Posts Tagged ‘DNL’

Report from ACI-NA Annual Conference and Pre-conference Workshops

Wednesday, October 6th, 2010

by Mary Ellen Eagan

I’m still collecting my thoughts from nearly a week in Pittsburgh at ACI-NA’s 19th Annual Conference and Exhibit.  Here are the highlights:


I attended the GRI Workshop on Friday, September 24th (that would be the workshop that preceded the pre-conference seminar).  For those of you unfamiliar with the Global Reporting Initiative, it is an international framework for reporting on sustainability initiatives.  Four North American airports (Denver International, Portland International, San Diego International, and Toronto Pearson International) have participated over the last two years in the development of a Draft Airport Operator Sector Supplement (AOSS).  As the name implies, the AOSS is meant to provide additional airport-specific sustainability information that is not already provided through the G3 Sustainability Guidelines, which is the cornerstone of the GRI Sustainability Reporting Framework.  One obvious example is aircraft noise.  Here is a description of the proposed new performance indicator for airports to report on noise exposure:

  • 2.1 Identify the index most widely used in your country or at your airport to calculate the number and percentage change of people residing in areas affected by noise. Where no indicator exists, report using the Day Night Level (DNL), showing the number of people exposed to (55 and) 65 DNL. Where the metric covers a 24 hour period, information on noise during the night-time period can be expressed using a default Leq metric for an 8 hour period. The reporter must define the 8 hour period although flexibility is provided to set the start time to reflect cultural differences (for example, some reporters may regard night as being 22.00 to 06.00, while others may think 23.00 to 07.00 is more appropriate to local circumstances). 
  • 2.2 Specify the metric and the time period adopted and the thresholds applied for calculating exposure. To aid comparability between airports, the reporting threshold chosen should reflect the onset of significant annoyance.
  •  2.3 Report the number and percentage change of people residing in areas affected by noise. If metrics exist to calculate the number and percentage change of people residing in areas affected by noise for both day and night periods, please report information for both.

I’m still trying to interpret this recommendation, but my guess is that U.S. airports will be fine to simply report on the number of people exposed to DNL 65 dB and higher.  What’s not clear is whether airports should also report on the number of people exposed to DNL 55 dB and higher (not a common practice for most US airports).  This is an even more complicated question when you consider the statement that “the reporting threshold chosen should reflect the onset of significant annoyance” in the context of current ISO and other efforts to update the Schultz Curve.

Environmental Affairs Seminar

The Environmental Affairs Seminar was a two-day whirlwind of updates on a range of environmental issues facing airports:

Presentations from the seminar will be posted on the ACI-NA website shortly.

Then the conference began.

The annual conference is generally pretty light on substance (a good thing, after three days of intense meetings), but I did enjoy two sessions in particular:

Nick Bilton, Source: ACI-NA

Nick Bilton, Source: ACI-NA

  • Nick Bilton, lead technology writer for the New York Times Bits Blog gave an engaging keynote address on the use of technology and communication, with a particular emphasis on social networking.  I learned about foursquare, and though I don’t have enough of a social life to take advantage, I can see that it offers potential for airports.  He also showed an amazing video on instantaneous information flow, as illustrated by the death of Michael Jackson.
  • Deb Meehan of SH&E also gave an entertaining update on state of the airline industry.  She emphasized her belief that airline profits in the last 18 months have come at the expense of the traveling public – especially in terms of comfort – and that we should look for airlines to start competing on service.

 Looking forward to next year in San Diego!

From Whence Came Ldn / DNL 65?

Thursday, April 1st, 2010

by Nick Miller

With FAA developing a research roadmap, and fears (hopes?) expressed by many in our airport noise community that the compatibility guideline might change, I became “curiouser and curiouser” about the real origin of 65 DNL as various claims were made about its origin, its immutability, its arbitrariness, and its scientific basis or lack thereof.  What follows is my take on what seems to have happened.  Please forgive oversights, it’s the best I could do with what materials I could quickly dig up.

This is, indeed, a topic with a tortuous and uncertain history.  Apparently, many efforts from the 1950’s on to the late 1970’s were underway to determine levels that could be identified as the threshold between compatibility and incompatibility with noise.  Efforts were pursued in many countries.

In the U.S., it appears that a “west coast”, an “east coast”, and a U.S. EPA effort were simultaneously underway.  The various engaged personalities were surely aware of each others’ work, and it is likely that most of them attended the legendary 1973 International Conference on “Noise as a Public Health Problem” at Dubrovnik, Yugoslavia, but produced separate reports.  (Legend has it that during that conference in a taxi cab, Ken Eldred and Liz Quadra derived the relationship between population density and Ldn.  Another legend is that Henning von Gierke finished drafting the “Levels Document” in his hotel room at 5 in the morning.)

On the west coast, Wyle Laboratories provided a report Supporting Information for the Adopted Noise Regulations for California Airports, WCR 70-3(R), January 29, 1971.  This report documents the science behind the California airport noise criteria that were adopted in November 1970.  The criteria limited airport noise in residential communities to 65 CNEL.  The report shows that behind selection of this level, however, was a review of considerable research on the effects of noise on people.  Data on speech and sleep interference, hearing loss, physiological stress and health effects, annoyance and community reaction were all reviewed.  In the end, using community reaction data, 65 CNEL was chosen as the apparent “threshold of complaints,” suggesting that complaints are a reasonable indicator of annoyance. Of note, and generally suffering from benign neglect, is the report’s clear recommendation that: “The CNEL limit should be periodically reviewed by the State with a view to the possible necessity of reducing the limit in light of any new human factors research which may become available,” and that the review should be every five years, at maximum.

On the east coast, Ted Schultz at Bolt Beranek and Newman was hard at work assisting HUD develop compatibility guidelines.  In BBN Report No. 2005 R, Technical Background for Noise Abatement in HUD’s Operating Programs, 8 November 1971 he reviewed noise ratings (dBA, loudness, NNI, etc.), made comparisons across noise ratings, compared noise ratings with subjective judgments, criteria of acceptability, including social surveys and existing noise exposures, and criteria in different countries.  (His work investigating surveys appeared in the “Synthesis of social surveys on noise annoyance,” in JASA, vol. 64, No. 2, August 1978.)  Ted developed criteria for non-aircraft noise that were identified as “clearly acceptable,” “normally acceptable,” “normally unacceptable” and “clearly unacceptable.”  These were indicated on simple graphics that showed areas of level versus percent of time exceeded, over which a measured distribution could be traced or laid and acceptability determined.  However, these were probably too complicated for practical use, since sound distributions were at the time almost impossible to predict – how would a proposed project be judged?  The distributions were also stated first in terms of L33, then as NEF values in 1971, then finally as Ldn values in 1978.

For our purposes, i.e., for aircraft, in Report No. 2005R, he identified “about NEF 30” (~DNL 65) as the criterion of acceptable exposure in the U.S.  This criterion appears to be a synthesis of what other countries were doing.  But note what he says about this criterion: “It should be emphasized that criteria in the NEF 30 range must be regarded as provisional.  In each of the national studies in which these limits were developed, these levels of noise showed up as ‘maximum tolerable’ and were regarded as turning points above which annoyance increased very rapidly; but sizable portions of the population were seriously disturbed at much lower levels.  These turning points, however, were seized by the authorities and treated as acceptable levels such that special precautions and noise abatement measures are required only for more severe exposure.” [Ted’s emphasis] “The situation is even more extreme in the U.S., since the criteria are based on overt action in terms of complaints or legal action.  It is well known that serious public annoyance is prevalent long before official complaints are lodged.  It is therefore obvious that these criteria are not adequate for aircraft noise abatement in the long run, since they are deliberately permissive.”

Schultz’ “Synthesis” JASA article, after long analyses and descriptions, provides a way to choose a “community noise level suitable for a living environment….”  He does this in a graph (Figure 23 in the article) that plots, as a function of Ldn, % U.S. populations exposed to values of Ldn or higher, and % of people experiencing different types of effects at a given Ldn – high annoyance, sleep or speech interference.  What he tries to offer decision-makers is information that balances what is desirable with what is feasible.  We have forgotten, or never knew, that high annoyance was only one of the effects he proposed minimizing or limiting in selecting a level for a suitable environment.

Meanwhile, the U.S. EPA’s Task Group III, led by Henning von Gierke, in responding to the Noise Control Act of 1972, recommended Ldn 60 as the limit of compatibility, and based this conclusion on minimizing annoyance, complaints and community reaction, and speech interference both outdoors and indoors. (See the EPA report Impact Characterization of Noise Including Implications of Identifying and Achieving Levels of Cumulative Noise Exposure, PB224408, 27 July 1973.)

Finally, we also know that for the Maryland Aviation Administration in 1975, Schultz recommended Ldn 65 as the residential standard, to be reduced to Ldn 60 when “the U.S. fleet noise level is reduced 5 dB below 1 July 1975 levels,” Maryland Department of Transportation State Aviation Administration, Selection of Airport Noise Analysis Method and Exposure Limits, January, 1975.

My conclusions? These folks at the beginning tried to account for all the effects they were aware of and had confidence in, and balance what might be desirable with what would be feasible.  And they all suspected or decided that 65 CNEL / Ldn was likely too high as a long-term goal.

History is not as simple as we’d like it to be.  Sorry.

Author’s notes: For people younger than about 55, the people mentioned are: Ken Eldred, now living somewhere in Maine, was a chief participant at Wyle and then at BBN in development of the background for metrics and effects of noise.  Liz Quadra, now lost to us in acoustics, was a major force in the U.S. EPA’s Office of Noise Abatement and Control (ONAC – defunded in 1981).  Henning von Gierke, deceased, was a scientist the U.S. managed to get from Germany after World War II and who lead research on the effects of noise and vibration on people at the U.S. Air Force research laboratories at Wright Patterson Air Force Base.  Everyone reading this should know Ted Schultz.  If not, check some of the above links.

Noise Outside DNL 65

Monday, October 5th, 2009

by Mary Ellen Eagan

Well, this is a blog post I’ve been thinking about for some time (probably since before I knew what a “blog” was – though I just learned that the term was coined in 1984 – ironically, the same year I started in this business), but is precipitated by the publication of ACRP Synthesis 16, Compilation of Noise Programs in Areas Outside the DNL 65, primary author, yours truly.


If you’ve been tracking my publications closely (or reading Airport Noise Report), you’ll already know the conclusions.  For those of you haven’t, I’ll summarize briefly.

The ACRP synthesis was based on an online survey of 43 airports, designed primarily to identify the airports’ reasons for addressing noise outside DNL 65, and the wide range of techniques used to address it.  The survey included five general questions regarding noise issues outside DNL 65.  I was not surprised by the results:

  • A majority of respondents (83%) indicated that noise issues outside DNL 65 were “important,” “very important” or “critical” to their airport.  The remaining 17% were evenly split, stating that noise issues outside the DNL 65 were “somewhat important” or “not at all important.”
  • How important are noise concerns outside DNL 65 for your airport?

    How important are noise concerns outside DNL 65 for your airport?

  • The most frequently listed method of minimizing noise outside the DNL 65 was operator education and outreach (74% of respondents), followed by noise abatement flight tracks (69%), preferential runway use programs (66%), noise abatement departure or arrival procedures (60%), and ground noise control (51%).
  • Eighty percent of respondents indicated that “community concerns” were the motivation for addressing noise outside the DNL 65; fifty-seven percent also indicated that “preventative planning” was a motivation.
  • Almost three-quarters of respondents (74%) indicated that more than 75% of their airport’s noise complaints came from people who live outside DNL 65.
  • The most common outreach tools to communicate with people exposed to noise outside DNL 65 are websites (74%), community meetings/forums (74%), online tracking (40%), and newsletters (40%).

The survey also found the following:

  • A majority of surveyed airports use noise abatement departure (63%) and arrival (51%) flight tracks and departure (54%) and arrival (40%) cockpit procedures to minimize noise over residential and other noise-sensitive neighborhoods.  However, among surveyed airports there is no consistency in methodology among airports for evaluating noise abatement outside DNL 65, and there is little guidance or support from the FAA on appropriate metrics or criteria for evaluating noise abatement procedures.
  • Most airports reported some procedures to minimize ground noise (69%); 25% of those airports reported that the procedures were developed primarily to address noise outside DNL 65, and an additional 38% reported that procedures were developed to address noise issues both inside and outside DNL 65.
  • More than half of the surveyed airports (57%) reported having land use compatibility measures that apply outside DNL 65.  The tools used by airports for land use compatibility planning include zoning, building permits that require sound insulation or residential and noise-sensitive non residential land uses, and disclosure to residents.
  • The majority of respondents (58%) do not provide sound insulation to homeowners living outside DNL 65.  However, 20% provide sound insulation for homes in contiguous neighborhoods (“block rounding”), and an additional 15% provide sound insulation for homes within the DNL 60 dB contour.
  • Nearly three-quarters of respondents (74%) reported that they use both websites and face to face meetings to communicate with people exposed to noise outside DNL 65.
  • The responding airports communicate with pilots about noise outside DNL 65 in a number of ways.  The most common are: pilot briefings (40%) and Jeppesen inserts (40%), posters and handouts (37%), and FAA standards (17%); other methods include airfield signage, Airport Facility Directory Special Notices, videos distributed through flight schools, and phone calls.

What does it mean?

As I said above, none of these findings surprise me – and for those of you who work around airports, you’ll probably feel validated.  The real question is what does it mean for public policy?  I will be talking about results of this survey twice in the next couple of weeks: first at the AAAE Airport Noise Mitigation Symposiumin Boca Raton, FL on October 6th, and the following week (October 11) at the ACI-NA Environmental Affairs Committee Seminar in Austin, TX.  I look forward to engaging discussion with you, and will try to post the highlights here for those of you that can’t join us.