantings attenuate noise. Alas, they do not. There are no trees or shrubs that will effectively reduce the level of freeway or highway noise on your property. What you need is a solid wall--not a wooden fence, but a masonry wall or earthen berm--a solid physical barrier between you and the source of the noise. Be aware, however, that if the highway is elevated, even a wall might not might not give much improvement.
Because prolonged exposure to noise may have lasting adverse health effects, you will want to do what you can to ameliorate the problem. Look at other homes on your block--what actions are your neighbors taking to address the problem? If the noise is severe enough, you may want to consider retaining the services of a noise consultant, who will measure the sound and discuss construction options with you. Your local city government may also be able to give you some advice.


    Bookmark   September 16, 2012 at 2:12AM
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Thanks Kay. We will be adding several noise-attenuation features (special matting in exterior walls, triple-paned windows, etc.) while doing remodeling; as well as adding some white noise features like fountains etc for outside areas. Unfortunately - the Hills area we live in, there is highway noise all over the hills - and we've been pointed to redwood tree plantings as one way to reduce that noise.
But thanks for your suggestions - we will be talking to a noise consultant as well.
Regards, blue

    Bookmark   September 16, 2012 at 1:28PM
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Sara Malone Zone 9b

Redwoods don't like smog...and unless you are in their microclimate (summer fog) you will need to provide a lot of supplemental water to keep them looking good.
Here in Sonoma County they were widely planted as freeway trees and the vast majority look awful.

    Bookmark   September 16, 2012 at 2:46PM
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jkom51(Z9 CA/Sunset 17)

Redwoods drink up to 300 gallons per day. Also, in many cities it is illegal to cut down trees over a certain size without a permit. Here in Alameda Cty, for example, you're not allowed to take out any tree with more than an 8" diameter trunk without applying for a city permit.

onederw is correct - only solid walls deflect noise. We hear 580 from our lot, but I've noticed in walking around the neighborhood there are many properties where the noise is either louder or softer, depending on the terrain.

    Bookmark   September 16, 2012 at 6:47PM
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How big do redwoods grow and how long do they live - are you joking? LOL. They can live thousands of years and are the tallest trees that exist. Where along 280 are you, are you in an area that gets fog? Redwoods prefer fog, however there are redwoods growing in Palo Alto, Mountain View, and Redwood City and no one waters them and they don't get much fog.

No one can tell me they do not block sound, because it is as silent as a cathedral in a redwood forest, they are massive and absorb sound.

BUT redwoods grow very very slowly. I doubt they will be big enough to muffle the sound within our lifetimes. It would be a gift to future generations to plant them, but perhaps not the most helpful to you.

The best thing for highway sound though is raised earth - do you have the space to make an earthworks?

Here are some alternative ideas - a living wall

acoustic noise walls

    Bookmark   September 17, 2012 at 12:14AM
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calistoga_al ca 15 usda 9

Too many redwoods are planted where they are able to grow, but never to prosper. Look around and see where nature has planted them. We have six acres of native woods, and the redwoods only grow along waterways where water is always available to roots able to spread 100 ft from the tree. Most redwoods planted are "Coast Redwoods" so named because this is their normal habitat. Many selections have been made and sold under various trade names. Along the summer foggy northern California coast, an average of 10 inches of water is extracted from the fog each summer by these trees. There are good reasons for planting and growing redwoods if you live where they will thrive, but a sound barrier is not one of them. Al

    Bookmark   September 17, 2012 at 9:10AM
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jkom51(Z9 CA/Sunset 17)

Redwood forests are quiet because there isn't any logging equipment or freeways around. Put thousands of cars going 70 mph next to them and you'll hear a whole lot of noise.

Actually, they do NOT grow slowly. Redwoods are one of the fastest-growing trees around when conditions are right, which means water. It's why they still plant and log them on tree farms. "Fast" is relative for a tree, but although it may not be as fast a shrub grows, redwoods are no slouches in the growth department.

If you ever take the Skunk train from Ft Bragg to Willits, there are several stretches where the conductor will say that in the 1940's, those acres were clear-cut as far as the eye could see for the war effort. The trees are now so thick and tall you can't see more than 5' from the train's windows, in those formerly clear areas.

Also, taking out a redwood is not as simple as cutting it down. Redwood stumps remain alive virtually forever and will continue to send out new branches in an attempt to replace itself. If you don't take out the root system you'll be cutting down saplings for the rest of your life.

    Bookmark   September 17, 2012 at 10:42AM
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hoovb zone 9 sunset 23

As previously mentioned by onederw, the most effective barrier is a berm of soil, as tall as you can legally make it. A block wall on top of that, if you can afford it. Most of the noise is from tires, actually. The soil absorbs the audible vibrations of tires quite effectively. Something to do with the wavelength of tire noise vs. the density of soil.

Trees will absorb a little noise, perhaps 2 db. It is somewhat difficult to discern a difference of 2 db, but some people can. The effect is mostly psychological.

    Bookmark   September 17, 2012 at 10:51AM
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hosenemesis(SoCal Sunset 19 USDA 8b)

Another vote against redwoods. I'd choose something else if you want a tall green screen- maybe podocarpus? They are very dense. The psychological effect matters, so I'd plant something thick and tall. Be prepared for the shade and litter, though.

    Bookmark   September 17, 2012 at 12:18PM
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jkom51, even near a highway if you stand in the midst of redwoods in say LaHonda, a short distance from a highway, you can definitely experience the quietness. Anything that massive is going to absorb sound! When the trees are old enough and massive enough, they most certainly absorb sound.

I should not have said slow growing, however, I should have said it would take decades for the trees to reach the size at which they would have a significant impact on sound - when they are hundreds of years old at least.

In any case plating redwoods is not going to be an efficient way to attenuate noise in the next few decades.

    Bookmark   September 17, 2012 at 12:33PM
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jkom51(Z9 CA/Sunset 17)

tinan, I doubt that noise is as easily abated by plantings as you may think. CALTRANS engineers are experts and even they have a hard time abating sound. Sometimes sound-deflecting walls are built only to find the sound, instead of being deflected upwards, goes in unexpected directions and creates headaches for another neighborhood which previously had no problems at all.

Land topography has more impact on noise deflection than anything else. If you walk along the Bodega Head trail, at certain sections the ocean noise is thunderous; yet 50' away without any change except for a shift 10' inland and a protruding cliffside edge, the wave noise drops by two-thirds. No trees or level change are involved at all; it is all topographic noise deflection. Take a side path below cliff level and suddenly you can't hear any ocean noise, everything is silent.

Certainly trees "en masse" will deflect noise. But you'd have to own a half-acre lot to plant enough trees to mass thickly enough to create a viable deflection wall on a level property.

Walk around a freeway underpass, and you'll probably find that in certain spots almost underneath the freeway (it needs to be solid, not the type with separate roadways) the car noises stop. Sometimes they merge into a deep booming noise that is more pressure than noise, a rather odd feeling.

All of us live in a geographically hilly area. This means that cell phone reception gives carriers nightmares and that noise from our maze of freeways travels upwards and outwards in a variety of directions, funneled by geography and climate.

I can occasionally hear train whistles from the Amtrak lines two miles west - but not always, only at certain times. If sound were a simple thing, I would ALWAYS be able to hear them - the tracks don't move, and neither does my house (unless there's a rupture in the Hayward Fault, LOL). But I can't, even though I know that the trains blow their whistles at the same crossing twenty times a day.

    Bookmark   September 19, 2012 at 12:56PM
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jkom51, I believe we are actually in agreement - I was saying that in large plantings, in a few decades, redwoods would help. But that they would not be an efficient way of reducing sound any time in the near future... and I also suggested an earthwork/earth filled wall or acoustic wall :)

    Bookmark   September 20, 2012 at 10:29PM
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peachymomo(Ca 8)

I'm no expert, but in my opinion an earthen berm with a stone wall on top would be a much better start for a landscape than a row of redwoods. The trees would create a shady yard where little will grow whereas a berm and wall would be the perfect canvas for a nice garden view.

If it were my property I would install a good sized berm with a fieldstone wall at the top, then I would plant small trees or large shrubs on the far side of the wall for privacy and depth. On the inside I would have mixed plantings of native and drought tolerant perennials and grasses that would provide year round color and attract wildlife. At the bottom of the berm would be the living space with views of the garden instead of the highway.

    Bookmark   September 21, 2012 at 11:59AM
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@ onederw, jkom51, tinan, hoovb and peachymomo - thank you all. Yes - we have an earthen berm on part of the boundary, and had been thinking of extending it to as much as possible. Unfortunately - because of the slope of the land and its placement with respect to the freeway - the berm will not help by itself, we will have to have a masonry wall on top as well. We've been wondering if it was feasible - and have decided that we really should talk to a good sound engineer.

Accordingly, we have been in touch with a firm that consults for Caltrans - so will update once their recommendations are in.

@ jkom, formandfoliage, calistoga and hosenemesis - thank you for the detailed info on the redwoods - I will certainly not be planting them at the rate of water they need, and we do not live in an area where they would get the coastal fog.

@ hosenemesis - podocarpus sounds interesting. I will definitely check it out.

@ peachymomo - that's exactly the thought I had - except I was thinking of bougainvilleas on the masonry wall, and thick trees (not redwoods, maybe podocarpus instead?) on the outside of the berm (that faces the highway. Then on the inside - native, drought and deer tolerant shrubs/grasses.

Thank you wall very much - you've pointed us in the right directions.


    Bookmark   September 22, 2012 at 1:55AM
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As you proceed, please come back and post photos of what you're doing. And let us know how successful your noise suppression efforts are. This is such a common problem--we'd all love your input on what works for you.


    Bookmark   September 22, 2012 at 6:43PM
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Hi, our property also backs onto 280 (with an empty lot in between). Honestly, we have only double pane windows and regular insulation and we cannot hear the cars (in general without opening the windows, except the occasional siren or motorcycle :-)) The previous owners planted eucalyptus along the back wooden fence which was absolutely useless. We tried to add redwoods which didn't survive because they need so much water and the animals (you know the squirrels, rabbits, gophers or what not)kept chewing up the drip system. If you do find something that works, please do post back and help us as well. The noise outside the house will improve with a water feature (and outdoor sound system)-but not 100% tranquil, so you just get used to it. Plus if you are higher than 280, a sound wall won't fix it because sound travels upward and there's a limitation on the high of a sound wall. Good luck!

    Bookmark   October 23, 2012 at 3:37AM
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nil13(z21 L.A., CA (Mt. Washington))

There are two ways of looking at the problem. The first is what has been discussed where the sound is blocked. The second is to cover up the sound with more sound that may be more pleasing. A really loud fountain can do this, or you can plant something like bamboo that is very noisy when the wind blows.

    Bookmark   October 23, 2012 at 11:51AM
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nil13(z21 L.A., CA (Mt. Washington))

or you can pester CalTrans to approve sound dampening asphalt as a road covering.

    Bookmark   October 23, 2012 at 11:54AM
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