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A Method to Determine Reasonableness and Feasibility of Noise Abatement at Special Use Locations

II. Technical Summary


The first phase of methodology development was to assess the current state policies concerning special land use. This was accomplished by mailing a survey to noise representatives from each state DOT. Additional surveys were mailed to other groups and individuals to develop more insight of the problem. For non-responding state DOTs, follow up telephone calls were made requesting completion of the survey. The survey was designed to determine whether any formal policies concerning special land use existed. If there were none, the survey sought to ascertain what the respondents considered to be key items for a policy of this type. For example, question 7 of the survey asked the respondees to choose from a list of items those items they considered to be of importance when determining abatement feasibility and reasonableness. Question 8 asks the respondees to rank the items they chose in question 7. Question 8 was later used as a key indicator of which items should be included in the feasible/reasonable determination for special land uses. The survey also asked the respondees to provide some methodology for the items they chose as most important for this task. This information was invaluable in development of a matrix and methodology to assess the feasibility/reasonableness of a special land use site. The survey used for this research effort is included in Appendix A, while the list of responses is shown in Appendix B.

Survey Response

The content of the Reasonableness Matrix required a research effort to determine if any state currently had a Special Land Use Reasonableness policy. The appendix contains a listing of responses to each survey question. While all responses are included in Appendix B, only the most important responses are discussed. Thirty five states responded to the survey along with three environmental professionals. Results from two survey questions are summarized in Table 1.

Table 1. State Survey Responses

Has your state had difficulty in determining reasonableness for special land uses? 1817
Does your state have a policy for special land uses? 4a31

aThese policies were determined to be for residences

Table 1 indicates that about one-half of the states are dealing with the problem while the other one-half are having difficulties. Table 1 also shows there is a need for a formal noise abatement policy for special land uses. Four states reported they had a formal policy for special land uses, but upon review of their policies it was found that the policies were actually for residences. No states currently have a formal policy for special land uses and the majority of states responding have had difficulty in determining reasonableness for these land uses. Twenty seven respondents did not answer the question of how they determined reasonableness/feasibleness of special land uses. The remainder of the respondents generally stated that they evaluated special land use sites on a case by case basis.

Question 8 of the survey asked the respondees to list what they believed to be the top three criteria for determining abatement reasonableness. Table 2 contains a summary of the responses to this question.

Table 2. Top Criteria for Abatement Reasonableness (DOT Response)

Cost 25
Approach or exceed Noise Abatement Criteria (NAC) levels 18
Noise Level Increase 15
Type of Use 9
Amount of Use 7
Development after Highway date of public knowledge 6

Table 2 indicates that the respondents consider abatement cost to be the most important criteria for reasonableness. The second highest number of survey responses pertained to whether the site approached or exceeded the noise abatement criteria levels. Noise level increase at the site received the third highest response rate. The type of use of the site and the amount of use that the site received were also mentioned by several respondees as important items. Several respondents stressed the importance of development of the site after date of public knowledge of the transportation project and its relevance to reasonableness. Question 9 asked the respondents to suggest a methodology to determine reasonableness for the top items they selected in Question 8. These top items and the suggested methodologies were incorporated in the first draft feasible/reasonable decision process as described below.

Reasonableness Matrix First Draft

The results shown in Table 2 and the suggested methodologies from Question 9 were used as a starting point to develop the first Reasonableness Matrix . In addition, fifteen states provided their reasonable/feasible policies for residences. The residence policies of the fifteen states were reviewed and summarized along with the responses to other survey questions. These state policies identified several common themes among states such as barrier cost per benefited receiver. In other cases, some state policies included reasonableness items similar to those needed for the special land use policy. The guidance of existing state and federal policies, the survey responses, and the guidance provided by the FHWA regulations (Code of Federal Regulations part 772; 23CFR772), were used along with the guidance of FDOT and the author's experience to develop the first draft Reasonableness Matrix for special land uses.

The first draft Reasonableness Matrix was designed to include the top criteria items chosen by the DOT survey respondents along with other items that were considered to be important for reasonableness. The decision matrix was designed so that the top items shown in Table 2 were given higher weighting than other matrix items in the decision process. This methodology produced the first draft Feasible/Reasonableness matrix shown in the Figure below. The matrix includes items that are given higher weighting than others such as whether the site is used daily as opposed to weekends only. The final answer was a numeric score. A high positive value represented a very reasonable and feasible project. A score near zero represented a transitional area if abatement was reasonable or feasible. A low negative value showed the abatement not to be reasonable and/or feasible. The matrix was prefaced by several notes to the preparer that provided information on how to complete the matrix and perform the noise analysis for the site. The matrix also included several "FATAL" items that direct the preparer to stop the analysis since abatement is deemed not feasible or unreasonable at mat point. This draft matrix was submitted to the Florida Department of Transportation Noise Task Team for review.

Comments Received on First Draft Reasonableness Matrix

The FDOT Noise Task Team reviewers suggested several useful modifications to the original Reasonableness Matrix. These modifications included better clarification of the barrier cost matrix items and a different method of scoring the matrix responses. Table 3 lists the important review comments from the Noise Task Team.

Table 3. Noise Task Team Review Comments

Noise Task Team Review Comments
Owner's opinion and owner's desires are the same item
Who are the owners in question?
Remove item about traffic volume
Clarify the barrier cost calculation
Replace the dB(A) increase items with dB of insertion loss (IL) values
Revise weighting of weekend vs. weekday use
Date of public knowledge item is weighted too lightly and it addresses two issues, antiquity and local controls
Cost as percentage of total project was considered inappropriate
Percentage of land protected by abatement requires more detail or should be deleted
"cost" of barrier aesthetics is not discernible in a barrier cost since this is an average value

Figure 1. Draft Reasonableness Matrix

*Analysis notes to preparer:

  1. Place receptors only at areas of frequent human use, for example a park bench or pavilion. This excludes areas such as the edge of the property when not used, bar ditches, etc.
  2. Parking lots are not to be considered valid receptors locations.
  3. Complete the matrix to determine if the special land use is reasonable and feasible.
  4. If Reasonableness Matrix score is negative, then abatement is not reasonable and feasible. A positive score indicates that the project may be reasonable and feasible. The degree of the number indicates the degree of strength of the evaluation (i.e., a positive 4 is considered more reasonable and feasible that a value of positive 1). Any FATAL item results in an immediate exit from the matrix and is not considered to be reasonable and/or feasible.

Special Use Facility Reasonable/Feasible Matrix

1 Can abatement provide 5 dB(A) protection for benefited receivers?0FATAL1
2 Is the NAC level approached or exceeded at site?+1 (goto #4)-1 (goto #3)
3 Is the dB(A) increase >10 dB(A)?+1FATAL1
4 Do the owners want abatement? +1FATAL1
5 Does the owner consider abatement to be of substantial benefit?+1FATAL1
6 Is the site a cemetery?FATAL10
7 Does time of use correspond to peak traffic volumes?0see below2
8 3Is barrier cost/receptor hour<$1000+1-1
9 dB(A) Increase < 5 dB(A)-10
10 dB(A) Increase 5 - 10 dB(A)+10
11 dB(A) Increase > 10 dB(A)+10
12 dB(A) Increase > 15 dB(A)+10
13 Is the site used daily?+20
14 Is the site used more than 2 days per week?+1-1
15 Is the site used weekends only?-10
16 Site Developed after date of public knowledge?-10
17 Is barrier cost<=10% of total project cost?40-2
18 Does abatement detract from aesthetics?-1+1
19 Will barrier aesthetics increase cost?-1+1
20 Is the site NAC category A?+20
21 Is the site NAC category B?+10
22 Is the site NAC category C?-100
23 Is the site NAC category D? -120
24 Is the site NAC category E and indoor noise levels are of extreme importance? (i.e., school, church)+20
25 Is percentage of impacted land that can be provided 5 dB(A) of abatement > 10%?+1-1
26 Amount of land exceeding NAC where activity exists > 10%?+1-1
  Site Score (sum all answers unless FATAL item noted)  

1Fatal = Exit Matrix, abatement not reasonable and/or feasible.

2Perform analysis with traffic volume corresponding to time of use for all following questions.

3Calculated by dividing the amount of time for special facility use, on day of use, by abatement cost.

4This applies to Type I projects only.

Development of Methodology

The matrix was revised to address the comments listed in Table 3 as considered appropriate. The draft matrix of Figure 1 attempted to include both feasibility and reasonability issues in the same matrix and present varying degrees of reasonable/feasible by the change of the final answer around zero. This appeared to cause some confusion and for this reason the feasibility items, known as the "FATAL" items were taken out the of matrix and put into a separate flow chart format. The flow chart format provided a visual depiction of the feasibility issues. If certain criteria are not met in the Feasibility Flowchart, such as minimum barrier insertion loss, the flowchart directs the preparer to stop the analysis and declares abatement not feasible. The flowchart and its items are discussed in detail later in this report.

The Feasibility Flowchart also addresses the issue of off peak use of the site and instructs the preparer to subtract a decibel value from the predicted receptor levels if the site is operated during off peak hours. Questions 9-12 of the draft matrix assessed reasonableness based on the noise level increase at the site. This issue is now addressed in the Feasibility Flowchart. Questions 4 and 5 of the draft matrix which addressed opinions and desires of the "owners" of the site are now also addressed in the Feasibility Flowchart as is the date of public knowledge reasonableness item, question 16.

The items included in questions 13-15 evaluated site usage during the week. These questions are included in the Feasibility Flowchart which subtracts a value from the predicted noise level at the receptor if the site is operated primarily during off peak traffic hours.

"Abatement cost factor"

Abatement cost had the highest priority according to the survey when considering reasonableness. The first draft Matrix contained a cost value that included many considerations and concepts such as amount of use at the special facility, size of a barrier necessary to abate the traffic noise and activity areas protected. This led to a cost scheme that takes into account the time that people actually use the site, the areas receiving significant abatement, and equates a cost to the barrier size. The results were development of a special land use "abatement cost factor".

The methodology of determining the "abatement cost factor" uses currently accepted residential abatement cost scenarios and extrapolates that information into a cost for special land use sites. Development of the "abatement cost factor" followed these steps:

  1. Use FDOT accepted barrier cost per residence ($30,000).
  2. Assume residences are used 24 hours/day.
  3. Determine average frontage of a residence (100 ft; 30.5m).
  4. Determine the average height of a barrier (14 ft; 4.3m).
  5. Use the average frontage of a residence and barrier height to determine the area of a hypothetical barrier per residence frontage.
  6. Determine state average number of people per dwelling unit.
  7. Use these data to determine a criteria barrier cost per hour of usage and area of barrier.

The values shown were chosen from current FDOT policy, FDOT guidance, Census data, and the experience of the authors.

The "abatement cost factor" derivation process begins by applying the anticipated FDOT accepted cost of abatement per benefited residence of $30,000 per residence. Next, steps are taken to translate this cost from a residential scenario to one that can be applied to other land uses. The concepts of site usage and the overall size of the barrier are important aspects of whether the barrier is considered reasonable. The "abatement cost factor" derivation quantifies typical residential usage and considers a hypothetical barrier section that would occupy the frontage of a typical residence. Note that this is purely a hypothetical situation and does not imply that this barrier section would provide adequate abatement at the residence, rather it estimates the size of a barrier that would occupy the frontage property of a typical residence.

The typical residential usage and hypothetical barrier size per residence are combined with the FDOT barrier cost per residence to provide a basis for the "abatement cost factor" based on person hours of usage and barrier area. Assumptions were made on input values specific for Florida that may not be sufficient for other states. If better data are available replacement may be made depending on administrative decision. Individual states may also change values to be state specific.

The typical residence usage is derived from 1990 HUD Census data for the state of Florida which reports that the number of persons per residence ranges from 2.18 persons/residence in Pinellas County to 3.00 persons/residence in Baker County and an average of 2.46 persons per residence. This average value of 2.46 persons per residence was used to derive the person-hours of usage for a typical residence. It was assumed that the residences are in use 24 hours per day. It was also assumed that all individuals should receive equal treatment. These data and assumptions lead to the residence usage of 2.46 persons per residence per day and these persons use the residence for 24 hours per day. The FDOT barrier cost per benefited residence is divided by the number of persons per residence per day and the hours of usage per day which gives a preliminary "abatement cost factor" based on hours of usage. This calculation is depicted below in English units.

equation: preliminatry cost factor equals $30k/residence times residence/2.46 person times usage/24 hours equals $508.13 per person hour

Equation (1) provides a preliminary "abatement cost factor" based on hours of usage only. Notice that if this "abatement cost factor" were derived for a special land use site using the hours of usage in Equation (1), a lower "cost factor" occurs as the number of on site usage hours increases. This preliminary "abatement cost factor" varies inversely with hours of usage. The preliminary "abatement cost factor" must be adjusted to account for actual size of the proposed barrier otherwise a barrier of any size will be deemed reasonable as long as the site has high usage.

Barrier size is included in the "abatement cost factor" by first determining the hypothetical size of a barrier that would occupy the frontage of a residence. The assumption is made that a typical residence has 100 feet (30.5 m) of frontage and that an average barrier has a height of 14 feet (4.3 m) in Florida. These two values are used to obtain the surface area of this hypothetical barrier and are then applied to the "abatement cost factor" equation as shown below in English units.

 equation: abatement cost factor equals $30k/residence times residence/2.46 persons times usage/24 hours times (14ft times 100ft) equals $711,382/person-hr/ft2

This further derived "abatement cost factor" contains additional units of square feet (or square meters) and now considers actual barrier size. Once again, this "abatement cost factor" is simply a derivation of a value that can give a comparative measure of cost associated with the proposed abatement. This "abatement cost factor" should not be confused with having any direct relation to real barrier costs such as a dollar value per square foot of a barrier.

At this point we have taken the FDOT barrier cost per residence and translated this cost into a factor that accounts for site usage and actual barrier size. This "criteria abatement cost factor" can now be compared to an "abatement cost factor" derived for special land use sites.

Abatement cost is considered reasonable if the calculated "abatement cost factor" is below the "criteria abatement cost factor" of Equation (2) [$711,382 /person-hr/ft2 or $66,083 /person-hr/m2].

This revised abatement cost criteria combines several related Reasonableness Matrix items in a simplified fashion.

It is important to note that the revised Reasonableness Matrix retains the percentage of land protected by abatement criteria by including only those individuals that receive at least a 5 dB(A) benefit from abatement. This percentage is based on total land use area of the site. Abatement at the site is more reasonable when the protected land area encompasses greater numbers of persons using the site. The section "Receiver Placement for Noise Impact Analysis" contains a detailed explanation of two methods of determining the number of "benefited" receivers.

The revised Reasonableness Matrix has a worksheet format that prompts the user to enter site specific values and perform calculations. The worksheet leads the user to a final reasonableness decision.

Updated: 7/6/2011
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