REPORT NO. DOT-TST-76-49

TRUCK NOISE l-C

PAVEMENT SURFACE EFFECTS ON THE

GENERATION OF TRUCK TIRE NOISE

R. D. Kilmer

W. A. Leasure, Jr.

D. E. Mathews

< OF TR4*.

FINAL REPORT

OCTOBER 1975

Availability is unlimited. Document has been

released to the National Technical Information

Service, Operations Division, Springfield, Virginia

22151, for sale to the public

U.S. DEPARTMENT OF TRANSPORTATION

Office of the Secretary

Office of Noise Abatement

Washington, D.C. 20590

TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. DOT-TST-76-49

2. Government Accession No. 3. Recipient's Catalog No.

4. Title ond Subtitle Truck Noise I-C

Pavement Surface Effects on the Generation of

Truck Tire Noise

5. Report Dote October 1975

6. Performing Organization Code

7. Author's) Kilmer, W. A. Leasure, Jr., and

D . E . Mathews

8. Performing Organization Report No.

9, Performing Organization Name and Address National Bureau of Standards

Departmen.t of Commerce

Washington, D.C. 20234

10. Work Unit No.

11. Controct or Grant No. DOT-AS-10004

13. Type of Report and Period Covered

Final

12. Sponsoring Agency Name and Address U. S. Department of Transportation

Office of the SecretaryOffice of Noise Abatement

Washington, D.C. 20590

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract This report presents data showing the effect that pavement surface has on the

generation of truck tire noise. Three different tread designs -- rib, cross-bar

and pocket -- were tested at speeds of 40, 50 and 60 mph (64.4, 80.5 and 96.5 km/hr)

while coasting on eight different pavement surfaces at the Texas Transportation

Institute. These surfaces represent a wide range of surface texture. Also presented are the results of one method of quantitatively characterizing pavement

surface texture; namely, the mean square value of the macrotexture profile,

obtained utilizing a macrotexture profile tracer. Plots of tire noise versus this

particular measure of surface texture show that up to a certain macrotexture the

generated noise is tire dependent while above this value the pavement macrotexture

appears to be the controlling parameter. Because of the wide variation in noise

level with changes in surface texture for the pocket retread, this tire is investigated as a possible simple calibrator of surface texture. These investigations

serve as the basis for evaluation of the effect of surface texture on the generation of tire noise.

17. Key Words Acoustics; noise measurement; noise

(sound); tire noise; transportation

noise; truck.

18. Distribution Statement Availability is unlimited. Document may

be released to the National Technical

Information Service, Operations Division,

Springfield, VA 22161, for sale to the

public.

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Poges 111

22. Price

1 Form DOT F 1700.7 (8-69)

Table of Contents

Page

1. Introduction 1

2. Field Test Program (Data Acquisition) 2

2.1. Field Test Site 2

2.2. Test Tires 2

2.3. Test Vehicle 7

2. U. Test Procedure 7

2.5. Test Pavement Macrotexture I5

a. Pavement Surface Characteristics I5

"b . Measurement of Pavement Macrotexture I6

c. Macrotexture Profile Tracer I6

3. Parametric Study I8

3.1. Tread Design and Speed 22

3.2. Pavement Surface 25

3.3. Spectral Characteristics 25

3. ^. Surface Texture Measurement Results 33

3.5. Conclusions I13

h. Appendix A. Truck Tire Noise Data lj.5 5. Appendix B. Macrotexture Profile Measurement Results. ... 67

6. Appendix C. Instrijment Descriptions Qk

7. Appendix D. Description of Macrotexture Profile Tracer 37

8. Appendix E. Description of Test Pavements 93

9. References IO8

i

1. Introduction

The National Bureau of Standards, under the sponsorship of the U. S.

Department of Transportation, has over the past five yej^s established an extensive data "base of truck tire noi3e[l, 2 , 3 , h , ^] .— As a result of this

program and the work of other researchers [6 , 7? 8, 9 5 10, ll], pavement surface

has been identified as a major factor which influences tire-road interaction

noise. Although this dependence has been noted, the lack of an appropriate

method for characterizing the pavement texture in a quantitative manner has

hindered the understanding of the effect of surface texture on the generation

of tire noise. This deficiency is troublesome from at least two standpoints.

First, without a quantitative pavement texture description over the proper

text-ure scale, it is very difficult to authenticate any of the currently

proposed models of tire noise. Second, testing of tires to establish

compliance with certification standards will require quantitative specification

of pavement textures. The terms . "smooth" or "rough" and "asphalt" or "concrete" are obviously insufficiently precise i Also, the degree of

compliance of motor vehicles with noise standards enforced by roadside

monitoring is, and will be, subject to variability from texture differences

until the texti.res of monitoring sites can be specified quantitatively in

noise-related terms

.

This report presents data showing the effect of different pavement

surfaces — representing a broad range of surface textures — on tire noise.

The data consist of maximum A-weighted sound levels and spectral information

for- truck coastbys over eight different pavement surfaces. The measiarements were made utilizing two tripod mounted microphones at a height of ^8 inches

(1.2 m) above the roadway surface and located 25 and 50 feet (7-6 and 15.2 m)

from the centerline of the test pavement. Also presented are data resulting

from one approach of quantitatively characterizing pavement surface texture.

These data consist of 1/3-octave band (spatial frequency) profile spectral

information for the eight test pavement^. These data are compared with the

corresponding tire noise levels in an attempt to correlate pavement surface

texture with tire noise. The results are presented in both tabular and

graphical form as well as in the form of summarT'' plots showing general trends.

— Figiires in brackets indicate the literature references at the end of this

report

.
2. Field Test Program (Data Acquisition)

This test program vas similar to previous DOT/NBS truck tire noise studies

vith the exception that a nev field test site was utilized. A discission of

the details associated with the test program for the evaluation of the effect

of pavement surface on truck tire noise follows.

2.1. Field Test Site

The research runway of the Texas Transportation Institute (TTl) located at

the Texas A & M Research Annex, College Station, Texas, was selected as the

test site for the data acquisition phase of the program. This test site,

located on property previously used as a jet-trainer airfield, provided an adequate stretch of pavement [TCOO feet (2133-6 m)], a flat terrain providing a well-defined reflecting surface without any unusual reflection or attenuation

effects, and most Importantly, eight different pavement surfaces representing a broad range of surface textures.

The eight different pavements were one portion of a skid test facility.

Each test pad was 2h feet (T-S m) wide and 600 feet (l82.9 m) long with a cross slope of about 1/8 inch per foot (1.0^4 cm/m) . These test pads were located

approximately midway along runway B which is 150 feet (U^.J m) wide and 7000

feet (2133.6 m) long. The overall layout of the Texas A Sc M Research Annex

showing the location of runway B and the test pads is given in Figure 1.

Figure 2 is a detailed layout of the eight test pads as constructed on runway

B.

These test pads were designed as reference surfaces for the comparison of

the skid characteristics of various tires and for the calibration and

correlation of skid resistance measuring devices[l2, 13, 1^]. Since the skid

characteristics are extremely dependent on the surface condition of the

pavement, these test surfaces were carefully constructed, and in certain cases polished or coated to achieve a uniform surface texture.

The test pads can be categorized into three groups based on their

materials and methods of construction. Group 1 (test pads 3, ^, 5 and 8) is

comprised of hot-mixed asphaltic concrete courses which were surface finished

by a variety of methods for developing a consistent surface texture. Group 2

(test pads 1 and 2) consist of surfaces prepared by cleaning or surface coating

previously constructed asphaltic concrete or portland cement courses. Group 3

(test pads 6 and T) consist of asphalt chip seal surfaces. Photographs showing

the surfaces of these eight test pads are presented in Figure 3. Detailed

descriptions of the pavement surfaces are given in Appendix E.

2.2. Test Tires

Based on previous DOT/WBS studies, new tires representing three basic

tread designs were chosen — rib, cross-bar, and pocket retread. The

characteristic tread element patterns for the three tires used in this study

are shown in Appendix A.

2
3
RUIiWAY

CENTERUNE

24 FT. (7.3m)

PORTLAND

CEMENT

CONCRETE

PAD

NO. t

24 FT. (7.3m)

JENNITE

FLUSH

SEAL

PAD

NO. 2

24 FT. (7Jm)

LIMESTONE

HOT MIX

TERRAZZO

FINISH

I. 3

CRUSHED

GRAVEL

HOT MIX

PAD

NO. 4

ROUNDED

GRAVEL

HOT MIX

NO. 5

LIGHT - WEIGHT

AGGREGATE

CHIP SEAL

PAD

NO. 7

LIGHT -

I WEIGHT

AGGREGATE

HOT MIX

PAD

NO. 8

ROUNDED

GRAVEL

CHIP SEAL

NO. 6

»- E

»- E

o csl O CO

E

csi

9)

esi

Figure 2. Plan of test pads on runway B.

4
PORTLAND CEMENT lENNITE FLUSH SEAL, LIMESTONE HOT MIX

CONCRETE, PAD-I PAD-2 TERRAZZO FINISH, PAD-3

CRUSHED fiRAYEL ROUNDED GRAVEL ROUNDED GRAVEL

HOT MIX, PAD-4 HOT MIX, PAD-5 CHIP SEAL, PAD-6

5
The rib tire (tire TB) has ribbed, miilti-siped, rounded shoulders. It is

representative of a type of tire primarily utilized on the steering and trailer

axles

.

The cross-bar tire (tire TD) has a circumferential tread ,face ceftter

(central rib) for lateral traction with shoulders of laterally aligned bars

vith sipes for added traction.

The pocket retread pattern is not a design used by major tire

manufacturers but represents the work of independent retread companies. For

this reason, many varieties exist and the tire is known to different people

under different titles. This design traps air in the pockets as it seals

against the road surface and releases the entrapped air when the pocket

unseals.. The pocket retread (tire Tl) was directional (should be mounted one way for most efficient operation), having slanted cups or pockets, with a bar

across the center of the pocket, and a shouldef- rib. The pocket retread tire

was selected for testing because of its potential as a simple calibrator of

pavement surface texture. Previous studies [l, 2] have shown the pocket tread

tire to be more sensitive to surface texture variation than tires with either a cross-bar or rib tread design. More is said about this in Section 3.

In accordance with standard operating procedure the tires utilized during

this test program were not balanced. When new tires are installed on a truck,

balancing is not performed unless there is a definite handling problem or severe vibration reported which might jeopardize the safety of the vehicle.

When such a problem arises, the entire front end assembly, not just the tires,

is checked. Unlike the normal practice with automobile tires, only front

(steering) tires are ever balanced on trucks.

A tire was not considered acceptable as a test specimen for the tire noise

investigation until it had undergone a -break-in period of sufficient mileage

under actual driving conditions to ensure the removal of all mold marks and

manufacturing irregularities. Immediately prior to the actual noise testing of a given set of tires, a warm-up procedure was followed which normally required

a minimum trip of approximately 10 miles (l6.1 km).

Tread depth measurements for each test tire were taken at four equally

spaced locations around the tire circumference. The device utilized for this

measurement was a depth gage with 1/32 inch (0.8, mm) graduations. The operator

located the depth gage, over a major groove (not over the sipes or other small

grooves), depressed the probe into the groove, and noted the tread depth

directly from the instrument. The resulting data are given in Appendix A.
2.3. Test Vehicle

The vehicle used throughout this test program was an International— Model

1600 ^hassis equipped with a 20-foot stake body and hydraulic tail gate. This

4x2— single-chassis vehicle (similar to that utilized in previous rOT/NBS[l,

2] truck tire noise programs) was equipped with a V-392 gasoline engine,

13-inch clutch, 5-speed transmission, 2-speed rear axle, and 11.00 x 22.5

tires. This vehicle had a gross weight capacity of 25,000 pounds (11,36a kg).

Figure 4 provides an overall view of this test vehicle.

The truck was operated in the loaded condition. Figure 5 shows the

loading arrangement. A variety of weights (4 concrete blocks, 2 scrap

electrical motor casings and several bags of sand) were distributed to develop

a loading equivalent to 75 percent of the rated tire load at 70 psi (4.8 x 10

Pa) per Tire and Rim Association recommendations. The weight distribution was

as follows:

front axle 7.880 pounds (3582 kg) rear axle 17,730 pounds (8059 kg)

gross vehicle weight 25,610 pounds (11641 kg)

.The test tires were always mounted on the drive axle and rib tires whose

characteristic tire noise level was known to be low were always mounted on the

steer.ing axle.

2.4. Test Procedure

Prior to a discussion of the test procedure, a few words of description

are necessary to establish the placement of all instrumentation within the test

section. Figure 6 shows the placement of the microphones, radio transmitters,

and the path of the test vehicle.

The two m.icrophones were located at 25 and 50 feet (l .b and 15.2 m) from

the centerline of the lane in which the vehicle travelled along a line perpendicular to the path of travel of the test vehicle. Radio transmitters, activated by the truck running over a tape switch, were located along the test lane

parallel to the; path of the- vehicle. Coaxial cables connected the microphones

with the tape recording and monitoring equipment which was located more than

150 feet (45.7 m) back from the edge of the test pads.

— The commercial vehicles utilized are identified in this report in order to

adequately describe the vehicles on which the test tires were mounted throughout this program. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that these

vehicles were necessarily the best available for the purpose.

3/ — The nomenclature 4x2 relates to the number of wheel positions — 4, and the

number of driven positions — 2, but has no relationship to the number of

tires — 6. Thus, ci 6 x 4 would have 10 tires mounted at 6 wheel positions,

4 of which are driven.

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9
600 FT (182.9m)

VEHICLE PATH

T-1 25 FT (7.6m)

A M-1-^

T-2

AM-2

50 FT (15.2m)

• TRANSMITTER

A MICROPHONES

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vehicle path (not to scale). Microphones were placed at 25 and 50

feet (7.6 and 15.2 m) from the centerline of the lane in which the

vehicle travelled and along a line perpendicular to the path of

travel. Radio transmitters (activated by tape switches) remotely

controlled the en/off sequence of the tape recorder.

10
For a nominal 50 mph (80.5 km/hr) run (the vehicle shoiild be travelling 50

mph (80.5 km/hr) as it passed the microphone array) the driver of the test

vehicle accelerated the truck to slightly more than the desired speed to com- pensate for the deceleration characteristics of the particular vehicle.

As the truck passed over the initial tape switch, the tape recorder was remotely commanded to turn on via the signal from the radio transmitter. The

initial tape switch/radio transmitter system was located such that the tape

recorder was up to speed "by the time that the test vehicle entered the test

section. (The location was selected based on the maximum test speed of the

vehicle during the program. ) Following a time delay a signal was recorded on

the FM channel of the tape recorder which designated the start of data. As the

truck left the test section, a second tape switch was activated. The radio

transmitter sent a signal to the tape recorder identifying the end of data and

then the tape recorder was remotely turned off. The data start and data end

signals were transmitted to the receiver at different frequencies . An elapsed

time clock indicated the time it took for the vehicle to cover the known distance between the tape switches from which the average speed of the vehicle was

calculated.

Figure T identifies the components that constituted the data acquisition

system — a one-inch condenser microphone, a battery-operated microphone power

supply (to supply the polarization voltage to the microphone) , a step

attenuator which provided the capability for selection of gain over a range of

60 dB in 10 dB steps, and a three-channel analog tape recorder. The system

included both a flat frequency response hold capability — which" provided an indication as to whether or not a tape channel had saturated (saturated runs were repeated) -- and an A-weighting hold capability — which provided a direct

reading, in the field, of the maximum A-weighted so\md level observed dixring a passby without having to return to the laboratory for the analysis of the

tapes. The measurements were performed out-of-doors; therefore, windscreens

were placed over the microphones to reduce the noise produced by wind passing

over the microphone. A single point calibration utilizing a pistonphone which

produced a 12h dB sound pressirre level (re 20 yPa) at a frequency of 250 Hz was used for system calibration in the field. Calibration tones were recorded on

the data tape once each hour as well as at the beginning and end of each data

tape. Figure 8 shows the microphone array and associated instrumentation in

the field at the Texas Transportation Institute test site.

Once the data had been recorded, the analog tapes were returned to the

National Bioreau of Standards for reduction and analysis. Figure 9 identifies

the equipment which was utilized for analysis purposes. Each tape was played

back a channel at a time through the real-time analyzer. An interface-coupler

was necessary to make the real-time analyzer compatible with a mini-computer.

When a timing signal appeared on the analog tape, the real-time analyzer was commanded to begin analysis. A time constant of 0.2 second above 200 Hz and

one which below 200 Hz followed a straight line to 3.15 seconds at 12.5 Hz was utilized to obtain the root-mean-square (rms) value of the level in each

one-third octave band at the output of the analyzer. Once all data had been

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analvzed in one-thiri oc~ave bands, the coinp-a'cer stored the data and d'jiiped it

cntc digital nagnetic tape. Tnis tape vas fomated to "be acceptatle to the

large !3S cor^uter vhich was utilized for further analysis. Tnis

instrunenxation system provided for efficient data acquisition and data

handling for the thc'osands of data points generated for each truck passhy.

Appendix C contains a brief description of the instruments utilized for

data acquisition, reduction and analysis.

2.5. lest Pavement ^'^acrotexture

In order to correlate tire noise vith pavement suxface, a technique of

characterizing the pavement surface variations is needed. A discussion of

pavement surface textijre and one method for quantitatively describing surface

texture is discussed belov.

a. Pavement S'-irface Characteristics

The surface variations of a roadway can be classified into three regimes:

roughness, macrotexture, and miorotexture . Inese classifications are based on

the size of the variations, and range from roughness which is the largest

meas'ore of surface variations to microtext'ore vhich is the smallest.

Rotighness refers to the waves, pot holes, and surface deterioration on the

overall roadway surface. Such large scale irregularities are normally meas^ared'

in inches per mile and have no relationship to irregularities as small as the

individual pieces of aggregate. The pavement roughness is the roadway

characteristic that detennines vehicle ride quality. Previous studies have

shown that variations in the surface of less than l/2-inch (l.2T cm) in length

do not materialljT affect the riding quality and have been classified as pavement text-jre[l5] •

Macroscopic texture, or macrotexture, refers to the large-scale texture of

the pavement surface governed b;^ the size and shape of the stirface aggregate.

The scale of macrotexture generally spans the range cf sizes of particles in

the pavement aggregate — approximately from 0.01 to O.k inches (0.25 to 10

imn)[l6].

I-licroscopic text\are or microtexture refers to the fine-scale texture con- tributed by individual small asperities on the individual aggregate particles

The scale of microtexture generally ranges below that for macrotexture with

some overlap in the region separating the two regimes

Of these three regimes of s-jrface variations, macrotexture is believed to

have the most influence on tire noise. This assumption is based on a consideration of the size of the tread element spacing relative to the texture

variations (see Section 3.2). Since macrotexture is approximately on the same scale as the tread element spacing, it is this characteristic of the pavement

surface which is thought to be important in at least some tire noise sc^ce

mechanisms

15
The macrotexture is due largely to the physical, mechanical, and chemical

properties of the aggregate forming the surface of the roadway. The physical

properties, vhich include the size, shape, and pore structure of the material,

are the major controlling factors of' pavement texture. The particle size is

measured hy the particle grading, which is the distribution of different

particles of aggregate among various sizes; e.g., the relative amounts of

3/8-inch to 1/2-inch (0.95 cm to 1.2? cm) size, l/ii-inch to 3/8-inch {0.6h cm

to 0.95 cm) size, etc. The particle shape, generally classified as either

uncrushed (rounded) or crushed -( angular or cubical), influences not only the

macrotexture but also the microtexture of the pavement surface. The pore

structure which is the size, volume and shape of the void spaces within the

aggregate, is partially controlled by the maximum particle size and the

material used for the pavement binder. The mechanical and chemical properties

of the aggregate relate more to the wearing and erosion characteristics of the

individual aggregate particles; but, these properties are also important since

they will determine how the macrotexture changes with vehicle usage and

weathering.

In addition to the aggregate properties, another important factor which

affects the surface macrotexture of pavements is the method of surface

finishing, including surface treating or coating.

b. Measurement of Pavement Macrotexture

To determine pavement macrotexture, a measuring technique which is capable

of accounting for aggregate size, shape and pore structure and irregularities

due to surface finishing is needed. The National Bureau of Standards, under

the sponsorship of the U. S. Department of Transportation, supported a study by

the Pennsylvania Transportation Institute (PTI), University Park, Pa., which

investigated the feasibility of physically characterizing surface macrotexture

by profile spectral analysis. The technique investigated by PTI characterizes

pavement macrotexture through the use of space frequency spectrum analysis of

the surface macrotexture profile as measured by a profile tracer recently

developed by PTl[l6]. The space frequency data represent a measure of the

physical size distribution of the surface profile variations and as such are

not a function of velocity. Correlation between pavement macrotexture spectra

and tire-roadway interaction noise spectra requires a scale-up of the space

frequency spectra to the tire passage speed, i.e., the space frequency is

multiplied by, for example, 50 mph (80.5 km/hr). Further discussion of space

frequency and its relationship to the generated noise is presented in Section

3.^. A general description of this device and how it operates follows.

c . Macrotexture Profile Tracer

The profile tracer developed by PTI and used in this study is shown in

Figure 10. This device is designed to accurately measure the local variations

in surface geometry by transversing a section of pavement and recording the

changes of profile height as measured by a displacement transducer. 'More

details of the profile tracer and its calibration are given in Appendix D.

16
Figure 10. The macrotexture profile tracer.

17
The general operating procedure consists of setting the profile tracer on the pavement and adjusting the three legs so ths.t the bed is parallel to the

plane of the pavement. The sled is then made to traverse tb.e bed at the rate

of 0.0128 ft/sec (0.0039 m/sec) by switching on the synchronous motor. The

stylus, which follows the profile of the pavement surface, displaces the

cantilever spring suspended stylus holder which in turn moves the core of the

linear variable differential transformer (LVDT) . This motion of the core changes the dc-voltage output of the transducer in a manner directly

proportional to the stylus displacement. This variable dc-voltage output of

the LVDT is then recorded on one track of an FM tape recorder. In each case, a minimum of five pavement traverses were made, each in the direction of vehicle

travel. (The study performed by PTI[16j showed that except where the surface

had been intentionally brushed or fluted, the direction of traverse was not

important for relatively new pavements. Similar data have not been collected

for sites which have undergone substantial polishing, so the important question

of macrotexture dependence on direction of traverse for well-traveled roads

remains to be answered.) The system used to obtain these profile data are shown in Figure 11

.

The tapes of the recorded profile data were conveyed to the spectrum

analysis facility at the Applied Research Laboratory (ARL) , University Park,

Pa., for playback and processing. The original tapfes, recorded at a tape speed

of 6.0 inches per second (ips) were copied with another FM recorder at 1 7/8

ips and the analysis was then performed on the copy tapes. Analysis of the

copy tapes rather than the original recordings introduces a potential 6 dB'

decrease in the signal-to-noise ratio, depending upon the dynamic range of the

two FM recorders. Provided that the signal level is sufficiently above the

noise floors of the recording and analysis systems, this should not affect the

validity of the data. Figure 12 is a diagram of the tape copying equipment

set-up

.

A one-third octave band analysis of the data on the copied tapes was

performed. The tapes copied at 1 7/8 ips were played back at 60 ips. This

resulted in a time scale compression (playback to record ratio) of 32:1 that was required to match the slowly scanned profile signals to the ARL analysis

equipment. The 32:1 ratio provided an apparent profile scan rate of 0.41

ft/sec (0.125 m/sec), which greatly reduced the required analysis time.

The level in each of the one-third octave bands was obtained utilizing a time constant of 2 seconds (equivalent to 64 seconds at the original time

scale) . These one- third. octave band data were then plotted using both an x-y

recorder and a digital printer. Figure 13 identifies the equipment which was utilized for the spectral analysis.

3. Parametric Study

The data acquisition program was designed to address the following

questions

BWhat is the effect of roadway surface texture on the noise level generated

by truck tires?

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4> <

CO m

N 8 8

1^

H

Ph

Xl

(U

CO

CO

nJ 4J

CO -a

(U iH

•H

14-1 OU

CO •H

CO>^ iH

CSC

cfl 13

c:

CO>

CCJ 4-1 oo

13u

•H,C

4JICUCouoop

m

CO CO

CO

rH

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60

•H

Pt4

21
H Can pavement surface texture "be quantitatively measured and correlated

"with truck tire noise levels?

H Can a given tire design be used as a simplified calibrator of pavement

surface textixre?

In order to develop the data base necessary to address these questions,

two coastbys each at nominal speeds of hO , 50, and 60 mph {6h.h, 80.5, and 96.5

km/hr) over each of the eight test pads were made. "Sound level measurements

were performed at both 25 and 50 feet (7-6 and 15.2 m) from the centerline of

each of the test pads. The maximum A-weighted sound level data for all test

runs are tabulated in Appendix A, along with the corresponding spectral data

and the decrease in A-weighted sound level observed from 25 to 50 feet (7*6 to

15.2 m) . Also included are photographs showing characteristic tread design

patterns otf the test tires and the associated tread depth.

Profile measurements of the eight test pads 'were made by, PTI personnel

using the macrotexture profile tracer. These data are presented in Appendix B

in terms of individual profile band levels for the one-third octave bands

corresponding to the space frequency from 25 to 10,000 cycles per meter. The

space frequency is related to temporal frequency through the velocity of the

vehicle, i.e., the temporal frequency equals the velocity times the spacial

frequency

.

. " In this section, the so"und level data for the 50 foot (15-2 m) microphone

location are the basis for summary plots which are presented to show the effect

of tread design, speed, and pavement s"urface'on the noise level generated by

truck tires. Also presented are selected spectral data to show the variations

in frequency content of truck tire noise for the varipus test pads. Finally,

profile data for the eight test pads are given and the correlation between

truck tire noise level and the pavement texture is discussed.

3.1. Tread Design and Speed

In order to investigate the effect of tread design and speed on generated

noise levels, plots of maxim"um A-weighted sound level versus speed with tread

design as a variable were developed (Figures ih and 15). These data represent

measurements at 50 feet (l5-2 m) for coastby runs of the loaded h x 2

single-chassis vehicle on the eight test pads. An increase in speed res"ulted

in an increase in the maximum A-weighted sound level. The increases were on the order of 1+-7 dB for^test tire TB, 3-5-7 dB for test tire TD and 5-10 dB for

test tire TI for speed changes from ^+0 to 60 mph {6h.k to 96.5 km/hr). On the

average, the increases were 5-8 dB. This corresponds to the sound level

increasing as the third to fourth power of speed. The only exceptions to this

general trend were for test tire TB on pads 2, 3 and h. For these three cases,

the maximum A-weighted sound level decreased by 1/2 to 1 dB for a speed

increase from 50 to 60 mph (80.5 to 96.5 km/hr).

In every case, tire TI (pocket retread) was the noisiest of the three tire

tread designs; followed by tire TD (crossbar); with tire TB (rib) the least

22
SPEED, km/hr

70 to 90 100

TEST PAD 3

a

e 90

3

<i TM

s

><<z • TIRE TB

TIRE TD ATIRE Tl

50 SPEED, mph

SO

1M I

S 90

o 80 -

1 70 -

SPEED, tonvTsr

Ttl M 90 100

TEST PAD 4

• TIRE TB

TIRE TD

* TIRE Tl

SPEED, mph

SO

;ure lA. Maximum A-weighted sound levels, as measured at 50 feet (15.2 m) versus speed with tire tread design as variable for vehicle

coastbys on the indicated test pad. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

23
SPEED, km/hr SPEED, km/hr

60 70 80 90 100 60 70 80 90 100

SPEED, mph SPEED, mph

Figure I5. Maximum A-weighted soiind levels, as measvired at 50 feet (15.2 m) , versus speed with tire tread design as a variable for vehicle

coastbys on the indicated test pad. New rib tires were ino\inted on

the steering axle and the test tires on the drive axle.

24
noisy of the tires tested. The difference in ncise level between the three

tires was strongly influenced by the pavement surface. In general, the widest

spread of noise levels occured on the smooth pavements (pads 1, 2, and 8);

whereas on the rough surfaces (pads 4 and 7) there was a much smaller variation

between the different tread designs. As sho^ra in the previous figures, the

spread of noise levels between tire TB and tire TI was 11-18 dB on pads 1, 2

and 8, but only 2-7 dB on pads 4 and 7. Thus, as expected, the noise generated

by truck tires is dependent not only on the tread design and speed range over which the vehicle is operated, but also on the type of pavement surface.

3.2. Pavement Surface

The exact dependence of the generated noise level upon pavement surface is

difficult to determine since other factors such as tread design and speed also

come into play. To investigate the effect of pavemert surface on the

generation of truck tire noise, plots of maximum A-weighted sound level versus

speed with pavement surface as a variable were developed (Figures 16 to 18)

These data represent the aritbjuetic average of the two measurements at 50 feet

(15.2 m) for coastby runs of the loaded 4x2 single- chassis vehicle for the

three types of tires tested. As expected, pavement surface has a greater

effect on the noise generated by tire TI than by tires TB and TD. The maximum

A-weighted sound levels at any one particular speed have a range of 10-20 dB

for tire TI, but only 4-6 dB for tires TB and TD.

3.3. Spectral Characteristics

To better understand the influence of pavement surface texture on tire-road interaction noise, the data measured at the 50 foot (15.2 m)

microphone at the time corresponding to the occurrence of the maximum

A-weighted sound level have been analyzed in one-third' octave bands. One-third

octave band data are not fine enough to distinguish many spectral

characteristics of tire-road interaction noise; however, it does allow the

identification of a range of frequencies associated with certain tire noise

generation mechanisms. These data, for a vehicle coastby at 50 mph (80.5

km/hr) over each of the test pads, are plotted in Figures A--4 to A-11 in

Appendix A.

These spectral data can be best explained b}" considering the mechanisms by

which tire-road interaction noise is generated. As sumirLarized in references

[3,17], at present three generic types of tire noise source n.echanisms have

been postulated — aerodynamic, air pumping and vibration.

In addition, it may be helpful to introduce the concept of ioise floors".

With today's technology in the area of tire structural design, the apparent

limit — i.e., the quietest tire — is a smooth tire (nc tread) operating on a smooth road (no texture). This case represents the Aiihimum noise floor '. If

either tread is added to the tire (tire with tread/smooth surface) or texture

is added to the pavement surface (smooth tire/surface with texture), the noise

level will increase and a- "feecond level noise floor" vrill exist. Finally, in

25
CO

QOS

ca

UJ

85

60

SPEED, km/hr

70 80 90

TIRE TB

o

C(0

X

<

65

f/

TEST PADS

o —1 • —

5

—2 —

6

o —3 # —

7

A —4 A —8

40 50

SPEED, mph

60

Figure l6. Maximum A-weighted soiind levels, as measured at 50 feet (15-2 m)

,

versus speed with pavement surface as a variable. These plots

correspond to vehicle coastbys with new rib tires mounted on the

steering axle and test tires TB on the drive axle.

26
SPEED, km/hr

60 70 80 90 100

SPEED, mph

Figiare IT- Maximimi A-weighted sound levels, as measured at 50 feet (15.2 m) , versus speed with pavement surface as a variable. These plots

correspond to vehicle coastbys with new rib tires mounted on the

steering axle and test tires TD on the drive axle.

27
SPEED, km/hr

60 70 SO 90 100

40 50 60

SPEED, mph

Figiore l8. Maximum A-weighted sound levels, as measujred at 50 feet (15»2 m)

,

versus speed with pavement surface as a variable. These plots

correspond to vehicle coastbys with new rib tires mounted on the

steering axle and test tires TI on the drive axle.

28
the real vorlci situation — tire with tread operating on a surface with texture — the noise level will increase further and a "third level noise floor" will

be present. The noise level which characterizes any "noise floor" is

determined by the complex interaction of the vibration, air-pumping and

aerodynamic tire noise source mechanisms.

Aerodynamic sources refer to unsteady flow over the tire, attributable

largely to the whole-body motion of the tire through nearly-stationary air.

Siddon [18] speculates that fluctuating pressures from vortices generated at

the trailing edge of a tire near the road are sufficient to contribute

substantially to roadside noise. While this may be a factor in determining the

"minimum noise floor", it hardly seems likely to be a major source in view of

the overwhelming data demonstrating a dependence of tire noise on road

roughness and tread design.

Investigators are in general agreement that air pumping can be a major

contributor to tire noise. As a tire tread segment contacts the road surface,

air is squeezed out of the small depressions in the road and tire interstices

in sufficient volume to create significant noise. As the tread segment leaves

the surface, air rushes back to fill the voids. Hayden [7] modeled this

oscillating flow by assuming a compact array of monopole sources of noise

associated with the leading and trailing parts of the contact area and

developed an empirical expression for estimation of the overall sound pressure

radiated by a single tire as:

SPL = 68.5 + 20 log (^) + 40 log v

(1)

+ 20 log f + 10 log n - 20 log r

Where, 6 = tread depth, w = width of a single cavity or groove in the tread, S = circumferential distance between tread grooves, v = vehicle velocity, f = fractional change in cavity volume, n = cavities per tire width and r = distance from tire to observation point. A similar concept is said to be

applicable when one treats the roadway depressions in the same manner as the

tread interstices.

Vibration of the tire carcass (caused by tire-road interaction) is

believed to be a third source of noise. There exist numerous possible

excitation and radiation mechanisms as well as types of tire response that

could characterize tire vibration and attendant sound generation.

The primary excitation mechanisms are the periodic deflection of the

toroid in the contact patch area (tire-road interaction zone) as the tire rolls

along and the interaction of the tread elements with roadway-surface

irregularities. Roadway-surface irregularities may be thought of as a continuous process at low frequencies, where the lengths of waves associated

with the roadway wavenumber spectrum are long compared with the length of the

tire-contact patch (e.g., <100 Hz for automobile tires at highway speeds). At

higher frequencies, however, the process becomes discontinuous as segments of

the tire impact individual roadway surface asperities.

29
Another potential excitation mechanism results from tire nonuniformities — both of the tire itself (not really roimd or a fla-w in construction) and the

tread (uneven wear) which give rise to force variations in the tire. The

fiondamental component of this mechanism is related to the xire rotation rate

(i.e., a variation of the fo^-ce each time the nonuniformity impacts the

roadway) which •^ould correspond to about 10-20 Hz for automobiles operating at

highway speeds.— It is unlikely that harmonics of this will be significant in

the frequency regime of substantial sound radiation ('^^300-500 Hz).

Nonuniformity of mass distribution (.tire balance), however, can cause significant modulation of tire noise.

Based on the results of several laboratory studies[l9, 20, 2l], tire

vibrational characteristics and mechanisms of sound generation may be evaluated

in three frequency regimes — low frequency, mid frequency and high frequency.

The low frequency regime covers the range from 20 Hz (below 20 Hz the tire

responds approximately as a rigid mass on a spring) to frequencies just below

the first carcass moae, which can vary from 80 to l80 Hz depending on the tire

size, construction and inflation pressure. In this frequency range the tire

responds only in the vicinity of the contact area. Sound radiation is likely

to be monopole in nature, with an equivalent volume velocity corresponding to

the change in tire volume accompanying a fluctuating load. 'However, because

these frequencies are so low and because human hearing is largely insensitive

to low-frequency sound, this range of tire vibrations is not likely to be of

consequence

.

The mid frequency regime extends from the first carcass moae ("v^SO-lSO Hz)

to about hOO Hz, again depending upon the size, construction and inflation

pressure of the tire. In this frequency range, the carcass responds in a modal

manner, whicn causes the tire to behave like a dipole sound soijirce. The

efficiency of sound radiation depends on the distance between the contracting

and expanding parts of the tire and on the frequency of vibration, or,

equivalently , the wavelength of sound X corresponding to a given frequency.

Since X is much greater than the distance between the contracting and expanding

parts of the tire, tire modes are inefficient sound radiators.

In the high frequency regime (>U00 Hz), waves are generated in the carcass

at the tire-road interface, however, these waves are damped rapidly in the tire

as they propagate away from the contact area. If the phase velocity of these

waves is above critical (i.e., above the speed of sound in air) the waves will

radiate very efficiently. However, even subcritical waves may radiate

significant sound levels owing to low wavenumber components associated with the

excitation point.

— The frequency of the force variation and resultant tire vibration due to the

impact of the tire nonuniformity with the roadway is approximately equal to

the speed divided by the tire circumference. For example, an automobile tirt

with a circumference of 25 inches (63-5 cm) traveling at 50 mph (80.5 km/hr)

corresponds to a frequency of about 11 Hz

.

30
Tire tread and carcass vibration as sources of tire noise are actively

being investigated by researchers at North Carolina State University [22] . This

on-going analytical and experimental program, under the sponsorship of the

Office of Noise Abatement, Department of Transportation, should provide

considerable insight into the role of tire vibration as a tire-noise source

mechanism.

The tire noise spectrum is composed of two parts: a periodic variation

due to the tread pattern and tire nonuniformities and an aperiodic variation

due to the road surface features. The periodic component exhibits spectral

peaks at discrete frequencies and the aperiodic component exhibits a more

continuous spectrum. The frequencies of the spectral peaks are associated with

the tire design (tread spacing) and the tire rotational rate. The fundamental

frequency can be predicted by calculating the number of tread elements which

pass through the footprint per second. If the distance between consecutive

tread elements is uniform, the sound produced is nearly a pure tone whose

frequency is given by [23]

f = (2) a where, f = fundamental frequency, Hz

V = vehicle speed, km/hr

a = tread spacing, cm

Most tire manufacturers, however, do not utilize a uniform element spacing.

The pitch lengths are usually varied in some manner so as to produce a less

intrusive sound than a pure tone. While this serves to reduce the perceived

noisiness of tires, it raises the difficulty for researchers of defining an equivalent tread spacing. Modern tires are produced by molding into the tread

major grooves (in the case of rib tires major grooves are oriented in the

circumferential direction while for cross-bars the grooves are oriented in the

lateral direction) and secondary grooves or slots called siping, all of which

contribute in some unknown way to the complex acoustic signature of the tread

pattern.

Table 1 shows the major tread spacing for the tires tested, the predicted

frequency of the fundamental based on major tread spacing, and the one-third

octave frequency band in which the fundamental was actually measured (see

Figures A-4 to A-11 in Appendix A) . The calculations are based on a vehicle

speed of 50 mph (80.5 km/hr). Although present understanding of tire noise

source mechanisms does not allow one to identify the mechanism — air pumping

and/or vibration — excited by the tread elements interacting with the road

surface, in most cases the one one- third octave band in which the maximum

signal level could be found was predictable on the basis of tread spacing

considerations. Tread element spacing appears to be an important variable in

either noise generation mechanism as presently postulated.

31
Table 1. Predicted and measured fundamental tire noise frequencies based on major tread spacing considerations corresponding to a vehicle speed

of 50 mph (80.5 km/hr).

Tire -.

Major Tread

Spacing,

in. (cm)

Predicted Fundamental

Frequency

,

Hz

Band Limits

of One-Third Octave

Band(s) Containing the

Measured Fundamental

Frequency, Hz

Tire TB 2.00 - 2.37 371 - hko 355 - hhl

(Eib) (5.08 - 6.02)

Tire TD 3.35 263 22h - 355

(Cross-Bar) (8.51)

Tire TI 2.I18 355 282 - 355

(Pocket Retread) (6.30)

The sound generated by the rib tire (tire TB) contained only one spectral

peak, which corresponded approximately to the predicted fundamental frequency

(371-440 Hz) based on the major tread spacing. This was true in general,

except for test pads 6 and 7 which did not exhibit this spectral peak (Figures

A-9 and A-10) . This indicated that for these two test surfaces, the pavement

texture has more influence on the generated noise than does the tread element

pattern of this particular tire.

The same general results were true for the cross-bar tire (tire TD)

.

There was in general one dominant spectral peak corresponding to the

fundamental tread spacing frequency (263 Hz) , but there was also a secondary

plateau which included the apparent second and third harnjonics. Again, the

results for test pads 6 and 7 did not show any spectral peak at the fundamental

frequency, thus indicating the dominance of the pavement texture.

32
For the pocket retread (tire TI) there were three types of distinguishable

frequency spectra. For test pads 1, 2, 3, and 8, there were three well-defined

spectral peaks which corresponded approximately to the frequencies of the

fundamental (355 Hz), the second harmonic (710 Hz) and the third harmonic (1065

Hz) predicted on the basis of the major tread spacing. For test pads 4, 5, and

6, there was one dominant spectral peak corresponding to the fundament^al

frequency, and a secondary plateau in the range of the second harmonic. The

level of this plateau was approximately 10 dB below that of the fundamental.

For test pad 7, there was no distinctive spectral peak which indicated that the

pavement texture was the controlling factor in the noise generated on this

surface as it was for the rib and cross-bar tires. These results might be

expected since the primary mechanism of sound generation for tire TI (pocket

retread) is believed to be air pumping. The effectiveness of the air pumping

is dependent on how well the tire and roadway seal. This obviously depends on

the tread pattern of the tire and the texture of the pavement surface. For the

pocket retread and pavements with a smooth surface texture, a good seal is

possible, which results in both higher sound levels and more well-defined

spectral peaks than for pavements with a coarse surface texture.

Based on the spectral data for tire TI, the eight test surfaces could be

roughly classified into three ranges of pavement texture: test pads 1, 2, 3,

and 8 as smooth; test pads 4, 5, and 6 as intermediate; and test pad 7 as coarse. This crude classification does not solve the problem of quantitatively

relating pavement texture to truck tire noise, but it does indicate that there

should be a relationship between these two quantities.

In order to physically relate pavement surface -^to tire noise, a quantitative measure of the surface macrotexture is needed. The quantity used

in this study to characterize macrotexture is the mean square value of the

variation of the pavement profile, compfuted from the data obtained with the

macrotexture profile tracer. The profile data, given in Appendix B,^^onsist of

individual profile band levels in decibels referenced to 1 meter rms— for the

one-third octave bands corresponding to the space frequency from 25 to 10,000

cycles per meter. The data are given in terms of an arithmetic mean and

—The authors realize that the profile band levels defined in this report should

be expressed in units of decilogs since the logarithmic ratio is one of displacement rather than power. This usage, however, is not common and might

create confusion; therefore, the profile band levels will be expressed as decibels with the added note that this logarithmic ratio is referenced to

1 meter rms

3.4. Surface Texture Measurement Results

dB re 1 m rms = 20 log

measurement band rms displacement (m)

10 1.0 (m)

33
standard deviation based on five profile measurements. These arithmetic mean

values of the one-third octave band levels are plotted versus the space

frequency in Figures B-1 through B-8. Using this information, the mean square

value of the profile displacement can be computed by taking the antilog of the

profile band levels divided by ten and summing these values over the

twenty-seven one- third octave bands from 25 to 10,000 cycles per meter.

where PEL. is the profile band level in dB re 1 m rms . This summation defines

a single number descriptor of macrotexture which is equivalent to the area under the curve of a se^i-log plot of the one-third octave band profile

displacement squared (m ) versus space frequency.

The resultant mean square values of the macrotexture for the eight test

pads are given in Table 2. On the basis of these data, a relative rank

ordering of the surfaces from smooth (identified as a) to coarse (identified as

h) is established.

'Two alternative techniques for calculating the mean square value of the

pavement macrotexture were also investigated. First the space frequency data

were converted to temporal frequency data by multiplying by the vehicle speed.

For instance, a space frequency of 25 cycles per meter is equivalent to a temporal frequency of 560 Hz for a vehicle speed of 50 mph (80.5 km/hr) . Then,

utilizing Equation 3, the band levels were summed directly (second column of

Table 3) or were A-weighted and then summed (third column of Table 3). A

comparison of these values with the corresponding values listed in Table 2 shows that the mean square values calculated by these three methods differ only

slightly and that the relative rank ordering of the pavement texture is the same regardless of the technique utilized.

A typical A-weighted profile spectrum [scaled up to temporal frequencies

for a vehicle speed of 50 mph (80.5 km/hr)] and a corresponding A-weighted

acoustic spectrum for a vehicle coastby on this surface at 50 mph (80.5 km/hr)

are shown in Figure 19. It should be noted that data below 560 Hz [25 cycles

per meter at 50 mph (80.5 km/hr)] are not available because of the limitations

of the PTI analysis system. Although the lower frequency data would be

valuable for investigating correlation between the surface profile and acoustic

spectra, the profile data below 25 cycles per meter would have little effect on

the over-all A-weighted mean square value unless the profile band levels were

to increase rapidly at these low frequencies so as to counterbalance the effect

of the A-weighting. Coherence and/or correlation analysis between the surface

profile and acoustic spectra was not attempted due to the fact that there was a potential error of +10 percent in the recording speed of the profile data

tapes — and thus also in the estimation of space frequency — due to power

fluctuations of the gasoline driven inverter which was utilized to drive the FM

tape recorder in the field. This does not, however, affect the mean square

value of the pavement macrotexture since this quantity is simply a summation

over all one-third octave bands and as such is not directly related to

frequency

.

27 PBL./IO

Mean Square Value = of Pavement Macrotexture

10

1

i=l

34
Table 2. Mean square values of the pavement

macrotexture for the eight test pads

,

determined from the one-third octave band

data (25 to 10,000 cycles per meter) of

profile displacement as measured vith the

macrotexture profile tracer, and the

relative rank ordering of the surfaces from

smooth (a) to coarse (h) based on these

values

Test Pad

Number

Mean Square Value

of the Profile

^ Displacement, m

U.85

T.95

U.08

X 10

X 10

X 10

8.89 X 10

U.35 X 10

8.07 X 10

6.79 X 10

1.90 X 10

-8

I -9

-7

-7

-7

-7

Relative Rank

Ordering of

Pavement Macrotexture

Smooth Coarse

(a) (h)

b

a

d

h

eg

f

c

Table 3. Mean square values of the pavement macrotexture for the

eight test pads , determined from the one-third octave band

data (bands corresponding to the temporal frequencies from.

500 to 10000 Hz) of profile displacement. "Vehicle speed is

50 mph (80.5 km/hr)

Test Pad

Number

Mean Square Value of the

Profile Displacement for

the Temporal Frequencies^

from 500 to 10,000 Hz, m

A-weighted Mean Square

Value of the Profile Displacement for zhe Temporal

Frequencies from 500 to,

10,000 Hz, m

1 k.hl X

10-8 U.50 X 10-8

2 5.06 X 10-5 h.h3 X 10-5

3 3.92 X

10-T h.39 X 10-^

1+ 8.31 X 10-^ 8.71 X 10-^

5 U.15 X

10-^ U.50 X 10-^

6 7.92 X 10-^ 8.60 X

10-^

T 6.52 X 10-T 6.77 X 10-^

8 1.76 X 10-T 1.85 X

10-T

35
CSI

03

T3

CQ

C_3 O

a

o

o

CD

80

ACOUSTIC SPECTRUM

PROFILE SPECTRUM

70

T: 60

50 —

I I I 'I I I I I I I

-70

-80

90

-100

0.1 1i) 10.0

COE

cu

GQ

CD

O

o

o

cc

QCD

BAND CENTER FREQUENCY, kHz

Figure 19. A-weighted profile spectrum for pad 1 scaled-up to temporal

frequencies for a vehicle speed of 50 mph (80.5 km/hr) and a corresponding A-weighted acoustic spectrum for tire TB at 50 mph

(80.5 km/hr) on pad 1. The profile data are plotted at the center

frequency of the one-third octave band in which the temporal

frequency lies, e.g., 560 Hz profile data are plotted at 500 Hz.

36
Since the results from these three techniques are similar, the mean square

values obtained for the space frequencies from 25 to 10,000 cycles per meter

(Table 2) are used to investigate the correlation between surface macrotexture

and tire noise. The maximum A-weighted sound levels measured at 50 feet (15.2

m) are plotted versus the corresponding mean square value of the pavement

macrotexture of each test pad in Figure 20. These data correspond to vehicle

coastbys at 50 mph (80.5 km/hr) for each of the three test tires. The

variation in sound level due to road surface effects is much greater for the

pocket tread tire than for either the rib or cross-bar tire. This result was expected based on previous stu(^i^s[l,2,4,6] . Up to a certain macrotexture

scale — approximately 4 x 10 m the characteristic sound level appears to

be tire dependent. Above this value, however, the pavement macrotexture

appears to be the controlling factor — sound levels for all tires, regardless

of tread design, are essentially the same (within 5 dB) for the five surfaces.

It appears that the mean square value of pavement macrotexture as determined

from profile tracer space frequency data properly ranks the pavements according

to surface texture; however, there is no obvious method of predicting the

resultant tire noise on the basis of macrotexture data. This problem is not so much a deficiency in the profile tracer technique as it is a lack of

understanding of the tire noise generation mechanisms and how they are affected

by pavement surface texture.

Other investigators have attempted to relate tire noise to the texture

depth and skid number of the pavement[24,25] . The tire noise data resulting

from this study are plotted versus average texture depth CFigure 21) and skid

number, SN^^ (Figure 22). The texture depth was determined using the putty

impression method [26] and the skid numbers were measured according to ASTM E

274-70 procedures [27 ] using a skid trailer. A review of these two plots

reveals no apparent direct relationship between truck tire noise and either

texture depth or skid number.

Since the pocket tread tire exhibits such a variance in sound level with

changes in surface texture — due to the fact that the sealing required for

efficient entrapment of air within the pockets becomes less effective as the

road surface becomes rougher — an evaluation of the pocket tread tire as a simple calibrator of surface texture was made[28]. The maximum A-weighted

sound levels were plotted against pavement surface (Figure 23) , with the

location of the various surfaces on the abscissa being selected such that the

sound level data versus surface for the pocket tread tire formed a straight

line. A comparison of Figures 20 and 23 shows that, in general, the curves are quite similar. Rib and cross-bar tires could not be considered as simple

calibrators for surface texture since the sound levels characteristic of these

tires do not change sufficiently with surface texture changes.

The data for the rib and cross-bar tires using the pocket tread tire as a calibrator are replotted in Figures 24 and 25, respectively. In these plots,

the solid lines are the regression lines obtained by simple linear regression

analysis and the dashed lines represent the 95% confidence limits on the mean

value. From these figures it is seen that by using the pocket tread tire as a calibrator, the noise level generated by tires TB and TD could be predicted

from the regression lines with 95% confidence that the mean value of the actual

noise level would be within +3 dB.

37
Figure 20. Maximum A-weighted sound levels, as measured at 50 feet (15.2

m) , versus the mean square value of the pavement macrotexture

with tread design as a variable. These data are for vehicle

coastbys at 50 mph (80.5 km/hr) over each test pad.

38
0.4

AVERAGE TEXTURE DEPTH, mm

0.6 0.8 1.0 2.0 4.0

O

a

UJ

LU

o

LU

<

X

<

90 -

80 -

70

TT

PAD

PAD p..

PAD PAD 1 5

3 ^fl -4

• TIRE TB

TIRE TD

A TIRE Tl

PAD PAD

J7_^

0.01 0.02 0.04 0.06 0.08 0.1

AVERAGE TEXTURE DEPTH, In.

6.0

0.2

Figure 21. Maximiam A-weighted sound levels, as measured at 50 feet (15.2

m) , versus the average texture depth with tread design as a variable. The average texture depth was measured by the puttyimpression method. These data are for vehicle coastbys at 50

mph (80.5 km/hr) over each test pad.

39
Figure 22. Maximum A-weighted sound levels, as measured at 50 feet (15.2

m) , versus skid number, SN,^, with tread design as a variable.

The skid number is measured according to ASTM E 27A-70

procedures using a skid trailer. These data are for vehicle

coastybs at 50 mph (80.5 km/hr) over each test pad.

40
Figure 23. Maximum A-weighted sound levels, as measured at 50 feet (15.2

m) , versus pavement surface with tread design as a variable.

The abscissa was adjusted such that the sound level data versus

surface for the pocket retread formed a straight line. These

data are for vehicle coastbys at 50 mph (80.5 km/hr) over each

test pad.

41
a.

a.

aLU

I—

LU

I

Figure 24

90

1 1 1

1•

II 1

1

TIRE TB A TIRE Tl

-

• • •

-

• • • _

PAD PAD -2 . 1

1 1

PAD rMU

8

1

DAn PAD

3

1

PAD PAD PAD

'vG 4 5 -

Ni 1 1 '^PAD 7 PAVEMENT SURFACE Maximum A-weighted sound levels generated by tire TB versus

pavement surface using the pocket tread tire as a calibrator.

The solid line corresponds to the linear regression line and the

dashed lines to the 95% confidence limits on the mean value.

These data were measured at 50 feet (15.2 m) for vehicle coastbys

at 50 mph (80.5 km/hr) over each test p^d.

a.

" 90 m-o

LJJ £

ozZ3OCOS 80

UJ

I

70

1 1 1

1 II 1

TIRE TD

TIRE Tl

1

— J"

— PAD

2

1

PAD

1

1

PAD

8

1

PAD PAD PAD

3 ^64

1 NI 1

PAD —

5

1 PAD 7 PAVEMENT SURFACE Figure 25. Maximum A-weighted sound levels generated by tire TD versus pavement surface using the pocket tread tire as a calibrator.

The solid line corresponds to the linear regression line and the

dashed lines to the 95% confidence limits on the mean value.

These data were measured at 50 feet (15.2 m) for vehicle coastbys

at 50 mph (80.5 km/hr) over each test pad.

42
It should "be noted that many of the pavement surfaces characteristic of

the eight test pads at the Texas Transportation Institute are not typical of

road surfaces utilized for today's highways. Of the eight surfaces investigated, pad 1 (portland cement concrete) and pad 8 (asphaltic concrete) are most

representative of typical road surfaces. More information is needed to

correlate the noise generated "by pocket tread and other tire designs on typical

road surfaces in order to thoroughly evaluate the pocket tread tire as a pavement calibrator.

Subsequent studies [29] have shown that road surface has a greater effect

on the noise of passenger car tires than on truck tires. This is due to the

fact that the pavement texture within the tire-road interaction area is on the

same scale as the tread element spacing typical of passenger car tires. Thus,

it would be interesting to correlate the noise levels from passenger car tires

running on these eight surfaces with the measured surface macrotextiire data.

It might be useful to evaluate a blank tire as a simple calibrator of

surface texture rather than the pocket tread tire. Tire noise data obtained by

Hillquist and Carpenter [lO] for continuous and discrete block rib passenger car tires rionning on six different surfaces are plotted in Figures 26 and 27,

respectively 5 using a- blank tire as a calibrator. Based on this limited set of

data, it appears that the blank tire potentially could be used as a surface

calibrator. More data concerning the use of blank tire calibrators are needed.

3 '5- Conclusions

Based on the data obtained during the conduct of this test program and

subsequent studies, the following conclusions can be drawn:

Pavement surface had a greater influence on the noise generated by the

pocket tread tire — a range of 10-20 dB for the surfaces tested — than

by the rib or cross-bar tires — a range of k-6 dB.

M Plots of tire noise level versus macrotexture data showed that there were

two factors influencing the tire noise generation mechanisms depending on the svirface texture. Up to a certain macrotexture scale the generated

noise appears to be tire dependent, while above this value the pavement

macrotexture appears to be the controlling factor.

Information is needed to thoroughly understand road surface effects and to

determine which tire mechanisms are important and how they are affected by

road surface texture.

Based on subsequent studies, road surface appears to affect passenger car tire noise more than truck tire noise. A detailed investigation similar

to this study using passenger car tires may reveal more information on the

effects of road surface. Also, further testing using a blank tire may

prove useful.

The pocket tread truck tire shows potential as a sim.ple calibrator of

STorface texture, especially in the reg;ion — in the case of truck tires .

where tire characteristics dominate surface effects.

43
1=1 aCOs

UJs

^ 75

=3

1 -

1 1 i

1 1 -

• CONTINUOUS RIB

BLANK

60mph (96.5km/hr)

-

25 FEET (7.6 m) -

GM-6

1 GM-51 GM-4

1 GM-2

1 GM-1

1 GM-3

1

PAVEMENT SURFACE Figure 26. Maximum A-weighted sound levels generated by a typical

automobile continuous rib tire versus pavement surface

using a blank tire as a calibrator. The solid line corres- ponds to the linear regression line. These data were measured by Hillquist [10 ] at 25 feet (7.6 m) for passenger

car coastbys at 60 mph (96.5 km/hr) over six different

pavements

.

PAVEMENT SURFACE Figure 27. Maximum A-weighted sound levels generated by a typical

automobile discrete block rib tire versus pavement surface

using a blank tire as a calibrator. The solid line corresponds to the linear regression line. These data were measured by Hillquist [10] at 25 feet (7.6 m) for passenger

car coastbys at 60 mph (96.5 km/hr) over six different

pavements

.

44
h. Appendix A

Truck Tire Noise Data

This appendix, vMch. presents the truck tire noise data, is conrprised

of three separate parts. First, the tahiolated values of A-veighted sound

level (r^aximucn value of the A-veighted sound level during a passby)

measured at the tvo microphone locations [25 and 50 feet (T-6 and 15-2 m)

]

are reported. The data are organized according to tire tread design,

vehicle speed and pavement surface. A photograph shoving the

characteristic tread element pattern for each of the test tires is

presented along vith the average tread depth of the test tires. Second,

spectral data are presented for the three test tires and each of the eight

pavement s-orfaces. The one-third octave hand spectra shovn are those

measured at the 50 foot (15-2 m) microphone location during a 50 mph (80.5

km/hr) coasthy at the time corresponding to the occirrrence of the maximum

A-veighted sound level. Finally, the last three tables of this .appendix

tabulate the decrease in A-veighted sound level observed betveen the 25 and

50 foot and 15-2 m) measijrement locations for each test tire and test

pavement for vehicle coastbys at nominal speeds of Uo, 50 and 60 mph {6k.

80 •5 ana 96.5 km/hr).

45
Figure A-1. Characteristic tread element pattern of tire TB (rib tire).

The nominal new tread depth for this tire was 17/32 inch (1.35

cm)

.

46
Tire TB

Pad 1, Portland Cement Concrete

A-veighted Soizii Level, 53 re 2C

l\loinir.£L S^oeed, mph (km/hr)

20 (61^.1^) 1x0 (6L.li) 5c :S:".5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

78.8 79.0 61.2 83.0 83.0 83.6

75.2 T3.6 76.6 77.6 78.0 78.6

rad 2, Asphaltic Concrete with Jennite i-lush Sea^

A-veighted Sotmd Level, dB re 20 yPa

Mi 2rc"chone ll'ominal Speed, nrph (km/hr)

20 (61^.1;) ho (61;. L) 50 (8o'".5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

76.8 ~".5 81.2 52.: 80.2 81.0

71.8 ^2.2 77.0 77. 2 76.6 76.6

Pad 3, iiimestone Hot-Mix Aspha_-ic Ccncrete (Terrazo Finish)

A-veighted Soimd Level, d3 re 20 y?a

-cca.ion, 2^ ,n. Lcnir.aL Speed, nph (km/hr)

-C (62.2) 2o (62.2) 50 (8o'.5) 50 ^80.5) 60 (96.5) 60 (96.5:

25 (7.6)

50 (15.2)

76.0 11. h 81.0 82.0 81.2 81.0

Pad h, Cnished. Gravel Hot-Mix Asphaltic Concrete

A-veighted Soimd Level, dB re 20 yPa

I'licrophone

Location, ft (m)

Nominal Speed, mph (km/hr)

20 (62.2) 2o (62.2^ 50 (8O.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

77.4 78.2 82.2 82.2 81.2 82.2

72.2 ^^2.2 77.8 77.0 76.6 77.2

±-ad 5, --.c'lnded 3-ravex Hoo-I'lix Asphaltic Concrete

A-veigh-ei So"jnd Level, dB re 20 vVa

Microphcne

Location, ft (m)

Itominal Speed, mph (km/hr)

2o (62.2) lio (62. U) 50 (8o'.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6:

50 (15.2)

-6.6 -5.6 ^9.2 "9.6 80.8 50.6

70.8 ^0.6 76.2 7-.^ 76.2 -£.-

47
Pad 6, Rounded Gravel Asphalt Chip Seal

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

ho {6h.k) ho {Gh.h) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

75.1+ 75.0 78.8 79.0 82.0 81.6

72.2 72.8 75.6 75.6 78.2 79.0

Pad 7, Lightweight Aggregate Asphalt Chip Seal

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (61+. 1+) ho (61+. U) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

78.2 78. U 82.6 82.6 85.0 85.2

73.8 7I+.I+ 78.2 78.0 81.0 81.1+

Pad 8, Lightweight Aggregate Hot-Mix Asphaltic Concrete

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

UO (61+. 1+) 1+0 (61+. U) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

72.6 73.8 77.0 78.0 80.8 80.0

68.2 68.8 73.2 73.1+ 76.2 75.^

48
Figure A-2. Characteristic tread element pattern of tire TD (cross-bar

tire). The nominal nev tread depth for this tire vas 28/32

inch (2.22 cm)

49

Tire TD

Pad 1, Portland Cement Concrete

A-weighted Soimd Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

ho {6h.h) ho (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (T.6)

50 (15.2)

81.1+ 81.2 85.2 81+. 2 85.1+ 86.0

TT.2 TT.^ 81.2 81.1+ 83.0 82.0

Pad 2, Asphaltic Concrete with Jennite Flush Seal

A-weighted Soiand Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (61+. 1+) 1+0 (61+. U) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (T.6)

50 (15.2)

83.0 81.1+ 83.8 82.2 85.1+ 85.1+

78.0 T9.0 80.8 T9.6 81.8 82.0

Pad 3, Limestone Hot-Mix Asphaltic Concrete (Terrazo Finish)

A-weighted Soiind Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (6U.1+) 1+0 (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (T.6)

50 (15.2)

79.8 81.0 82.1+ 82.2 83.6 85.8

75.8 76.0 78. 0 TT.1+ T9.2 T9.8

Pad h. Crushed Gravel Hot-Mix Asphaltic Concrete

A-weighted Sound Level , dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (61+. 1+) ho (6U.1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (T.6)

50 (15.2)

80.0 T9.8 82.2 82.6 81+.^ 83.6

73.1+ Ih.h 16.6 76.8 T8.6 80.O

Pad 5, Romded Gravel Hot-Mix Asphaltic Concrete

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (61+. 1+) 1+0 (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (T.6)

50 (15.2)

77.1+ 7T.2 81.0 80.8 83.8 83.1+

T3.0 13. h T5.2 T5.1+ T8.6 T9.0

51
Pad 6, Rounded Gravel Asphalt Chip Seal

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

Uo i6h.k) ho {6k. h) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

81.2 81.0 Qk.k 8)4.6 87.0 87.8

76.0 75.6 79.0 79-2 81. U 82.0

Pad 7 J Lightweight Aggregate Asphalt Chip Seal

A-veighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

Uo {6k. k) ko {6k.k) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

79.6 79.8 8I4.2 83.2 87.0 86.

k

TU.I4 Ik.k 78.8 78.0 81.6 81.6

Pad 8, Lightweight Aggregate Hot-Mix Asphaltic Concrete

A-weighted Sound Level, dB j-q 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

Uo {6k. k) ko {6k. k) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

81. 14 81.2 83. u 83.8 85.^ 85.8

75.8 76.2 78.0 78.2 80.8 81.0

52
Figure A-3. Characteristic tread element pattern of tire TI (pocket

retread) . The noininal new tread depth for this tire was 12/ id

inch (0,95 cm)

53
7 \ \
Tire TI

Pad 1, Portland Cement Concrete

A-veighted So^^id Level, dB re 20 yPa

Mcrophone

Location, ft {zl)

Nominal Speed, mph (km/hr)

ho (6li.li) ho {6h.h) 50 (80.5) 50 (80.5) 6o (96.5) 6o (96.5)

25 (7.6)

50 (15.2)

91.6 91.6 95.6 95-1+ 97.2 98.0

85.6 85.1+ 89.6 90.8 92.8 92.6

Pad 2, Asphaltic Concrete with Jennite Plush Seal

A-veighted Sound Level, dB re 20 yPa

1*11 crophone

Location, ft (n)

Nominal Speed, mph (km/hr)

ho (64.1+) 1+0 (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

93.8 93.1 97-6 98.2 100.2 99.0

59.6 89.8 92.8 93.5 9^.2 9^.6

Pad '3i Limestone Hot-Mix Asphaltic Concrete (Terrazo Finish)

A-weighted Sound Level, dB re 20 uPa

Microphone

Location, ft (m)

llomlnal Speed, mph (km/hr)

i+0 (61+. 1+) 40 (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

8I1.O 83.6 87-8 88.0 92.8 9^.0

^7.e 77.1^ 82.8 81.6 87.1+ 87.0

Pad h. Crushed Gravel Hot-Mix Asphaltic Concrete

A-veighted Sound Level, dB re 20 yPa

Mcrophone

Location, ft (m)

l^ominal Speed, mph (km/hr)

ho (61+. 1+) Uo (6i+.i+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

79.6 80.2 81+. 8 87.1+ 88.2 88.2

73.8 7I+.8 80.6 19-h 83.8 83.8

Pad :? , r.c-onded C-raveJ. £ot-Mix Asphaltic Concrexe

A-veightel So-ond Level, dB re 20 iiPa

Microphone

Location, ft (m)

nominal Speed, mph (km/hr)

1+0 {6h.h) 1+0 {Gk.k) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6:

50 (15.2)

5- .0 81.2 84.6 86.6 91.6 90.8

7I+.6 75.0 78.6 78.6 Si+.8 81+.

8

55
Pad 6, Eounded. Gravel Asphalt Chip Seal

A-weigh-ted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

ko {6k. h) ho {6k.h) 50 (80.5) 50 (80.5) 60 (9^-5) 60 (96.5)

25 (7.6)

50 (15.2)

81.8 81. U 86.1+ 86.1+ 89.0 88.2

77. 6 76.0 80.2 81.2 81+. 0 81+.

0

Pad 7? Lightweight Aggregate Asphalt Chip Seal

A-weighted Sound Level, dB re 20 yPa

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 (61+. 1+) ho (61+. 1+) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

82.2 81.8 85,6 86.2 87.8 88.2

77.1+ ll.k 80.0 81.2 85.0 81+. 1+

Pad 8, Lightweight Aggregate Hot-Mix Asphaltic Concrete

A-weighted Sound Level, dB re 20 yPa

Mi crophone

Location, ft (m)

Nominal Speed, mph (km/hr)

1+0 {6h.h) 1+0 (61+. U) 50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5)

25 (7.6)

50 (15.2)

88.0 87.8 9h.6 92.6 96.6 95.^

81.6 82.8 89.0 88.6 90.6 91.0

56
TEST PAD 1

CM

"J 70 -

< 50 -

I I I I I I I I I I I I I 10.0

50

40 I i I I I I I I t I I I I I I ill

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-4. One-third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A-weighted

sound level. These plots correspond to a vehicle coastby of

50 mph (80.5 km/hr) on test pad 1. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

57
TEST PAD 2

80

QCSJ

CD

LU

<

CD

LU

<

I—O

o

a

C3C

UJ

o

70 -

601-

50

TIRE TB

I I I I I I I I I I I I I I I

I I I I I I I I I I

50

40 I I I I I I I I I I I I f I I I I I I I I I I I I I

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-5. One- third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A-weighted

sound level. These plots correspond to a vehicle-coastby of

50 mph (80.5 km/hr) on test pad 2. 'New rib tires were mounted

on the steering axle and the test tires on the drive axle.

58
TEST PAD 3

^ 40 I I I '

I I I ' 1t 'I i I I I I' I I 1I I I I I I 0.1 1.0 10.0

40 I I I 'I I I I ' I I I ' I I I I I I I I I I I I I I 0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-6. One- third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A-weighted

sound level. These plots correspond to a- vehicle coastby of

50 mph (80.5 km/hr) on test pad 3. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

59
TEST PAD 4

80

CD

<

00

<

Io

TIRE TB

I 'I I I t I I I i I I i I 1 I I I I I I

70 -

60

60

0.1

TIRE TD

1.0 10.0

I I I I I I i [ I i I I I I I I I I I I I 1.0 10.0

1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-7. One-third octave band sound pressure levels versus frequency

as measured at the~ 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A-weighted

sound level. These plots correspond to a vehicle coastby of

50 mph (80.5 km/hr) on test pad 4. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

60
TEST PAD 5

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-8. One-third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A—weighted

sound level. These plots correspond to a vehicle coastby of

50 mph (80.5 km/hr) on test pad 5. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

61
TEST PAD 6

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-9. One-third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 m) microphone at the time

corresponding to the occurrence of the maximum A-weighted

sound level. These plots correspond to a vehicle coastby of

50 mph (80.5 km/hr) on test pad 6. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

62
TEST PAD 7

CO

LU

<

O

o

0.1 1.0

BAND CENTER FREQUENCY, kHz

Figure A-10. One-third octave band sound pressure levels versus frequency

as measured at the 50 foot (15.2 n) microphone at the time

corresponding to the occurrence of the maximum A-veighted

sound level. These plots correspond to a vehicle coastby of

50 mph (80.5 km/hr) on test pad 7. New rib tires were mounted

on the steering axle and the test tires on the drive axle.

63
TEST PAD 8

, 80 r- —

40 I ' I I' I i I I i 'I I I ' I I I I I I I I I I I i

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-11. One- third octave band sound pressure levels versus

frequency as measured at the 50 foot (15.2 m) microphone

at the time corresponding to the occurrence of the maximum

A-weighted sound level. These plots correspond to a vehicle coastby of 50_mph (80.5 km/hr) on test pad 8. New

rib tires were mounted on the steering axle and the test

tires on the drive axle.

64
TalDle A-1. Decrease in maximim A-weighted sound level

(in decibels re 20 yPa) from 25 to 50 feet

(7-6 to 15.2 m) observed for test tire TB

running on the various test pads. The

speeds Uo, 50 and 60 mph correspond to 6h.k,

80.5, and 96.5 km/hr, respectively.

Pad ^(25) - L^(50) Average

IxO rrmVi 50 mph 60 mph

1 ^.5 5.0 5.0 h.Q

2 5.8 h.6 l+.O h.Q

3 5.5 h.l h.6 h.l

h 5.6 h.9 h.Q 5.1

5 5.h h.l h.3

6 2.7 3.3 3.2 3.1

7 h.2 ^.5 3.9 h.2

8 6.1 h.2 h.6 5.2

Average 5.1 h.3 h.3 1+.6

Table A-2. Decrease in maximum A-veighted sound level

(in decibels, re 20 yPa) from 25 to 50 feet

(7-6 to 15.2 m) observed for test tire TD

running on the various test pads. The

speeds hO, 50 and 60 mph correspond to 6h.h,

80.5, and 96.5 km/hr, respectively.

Pad

Number

L^(25) - La(50) Average

ho mph 50 mph 60 mph

1 h.O 3.U 3.2 3.5

2 3.1 2.8 3.5 3.3

3 h.3 h.6 5.2 1+.8

k 6.0 5.7 h.6 3.h

5 l+.i 5.6 5.3 5-0

6 5.3 5.U 5.7 5.5

T 5.3 5.3 5.1 5.2

8 5.3 5.5 ^.7 5.2

Average h.Q li.8 ^.7 h.l

65
Table A-3. Decrease in maximiun A-weighted soiind level

(in decibels re 20 yPa) from 25 to 50 feet

(7.6 to 15.2 m) observed for test tire TI

r\mning on the various test pads . The

speeds ho, 50 and 60 mph correspond to 6k. k,

80.5? and 96.5 km/hr, respectively.

Pad L^(25) - L^(50) Average

ho mph 50 mph 60 mph

1 6.2 5.3 h.Q 5.h

2 3.9 h.l 5.2 U.6

3 6.2 5.7 6.2 6.0

1+ 6.1 6.1 h.h 5.5

5 6.3 7.0 e.h 6.6

6 i+.8 5.7 h.6 5.0

T k.l 5.3 3.3 h.2.

8 5.7 h.Q 5.2 5.2

Average 5.U 5.6 5.0 5.3

66
5 • Appendix B

Macrotext\n'e Profile Measurement Results

The macrotexture profiles measured with the macrotexture profile ti^acer are reported for the eight test pads located at the Texas Transportation

Institute, College Station, Texas. These measurements vere made by the personnel of the Pennsylvania Transportation Institute, University Park, Pa.,

under contract to the National Bureau of Standards (program sponsored "by the

U. S. Department of Transportation). The data are presented in tabular form

as an arithmetic mean and standard deviation of the profile (displacement)

band level in dB re 1 m (rms) for the one-third octave bands corresponding to

the space frequency from 25 to 10,000 cycles per meter. These data are based

on five profile traverses in a direction parallel to the traffic flov. The

data are also presented in graphical form as plots of one-third octave band

macrotexture profile levels in dB re 1 m (rms) versus space frequency for the

eight test pads

67
Table B-1. Mean and standard deviation of the profile band levels for test

pad 1, as measured vith the macrotexture profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in

for the one-third octave bands corresponding to the space

in cycles /meter

.

dB re 1 m (rms)*

frequency

Band Center

Frequency" 25 31.5 ho 50 63 8o 100 125 l6o

Mean 82.8 83.9 Qk.k 8U.7 83.1 82.3 83.1 87.1 87.0

Standard

Deviation 2.U U.5 1.9 1.8 ^.5 1.2 2.7 1.8 1.^

Band Center

Frequency 200 250 315 i+00 500 630 800 1000 1250

Mean 86.3 86.9 88.1 87.8 90.

U

91.5 92.6 93.6

Standard

Deviation 1.7 1.3 1.0 0.7 0.7 1.1 1.0 1.0 0.7

Band Center

Frequency 1600 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 9^.2 97.

6

97.7 99.1 98.9 102.1 100.7 102.2 100.9

Standard

Devi ation l.k 2.2 2.1 h.5 3.9 l.k 3.5 2.k 2.5

*A11 dB values are negative.

f

68
I aso>•o

LU

o

LU

<

Q.

C/3

0 CJ CQ •H

0)o

a) 03 P< CQ u

m (U -p

;3 m -p iH 0

03 CQ <D > -p

-po o

!> 03 -P o 0

CQ 03 g r-i g 0

<U a H

> •H r-\

-!-) 03 H -P ^

s 03

(U iH -P -p

•H H •H o O o3 •H

-P

ft (U 0 O

^ 0

-p %i

03 •H

o3 0 TZf -p 0

X s o3 03

0) -p CQ CQ o 03 -p •H ^ a

o •H to iH o 0

Pi CQ

%i

03 03 0

Ph -P >

g3 03 ^ -p O

CQ -P

d) !> 0

03 fs H

-P 0 •H o O O

O 03 o

U

13 -P U

•r-i 0 0

CD ^^ t> -p H •H

1 o G

o O

H

I fP0

•H

CO

I in

I in

I LA LA

suiJ lut aj gp '13A3T QNVfl 3AVi30 adlHi-3N0

69
Table B-2. Mean and standard deviation of the profile band levels for test

pad 2, as measured with the macrotexture profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in

for the one-third octave bands corresponding to the space

in cycles /meter

.

dB re 1 m (rms)*

frequency

Band Center

Frequency 25 31.5 ho 50 63 80 100 125 l6o

Mean 92.5 90.1 89.7 91.5 9^.0 96.3 98.1 98.6 98.6

Standard

Deviation l.T 3.9 2.U 2.1 h.O h.k 6.0 6.5 5.8

Band Center

Frequency 200 250 315 i;00 500 630 800 1000 1250

Mean 98.6 99.1 99.2 98.

H

98.2 98.3 97.

6

97.6 95.7

Standard

Deviation 5.3 I^.2 3.0 1.9 1.2 1.6 1.6 1.5 0.7

Band Center

Frequency l600 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 95.2 96.9 95.6 95.6 95.3 9^.8 97.6 96.6 102.5

Standard

Deviation l.T 1.1 0.5 h,6 0.6 1.3 2.9 2.7 1.5

*A11 dB values are negative.

70
I O

o

>-

LJJ <

0

o

03 Ch

05U

-P

-PO

-P

(U H -P

CD ^

H -P-H

Cm > O

ft (U

• U

J3W

o3

CD

H

03

03ft

-P s

(D -P CQ O 05 U

O '

C6 CM

•H C

^ O

o3 -H

-p

0) o ^ 0) p ^

•H

(D ^

U

03

•H G

-P

I a" a u O Cm

CVl

I pq

•H

-P -H •H ra O 0

ft 02

o5 0

-p >

o5 c6 Q ^

-p

• 0

^ -H 0 -H O Ch

o5 O

fn ^

-p ft 0 0 H >

•H -H • <M Cm >

o o

ft O Cm

SlUJ lui. 8J gp 'n3A31 QNVfl 3AVi00 a«IHi-3N0

71
Table B-3. Mean and standard deviation of the profile "band levels for test

pad 3, as meastired with the macrotextiire profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile hand levels in

for the one-third octave hands corresponding to the space

in cycles/meter.

dB re 1 m (rms)*

frequency

Band Center

Frequency 25 31.5 i+O 50 63 80 100 125 160

Mean 79.

5

76.

5

76.9 Ik.h 72.6 72. i+ 7ii.5 75.0 7U.2

Standard

Deviation 2.3 3.U h.3 1.2 2.h 1.6 1.0 O.h l.h

Band Center

Frequency 200 250 315 Uoo 500 630 800 1000 1250

Mean 76.1 79.0 80.3 82.5 Qh.3 85.0 Ql.h 87.3

Standard

Deviation l.T 1.3 1.1 1.5 0.8 1.3 1.8 1.6 1.3

Band Center

Frequency l600 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 89.0 91.^ 92:5 93.3 9h.l 9^.2 95.1 95. i+

Standard

Deviation 1.5 2.0 1.9 1.9 l.h 1.7 0.5 0.1 0.0

*A11 dB values are negative.

72
«

EI o>«u

O

UJ

<

0 o

w •H

03 Ch o ,Q «H

03 03 ft w ?H w

^

-P w H (U

pi o3 w 0) t> +^

!h -P

(D o O

!> cr ea +^ w o3 H

H e (D

(U o H

> •H H

0) -P o3 H -P (L) ar

<D ft

rH -P -P •H •H •H a

Ch > !h o

O o3 •H

fn -P ft O

(U

<U -P P

as TP

+^ (U X S o3 oi

(D +J CO O 03 -P •H ^

CJ •H m

o3 on o 0

S

t:! ft w^

t5 03 cd 0

f3 ft -P t> o3 o3 k3 ^ St Q tr > -p 0

o3 ^ H 4J •H O o o Ch o o3 O

^

>-5 -p ft o

•H a 0) 0

(D H !> -P •H •H

1 <W >

0) O o

a ^( H

o ft o

CO

I pq

•H

in

CO

in m

I in in

SUJJ uii. 8J gp '13A31 QNVa 3AV130 aUIHi-3N0

73
Table B-h. Mean and standard deviation of the profile band levels for test

pad h, as measured with the macrotexture profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in

for the one-third octave bands corresponding to the space

in cycles /meter

.

dB re 1 m (rms)*

frequency

Band Center

Frequency 25 31.5 ho 50 63 80 100 125 160

Mean 72.5 71.1 70. 14 73.0 70.7 70.3 71.3 70.8 72.3

Standard

Deviation 1.5 2.2 1.0 2.2 2.1 1.0 2.1 1.3 2.1

Band Center

Frequency 200 250 315 1+00 500 630 800 1000 1250

Mean . 72.

T

7i+.5 75.3 76.1 77.5 78. 1; 79.2 81.7 82.5

Standard

Deviation 1.9 2.3 1.6 1.7 1.7 2.1 1.6 116 2.0

Band Center

Frequency 1600 2000 2500 3150 J+000 5000 6300 8000 10000

Mean 83.2 85.3 86.9 88.3 89.5 89.

U

91.6 90.5 91.9

Standard

Deviation 2.3 2.2 2.1 2.9 2.k 3.6 h.3 3.9 1.2

*A11 dB values are negative.

74
_ s

CM

EI o>•o

O

LU

O

LU

LUO

C/3

(U 0

•H

Ch O <HIo3 Ph 0) m h ue P

CQ -p H 0

X

<i) > u +j

(L) o 0

!> ^ 03 -P o <u

Ul rH H e 0

(U o H

;> H+J 03 H -p ^

s o3

(U 4::; ft H -p -p

•H •H •H

Ch > 0

O o3 •H U -P

ft (D 0

^1 ^ 0

(D -P U

•H p ce 0

+J (US 03 o3 (U -p m m

o 03 -p H

u

u r. •H0 0

ft m

U

o3 0

ft -p >

cd o3 o3 -p Q eM, to -P

CD (U !> -p 0

cd H

-P 0 •H o o 0 Ch O cS 0

U

-p ft O

•H 0 0

(U H

+^ pl •H •H

1 Ch

<u (UU G

o Ch ft 0

-It

I

(90 •H

P4

10 10

sujj UJMJ 8P '13A31 QNVa BAViOO QUIHl-BNO

75
Tatle B-5. Mean and standard deviation of the profile "band levels for test

pad 5, as measured "with the macrotexture profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in

for the one-third octave bands corresponding to the space

in cycles /meter

.

dB re 1 m (rms)*

frequency

Band Center

Frequency- 25 31.5 ko 50 63 80 100 125 160

Mean 75.

T

77.2 75.6 72.6 73. i+ 72.6 73.1 Ih.h 75.1

Standard

Deviation 2.9 6.U 2.0 1.7 2.8 0.9 1.8 1.5 1.6

Band Center

Frequency 200 250 315 Uoo 500 630 800 1000 1250

Mean 76.6 77.6 79.3 79.7 81.2 82.3 83.2 85.9 86.0

Standard

Deviation 1.6 0.7 l.h 1.9 1.7 2.6 2.1 2.7 2.0

Band Center

Frequency i6oo 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 87.3 89.8 91.6 93.5 gh.o 9U.9 95.3 95. i+ 9^-5

Standard

Deviation 1.3 0.9 2.2 2.5 1.6 1.2 0.I4 0.1 2.2

*A11 dB values are negative.

76
in

I C/3 u

u

LU

CO

0 0

CQ •H

03 <M

CJ ^ <M

03 o3 P< CO

CO 0

w -p t—

0

><i o3

CO (U f> 4J 4^ 0 o 0

>. o

c30

4J

CO 03 g rH g 0

0 H

> 0) •H

CD 4-> rH 0 u

(j3 CJ ft H -p -p •H •H •H fil Is 0

is •H

-p

ft <D 0 0

'rH 0

CD pi -p ^.

CO •H ^ 0

-p (U X S cS iS

0) 4J CD CO G

o CS -p •H o r\ •H CQ

cS UA 0

ft CQ^

g3 03 0

ft 4J f>

c3 o3 St Q tr

Q) 0

> -P 0

^ r-i -P 0 •H o 0 0 <^ o Ch o3 0

t:! !>> -P ft

^1 u

•H 0 0 H !> ^ •H H

1 Ch 0 0 0 0

5^ ^1 O «H ft 0

i pq0

u

pi

•ri

F>4 m

CO

i in

00

lA

I un to

siuj lui. 8J gp '13A31 QNVa 3AVi00 aaiHi-3N0

77
Table B-6. Mean and standard deviation of the profile band levels for test

pad 6, as measured with the macrotextiire profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in dB re 1 m (rms)*

for the one-third octave bands corresponding to the space frequency

in cycles /meter

.

Band Center

Frequency 25 31.

5

)i n 50 d3 AnoO ~\ r\r\ 100 HOC 125 loO

Mean 72.

6

TU.6 70.3 71.6 69.6 70.3 70.5 70.2 73.0

Standard

Deviation 2.2 3.2 1.6 2.2 2.h 2.8 2i7 1.2 1.3

Band Center

Frequency 3-L> D Ann ouu ±uuu

Mean 75.5 77.6 79. i+ 81.

U

82.7 85.2 87.5 87.3

Standard

Deviation 2.0 2.1 2.2 3.1 3.U 3.2 2.8 2.9 1.^

Band Center

Frequency 1600 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 88.9 92.1 91.8 93.6 9U.6 95.1 95.1 95. i+ 95.5

Standard

Deviation O.T 0.9 1.5 1.2 1.2 0.7 0.7 0.1 0.1

*AJ.l dB values are negative.

78
CM

09

09

E

e/9 J9o

o

>-'"

<

CO

0 o

tn •H

0) o3 Ch o tH

cd 03 ft 0 m !h w u ue -P

us al he 0 ;> p

+^O o

> cr ea +^ S H

H S 0

0) o H > 0 •H rH

OJ +^ o3 rH

me ar le th -p ft •H •H •H

Ch o

O 03 •H

!h X3 -P

ft 0 0 O

0

(U -P ^

U •H

7i 03 0

+^ 0 U

x; S 03 o3 0

-p CO W

o cd -P •H u

o •H K! VD O 0

t3

ft rs

cd 03 0

ft 4J >

oj o3 o3 St Q tr 0

> +^ 0

^ H 4J !^ 0 •H o O O o ra ro -p ft o

•H 0 0

0 H >

-p ;=! •H

1 Ch 0 0 O o

u ^ H O ft o

VD

I pq0

•H

(O

I lA

I in A

SUIJ Ult 8J gp *13A31 QNVfl 3AViOO aUIHi-3N0

79
Table B-T- Mean and standard deviation of the profile band levels for test

pad 7 , as measixred with the macrotextiire profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard

for the one-third

in cycles/meter.

deviation of the profile band levels in

Dctave bands corresponding to the space

dB re 1 m (rms)*

frequency

Band Center

Frequency 25 31.5 ho 50 63 80 100 125 160

Mean 71.0 lh.9 71.6 72.2 11.

k

72.1 71.6 72.1 73.1

Standard

Deviation l.T 5.0 1.2 2.9 1.8 2.0 2/6 2.2 2.h

Band Center

Frequency 200 250 315 hOO 500 630 800 1000 1250

Mean 75.1 76.0 11.

h

78.7 80.5 81.^ 82.5 Qk.h 8U.9

Standard

Deviation 1.9 2.3 1.5 1-9 3.0 2.6 2.5 1.7 1.9

Band Center

Frequency i6oo 2000 2500 3150 Uooo 5000 - 6300 8000 10000

Mean -86.0 87.9 89.9 90.7 91.

h

91.6 9h.2 95.0 95.0

Standard

Deviation 2.2 2.1+ 1.7 1.9 1.8 h.O 2.h 1.2 1.1

*A11 dB values are negative.

80
- 8

CM

5?

EICO

o

u

<

1) 0

CO *rH o3 <iH o ^ Ch

03 o3 n. (l) CO !h CO (U

;ii -P

CO P-l

1—' o3 ^

CO <u |> -P

^1 O 0

cr -P

CO o3 g H

fi 0)

(U o H

[> •H H

(U 4J 03 +i OJ !h

<D Xi 5

pa

r-\ -P 4J •H •H H a

(in > 0

o •H

t3 -P

ft QJ

Ih a>

0)

to Im •H 3 o3 +j

><; o3 o3

(L) CO CO o 03 -p •H o •H CO

03 t~- 0 0) g ft CO^

o3 05 0) ft -P >>

03 o3 o3 St 0 tr

0)

t> p 0)

oJ U H

-p u Q) •H o o 0 «H o ra ro -p ft o

•H QJ (D

<U H t> -P pi •H •H

1 tH «H

(D 0 0

^^ H O ft 0

SUM uii. 8J gp '13A31 QNVS 3AV130 aUIHi-3N0

81
Table B-8. Mean and standard deviation of the profile band levels for test

pad 8, as measured with the macrotexture profile tracer. Data

are based on five profile traverses in a direction parallel to

the traffic flow.

Mean and standard deviation of the profile band levels in dB re 1 m (rms)

for the one-third octave bands corresponding to the space frequency

in cycles/meter.

Band Center

Frequency 25 31.5 ko 50 63 80 100 125 160

Mean 78.9 77-6 79.3 79.9 78.9 78.2 78.7 77.1 77.2

Standard

Deviation 5.0 3.0 3.2 h.l 3.3 3.3 2.8 1.2 1.3

Band Center

Frequency 200 250 315 1+00 500 630 800 1000 1250

Mean 78.

5

80.3 81.0 81.5 83.0 Qk.3 85.6 87.5 88.0

Standard

Deviation 1.0 2.0 l.h 2.k 1.8 1.9 2.1+ 2.0 1.1

Band Center

Frequency l600 2000 2500 3150 Uooo 5000 6300 8000 10000

Mean 89.2 92.1 92.9 93.7 9H.O 9h.J 9U.7 9I+.3 95.3

Standard

Deviation 1.7 1.9 2.3 2.h 2.0 1.2 1.2 1.8 0.5

*A11 dB values are negative.

82
CM

in

to

in

CO

I I in

O

o

o

o

Z

LU

<

C/3

0)o

03Ph (U w -p ? X

Ui d) U -P

(D O

f> ^

CJ w cs3 H S

t> <u

<u ^

H -P

<u ^

H -P •H -H o

ft <U

pi -P

!>< 0) -Po

O

cS CO

ft

,^2 -P > -P

ce -p ^

o o

O «H

?M a

o

03 +J

O H

•H H

-P 03 <D Sh S o3 2 ft H C

Jm O

03 -H

-p

0) o

0

P fM •H

03 03

•H

1 0 0) O «H

CO

pq

•H

-P -H

•H W

O <U ft W

o3 (U -P >

03 03 P ^

-P

• 0) ^ H

0) -H O '+H 03 O

U U

-P ft

0) 0) H !> •H -H • o o

!h C H

ft O Ch

SIUJ lUMJ gp *liA31 QNVa 3AVi30 aaiHi"3N0

83
6. Appendix C

Instrioment Descriptions

6 / Unless otherwise stated, all instruments are Brilel and Kjaei^ .

Type UA 0207 Windscreen : When a microphone is exposed to wind, and wind

velocity variations, the turhulence created cause a noise to be generated

due to a variation of air pressure on the diaphragm. To reduce this

extraneous wind noise, a spherical windscreen constructed of specially

prepared porous polyurethane sponge was utilized.

Type k220 Pistonphone : This instrument is a small, battery-operated precision

sound source which provides quick and accurate direct calibration of sound

measuring equipment. When fitted to a B & K microphone, the pistonphone

produces a sound pressure level of 12k +0.2 dB, re 20 yPa, at a frequency

of 250 Hz +1% (controlled by means of a transistor circuit). Maxim.um

stability and a very low distortion (less than 3% at 250 Hz) result from

the piston arrangement consisting of two pistons moving in opposite phase.

The calibration of the pistonphone is performed at normal atmospheric

pressure. Ambient pressure corrections are necessary for pressures other

than 760 mm Hg. This calibration is not influenced by relative hiomidities

up to 100^ or temperatures within the range of 0 - 60°C (32 - lUo°F).

Microphone : When one speaks of a microphone, a three part minimum system is

implied: (l) a protecting grid; (2) a condenser microphone cartridge; and

(3) a microphone preamplifier or cathode follower. For this testing the

following components were utilized.

Type U16I One-inch Condenser Microphones : The one-inch free-field con- denser microphone is a type possessing relatively high sensitivity and

covering a range of applicability from 2 Hz to I8 kHz (frequency range)

and 15 dB to iho dB (dynamic range). A feature of these microphones is

long-term stability under a variety of environmental conditions and

insensitivity to temperature variations. Condenser microphones, in

addition, were chosen because of their higher dynamic range, ease in

calibration, and uniform frequency response. The cartridge which houses

the microphone diaphragm is protected by the grid on one side and on the

other is normally screwed onto the preamplifier. This particular microphone vents into a dehumidifier (which is located between the microphone

and the preamplifier) rather than air. The silica gel drys the air used

by the microphone for pressure equalization.

— Commercial instruments are identified in this report in order to adequately

specify the experimental procedure. In no case does such identification

imply recommendation or endorsement by the National Bureau of Standards, nor

: does It imply that the equipment identified is necessarily the best available

for the piorpose.

84
Type UA 0310 Dehumldifier : The dehiomidifier is designed to be moionted

between the hl6l condenser microphone and its amplifier. It contains

silica gel to dry the air used "by the microphone for pressure equalization. When used in 100^ relative humidity situations, the silica gel

requires drying approximately once a month. The drying is accomplished by

heating the silica gel for some hours at a temperature of 100°C.

Type 2619 Half-inch FET Preamplifier : This preamplifier features a very

high input impedance field-effect transistor, which represents virtually

no load to the microphone cartridge. To mate the 2619 with the ^l6l a suitable adapter must be utilized (model DB-03T5)'

Built into the preamplifier itself is a 5.3V heating coil to prevent

condensation when operation miust be carried out in cold or humid environments .

The above described microphone subassembly jprovides reliable operation

over a wide range of temperature, numidity, and vibration and allows

precision soTind pressure measurements to be made over a wide frequency and

dynamic range.

Type 2Qok Two Channel Power Supply : This unit is a portable, batterydriven supply unit designed to provide the necessary polarization voltage

for condenser microphones and their accompanying preamplifiers.

NBS Field Instinmentation : To facilitate data acquisition in the field, this'

battery-powered instrumentation system. was designed and fabricated by KES

specifically for application to passby noise measurements. The unit

contains a 60 dB variable gain amplifier which provides the needed signal

conditioning (ampli fication/attenuation) prior to recording. In addition

to recording the signal, weighting networks and hold circuitry are included to allow for direct readijag of the linear and A-weighted fast

response sound level observed during the passby. The hold circuitry and

weighting networks meet the Type 1 requirements for the fast dynamic

characteristic and the A-weighting response, respectively, of American

National Standard Specification for Sound Level Meters, S1.U-19T1. The

flat frequency response hold circuitry provides an indication as to

whether or not a tape channel, had become saturated (i.e., the signal had

exceeded the dynamic range of the recorder) and thus the data were not

acceptable. The A-"Vfeighted hold circuitry allowed for. direct reading of

the A-weighted sound level observed during a passby without the necessity

for returning the 'tape recordings to the laboratory for reduction and

analysis.

Nagra Model SJ Tape Recorder : This unit is a portable 3-track (l/U inch

magnetic) tape recorder with two high quality amplitude modulated sound

tracks (25 Hz to 35 kHz), plus a third FM track for recording very low

frequencies (dc to h kHz), commentaiy, synchronization signals or timing

85
information. The ins.triiment records and reproduces at four speeds — 15,

T-l/2, 3-3/^, and 1-1/2 ips . The two-amplitude modulated channels can be

fed from separate microphone inputs. The volume is controlled by separate

step attenuators.

Type 33^7 Real Time Analyzer : The real time analyzer is composed of two

basic units: (l) type 2130 frequency analyzer and (2) type h^lO control

and display unit.

The 2130 contains a measuring amplifier, filter channels with 1/3-octave

bandwidth, a flat frequency response channel, weighting channels, true RMS

detectors, and the synchronization system for scanning the channels.

The analyzer contains 38 parallel channels. 33 of these channels contain

l/3-octave filters with center frequencies from 12.5 Hz to 20 kHz. The

remaining five channels are reserved for the four weighting network

filters — A, B, C, and D -- and one flat frequency response channel.

The ^710 contains the circuitry for the 12-inch cathode ray tube (CRT),

the Nixie displays, digital readout, and the logic control. The logic

control section controls the analog/ digital conversion and the commimicat-ion sequence for external systems, as well as the internal synchronization in the 33^7 during display or read-out modes.

The level in each channel can be read in dB directly on the screen, while

a Nixie display shows the' output level of any selected channel. This

channel is indicated on the CRT as a brighter trace. The complete channel

display is renewed every 20 msec.

Outputs are provided for both analog instriments (X-Y or level recorders)

as well as digital (on-line computer or tape puncher). The digital output

is in binary coded decimal (BCD) code.

Time constants may be selected from 20 msec to 20 sec so that confidence

limits can be maintained throughout the frequency range.

Model 70^ Raytheon Computer System : The Raytheon 70U computer system is a general purpose digital system that provides a l6-bit central processor

unit with 900 nanosecond cycle time for on-line, real time applications.

The hardware configuration includes an 16K (expandable to 32K) memory system, direct input/output bus, automatic priority interrupt, direct and

indexed addressing, and byte and word addressing and instructions.

Standard peripherals such as high speed paper tape, ASR~33 teletype, card

equipment, and a magnetic tape unit are also included.

86
7- Appendix D

Description of Macrotextiire Profile Tracez^

The profile T;racer used in ttiis study is shovn in Figure 10. The "bed of

the profile tracer consists of a plate on which the drive motor, limit

switches, and dead weight tension restraint system are mounted. The bed is

supported on the pavement "by three adjustahle legs so that it may he aligned

parallel to the plane of the pavement. The hed provides a reference plane

along which a sled is drawn ca"using the stylus to traverse the pavement. The

st3'"lus is attached to the sled through a cantilever spring which maintains a positive stylus pressure to ensvjre contact between the stylus and the pavement

surface. The core of a displacement transducer ,r>a linear variable differential

transformer (LVDT) (H-P Sanborn Model TECDT-500)— , also mounted on the sled,

is spring-loaded against ~":ie stylus holder so that the LvDT core follows the

vertical motion of the stylus as it traverses the pavement. Teflon pads on the

sled provide smooth motion of the sled as it is drawn along the bed. The draw

wire for the sled is taken up gn a pialley driven at 3 rpm by a synchronous

motor (Bodine Model KYC-22T5A1— ) . Tension in the draw wire is maintained

nearly constant by meajos of a restraining wire attached to the rear of the sled

and loaded with a weight. The draw wire and restraining vire are attached ir. such a way that they provide a slight downward component to assure that ~he

sled renains in contact with the bed during the traverse.

The total traverse lengi^h of the sled is 0.305 meters and the horizontal

traverse rate is approximately 0.0039 meters/sec. The LYDT contains an internal modulator-demodulator such that when excited by a DC voltage , it

produces a DC analog signal proportional to the core displacement. The LvDT

has a sensitivity/" of approximately O.I89 volts/cm over a total of the 2.5 cm

linear range.

The styli used in this projec~ vere

steel with an approximate 22'' ccne angle

were oil quench hardened to an es~t"s.':ei

Actual dimensions of two of the s"vli us tor are shown in Fig-jjre I-l.

turned from O.lc cn aian:e~er carbon

7/ . — Details of the operation and calioratxon 01 thxs aevxce vere za^en ircr: a report [16] prepared for the ITational Bureau of Standards imder sponsorship

of the U. S. Department of Transportation by the Pennsylvania Transportation

Institute (PTI), University Park, Pa.

g / — Commercial instr\mients are identified in this report; in order to adequately

specify the experimental prcced'ore. In nc case ices such iien~iii cation

imply recommendation or endcrseneni; by the ITaxicnal I'oreau of Standards,

nor does it imply that the equipment identified is necessarily the best

available for the piorpose.

87

Direct cali"bration of the profile tracer is performed by traversing carefully prepared, sinusoidal calibration s\arfaces (Figures D-2 and D-3) • These

surfaces vere manufactured by photographically reducing computer plotted sine

fimctions and chemically etching stainless steel sheets having a thickness of

0.0127 cm (0.005 in.). Holes for locating pins were etched simultaneously so that the etched sheets could be assembled to provide a laminate approximately

1.3 cm thick. The calibration surfaces contained five sine functions vith

amplitudes and wavelengths as given in Table D-1.

Table D-1. Amplitudes and wavelengths of sinusoidal

calibration surfaces.

Amplitude Wavelength

meters ( in.

)

0.0127 (0.5)

0.00635 (0.25)

0.00318 (0.125)

0.00158 (0.0625)

0.00079^+ (0.03125)

meters (in.)

0.025^ (1.0)

0.0127 (0.5)

0.00635 (0.25)

0.00318 (0.125)

0.00158 (0.0625)

In addition to the sinusoidal calibration surfaces, a steel wedge having 1.25 cm high ramps with nominal 10° and ^5° slopes from the horizontal (Figures T)-h

and D-5) was also used. The actual angles were measured using an optical

comparator. For all calibration surfaces and -for some of the pavements a light

coating of lubricating oil was found to be helpful in reducing chatter and

reducing horizontal drag forces on the stylus on steep slopes.

89
90
Figure D-4. Ramp calibration surfaces.

91
92
8. Appendix E

9/ Description of Test Pavements—

The TTI skid test pads were prepared by placing a controlled surface

course on top of the existing pavement structure — a well-constructed

Portland cement concrete runway of a former jet-training airfield (the one exception was pad 1 which was the original concrete runway). The surfaces,

which represent a number of different construction methods and materials, were

designed to have a range of skid numbers from 20 to TO in several distinct

steps

Each of the eight test pads used in this study were 2k feet (T-S m) in

width and 600 feet (182.9 m) in length with a cross slope of approximately I/8

inch per foot (l.oU cm/m). The pavement surfaces were chosen so as to exhibit

widely different friction levels, friction-velocity gradients, drainage

capabilities, mineralogical properties, and textural classifications. Based

on the materials and methods of construction, these test pads can be

categorized into three groups.

B Group 1 (test pads 3, ^, 5 and 8) was comprised of hot-mixed

asphaltic concrete courses which were surface finished by a variety of

methods for developing a consistent macrotexture and microtexture . The

asphaltic concrete used in these pads was produced in a commercial size

hot-mix batch plant located at the Texas A 8e M Research Annex. These

paving mixtures were placed with a Jgrber-Greene ^lA laydown machine,

Barber-Greene Co., Aurora, Illinois— , in layers approximately 11/2

inches (3-8 cm.) thick. Compaction was accomplished by use of a twelve

ton tandem steel roller using 8 passes, and by a light pneumatic roller

using 15 passes. Asphalt contents in the paving mixtures used in the

construction of these pads were held slightly above optimum to minimize

stripping by the action of water. A single grade and source of asphalt

cement was used. This rnaterial had a relatively flat

viscosity-temperature curve and good durability predicted by laboratory

oxidation and radiation tests (see Table E-l)

(B Group 2 (test pads 1 and 2) consisted of surfaces prepared by cleaning or surface coating previously constructed asphaltic concrete or Portland cement courses.

— Details of the composition of each test pad were taken from references

[El, E2, and E3] listed at the end of this appendix. —'^The conunercial equipment utilized is identified in this report in order to

adequately describe the method of construction of the test pads used throughout this program. In no case does such identification imply recommendation

or endorsement by the National Bureau of Standards , nor does it imply that

this equipment was necessarily the best available for the purpose.

93
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94
B Group 3 (test pads 6 and 7) consisted of asphalt chip seal surfaces.

These test pads were constructed by first laying down a 1 inch (2.5^1 cm)

layer of hot-mix asphaltic concrete (similar to Group l). The asphaltic

concrete vas then hot covered vith asphalt , followed by a layer of ,the

chip aggregate. Final compaction was produced by a light pneumatic

roller using 6 passes.

A discussion of the materials used and the techniques of surface

finishing or coating of each of these test pads follows.

Pad 1: Portland cement concrete

Pad 1 consisted of a surface prepared by initially cleaning the

existing runway using a high pressure spray, followed by periodic

cleaning using a rotary broom and water. The existing runway was constructed of portland cement concrete with a belt drag finish. A

summary of the characteristics of pad 1 is given in Table E-2.

Pad 2: Asphaltic concrete with Jennite^^ flush seal

Pad 2 consisted of a previously constructed asphaltic concrete

course that was surface coated with a clay-filled tar emulsion

available commercially under the tradename Jennite.

The asphaltic concrete course was constructed using the same methods

as previously described for the Group 1 test pads, except that final

compaction by the light pneumatic roller was increased from 15 to 30

passes

The pavement was then thoroughH.y scrubbed using water and fine sand

in a power driven rotary broom. Following the cleaning operation,

four coats of Jennite were applied ^t an approximate application

rate of 0.12 gal/yd (0.5^ liters/m ). The completed surface was allowed to cure and harden three days and then was polished by a large rectangular sponge rubber float towed behind a truck at 8 to

10 mph (12.9 to 16.1 km/hr) . During the polishing of the pavement,

the surfaces were kept wet and fine sand and fly ash were used as polishing aids. ,A summary of the characteristics of pad 2 is given

in Table E-3 (also Figure E-l)

-— Jennite is a commercially available clay-filled tar emulsion manufactured

by the Jennite Company, Houston, Texas. This material is identified in

this report in order to adequately describe the method of construction

of one of the test pads used in this program. In no case does such

identification imply recommendation or endorsement by the National Bureau

of Standards, nor does it imply that this material was necessarily the

best available for the p\irpose.

95
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97

Pad 3: Limestone hot-mix asphaltic concrete "with a terrazo finish

Pad 3 consisted of a hot-mixed asphaltic concrete coiarse that had

been specially siirface finished. The asphaltic concrete covirse,

vhich used limestone as the major aggregate, was produced, layed

down and compacted as described previously for Group 1 test pads.

The pavement was then ground using a gasoline powered terrazo grinding machine eqi^iipped with No. 8o grit carborundum stones. Grinding

was continued tint il all the pavement surface texture presented by

the crushed stone was essentially eliminated. The result was similar to a terrazo floor. After this grinding operation, the

pavement was polished by the same method as pad 2 using the sponge

rubber float and water. Again, fine sand and fly ash were used as polishing aids. A summary of the characteristics of pad 3 is given

in Table E-i+ (also Figure E-l).

Pad h: Crushed gravel hot-mix asphaltic concrete

Pad h consisted of a hot-mixed asphaltic concrete course using

crushed gravel as the major aggregate. The asphaltic concrete

course was produced, layed down, and compacted as described

previously for Group 1 test pads. Following this, the pavement was polished by the same method as pad 2. A summary of the

characteristics of pad h is given in Table E-5 (also Figure E-l).

Pad 5: Rounded gravel hot-mix asphaltic concrete

Pad 5 consisted of a hot-mixed asphaltic concrete course similar to

pad k except that rounded gravel was used as the major aggregate.

The asphaltic concrete course wap produced, layed down, and

compacted as described previously for Group 1 test pads . Following

this , the pavement was polished using the same procedure as described for pad 2. A summary of the characteristics of pad 5 is

given in Table E-6 (also Figvire E-l).

Pad 6: Rounded gravel asphalt chip seal

Pad 6 consisted of an asphalt chip seal surface, which used rounded

gravel as the c]}i-p aggregate. This test pad was constructed by

first laying down a 1 inch (2.5^ cm) layer of hot-mix asphaltic

concrete using methods similar to that used to construct the Group 1

test pads. This hot-mixed asphaltic concrete was then hot covered

with asphalt "^ith an approximate application rate of 0.33 gal/yd

(1.5 liters/m ). This was followed by a layer of rounded grave^

aggregate with a coverage of approximately 17 lb/yd (9.2^ kg/m ).

Compaction was produced by a light pneumatic roller using 6 passes.

The pad was allowed to set for 2k hours, and then was broom cleaned.

This was followed by 2 hours of rerolling with a light pneumatic

roller. A summary of the characteristics of pad 6 is given in Table

E-7 (also Figure E-l).

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Pad 7: Lightweight aggregate asphalt chip seal

Pad T consisted of an asphalt chip seal siirface similar to pad 6

except that instead of rounded gravel, a synthetic lightweight

material (fired clay) was used as the chip aggregate. Again, the

test construction consisted of first laying down a 1 inch (2.5^ cm)

layer of hot-mix asphaltic concrete using methods similar to that

used to construct the Group 1 test pads. This hot-mixed asphaltic

concrete was then hot covered w^th asphalt with^an approximate

application rate of 0.35 gal/yd (I.58 liters/m ). This was followed by a layer of synthetic lightweight aggregate (fired clay)

with a coverage of approximately 10 lb/yd (5-^ kg/m ). Compaction

was produced by a light pnexunatic roller using 6 passes. The pad

was allowed to set for 2k hours, and then was broom cleaned. This was followed by 2 hours of rerolling with a light pneumatic roller.

A summary of the characteristics of pad 7 is given in Table E-8

(also FigTore E-l) .

Pad 8: Lightweight aggregate hot-mix asphaltic concrete

Pad 8 consisted of a hot-mixed asphaltic concrete course using a synthetic lightweight material (fired clay) as the major aggregate.

The asphaltic concrete course was produced, layed down, and

compacted as described previously for Group 1 test pads. The

( pavement was then thoroughly scrubbed with a broom using water and

detergent. After this scrubbing, the pavement was polished using

the sponge rubber float and water as described for pad 2. Again

fine sand was used as a polishing aid. A summary of the

characteristics of pad 8 is given in Table E-9 (also Figure E-l).

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106
Refere::ces for Appendix S

[El] Gallavay, 3. M. , Epps , J. A., and Hargett, Z. ?.. , Design and acns-ruction

of full-scale stopping pads and spin-out curves to predetermine friction

values, Journal of Materials 5_ (2), 303-322 (1970).'

[12] Ivey, D. L., Stocker, k. J., et al. , Pilot field test and evaluation

center (Technical Report 797-3, Texas Transportation Institute, Texas

A & M University, College Station, Texas, 1972).

[E3] Gallavay, 3. M. , Rose, J. G-. , Scott, Jr., W. W. , and Schiller, R. Z.,

Influence of vater depths on friction properties of various pavement types

(Research Report 13S-6, Texas Transportation Institute, Texas A & M

University, College Station, Texas, 197^).

[e1|] American Society for Testing and Materials, D 5-71, Standard Methe d ;f

Test for Penetration of Zif^'ncjis Materials in Part 15 , 5cck of ASlZ'l Standards, 19'^^ (.ASrM, Philadelphia, Pennsylvania! 'Re-.tLsed 1973) .

[E5] American Society- for Testing and Materials, 1 2170-67, St

Test for Kinematic Viscosity of Asphalt in Part 15 , Bock of ASTM Standar:

197^ (ASTI-I, Philadelphia, Pennsylvania) (Revised 197^)

[S6] American Societ;;^ for Testing and Materials. D 113-69, Standard Method of

Test for Tuctility of Bit""-' ncis .'.aterials in Part 15 , Book of AST!-' Standards, 19""- 'AST!-:, Philadelphia, Per-nsylvania) .

[E7] American Society for Testing and Materials, D 36-70, Standard Method cf

Test for Softening Point of Asths.lts and Tar Pitches (Rins— and—3=11

Pennsylvania)

[e8] Gallavay, 3. M. , and Rose, J. 3-., Macrotext-^e , friction, cress slope,

and vheeltrack depression measurements on ^1 typical Texas highvay

pavements (Research Report 135-2, Texas T'ransportation Instit-j.te,

Texas A & V. University, College Station, Texas, 1970).

107
9. References

[l] Anon. , Truck noise-I, peak A-veighted soimd levels due to truck

tires, U. S. Department of Transportation Report OST-ONA-Tl-9

(National Bureau of Standards, Washington, D. C, 19T0) .

[2] Leasure, Jr., ¥. A., Corley, D. M. , Flynn, D. R. , and Forrer, J. S.,

Addendum to truck noise-I, peak A-weighted sound levels due to truck

tires, U. S. Department of Transportation Report 0ST/TST-T2-1

(National Bureau of Standards, Washington, D. C, 19T2).

[3] Leasure, Jr., W. A., and Corley, D. M. , Truck noise-IB, spectral and

directional characteristics of noise generated by truck tires, U. S.

Department of Transportation Report D0T-TST-T5-T1 (National Bureau

of Standards, Washington, D. C, 197^).

[h] Leas-ore, Jr., ¥. A., and Mathews, D. E. , Pecos truck tire noise

study: summary of results, NBS Report NBSIR Jk-hh6 (National Bureau

of Standards, Washington, D. C. , January 197^).

[5] Leasure, Jr., W. A., Mathews, D. E. , and Rinkinen, W. J., Truck

noise I-A, noise evaluation tests of military truck tires, U. S.

Department of Transportation Report DOT-TST-T^-21 (National Bureau

of Standards, Washington, D. C, February 197^).

[6] Tetlow, D., Truck tire noise, S)V Sound and Vibration 5. (8), 17-23

(1971).

[7] Hayden, R. E. , Roadside noise from the interaction of a rolling tire

with the road surface (Proceedings of the Purdue Noise Control

Conference, Purdue University, West Lafayette, Indiana, July li;-l6,

1971).

[8] Wik, T. R. , and Miller, R. F. , Mechanisms of tire sound generation,

published in SAE Report SP-373: Truck Tire Noise (Society of

Automotive Engineers, Inc^, New York, N. Y. , 1972).

[9] Corcoran, D. A, , Effects of operating parameters on truck tire

soiinds, published in SAE Report SP-373: Truck tire noise (Society

of Automotive Engineers, Inc., New York, N. Y., 1972).

[10] Hillquist, R. K. and Carpenter, P. C, A basic study of automobile

tire noise, presented at the 85th meeting of the Acoustical Society

of America, Boston, Mass. (April 1973).

108
[ll] Thurman, G. R., Effect of road surface and bed clearance on truck

tire noise, SAE Report 7^060T (Society of Automotive Engineers, Nev

York, New York, 197^).

[12] Gallaway, B. M. , Epps , J. A., and Hargett , E. R. , Design and

construction of full-scale stopping pads and spin-out curves to

predetermine friction values. Journal of Materials 5. (2), 303-322

(1970).

[13] Ivey, D. L. , Stocker, A. J. , et al. , Pilot field test and evaluation

center, TTI Technical Report 797-3 (Texas Transportation Institute,

Texas A & M University, College Station, Texas, 1972).

[ih] Gallaway, B. M. , Rose, J. G. , Scott, Jr., W. W. , and Schiller, R.

E. , Influence of water depths on friction properties of various

pavement types, TTI Research Report 138-6 (Texas Transportation

Institute, Texas A & M University, College Station, Texas, 197^).

[15] Hudson, W. R. , High-speed road profile equipment evaluation,

published in Design, Performance and Surface Properties of Pavement,

Highway Research Record, Number l89-, 1 50-16 5 (Highway Research

Board, Washington, D. C, 1967)-

[16] Lawther, J. M. , and Henry, J. J., Characterization of pavement

macrotextiore by profile spectral analysis. National Bureau of

Standards Report NBSGCR 75-35 (The Pennsylvania Transportation

Institute, University Park, Pa., 197^).

[17] Leas-ure, Jr., W. A., and Bender, E. K. , Tire-road interaction noise,

J. Acoust. Soc. Am. _58 (l), 39-50 (l975).

[18] Siddon, T. E. , Noise generation mechanisms for passenger car tires,

presented at the 8hth meeting of the Acoustical Society of America,

Miami, Florida (1972).

[19] Clark, S. K. (Ed.), Mechanics of pneumatic tires, NBS Monograph No.

122 (National Bureau of Standards, Washington, D. C. 1971).

[20] Chiesa, A., Oberto, L. and Tamburini , L. , Transmission of tyre

vibrations. Automobile Engineer 5^, 520-530 (December I96U).

[21] Reiter, Jr. , W. F. , Resonant sound and vibration characteristics of a truck tire. Tire Science and Technology, TSTCA, 2_ (2), 130-1^41

(May 197^).

[22] Reiter, Jr., W. F. , Eberhardt, A. C, Harper, L. J., and Atkinson,

T. L. , Truck noise VII-A, experimental investigation of truck tire

sound and vibration, U. S. Department of Transportation Report

DOT-TST-75-60 (Center for Acoustical Studies, North Carolina State

University, Raleigh, North Carolina, December 197^).

109
[23] Th\irman, G. R. , Characteristics of truck tire sound, published in SAE

Report SP-3T3: Truck Tire Noise (Society of Automotive Engineers,

Inc., New York, W. Y. , 1972).

[2h] Wisleder, D. E. , and Johns, J., Traffic noise versus roadvay

surfaces, presented at the 89th meeting of the Acoustical Society of

America, Austin, Texas (April 1975)

[25] Kay, R. A., and Stephens, J. K. , Porous friction courses and roadvay

surface noise, U. S. Department of Transportation Implementation

Package 7^-11 (U. S, Department of Transportation, Federal Highvay

Administration, Washington, D. C. , September 197^)

[26] Rose, J. G. , Hutchinson, J. W, , and Gallaway, Bi M. , Siniimary and

analysis of the attributes of methods of surface texture measurement,

published in Skid Resistance of Highway Pavements, ASTM STP530, 60-77

(American Society for Testing and Materials, Philadelphia, Pa.,

1973).

[27] American Society for Testing and Materials, E27^-70, Standard Method

of Test for Skid Resistance of Paved Surfaces Using a Full-Scale Tire

in Part 15 , Book of ASTM Standards, 197^ (ASTM, Philadelphia,

Pennsylvania)

[28] Close, W. H. , Regulatory implications of truck tire noise studies,

SAE Report 7^06o6 (Society of Automotive Engineers, Inc., New York,

N, Y. , 19lh) .

[29] Leasure, Jr., ¥. A., Mathews, D. E. , and Cadoff, M. A., Automobile

tire noise: results of a pilot study and review of the open

literature, U. S. Department of Transportation Report No.

DOT-TST-76-U (National Bureau of Standards, Washington, D. C, August

1975).

110
Acknowledgements

The authors "would like to recognize the contrihiitions made 'by the following organizations which have greatly aided this program: the staff of the

Pennsylvania Transportation Institute especially Dr. James M. Lawther and

Dr. John J. Henry; the Texas Transportation Institute in particular Mr. A. J.

Stocker and the staff of the Texas A&M University Research Annex; and the

tire companies which loaned the government the test tires used in this study.

The authors also express appreciation to Mr. W. J. Rinkinen for his

assistance in data acquisition and reduction, to Mrs. J. Russell for the typing

and preparation of the manuscript, and to Mr. W. H. Close (Office of Noise

Abatement', U. S. Department of Transportation) for his review and comments.

Ill