Traffic noise and air pollution adjacent to Maple Avenue, updated 7/28/2018

Anyone who has walked along Maple during rush hour knows that the traffic generates significant noise.   This page answers the question, just how noisy is it?

This is an important question for two reasons.  First, the only “public open space” that the Town appears to be getting is small paved areas directly adjacent to Maple Avenue, and the MAC zoning rules appear to enforce that.  The Town expects people to enjoy the space directly adjacent to the road.  Second, the Town promotes MAC as a way to make Vienna more “walkable“, by which I think they mean that they expect people living on Maple to walk to destinations on Maple.   For that as well, high noise levels will be a significant disincentive to walk to Maple Avenue destinations.

Let me put the results first, then provide the detail below.  Below is a summary of noise levels (in decibels or db) measured around 1 PM on Saturday 7/28/2018 in front of Tequila Grande.  The location where the noise was measured approximates the proposed outdoor restaurant seating area, and I extrapolated that to estimate the noise level at the streetside benches in the “plaza” in front of the building.  After dividing the hour’s worth of measurements into five-minute and then one-minute intervals, this table shows how often the noise level did NOT exceed the indicated level, in decibels.  I.e., it shows the count of “quiet” periods.

In other words, if you spent an hour on a Saturday afternoon sitting on the benches in front of the proposed 444 Maple West, you would never experience a five-minute interval without hearing noise at least as loud as you would hear standing three feet from a running garbage disposal.  You would never experience one full minute without hearing a noise as loud as you would hear standing 10 feet from a running vacuum cleaner.

It really doesn’t take a rocket scientist to say that the corner of Maple and Nutley is noisy.  But now I have hard data.  It’s not my opinion that this is a noisy location. This is, objectively, a noisy location.

The noisiness as measured here merely validates what you can see every day driving up and down Maple. There is only one merchant along Maple with tables set this close to the road — Sweet Leaf Cafe. That is a very space-constrained location, and those tables are approximately 30 feet from the curb on Maple.  It is rare, in my experience, to see someone sitting there during the day.  Tables at Potbelly Sandwich appear to be the next closest, at 60 feet from the edge of Maple.  At Tequila Grande, the outdoor seating area is 100 feet from Maple.  From that distance, you can hear the traffic noise, but you rarely feel as if you have to talk over it.

The only realistic conclusion is that, sure, they can build some nice-looking benches there.  And they can create pretty pictures of people sitting there in the middle of the day.  But it’s bordering on crazy to think that people are actually going to sit there and socialize on a Saturday afternoon.  It’s just not a very nice place to be,  due to the traffic noise.

Detail follows.

First, let me summarize this .pdf document of most recent Virginia Department of Transportation  traffic count data.  I have taken the relevant numbers from that, done one calculation, and placed them into the table below.   These are counts of vehicles (almost entirely cars) in both directions, along a given segment of the road (From – To).  The final column — implied weekend traffic — is my calculation from the two prior columns of data supplied by VDOT.

The first thing to note is that Maple gets a lot of traffic.  Roughly speaking, Maple Avenue handles about 20% of the volume of Interstate 66.  That’s pretty impressive given the difference in number of lanes and average speed.  The second thing to note is that weekend traffic is not that much lower than weekday traffic.   I.e., when people are likely to be using these new spaces on Maple, there will likely be some significant traffic on Maple.

The noise from that volume of traffic will depend on a number of factors.  Cars and trucks make engine noise, tire noise, and wind noise.  Larger vehicles are noisier, so the ratio of trucks/buses to cars affects average noise level.  Noise can be reduced by (e.g.) sound barriers adjacent to the road, or amplified by reflection from surfaces away from the road (such as the mandatory glass fronts of the new buildings).  Tire and wind noise increase with the speed of the vehicles passing by.   Finally, any project located at a traffic light (as 444 Maple West/Tequila Grande is) will get the engine noise of accelerating cars and trucks.

Road noise is one of those things that humans just instinctively hate.  And, as it turns out, there may be some good reasons for that.  I guess it’s no surprise, but living next to a busy road is bad for your health.  And that appears to be due, in part, to the noise.  Basically, living with high levels of road noise is associated with the same risk as living with other chronic low-level stressors.  It results in a modestly raised risk high blood pressure and strokes.  (There’s an overview article here, and some references from the National Library of Medicine here — just read the last couple of lines to get the gist reference 1, reference 2).  Separately — but no surprise — it’s also hard to think straight when subjected to high levels of road noise (reference 3).

Some of the health effects attributed to noise may plausibly be due in part to the high levels of air pollution directly adjacent to a busy road  (reference 4).  In effect, you can’t be subjected to one without the other.  There is ample evidence that chronic exposure to high levels of air pollution from living next to a busy road harms health, particularly in children.  You can read what the American Lung Association says, but this is so well established that the Federal government already has strategies to try to reduce the impactThat said, the best available evidence suggests that road noise, by itself, is harmful, on top of the effects of air pollution.

One aside on air pollution:  It is much higher directly adjacent to the road.   The biggest offenders are particulates from diesel, and ozone.  These affect not just outdoor air quality, but indoor air quality as well.  As with all such environmental hazards, it’s hard to say what a “safe” distance is,  but there’s pretty good agreement that living within 300 feet of a busy road is hazardous to your health.  The US Department of Transportation provides a good brief summary of the issue, but this isn’t rocket science — any web search will show dozens of credible references saying more-or-less the same thing.  This happened to be the first graph I came across, from this site from the government of Ontario.  (So distances are in meters, not feet.)

And that’s for an open roadway, not for a road with 60′ tall buildings flanking it.

Anyway, put all of that together, and from an air-quality standpoint, living directly adjacent to Maple will NOT be the equivalent of locating your house on the shoulder of I-66.  Based on traffic volume alone, it would only be about 20% as bad.  But, because city mileage is worse then highway mileage, the rate at which cars produce pollution (per mile) is about 40 percent higher in city traffic then on the highway.  Taking the exact seven-day traffic data, and boosting the city miles by 40 percent, I find (30,000*1.4/164000 = .256) living on Maple will only be about 25% as bad as living on the shoulder of I-66, based on traffic volume and gas mileage.  Plausibly, road geometry (you are closer to all of the traffic on Maple and the proposed 60′ buildings are much taller than the I66 sound barriers) would result an actual figure that is higher than that.  In any case, from an air quality and health perspective, the last place in town you’d want to live (and particularly, raise your kids) in Vienna is directly on Maple Avenue.

Back to noise:  The only way to quantify the noise on Maple Avenue is to go out and measure it.  To that end, I bought a decibel meter.  And this weekend, I plan to measure the noise level and report back on that.   So in keeping with the scientific nature of this, I’m going to set my benchmark first, then take the measurement.

In particular, because people are supposed to enjoy this road-adjacent space, I want a standard for the point at which normal conversation becomes difficult.  “Restaurant conversation” is typically given as 60 decibels.  Near as I can tell, from looking at a variety of sources and talking at my decibel meter, 65 decibels is both a commonly-cited upper limit for normal conversation, and the point at which, when the decibel meter was three feet away, I was talking loudly enough that I would not want to keep that up for an extended period of time.

So my question will be, on a Saturday afternoon in Vienna, at the Tequila Grande site, roughly where the proposed new benches will sit, how often can you go five minutes without the noise level exceeding 65 decibels?  That is, five minutes without having to raise your voice to have a conversation with somebody three feet away?  So I’m going to record the maximum sound level for consecutive five-minute intervals, and see what shows up. 

After getting rained out last weekend, I measured the sound level at that corner today (7/28/2018).  My wife and I had lunch at Tequila Grande, and left a decibel meter recording the sound level at our parked car for an hour, starting just before 1 PM.  (Reed model R8080, fast setting, recording decibels (dbA) to match the frequency response of the human ear, sitting on a soft pad on the roof of our car.)  We recorded the sound level of typical Vienna Saturday afternoon traffic at Maple and Nutley.

The nearest parking spot to the corner actually placed the meter substantially further from the road than most of the benches planned for the front of 444 Maple West.  We were about 40′ from the curb of both Maple Avenue and Nutley Road.   See below.  That put us almost as far from the road as you can get, at the proposed 444 Maple West.

In the picture below, we were roughly where the woman walking at the at the center of the picture is.  Bear two things in mind before looking at the results.

First, there was no sound-reflecting glass behind us.  My best estimate is that sound reflector would raise noise levels in the plaza by about 2 decibels.  Second, the benches are about 20′ closer to the road.  Based on distance to the center of the roadway,  that should add about 3 decibels to the noise level there.  All told, the noise level at the benches, as pictured, would be about 5 decibels higher than what I measured.  That would be perceived by the average individual as being “about 40 percent louder” than our actual recording location.

To understand the results, you have to know something about what a decibel means.  The key fact is that every increase of 10 decibels is perceived as “twice as loud” by the average individual.  Here’s a reference to a nice chart giving some examples. As I noted before I did the measurement, my standard for “loud” is 65 decibels.  That’s the point at which you have to raise your voice to be heard clearly in conversation.  I wanted to know how frequently you could have five minutes of conversation without having to raise your voice.

Here’s a graph of the sound levels.  The first is what I actually measured, 40 feet from both roads.

The second is what I estimate the sound level would be at the benches pictured above, 5 decibels higher due to shorter distance the road and sound-reflecting surface behind them.

Recall that a 10-decible increase sounds “twice as loud”. Normal conversation is about 60 decibels. I used 65 as the level at which you have to raise your voice to hold a conversation. A typical vacuum cleaner, ten feet away, is 70 decibels. Sounds at or above 75 decibels would be characterized by most people as “annoyingly loud”. A typical garbage disposal, from three feet away, is 80 decibels.

Let me now tabulate how often you would NOT be subject to significant noise levels, on a Saturday afternoon, sitting in front of the proposed 444 Maple West building.  I have divided the hour into 12 five-minute intervals, and then again into 60 one-minute intervals.  (This is the same table that was presented at the top of this article).

So, in either location, there was not a single minute where the noise levels stayed below the 65 decibel threshold at which you would need to raise your voice to talk.  No possibility of quiet conversation here.

What I think is more indicative is the five-minute-interval column.  If you were sitting on the benches in front of the proposed 444 Maple Avenue West, there would not have been even one five-minute interval when you were NOT subjected to a noise as loud as standing three feet from a garbage disposal.  That is due mainly to the flow of motorcycles and large trucks past that intersection.  Further from the road, you would have had no five-minute intervals without being subject to “annoyingly loud” noise at 75 decibels.