RETAINING WALL NOISE REFLECTION ANALYSIS · INTRODUCTION A. Purpose of the Analysis ... (Version 2.5) parallel barrier module to develop a cross-section based model of the retaining

I-70/I-71 SOUTH INNERBELT

FRA-70-8.93 PID 77369

SPECIAL REPORT

RETAINING WALL

NOISE REFLECTION

ANALYSIS

February 4, 2010

FRA-70-8.93 PID 77369 I-70/I-71 South Innerbelt

SPECIAL REPORT --- RETAINING WALL NOISE REFLECTION

ms consultants, inc. February 4, 2010 1

1. INTRODUCTION

A. Purpose of the Analysis

The purpose of this analysis was to estimate the potential traffic noise reflections associated with the large

retaining walls included in the preliminary design of the I-70/I-71 South Innerbelt project (See Figure 1).

Traditional traffic noise analysis has been conducted for the project and those results are presented in a

separate series of reports.

B. Description of the Project

In accordance with the National Environmental Policy Act (NEPA) an Environmental Assessment for the

project was prepared in 2008 and on July 10, 2009 the Federal Highway Administration issued a Finding of

No Significant Impact (FONSI) for the project. Additional information on the overall project is available at

www.dot.state.oh.us/projects/7071study. In general, the project will separate motorists traveling through

downtown from those traveling into/out of downtown. Motorists traveling into/out of downtown would use

modified city streets (Urban Arterial Streets) running parallel to the freeway to connect with the downtown

street network. The I-70 and I-71 mainline lanes will be 20’ – 30’ lower than the city streets and lined with

full-height retaining walls in several areas (See Figure 2 and Figure 3).

C. Description of the Project Area

The I-70/I-71 South Innerbelt project area is a montage of dense urban development and redevelopment

including single-family homes, multi-family homes, schools, hospitals, churches, and numerous

commercial structures. There are also numerous sites and districts listed on or eligible for listing on the

National Register of Historic Places in the project area.

2. ANALYSIS OVERVIEW

ODOT’s Standard Procedures for Analysis and Abatement of Highway Traffic Noise dated August 2008,

do not contain procedures for analysis of noise reflections from retaining walls. Therefore, ms

consultants, inc. conducted this analysis using two methodologies:

A. Image Roadways

This approach involved placing a new roadway (image roadway) at the same elevation as the actual source

roadways. The image roadway was offset behind the retaining wall under study by the distance from that

wall to the center of the actual source roadway. The traffic on the image roadway was then reduced by the

Noise Reduction Coefficient (NRC) of the retaining wall surface. For example, if the retaining wall was

covered with sound-absorptive material (NRC 0.80) the traffic on the image roadway was reduced to 20%

of the original source.

This approach resulted in very little (< 1dB) predicted increase in noise levels due to reflected noise.

Moreover, this approach proved very difficult to implement accurately because of the urban arterial streets

running parallel to the freeway mainline.

B. TNM Parallel Barrier module (RayVerb)

This approach involved using FHWA’s Traffic Noise Model (Version 2.5) parallel barrier module to

develop a cross-section based model of the retaining walls. Roadway, retaining wall, and receiver locations

were obtained from TNM models used in the traditional traffic noise analysis and preliminary cross-

sections currently under development. Traffic data was obtained from the Certified Traffic forecasts

developed specifically for the project. This approach provided a more accurate estimate of reflected noise

and the effectiveness of sound-absorptive material.

All analyses in this report are for the design year 2035.




3. ANALYSIS RESULTS

A. South Trench (I-70/I-71) Overlap

This study site near the Grant Avenue overpass includes the Africentric School building located south of

the I-70/71 mainline (See Figure 1). It also included the Livingston Avenue Methodist Church and a

residential dwelling along Livingston Avenue in the German Village historic district. The South Trench

study site also included the Market-Mohawk apartment building north of the I-70/71 mainline directly

across from the Africentric school. This study site was selected as the worst-case location on the south

trench because of the width of the trench and the proximity of sensitive buildings (See Figure 2).

Image Roadways

This approach resulted in a predicted increase of 0.9 dBA and 0.7 dBA at the Livingston Avenue

Church and Africentric School respectively from the “reflective” retaining walls (See Attachment 1).

A noise level change of less than 1 dB would not be perceptible by the normal person in an outdoor

environment. Furthermore, this approach indicated that covering the retaining wall with sound-

absorptive material would result in a predicted increase of 0.3 dBA and 0.2 dBA at the Livingston

Avenue Church and Africentric School respectively. In summary, the image roadway approach

indicated that there would be no difference in noise levels attributed to noise reflected from the

retaining wall and sound-absorptive material on the retaining wall would not change traffic noise

levels.

TNM Parallel Barrier module (RayVerb)

This approach resulted in a predicted increase of 1.1 dBA and 3.5 dBA at the Livingston Avenue

Church and Africentric School respectively from the “reflective” retaining walls (See Attachment 2).

Furthermore, it indicated a predicted increase of 3.5 dBA at the Market-Mohawk apartment building

which is directly across from the Africentric School.

This approach allowed the analysis of covering various portions of the retaining walls with sound-

absorptive material. Covering the top 10 feet, the top 20 feet, and all of the 28 foot high retaining wall

was evaluated. As shown in Table 1 covering all of the retaining walls was the most effective.

Table 1 South Trench

Predicted Increase in Noise Levels dB(A)

Receiver

2035 Noise

Level

Reflective

Wall

Absorptive

Top

Absorptive

Top/Middle

Absorptive

All

Market-Mohawk Apartments 69.8 +3.5 +3.5 +2.0 +1.0

Livingston UM Church 65.3 +1.1 +0.5 +0.2 +0.0

28L (German Village) 70.5 +0.0 +0.0 +0.0 +0.0

Africentric School 75.6 +3.5 +2.7 +2.0 +1.0

While Table 1 shows that covering all of the retaining walls was the most effective way to reduce the

increase in traffic noise due to reflections, it must be noted the sound-absorptive material only reduced

the increase 2.5 dB. Therefore, the effectiveness of the sound-absorptive material would not be

perceptible. Three (3) dB is generally considered the minimum change in outdoor noise levels that a

normal person can detect.




B. East Trench (I-71)

This study site included numerous residential sites both east and west of I-71 in the Near East Side and

Town Street historic districts along with the historic St. Paul AME church (See Figure 1). This study site

was selected as the worst-case location on the east trench because of the width of the trench and the

proximity of sensitive buildings (See Figure 3).

Image Roadways

This approach proved very difficult to implement accurately due to the urban arterial streets running

parallel to both sides of the I-71 trench and could not be used for the East Trench.

TNM Parallel Barrier module (RayVerb)

This approach resulted in a predicted increase of 0.3 dBA and 0.1 dBA at the Belmont Apartments and

St. Paul AME Church respectively from the “reflective” retaining walls (See Attachment 3).

Furthermore, it indicated a predicted increase of 0.0 dBA at the receivers east of the I-71 trench.

This approach allowed the analysis of covering various portions of the retaining walls with sound-

absorptive material. Covering the top 10 feet, the top 20 feet, and all of the 26 foot high retaining wall

was evaluated. As shown in Table 2 covering the retaining walls makes no difference in the noise

level.

Table 2 East Trench

Predicted Increase in Noise Levels dB(A)

Receiver

2035 Noise

Level

Reflective

Wall

Absorptive

Top

Absorptive

Top/Middle

Absorptive

All

Belmont Apartments (R37) 64.1 +0.3 +0.3 +0.3 +0.3

St. Paul AME Church (R48) 64.7 +0.1 +0.0 +0.0 +0.0

R30 (Near East Side) 70.4 +0.0 +0.0 +0.0 +0.0

Therefore, the effectiveness of the sound-absorptive material on the East Trench walls would not be

perceptible. Three (3) dB is generally considered the minimum change in outdoor noise levels that a

normal person can detect.




4. CONCLUSIONS

A. South Trench (I-70/I-71) Overlap

In the South Trench (I-70/I-71 overlap) traffic noise reflected from the retaining walls will increase noise

levels at the closest receivers up to 3.5 dBA. Since three (3) dB is generally considered the minimum

change in outdoor noise levels that a normal person can detect, this increase would be detectable.

In the South Trench, covering all of the retaining walls with sound-absorptive material was found to be the

most effective way to reduce the increase in traffic noise due to reflections. However, since the sound-

absorptive material only reduced the increase 2.5 dB, the reduction would not be perceptible.

Therefore, the installation of sound-absorptive material on the South Trench retaining walls is not

recommended.

B. East Trench (I-71)

In the East Trench (I-71) traffic noise reflected from the retaining walls will increase noise levels at the

closest receivers less than 1.0 dBA. Since, a noise level change of less than 1 dBA would not be

perceptible by the normal person in an outdoor environment this increase would not be detectable.

Therefore, the installation of sound-absorptive material on the East Trench retaining walls is not

necessary or recommended.



ms consultants, inc. February 2010

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Attachment 1

Image Roadway

Analysis




Attachment 2

TNM Parallel Barrier

Analysis

South Trench




Attachment 3

TNM Parallel Barrier

Analysis

East Trench

Documents

RETAINING WALL NOISE REFLECTION ANALYSIS · INTRODUCTION A. Purpose of the Analysis ... (Version 2.5) parallel barrier module to develop a cross-section based model of the retaining