final report for fhwa work order no. dtfh71 ......final report for fhwa work order no....
TRANSCRIPT
FINAL REPORT
FOR
FHWA WORK ORDER NO. DTFH71-83-3610-IA-12
Ef fec t iveness o f P a r a l l e l Noise B a r r i e r s
An Iowa Study
Ron Ridnour and Dale Vander Schaaf
5151239-1613
O f f i c e o f P r o j e c t Planning
Planning and Research D i v i s i o n
Iowa Department o f Transpor ta t ion
Ames, Iowa 50010
August 1987
SPONSORSHIP This report is based on work conducted by the lowa Department of Transportation and the Federal Highway Administration. This research project was funded through the Demonstration Projects Program of the U.S. Department of Transpor- tation. Federal Highway Administration
DISCLAIMER The contents of this report reflect the views of the author and do not necessarily reflect the official views of the lowa Department of Transportation or Federal Highway Administration. This report does not constitute a standard, specification or regulation.
ABSTRACT
Traf f ic noise monitoring using FHWA's Demonstration Projects Division
Mobile Noise Laboratory a t f r e e f i e l d , s ingle wall and para1 le l bar r ie r
s i t e on 1-380 i n Evansdale, Iowa i s described. Access t o 1-380 pr ior t o
i t s being open t o t r a f f i c afforded a controlled pass-by monitoring phase
involving d i f fe ren t vehicle types. A subsequent second phase entailed
identical measurement methodology t o monitor "real world" 1-380 t r a f f i c
noise. Phase I data indicated increases i n noise were s ign i f ican t under
the paral le l bar r ie r conditions fo r l i g h t duty vehicles operating in the
f a r lane. Phase I1 r e su l t s showed t h a t the actual 1-380 t r a f f i c mix
largely o f f s e t the e a r l i e r observed e f fec t , but minor increases in t r a f f i c
noise under the paral le l system were noted. These differences i n noise
bar r ie r system effectiveness a re judged t o be ins ignif icant a t t h i s par t i -
cular study location.
Effec t iveness of P a r a l l e l Noise B a r r i e r s - An Iowa Study
INTRODUCTION
The Iowa Department of Transpor ta t ion (Iowa DOT) is one of a number of
s t a t e highway agencies (SHA) which have cons t ruc ted p a r a l l e l no i se
b a r r i e r s . I n t h e f a l l of 1982, 2600 f e e t of p a r a l l e l s t e e l no i se b a r r i e r s
were cons t ruc ted adjacent t o I n t e r s t a t e 380 i n t h e City of Evansdale, Iowa.
It was determined dur ing t h e i n i t i a l no i se impact a n a l y s i s f o r t h i s p r o j e c t
t h a t some type of p a r a l l e l noise b a r r i e r s would have t o be cons t ruc ted .
The pre l iminary b a r r i e r des ign concept c a l l e d f o r t h e cons t ruc t ion of an
ear then b a r r i e r on one s i d e of t h e highway and a s o l i d wa l l on t h e oppos i te
s ide . It was f e l t t h a t t h e berm would not only reduce b a r r i e r c o s t s , but
v i r t u a l l y e l imina te any problems due t o r e f l e c t e d noise. However, because
of r e s t r i c t e d a v a i l a b l e r i g h t of way and o t h e r highway design
cons idera t ions t h e berm and wa l l concept had t o be el iminated i n the f i n a l
design. Using t h e b e s t p r e d i c t i o n models a v a i l a b l e a t t h e time (2,3), i t
was concluded t h a t a l though t h e i n s e r t i o n l o s s may not be a s h igh i f t h e
p a r a l l e l wa l l s were b u i l t , i n s t e a d of the o r i g i n a l berm and w a l l concept,
t h e e f f e c t i v e i n s e r t i o n l o s s would s t i l l be s i g n i f i c a n t enough t o be of
b e n e f i t t o t h e impacted r ece ive r s .
It was during t h e development of t h e 1-380 no i se b a r r i e r p r o j e c t t h a t
t h e Iowa DOT no i se a n a l y s i s s t a f f f i r s t became aware of t h e d i f f i c u l t i e s i n
analyzing t h e e f f e c t i v e n e s s of p a r a l l e l b a r r i e r s . Unlike f o r t h e s i n g l e
b a r r i e r a n a l y s i s , t h e r e were no computerized p red ic t ion models a v a i l a b l e
f o r p a r a l l e l b a r r i e r ana lys i s . The Federal Highway Administrat ion (FHWA)
had provided t h e SHA's with a simple " p a r a l l e l b a r r i e r nomograph" (3) f o r
t h e a n a l y s i s of p a r a l l e l b a r r i e r s . Because the s t a f f was not t o t a l l y
confident i n t h e r e s u l t s of a simple nomograph p red ic t ion , a l i t e r a t u r e
search was made for data related to parallel barrier analysis. It was
discovered that although most noise abatement specialists concede that some
reduction in the insertion loss does occur when parallel barriers are
built, there is no consensus over just how significant the reduction could
be. Most of the data relating to the degradation problem is based on
theoretical acoustical analysis or scale model studies. Many of the
"laboratory" studies show that the effective insertion loss of one barrier
can be significantly reduced or even eliminated by the presence of an
opposite parallel barrier (4,5,6). At the same time the limited number of
full scale field measurements which have been made (5,6,8) have provided no
clear cut data which can be used to predict the potential reduction in the
insertion loss when parallel barriers are built.
In early 1983 the Iowa DOT received copies of two papers (1,7) which
not only provided much needed information on the subject of parallel noise
barriers, but also rekindled the noise analysis staff's concern over just
how effective the recently completed 1-380 parallel barriers would be. The
Bowlby and Cohn paper (1) described the development of an algorithm and a
computer program called IMAGE-3 for the analysis and design of parallel
barriers. This paper emphasized however, that although models which are
developed for analyzing the effectiveness of parallel barriers may be
mathematically and acoustically sound, few if any, well documented field
validation studies have been performed.
Because the Iowa DOT is always interested in the performance of any
noise barriers constructed along Iowa highways "before" and "after" noise
level data is often obtained for analysis. This data is used to not only
determine overall barrier performance, but to also test the accuracy of the
model used to predict barrier effectiveness. Although no formal study was
originally being proposed, the noise analysis staff was preparing to
! I undertake a more extensive than normal noise monitoring effort after 1-380 I I
was opened to traffic.
In August, 1983, noise analysis staff members attended the annual
summer meeting of the Transportation Research Board's (TRB) Transportation I
! Noise Committee in Boston, Massachusetts. Although no formal discussions
were held concerning the problem of parallel noise barriers during the 1 course of the meeting, it was learned that there has still been very little
field data collected in the vicinity of parallel barriers. The FHWA
personne'l present at the meeting made it known that the FHWA was concerned
about the parallel barrier reflection problem and were in the process of I
funding some experimental field work in this area. Upon hearing of the
increased involvement of the FHWA, Iowa DOT staff inquired as to the
possibility of having the FHWA provide support in obtaining noise data
along the 1-380 parallel barrier segment. The FHWA indicated that
assistance for this type of work was available.
Shortly after returning from Boston, the noise analysis staff
submitted a Research Work Plan (Appendix A) to the FHWA for the proposed
1-380 barrier study. Acting expeditiously, the FHWA approved the work plan
in September 1983.
The following interim report describes the procedures used in the
initial controlled passby phase of the project and discusses the noise data
collected.
11. COORDINATION WITH THE FEDERAL HIGHWAY ADMINISTRATION
The work plan submitted to the FHWA Iowa Division office described a
two-phase study at the 1-380 site in Evansdale. The first phase would
entail noise measurements from controlled vehicle passbys at each of three
barrier conditions - free field (no barrier), single wall and parallel
walls. A second phase to be undertaken after the highway is open to
traffic would collect noise data from the normal traffic mix at the same
three locations.
Federal Highway Administration participation was to consist of
providing the Demonstration Projects Division's noise analysis trailer
along with a technician and a project manager to oversee the use of the
FHWA equipment. A $10,000 grant was requested to be administered through
The Demonstration Projects Division to cover costs incurred by the State.
A preliminary report was to be prepared by the State upon completion
of the first phase of the study and a final report was to be prepared upon
completion of the phase two monitoring.
Provisions were also agreed upon to provide the study site details and
noise measurement data to Vanderbilt University for application of the
IMAGE-3 parallel barrier model.
111. STUDY SITES
The t h r e e b a r r i e r condi t ions a r e loca ted i n a s i n g l e mile-long s e c t i o n
of 1-380 a s shown on Figure 1 and i n t h e fol lowing photos:
1) The f r e e f i e l d site was an open f i e l d loca t ion wi th no major
obs t ruc t ions (Figure 2)
2) The s i n g l e w a l l s i t e was a state-owned p a r c e l l y ing between
t h e highway right-of-way and r e s i d e n t i a l land use.
(Figure 3)
3) The p a r a l l e l wa l l s i t e was t h e midpoint of t h e p a r a l l e l wa l l
s e c t i o n of 1-380 i n an e s t ab l i shed r e s i d e n t i a l a r e a (Figures
4 and 5)
Remote Microphones from t h e FHWA Demo P r o j e c t s no i se a n a l y s i s system
were pos i t ioned a t t h e following loca t ions :
Free F ie ld
1. 40' From c e n t e r l i n e N.L. (Near Lane) 5' above roadway 2. 40' From c e n t e r l i n e N.L. 15' above roadway 3. 90' From c e n t e r l i n e N.L. 10' above roadway 4. 90' From c e n t e r l i n e N.L. same e l e v a t i o n a s roadway 5. 140' From c e n t e r l i n e N.L. 5' above ground, same e l e v a t i o n a s
roadway 6. 190' From c e n t e r l i n e N.L. 5' above ground, same e l eva t ion a s
roadway 7 . I n Middle of median 50' from c e n t e r l i n e of each f a r lane , 5 ' above
roadway
Figure 1. Study s i t e locations
Single wall Parallel walls s i t e s i t e Free field s i t e
Figure 2. Free f ield studv s i t e
Figure 3. Sing1 e wal l study s i t e
Figure 4. Parallel walls study site
Single Bar r i e r
40' From c e n t e r l i n e N.L. 1' Behind wa l l , 5 ' above roadway 40' From c e n t e r l i n e N.L. 1' Behind w a l l , 5' above top of w a l l , 17' above roadway 90' From c e n t e r l i n e N.L. 15' above roadway 90' From c e n t e r l i n e N.L. 6' above roadway 140' From c e n t e r l i n e N.L. 5' above ground, 5' below roadway 190' From c e n t e r l i n e N.L. 5' above ground, 5 ' below roadway 240' From c e n t e r l i n e N.L. 5' above ground, 5 ' below roadway I n Middle of median 50' from c e n t e r l i n e of each f a r l ane , 5' above roadway
P a r a l l e l Barriers
40' From c e n t e r l i n e N.L. 1' behind wa l l , 5 ' above roadway 40' From c e n t e r l i n e N.L. 1' behind w a l l , 5' above top of wa l l , 17' above roadway 90' From c e n t e r l i n e N.L. 15' above roadway 90' From c e n t e r l i n e N.L. 6' above roadway 140' From c e n t e r l i n e N.L. 5' above ground, 3' below roadway e l e v a t i o n 190' From c e n t e r l i n e N.L. 5' above ground, 3' below roadway e l eva t ion 240' From c e n t e r l i n e N.L. 5' above ground, 3' below roadway e l e v a t i o n 290' From c e n t e r l i n e N.L. 5' above ground. I ' below roadway e l e v a t i o n I n Middle of median, 5 ' above roadway On south s i d e of south b a r r i e r 140' From c e n t e r l i n e N.L. 5' above ground, 3' below roadway
Addi t ional ly , a n independent microphone was loca ted on t h e highway
c e n t e r l i n e i n t h e median a t a he ight of 5 f e e t above the roadways. The
c r o s s s e c t i o n s of t h e monitoring sites and microphone l o c a t i o n s a r e shown
on Figures 6 and 7. A l l s i t e s a r e considered "soft" with low growing
g ras ses being t h e primary ground cover.
IV. EQUIPMENT AND CONDITIONS
Five vehicle types were used as controlled noise sources:
1. 1971 International truck tractor, 6 cylinder diesel, 270
horsepower, 855 cubic inch, Fuller 13-speed transmission, pulling
trailer carrying JD 450 dozer weighing 8 tons. Total Loaded
Weight 48,000 lbs. (Figure 8)
2. 1981 Ford LT8000 tandem axle, 8 cylinder diesel, 210 horsepower,
Caterpiller 3208 engine, Fuller R66-13 transmission (13-speed).
Total Loaded Weight 52,000 lbs. (Figure 9) -
3. 1975 Ford F700 two axle, 8 cylinder gas, 5-speed Clark
transmission. Total Loaded Weight 28,000 lbs. (Figure 10)
4. 1980 Ford F150 % ton pickup, 6 cylinder gas, 300 cubic inch
engine, automatic transmission. Carried No Load. (Figure 11)
5. 1981 Chevrolet Impala Station Wagon, 8 cylinder gas, 267 cubic
inch engine, automatic transmission.
The tandem axle and two axle trucks were equipped with Firestone Super
All Traction tires on the rear axles. These have a cross bar type of tread
design. (Figure 12) The semi tractor had Goodyear Super High Miler tires
on the rear which are also cross bar type. The remainder of the test
vehicle tires were of a conventional rib design. (Figure 13) The vehicle
drivers were instructed to cruise past the microphone site in normal
open-road gear at a steady speed of 50-60 mph. Actual passby speeds were
measured with a portable radar gun.
Figure 9. Tandem a x l e t ruck 1
Fisure 10. Two a x l e truck
Figure 11. Pickup truck
Figure 12. Cross bar type tread
I Figure 13. Rib desiqn tread i
Noise measurement equipment was provided by the FHWA Demonstration
Projects Division's Noise trailer. General Radio $ inch microphones were
connected to the Hewlitt-Packard data analysis system. A BBN Model 614
noise analyzer was located in the median and set on the threshold mode to
record peak noise levels for each passby. A sample of 70 seconds duration
was collected at each of the remote microphones during each passby.
Favorable meteorological conditions were noted for each test period:
free field - 0% cloud cover, wind 0-5 mph from the south humidity
50-60%, temperature 64-68 F.
single wall - 0% cloud cover, wind 3-8 mph from the southeast,
humidity 40-45%, temperature 60-65 F .
parallel walls - 100% cloud cover, wind 0-5 mph from the south,
humidity 45-50%, temperature 55-60 F.
Pavement conditions were dry for all passbys. Pavement texture was
118 inch transverse grooves at 518 - 16 inch spacing. (Figure 1 4 )
V. PROCEDURE
I Test vehicle passby sequencing was maintained through hand-held radio
contact with one of the vehicle drivers w h then would instruct the other I
I
vehicle drivers to begin their runs. The radios also permitted contact
between the roadside test area and the noise analysis trailer. Personnel 1 in the trailer were alerted at the beginning of each passby so that the 1
I passby noise curve would be included within the 70-second monitoring period
required by the computer. The roadside "coordinator" also measured passby 1
speed with the battery powered radar gun and made a notation of the
specific passby description on the BBN printout tape. In the trailer hard 1 1
copies of the Leq and Ln values measured at each microphone were printed.
Additionally a frequency analysis printout was prepared for microphone 1 number 6 located 190 feet from near lane (150 feet from wall) at each test
I site. The four truck types were used at all three sites. The automobile
was used at the free field site and the single wall site but was eliminated I 1
from the test during the parallel wall portion of the study. It was
observed that the automobile passby data were nearly identical to that of I I
the pickup and it was decided that the time spent at the parallel site
could be better used obtaining data from the other vehicle types.
VI. DATA OBSERVATIONS
A total of 102 vehicle passbys were recorded and were broken down as
follows: 28 free field passbys, 35 single barrier passbys, and 39 parallel
barrier passbys. The Leq and L1 values measured at each microphone are
shown on Tables 1, 2, and 3. After a preliminary review of the passby
data, the initial single barrier passhy was eliminated. As can be seen on
Table 2, although values were recorded for the initial passby, they were
much lower than would have normally occurred with a tandem axle truck
passby. In addition the underlined values shown on Table 3 were also
considered invalid. The occasional traffic on a nearby street influenced
the noise levels at these microphones to a greater degree than was
originally expected. The remaining data is summarized by the mean values
shown on Table 4, 5 and 6. These data represent noise levels at the
microphones located 100 feet and 150 feet from the wall and also at the
reference microphone and the median microphones respectively.
Upon reduction and review of the noise data definite trends could be
identified; however the limited number of passbys and the variance in
individual passby speeds and noise levels make the value of a larger data
base clear. From the data collected the following observations were made:
1. Noise data from all microphones show a tendency towards increased
noise levels under the parallel wall condition as compared to the
single wall.
2. This tendency for higher noise levels with parallel walls is
generally more apparent in the far lane passbys than the near
lane passbys with this tendency very obvious at the reference
microphone (Mic. 2) location.
Ta
ble
1.
Ve
hic
le
pa
ssb
y
da
ta-f
ree
fi
eld
F
ree
Fie
ld S
ite
T-T
Tra
cto
r T
rail
er.
T-
A
Tan
dem
A
xle
, 2-
A
Two
Ax
le 6
-Tir
e P -
Pic
ku
p,
A -
Au
to,
Wes
t=N
ear
Lan
e,
Eas
t=F
ar L
ane
Pas
sby
V
eh
icle
D
ire
cti
on
T
IME
SP
EE
B
Mic
.1
Mic
.2
Mic
.3
Mic
.4
Mic
.5
Mic
.6
mc
.7
Mic
.8
lied
fan
S
o.
Wal
l .. no.
Typ
e P
assb
y
MPH
L
eq
L1
Leq
L
l L
eq
L1
Leq
L1
Leq
L
1
Leq
L1
Leq
L
1 L
eq
L1
Leq
L
max
M
ic.
Lm
ax
0-1
T-T
0-2
T-T
0-2
T- A
0-2
2-A
0-2
P
0-3
T-A
0-3
2-A
0-4
T-A
N
0-4
2-A
0
0-4
P
0-4
A
0-5
T-T
0-5
T- A
0-5
2-A
0-6
T-A
0-6
2-A
Wes
t
Ea
st
Ea
st
Ea
st
Ea
st
wes
t
Wes
t
Ea
st
Ea
st
Ea
st
Fa
st
Wes
t
wes
t
wes
t
Ea
st
Ea
st
h .o Vi VI **--c--mmmmm ~~~IIIMIIIIII PZOOOOOOOOUOOO
Tab
le
3.
Veh
icle
p
ass
by
Passby
Vehicle
- Direction
KO.
Type
Passby
*2-1
T-
A
West
2-1
2-A
2-1
P
2-2
T-T
2-2
T-A
2-2
2-A
2-2
P
2-3
T-T
2-3
T-A
2-3
2-A
2-4
T-T
N
f-
2-4
T-A
2-4
2-A
2-4
P
2- 5
T-
T
2-5
T-A
2-5
2-A
2-5
P
2-6
T-T
West
West
East
East
East
East
West
West
West
East
East
East
East
West
West
West
West
East
da
ta-p
ara
llel
b
arrie
rs
Parallel Barrier Site
TIME
SPEED
Mic.1
Mic.2
Mic.3
Mic.4
Mic.5
Mic.6
Mic.7
Mic.8
Median
So.
Wall
Leq Ll
Leq L1
Leq L1
Leq L1
Leq L1
Leq L1
Leq L1
Leq L1
Leq Lmax Mic.
Lmax
13:Z
O
55
57 62
69
78
61
68
57
63
56
62
56
61
57
66 -
62 -
75
76
83
63
*Underlined Values Affected By Extraneous Noise Source
Ta
ble
Passby NO.
2-6
2-6
2-6
2-7
2-7
2-8
2-8
2-8
Vehicle Direction
Type Passby
T-A East
2-A East
P East
T-A West
P
West
T-T East
T-A EasC
2-A East
P
East
T-T West
T-A West
2-A West
P
West
T-T East
T-T West
2-8 West
T-T East
T-T West
2-A West
P West
TIHE SPEED
Mic. 1 Leq
L1
56 62
59 67
53 59
69 78
53 62
56 63
56 67
60 68
50 55
60 71
68 77
62 72
56 64
58 68
62 72
62 72
56 63
59 69
63 73
53 65
uic. 2
Leq L1
66 78
71 81
59 69
73 85
63 76
68 78
68 81
71 81
58 69
72 87
73 87
72 89
69 78
70 81
71 87
74 88
68 79
73 88
75 89
63 77
Mic. 3
Leq L1
59 70
63 71
53 60
62 73
54 62
60 68
60 71
63 71
51 59
60 71
63 75
59 70
60 68
62 71
62 71
61 70
60 69
60 69
62 71
55 68
Mic.4 Leq
L1
55 64
59 66
51 57
58 68
52 61
56 63
56 66
60 68
49 54
58 69
59 68
56 65
55 63
57 67
59 66
57 65
55 62
56 64
58 67
53 66
Mic.5 Leq
L1
53 60
56 63
50 57
55 64
52 64
55 64
53 59
58 68
48 53
56 67
55 64
53 61
53 59
55 62
57 65
54 62
53 59
54 61
56 64
53 66
Mic.6 Leq
L1
54 60
55 61
51 57
54 63
55 56
57 67
-
53 59
60 73
--
50 55
60 2
-
55 63
52 59
54 59
58 8
-
60
-
54 60
53 59
54 61
55 61
53 63
Mic. 7
Leq L1
57 66
-
56 63
52 59
55 5
-
60 72
-
61 2
-
53 61
64
-
53 58
63 2
-
55 64
53 59
56 63
60 8
-
65 -
54 60
53 59
55 63
57 63
53 60
MiC.8 Leq
L1
63 14
-
60 72
-
56 59
59 2
-
67 -
67 81
-
58 7
-
72 86
-
60 7
-
68 80
-
58 68
-
56 61
62 72
-
66 2
-
70 83
-
56 60
56 60
58 65
-
62 13 -
55 58
Xedian Leq
Lmax
75 82
78 86
71 74
77 86
71 74
77 83
76 83
77 86
72 75
77 84
77 87
77 86
71 74
78 85
79 86
78 86
77 83
77 84
78 86
71 74
So. Wall
Mic. Lm
ax
62
65
-- 64
-- 63
62
65
-- 62
65
64
-- 65
- -- 63
64
64
-
Tab
le
4.
Mea
n p
ass
by
no
ise
da
ta
1-3
80
Ev
an
sdale
Pa
rall
el
Ba
rrie
r S
tud
y
- T
yp
ica
l H
ouse
S
et-B
ack
D
ista
nc
e
Mic
rop
ho
ne
No.
5
100 F
ee
t F
rom
W
all
Mea
n P
assb
y
ve
hic
le s
pee
d a
nd
L
eq
I.
Wes
tbound
Ve
hic
le
Mea
n F
ree
M
ean
Sin
gle
M
ean
Pa
rall
el
(Nea
r L
ane)
T
ype
Spe
ed
Fie
ld
Sp
eed
-
Wal
l Spe
ed
Wal
ls
Mea
n P
assb
y
L1
Fre
e
Sin
gle
P
ara
lle
l F
ield
W
all
Wal
ls
11.
Eas
tbo
un
d
TT
60m
ph
59dB
A
54m
ph
53dB
A
56m
ph
55dB
A
70dB
A
58dB
A
6ldB
A
(Fa
r L
ane)
T A
5l
mph
59
dBA
49
mph
55
dBA
5l
mph
54
dBA
69
dBA
6l
dBA
60
dBA
Tab
le 5. M
ean p
assby
no
ise d
ata
1-380 E
van
sdale - P
ara
llel B
arrie
r S
tud
y
No
ise Le
ve
ls At T
yp
ica
l House
Set-B
ack D
istan
ce
Micro
ph
on
e No.
6 150 F
ee
t From W
all
I. W
estbound (N
ear Lan
e)
11. E
astbo
un
d
(Far L
ane)
Mean
Passb
y v
eh
icle
speed
and L
eq
Ve
hic
le
Mean
Fre
e
Mean
Sin
gle
M
ean P
ara
llel
Type
Fie
ld
Sp
eed
Speed
Wall
Speed
Walls
Mean
Passb
y L
1
Fre
e
Sin
gle
P
ara
llel
Fie
ld
Wall
Wall
Tab
le
6.
Mea
n p
ass
by
no
ise
da
ta
1-3
80
Ev
ansd
ale
Pa
rall
el
Ba
rrie
r S
tud
y
No
ise
Lev
els
A
t R
efe
ren
ce
Mic
rop
ho
ne
(Mic
.2)
And
A
t T
he M
edia
n M
icro
ph
on
e
Mea
n P
assb
y v
eh
icle
sp
eed
an
d
L1
Re
fere
nc
e M
icro
ph
on
e M
ean
Pas
sby
L
Med
ian ~
ic
ro
~%
$e
Ve
hic
le
Mea
n F
ree
M
ean
Sin
gle
M
ean
Pa
rall
el
Fre
e
Sin
gle
P
ara
lle
l I.
W
estb
ound
Type
Spee
d
Fie
ld
Sp
eed
W
all
Spe
ed
Wal
ls
Fie
ld
Wal
l W
alls
(N
ear
Lan
e)
TT
55m
ph
85dB
A
58m
ph
86dB
A
59m
ph
87dB
A
84dB
A
85dB
A
85dB
A
11.
Eas
tbo
un
d
TT
60m
ph
79dB
A
54m
ph
75dB
A
56m
ph
79dB
A
87dB
A
8ldB
A
84dB
A
(Far
Lan
e)
T A
5lm
ph
78dB
A
49m
ph
76dB
A
5lm
ph
8ldB
A
82dB
A
82dB
A
84dB
A
2A
5lm
ph
77dB
A
50m
ph
77dB
A
53m
ph
8ldB
A
83dB
A
84dB
A
86dB
A
3. The parallel barrier effect is generally more identifiable in the
higher frequency noise sources such as the pickup truck and in
the higher frequency components of the other noise source
vehicles.
4. Increases in passby noise levels from the single wall to the
parallel wall condition are generally in the 1-3 dBA range but
range up to 6dBA for the far lane pickup passby. This
observation is based on mean L1 values at microphone 6 which
represents the typical house setback distance.
VII. PHASE TWO RESEARCH
Measurements which will be taken at the same locations under normal
traffic conditions should reveal the extent to which reflected noise
actually reduces barrier effectiveness at the parallel walls. It will be
interesting to observe whether or not far lane noise in combination with
the near lane source causes comparable reductions in insertion loss.
Additionally we may be able to identify varying degrees of multiple
reflections depending on the percentage of automobile and other light duty
vehicles in the "real world" conditions. It might be expected, for
example, that 100% autos and other high frequency noise sources may result
in a significant reduction in insertion loss. This phenomenon would have
noteworthy implications in larger metropolitan areas where high automobile
volumes constitute the major traffic noise source.
V I I I . Phase Two Methods
The microphone loca t ions used i n the con t ro l l ed pass-by p o r t i o n o f
the study were rep l i ca ted a t each f i e l d s i t e t o measure actual 1-380
t r a f f i c no ise i n the f a l l o f 1985. This moni tor ing work was accom-
p l i shed w i t h the assistance o f s t a f f members from FHWA's O f f i c e o f
Environmental Po l i cy i n Washington, D.C. I t i s f e l t t h a t s u f f i c i e n t
data were co l l ec ted dur ing t h i s i n i t i a l " rea l world" sampling e f f o r t
t o character ize the ef fect iveness of the s ing le and p a r a l l e l b a r r i e r
systems under study. More extensive moni tor ing a c t i v i t y was
prevented by computer system mal funct ion i n the noise laboratory,
d i f f i c u l t y i n scheduling fol low-up monitor ing, and a reduct ion i n
Iowa DOT s t a f f i n g . The data reduced and reported here w i l l complete
the contractual study.
I X . Phase Two Results
The data co l l ec ted from actual 1-380 t r a f f i c can be analyzed from
three perspectives:
1) The three f i e l d s i t e s can be compared using noise data
co l l ec ted dur ing periods o f s i m i l a r t r a f f i c condit ions.
2) The s ing le and p a r a l l e l wa l l cond i t ions can be analyzed using
simultaneous and continuous moni tor ing o f hour ly noise l e v e l s
a t a given distance from each b a r r i e r system type.
3) The three f i e l d s i t es can be compared based on the frequency
spectra obtained dur ing sampling periods o f s i m i l a r t r a f f i c
condi t ions and comparable ove ra l l t r a f f i c noise levels .
Table 7. Mean Leq a t Each Microphone Pos i t ion
Mean Leq, dBA
Number of Microphone Pos i t ion
S i t e - Samples 40' h igh 40' low 90' High 90' Low 140' Low 190' Low
Free F i e l d 6 72.7 72.4 68.2 65.3 62.4 58.6
Single Wall 20 73.2 58.7 63.1 56.9 57.1 55.7
Para1 1 e l Wall s 17 73.2 58.9 62.2 58.9 56.4 55.1
A t the f r e e f i e l d s i t e s i x 15-minute samples were taken, a l l dur ing
mid t o l a t e morning off-peak hours. A t o t a l o f twenty 15-minute
samples were taken a t the s ing le wa l l s i t e and seventeen 15-minute
samples were obtained a t the p a r a l l e l wal ls s i t e . The mean Leq
computed f o r each'microphone loca t i on a t each f i e l d s i t e i s shown i n
Table 7. These data show a f a i r consistency between the s ing le wa l l
s i t e and the p a r a l l e l wal ls s i t e a t distances near the wal l and a lso
a t the more remote distances. However, a t the 90' low microphone
the noise l e v e l averages 2 dBA higher a t the p a r a l l e l wa l ls s i t e .
This would suggest t h a t mu1 t i p l e r e f l e c t i o n s might be in f luenc ing an
intermediate zone on the res iden t i a l s ide o f the p a r a l l e l wal ls . To
f u r t h e r examine t h i s mu1 t i p l e microphone data, i nd i v idua l sampling
periods w i t h s i m i l a r t r a f f i c condi t ions and reference mike
(40' high) noise levels were selected. Table 8 presents this I
comparison for off-peak traffic conditions. Again residential side I
noise levels are lower at the parallel site except at the 90' low I
location which indicates a tendency toward reduced barrier I
effectiveness in this intermediate zone, possibly due to mu1 tiple I ! ,
reflections. A similar tendency can be identified during peak hour
sampl ing, but unfortunately no corroborative traffic counts were I I
obtained during the periods which best demonstrated this effect. I
Additionally, continuous hourly samples were obtained simultaneously I I
at both the single and parallel sites at a distance of 100 feet from
the wall. Seventy-two such parallel samples were collected using a 1 I
BBN 614 Community Noise Analyzer and a Digital Acoustics Community
Noise Analyzer. For a typical hour the parallel walls site was I 1
0.7 dBA higher than the Leq measured 100 feet from the single wall. I
Nine hours of data were collected at the distance of 50 feet from I
the wall (which corresponds to the 90' from near lane low microphone I location discussed previously). The para1 lel site averaged 1.5 dBA 1
higher than the single wall site at this distance. These data also 1 I
support a finding of some reduction in barrier effectiveness under I
the para1 lel walls condition. 1 I
A frequency spectrum histogram for a selected microphone location 1 was obtained during each 15-minute monitoring period. Most of the I
I
frequency information was from the microphones near the noise wall I
(24 of 42 periods) and no significant differences could be identi- I I
fied at these locations among the frequency spectra printouts from
Table 8.
Com
parison of T
hree Field S
ites Under
Sim
ilar Traffic C
onditions
Traffic
Leq,
dBA
Autos - MT - HT
Microphone D
istance, P
ositio
n
Site
-
Date -
Time -
WB EB
40' H
igh 40'
Low 90'
High
90' Low
140' Low
190' Low
Free F
ield 11/8/85
11:05-11:20 40-2-11
57-1-10 73.9
73.1 69.2
66.4 63.4
59.4
Single W
all 11/5/85
1:50-2:05 50-2-8
61-0-6 72.0
58.1 64.4
55.6 57.7
56.7
Parallel W
all s 11/6/85
1:20-1:35 61-1-3
64-2-7 72.1
58.2 61.6
58.4 55.4
54.2 W
the three f ie ld study s i t e s . Frequency breakdown information from a
limited number of other microphone locations also proved t o be
inconclusive in attempting to compare the single wall against the
parallel wall si tuation. Lack of frequency component data from the
intermediate receiver zone identified previously can be considered
an oversight of t h i s research e f for t . Further longer term research
in t h i s subject area might serve t o smooth out t r a f f i c and meteoro-
logical variations and focus more directly on the frequency spectra
aspects of the parallel walls condition.
X. Summary and Conclusion
Both controlled pass-by and "real world" t r a f f i c noise was measured,
characterized, and interpreted in an e f for t to assess the acoustical
effectiveness differences between a single noise wall and parallel
noise walls on 1-380 in Evansdale, Iowa. Both phases of the study
resulted i n data which suggests minor reduction in noise wall
effectiveness as a resul t of mu1 t i p l e reflections within the paral - l e l barrier canyon. More extensive monitoring would serve t o remove
the influence of minor meteorological and t r a f f i c mix variations
which have probable b u t limited influence on th i s short-term study.
From a practical standpoint, the study suggests t h a t the degree t o
which barrier effectiveness i s compromised by the paral l e l si tuation
in t h i s part icular noise abatement system i s insignificant. The
steel barrier material and configuration, the s i t e geometrics
including barrier height and interbarrier distance, the use of
earthen berms and the transverse groove surface texturing a l l no
doubt influence the resul t ing t r a f f i c noise leve ls w i t h i n the study area.
I t would appear from this experience t ha t a s ign i f ican t influence of a
paral le l wall s i tua t ion would require very high walls of very re f lec t ive
material , a r e l a t i ve ly small in te rbar r ie r distance, and a higher proportion
of peak noise of the high frequency type being generated a t the
tirelroadway interface.
References i
1. Bowlby, W., and Cohn, L.F. "IMAGE-3: Computer Aided Design For
Parallel Noise Barriers." A Paper presented at the 1983 Annual
Meeting of the Transportation Research Board, Washington, D.C.,
January 1983.
1 2. Bowlby, W., SNAP 1.1 - A Revised Program and User's Manual for the
FHWA Level I Highway Traffic Noise Prediction Computer Program, Report I I
No. FHWA-DP-45-4, Federal Highway Administration, Arlington, Virginia, i
1980. 1
3. Federal Highway Administration, Demonstration Project No. 45: Highway I
I Noise Analysis (workshop notebook), Report No. FHWA-DP-45-2, Federal 1
Highway Administration, Arlington, Virginia, 1978.
4. Hajek, J.J., "Effects of Parallel Highway Noise Barriers," Proceedings
of the 1980 International Conference on Noise Control Engineering, I
Poughkeepsie, New York, 1980. i
5. Hajek, J.J., Noise Barrier Attenuation: Highway 401 North Side East
of Avenue Road, Toronto, Report No. 80-AC-01, Ontario Ministry of
Transportation and Communications, 1980.
6. Hajek, J.J., Performance of Parallel Highway Noise Barriers: Yonge
Street to Bayview Avenue, Toronto, Report No. 80-AC-01, Ontario
Ministry of Transportation and Communications, 1980.
7. Hajek, J.J., "The E f f e c t s of P a r a l l e l Highway Noise Bar r i e r s , " Draf t
Paper Offered f o r P resen ta t ion a t t h e Annual Meeting of t h e
Transpor ta t ion Research Board, Washington, D.C., January 1983.
8. Nelson, P.M., P.G. Abbott and A.C. Salvidge, Acoustic Performance of
t h e M-6 Noise B a r r i e r s , TRRL Laboratory Report 731, Transport and Road
Research Laboratory, Crowthorne, England, 1976.