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Construction Noise Handbook

Appendix B: Comparison Of RCNM Model And 1977 FHWA Special Report Manual Calculation Method. B-1

Problem 5 from
Reference 001: 1977 FHWA Special Report - Highway Construction Noise: Measurement, Prediction and Mitigation, Pages 25 and 26

Problem:

The project has now progressed to the point where contractors are bidding on the project. The special provisions require that the exterior L_eq(h) on school grounds be less than 75 dBA during school hours. A long fill is to be constructed adjacent to a school. One prospective contractor would like to use two dozers and three scrapers to construct this fill. The contractor has collected the data presented in Table B.1 on equipment used in previous projects.

Table B.1 Contractor equipment data.

Where:

L_j = Sound level measured using the SAE J88a test procedure.

L_m = Maximum sound level.

L_b = Reduced sound level of the work cycle.

T_a = Time spent at the maximum level (L_m) during the work cycle.

T = Work cycle time.

Compute the noise emission level of the equipment and estimate the L_eq(h) at the school.

Solution:

Step 1: The noise emission levels (E.L). in L_eq(h) at 15.2 m of the equipment is calculated by:

E.L. = L_j + E.F.

Where:

E.F. = Equivalency Factor derived from Table 2 of the 1977 Handbook

The noise emission levels (E.L.) are shown in Table B.2.

Table B.2 Equipment noise emission levels.

Step 2: Assign an average location to each piece of equipment. This is shown in Figure B.1.

Step 3: Compute the L_eq(h) for each piece of equipment using Equation 3-1 (Page 19 of Reference 001) and the overall construction noise level using Equation 3-2 (Page 19 of Reference 001).

Equation 3.1: L_eq equipment = E.L. + 10 log U.F. - k log D/D₀

Where:

L_eq equipment = A-weighted, equivalent sound level at a receptor resulting from the operation of a single piece of equipment over some time period.

E.L. = Noise emission level of the particular piece of equipment based on its work cycle.

K = Constant that accounts for topography and geometric spreading.

D = Distance from the receptor to the piece of equipment.

D₀ = Reference distance at which the noise level was measured for the piece of equipment = 15.2 meters.

U.F. = Usage factor that accounts for the percent time that the equipment is in use over the time period.

n

Equation 3.2: L_eq(h) site = 10 log Σ 10 ^{Leq (equipment)/10}

i =1

Where:

L_eq (equipment) = (E.L. - 20 log D/D₀) equipment.

Leq(h) site = One-hour, A-weighted, overall equivalent construction noise sound level obtained by summing the individual equipment noise levels on an energy basis.

N= Number of pieces of equipment included in the summation.

Figure B.1 Construction Site

The results are shown in Table B.3. The construction L_eq(h) of 80 dBA exceeds the specified goal by 5 dBA.

Table B.3 Results from Manual Calculation Method.

The 80 dBA value in the sixth column was obtained by dB addition. The value could also have been determined by:

L_eq(h) site = SUM L_eq(h) equipment

= 10 log (10^6.1 + 10^7.9+ 10^6.1 + 10^6.7 + 10^6.7)

= 80 dBA

RCNM Results

Roadway Construction Noise Model (RCNM), Version 1.0

Report Date: 01/19/2006

Case Description: 1977 Handbook Problem Number 5 (from page 26)

Table B.4 Receptor #1 data.

Table B.5 Results from RCNM Run (Daytime).