How far do I need to be from a highway/parkway to no longer hear it?
November 18, 2014 6:15 AM   Subscribe

How far do I need to be from a highway/parkway to no longer hear it? I hope to use this information to look at a map and find the nearest place that will be quiet in the middle of the night, to record sound. Local road noise or the occasional passing car is not a concern, just highways and parkways that will be busy all night.
posted by xo to Science & Nature (18 answers total) 2 users marked this as a favorite
 
It's going to depend a lot on local geographies and weather conditions. Sound carries better across water, for example, so even if you're [some miles] from a busy highway, if it's across the lake from you it may be much louder than if you have a hill between you and it.
posted by rtha at 6:19 AM on November 18, 2014 [6 favorites]


It's also going to matter what kind of sound remediation the city has done. A half a mile off the interstate in Ames and I can hear it. 300 yards off the interstate in Minneapolis I can't.

You also have varying vehicle noises. A semi makes more noise than a hybrid.

Now to the spirit of your question:

I would guess that if you are a mile off most roadways you'll be good. It's going to be less if the terrain is hilly, but I go to a state park on occasion and once you get in there a ways I can't hear anything, but there are a lot of trees and hills.
posted by cjorgensen at 6:30 AM on November 18, 2014


Also, when you say "record sound," what do you mean? Indoor or outdoor? Studio music or podcasts? What microphone quality?

For several years, I lived 200m from a busy 16-lane segment of the 401. You could hear it when you were standing on my front lawn (though not so loudly as to be intrusive), but it was undetectable when you were inside the house. I recorded a number of podcasts there and had no increased problem with background noise.

In this anecdotal case, incidentally, there was an earthen berm and a 4m high sound baffling fence running alongside the highway.
posted by 256 at 6:30 AM on November 18, 2014


I know a hill where I can hear a motorway about four miles away halfway up the hill, but not at the top or bottom. Sound is weird.
posted by Leon at 6:31 AM on November 18, 2014 [1 favorite]


As others have said above, the number of miles away isn't as big of a factor as you'd think.

For your purposes, I think you'd be better off Googling "noise pollution map" for your locality. If you can't find a map, your city/county/state Department of Environmental Health or Environmental Protection might be able to help you.
posted by Jacqueline at 6:46 AM on November 18, 2014 [3 favorites]


Time of year will be important, too. With the loss of leaves on the trees in our neighborhood the highway about a mile away will turn from a distant susurrus to a dull roar. You will find that flat fields will do much less to quiet your study area that rolling, tree covered hills. Having said that, I find that two miles is enough to forget that you are near a highway, and feel peaceful. This is probably what you are looking for, to make your recordings.
posted by Midnight Skulker at 6:46 AM on November 18, 2014 [1 favorite]


The wind direction will make a huge difference too. It really carries sound either to you or away from you.
posted by littlewater at 6:49 AM on November 18, 2014 [1 favorite]


As a data point, for about five years I lived 600 feet from a major freeway and I didn't hear it inside the house a single time. Outside, if I could hear it at all, it sounded like white noise. There were a lot of tall trees and stuff between me and the freeway, though.
posted by primethyme at 7:26 AM on November 18, 2014


A lot also depends on the construction and soundproofing. I lived a stone's throw from the busiest road and bridge in Sydney, and never heard any traffic from my 7th floor apartment unless the deck doors were open.
posted by RedOrGreen at 8:18 AM on November 18, 2014


The wind direction will make a huge difference too. It really carries sound either to you or away from you.

I live just under a mile from a four-lane highway, and about 2 miles from a regional airport. I can attest that what I hear of either of these has a lot to do with the direction of the wind, particularly in the winter when (where I live) most of the trees lose their leaves. Also the sound of air (jake) brakes on large trucks carries even farther than regular traffic background whooshing noise, though it only happens occasionally, and this can be a problem on 2-lane highways as well as freeways, particularly if there is a hill involved.

Also, many areas do get measured and have noise maps made, so you might want to google around and see if there are noise maps for the area you're interested in.
posted by aught at 8:43 AM on November 18, 2014 [1 favorite]


1 mile.
posted by IAmBroom at 9:08 AM on November 18, 2014


My anecdote--I live a mile from a freeway and regularly hear jake brakes and high-rpm motorcycles when I'm out in the yard. I live in DC, and there are many houses and trees and such between me and the highway, but no significant hills.
posted by MrMoonPie at 9:35 AM on November 18, 2014


It's not just the hills. Hills are separated by valleys -- creeks, streams -- and sound can travel up them. This only from experience, not book learning.
posted by LonnieK at 9:48 AM on November 18, 2014


I'm about a mile and a half straight-line from the DC Beltway, and let me tell ya: I hear it, especially at night. Relevant factors in my situation are that there are no hills between me and it, a couple years ago they cut down pretty much all the tree-belt along it (to reduce sound! and then they build totally useless concrete "soundwalls" instead....), and I live in a highrise building where the exterior walls act as a reflector.

So: the answer to your question is, when it comes to distance from a roadway it'll depend on a lot of variables. Are you talking about looking at a map of a wooded, rural area, or of a more heavily-buildup area? 'Soft' stuff, like trees, will absorb sound; hard stuff, like most buildings, will reflect sound.
posted by easily confused at 10:01 AM on November 18, 2014


Very interesting question.

My thoughts: let's assume that traffic noise approximates a broadband noise. Weighting for the broadband noise using A weighting, we'll say that traffic noise is 80 dB(A) at 50 feet. Now let's assume you have very normal hearing thresholds, around 15 dB (HL, but for the sake of this exercise we'll call this more or less equivalent to A weighting even though it isn't really). Sound follows inverse square law, so by my calculations that would put the traffic noise down at the 15 dB range (assuming the ~6 dB down point for intensity halving) at about 19 and a half miles.

Now, that would be in a temperature controlled anechoic chamber. That's also assuming you can hear in the outdoor sound field perfectly well at your lowest threshold. Neither of these things are going to be the case, however. So let's say that, still given a temperature of around 70 degrees in an open space, you'd get the traffic noise at a more reasonable (relatively conversational) level that you might actually hear at around 1600 feet, or like a third of a mile. This would give you the traffic noise at something around 50 dB. That's still probably going to be pretty clearly audible. But maybe at around 6400 feet, or just over a mile, you'll get the traffic noise down in the thirties, and you may not really hear that in the soundfield, especially if you have other masking white noise type stuff like wind.

Now, then you have to assume there's all this topography that's going to absorb a lot of that sound, but just how much is pretty variable. Are there lots of mountains? What shape are they? Snow? What kind of soil do you have? Also if it's cold, the sound will tend to be louder or at least lose a bit less intensity over space.

In conclusion, my professional opinion is 1 mile.
posted by Lutoslawski at 10:47 AM on November 18, 2014 [2 favorites]


I gotta say more than a mile, depending on the sorts of factors mentioned. Maybe even 3 or 4 miles if the sound is, say, rolling up a valley from the road to you.

Temperature and pressure gradients will bend the sound waves and can give unpredictable results.
posted by SemiSalt at 11:15 AM on November 18, 2014


It's not what you can hear, but what your microphone can hear. If you are recording speech and you mic super close to the mouth via eg a headset mic, you can go a lot closer to the road than you'd think. Something something inverse square law (I took a course on this but I've forgotten stuff). But the point is, the way sound works it doesn't drop off linearly, so by having a microphone hugely closer to one source of sound than the other you can record that wanted sound at so much more volume than the background noise that you then later turn down the volume on everything and miraculously the unwanted sound disappears while the deliberately recorded sound stays nice and clear.
posted by lollusc at 2:28 PM on November 18, 2014


I concur with the general consensus that "it depends -- on quite a lot of factors."

nearest place that will be quiet in the middle of the night, to record sound.

What kind of sound recordings are you wanting here? Because if the plan is, say, your voice or music, I think a proper recording studio can probably be found that is designed to block out outside noises. So maybe it would help folks to know what you are wanting to record. That might inform future answers as to how to advise you to accomplish this. I mean, because the wording makes me think of you going around outside with a microphone and pointing it at hoot owls and what not. In which case, the biggest problem might be "Oh, ick, it's a strange human we don't know, so we are all going to clam up and hide." (And solving that problem is a whole 'nother ball of wax from simply not having road noises interfere.)
posted by Michele in California at 4:35 PM on November 18, 2014


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