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Background Document to
PROPOSED INTERSTATE
MOTOR CARRIER
REGULATIONS
as Published in the
Federal Register Vol. 38, No. 144, Part 1
NOVEMBER 8, 1973
U.S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.C. 2046O
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550/9-73-005
Background Document to
PROPOSED INTERSTATE
MOTOR CARRIER
REGULATIONS
as Published in the
Federal Register Vol. 38, No. 144, Part 1
NOVEMBER 8,1973
Prepared by
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Noise Abatement and Control
Washington, D.C. 2O460
This document has been approved for general availability. It does not
constitute a standard, specification, or regulation.
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TABLE OF CONTENTS
Page
Seci.ion 1 - Statutory Authority 1
Section 2 - Motor Carrier Industry 4
Section 3 - Information Base for the Proposed 7
Regulation
Section 4 - Categories of Interstate Motor Carrier 12
Vehicles
Section 5 - Specific Noise Sources 17
Section 6 - Noise Emission Standards 35
Section 7 - Economic Impact of the Proposed Regulation 52
Section 8 - Environmental Impact of Proposed Regulation 55
Appendix A - Truck Noise Emission Data and Analysis 57
References 64
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LIST OF FIGURES
Page
Figure 1 - Propulsion System Noise Versus 20
Vehicle Speed and Engine Speed
Figure 2 - Propulsion System and Tire Noise for 21
a Typical 5 Axle Tractor Trailer
Figure 3 - Tractor-Trailer Noise Emission Distributions 22
at 35 mph and over 35 mph
Figure 4 - Truck Noise Sources and Cab Types 25
Figure 5 - Peak A-Weighted Sound Level, as 34
Measured at 50 Feet, Versus Speed
for a Loaded Single-Chassis Vehicle
Running on a Concrete Surface
Figure 6 - Estimated and Actual Cost Incurred in 48
Retrofitting Trucks to Various Noise
Levels
Figure 7 - Tractor-Trailer Noise Emission 49
Distributions at 35 mph and over 35 mph
Figure 8 - Truck Noise Emission Road Side Survey 50
Data for Speeds over 35 mph
Figure 9 - Tractor-Trailer Noise Emission 51
Distributions at 35 mph or Less on
Level Roadways
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LIST OF TABLES
Page
Tablt 1 - Estimated Costs to Retrofit Trucks to 37
Various Noise Levels
Table 2 - Percentage of Trucks Exceeding a Given 38
Noise Level During Typical Highway
Operation—California Data
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Section 1
STATUTORY AUTHORITY
RESPONSIBILITIES OF THE ENVIRONMENTAL PROTECTION AGENCY
Through the Noise Control Act of 1972 (86 Stat. 1234), Congress
established a national policy "to promote an environment for all Americans
free from noise that jeopardizes their health or welfare." In pursuit
of that policy, Congress stated, in Section 2 of that Act, "that, while
primary responsibility for control of noise rests with state and local
governments, Federal action is essential to deal with major noise sources
in conmerce, control of which requires national uniformity of treatment."
As a part of that essential Federal action, Section 18 of that Act (86 Stat. 1249)
directed the Administrator of the Environmental Protection Agency (EPA) to
publish proposed noise emission regulations for motor carriers engaged in
interstate conmerce. MDtor carriers subject to such regulations include
common carriers by motor vehicle, contract carriers by motor vehicle and orivate
carriers of property by motor vehicle as these terms are defined by raragraphs
(14), (15), and (17) of the Interstate Commerce Act (49 U.S.C. 303 (a).
The EPA regulations proposed under Section 18 of the Noise Control
Act are to include "noise emission standards setting such limits on noise
emissions resulting from operation of motor carriers engaged in interstate
co rrmerce which reflect the degree of noise reduction achievable through
the application of the best available technology, taking into account
the cost of compliance." Final regulations are to be promulgated only after
consultation with the Secretary of Transportation, to assure appropriate
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consideration for safety and for availability of technology. The regu-
lations are to take effect after such period as the Administrator of
EPA finds necessary, after consultation with the Secretary of Trans-
portation, to permit the development and application of the requisite;
technology. Further, appropriate consideration is to be given to the cost
of compliance within such a period. The regulations promulgated under
Section 18 may be revised from time to tine, in accordance with Subsection
18(a). They shall be in addition to any regulations proposed for new
motor vehicles under Section 6.
RESPONSIBILITIES OF THE DEPARTMENT OF TRANSPORTATION
After final interstate motor carrier noise emission standards have
been promulgated by EPA, the Secretary of Transportation is responsible
for promulgating regulations to ensure compliance with those standards.
This will be accomplished through the use of the Secretary's powers and
duties of enforcement and inspection as authorized by the Interstate Gomnerce
Act and the Department of Transportation Act. These enforcement regulations
are to be promulgated only after consultation with the Administrator of
EPA.
ROLE OF STATE AND LOCAL GOVERNMEiSITS
After the effective date of a regulation on noise emissions from an
operation of interstate irotor carriers promulgated under Section 18, no
state or political subdivision thereof may adopt or enforce a standard on
noise emissions from the sane operation that differs from the one promulgated
under Section 18. State and local governments may, however,
adopt a standard identical to such a Federal standard
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to add their enforcement capabilities to those of the Department
of Transportation.
Further, interstate motor carrier operations not covered by Federal
regulations will remain subject to state and local noise standards and
regulations. Such state and local regulations are limited, of course, by
the constitutional prohibition of state or local action that constitutes
an undue burden on interstate contnerce.
Finally, nothing in Section 18 shall "...diminish or enhance the
rights of any State or political subdivision thereof to estabish and
enforce standards or controls on levels of environmental noise, or to con-
trol, license, regulate, or restrict the use, operation, or movement of
any product if the Administrator, after consultation with the Secretary
of Transportation, determines that such standard, control, license,
regulation, or restriction is necessitated by special local conditions ^
and is not in conflict with regulations promulgated under this section."
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Section 2
MOTOR CARRIER INDUSTRY
This discussion briefly summarizes the organization,
size, and economics of the motor carrier industry in order to
provide a general perspective of the impact of EPA regulations
on that industry. There are over 15,000 firms in the motor
carrier industry. These firms are engaged in moving both
people and property. The majority of their trips are local,
with 70 percent in urban areas or between adjacent counties. (1)
Those firms involved in interstate commerce will be affected by the
proposed EPA regulations.
ORGANIZATION OF THE INDUSTRY
The industry is divided into two general classifications
of carriers: 1, private carriers which use their own or
leased trucks, to move their own goods, and 2. carriers which
provide transportation of others' freight. The latter group of
carriers is further divided into two categories: 1. common
carriers—available to the general public to transport given
types of freight at published rates, between authorized points,
2.] contract carriers—operate under contract with one or more
shippers to serve their distinct requirements;.
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The proposed standards are applicable to those motor
carriers meeting the definition of common carrier, contract carrier, and
carriers of property as set forth in the Interstate Commerce Act.
SIZE OF THE INDUSTRY
The motor carrier industry today is the largest transporter
of goods in this country. In 1971, the gross operating revenue
of the motor carrier industry (from the transportation of
goods) comprised approximately 53 percent of the total among
all regulated carriers. Regulated carriers include: railroads,
motor carriers, water carriers, oil pipelines, and airways.
The industry can be characterized as composed of a large
number of small carriers competing with a few very large carriers*
The number of trucks and buses engaged in the transport
of goods and people in this country has been steadily increasing.
During the period from 1960 to 1970, the total number of trucks
and buses increased from 12.2 to 19.3 million, for an average increase
C521
of 0.7 million vehicles per year.v ' Total miles traveled ner vear
have also increased. For trucks specificallv, total miles traveled-
have increased from 90.5 billion in 1950 tn 206.7 billion in
1969.
ECONOMICS OF THE INDUSTRY
In 1970, the larger intercity common carriers of general
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freight had average assets of $3,243,000, average operating
revenues of $6,837,000 and averaaed $89,300 net income after
taxes. ^
The average revenue for large intercity carriers of general
freight in 1970 was $1.24 per intercity truck-mile. Expenses
for these carriers averaged $1.20 per intercity vehicle-mile,
and of this, wages took $ 0.645 . repairs and servicing
(maintenance) took $ 0.076 fuel and oil $ o.03 (not
including State and Federal tax), and tires and tubes $ 0.019
cents. The major cost in carrier operation is, therefore,
operator wages, and tires and tubes rank fourth. Repairs
and servicing are approximately four times tire and tube costs.
The general economic health of the industry is reflected in
the 1970 financial ratios for large carriers, which include
4.96 revenue to worth, o.oe profit (net after taxes) to worth,
and 0.013 profit (net after taxes) to revenue. ^
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Section 3
INFORMATION BASE FOR THE PROPOSED REGULATION
DATA ACQUISITION
To develop the noise emission standards that constitute this
proposed regulation, it was necessary to establish a well defined
data base. In connection with motor carriers engaged in interstate
commerce, this data base included the following information:
1. The existing noise levels produced by the various
vehicles used by motor carriers under different
operating conditions.
2. The degree of noise reduction possible on these
vehicles, using available technology,
together with the cost associated with this reduction.
3. The percentage of vehicles that would require any
particular treatment or modifications to achieve various
noise levels.
\. The production supply of hardware necessary to achieve
those noise levels.
In order to gather and coordinate the input of the required
information, a Task Force was set up consisting of representatives
from various Federal and state agencies and consultants to the
Environmental Protection Agency. The Task Force reviewed and analyzed
the data and developed recommendations for consideration by the Agency
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in the development of the proposed regulations. In addition, the
Agency amassed technology and cost information submitted to the official
docket of the regulations as a result of the Advanced Notice of
Proposed Rule Making, and information previously developed by the
Agency as part of its hearings under Title IV, P.L. 91-604. ^'-*
AVAILABILITY OF DATA
In general, the main sources of existing highway noise data were
the Federal and State government agencies and knowledge of EPA consultants
Although a certain amount of retrofit information was available from
the vehicle manufacturers, a greater source was the individual component
manufacturer.
Data were analyzed from 5838 diesel trucks operating on freeways
in California in 1965, 531 trucks in the state of Washington in 1972,
and fron 1,000 trucks in New Jersey in 1972.8 These data, collected
before the California noise regulations took effect, and from states
not having noise regulations, were considered to be representative of
existing (1973) noise levels from trucks operating on freeways in
states not having noise regulations.
The noise level data for trucks accelerating at low speed (less
than 35 mph), were taken from 776 trucks in California in 1971 and from
*Since the regulations were proposed on July 27, 1973, additional
data have been gathered from eight other States. See Appendix A.
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239 trucks in the State of Washington in 1972.' For constant speed
operation at speeds less than 35 miles per hour, data were obtained from 340
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trucks in California in 1971.
An additional part of the data base consisted of noise levels
measured from stationary trucks by means of an engine run-up technique. The
data were obtained on 877 trucks by the Society of Automotive Engineers
Vehiclj Sound Committee. There was a paucity of data on the levels of
noise emitted by interstate motor carrier vehicles other than large multi-
axle trucks, which are primarily powered by diesel engines. It is known,
however, that vehicles such as gasoline trucks and buses are inherently
quieter thin large multi-axle diesel trucks, and should have no difficulty
in complying with any noise emission standard which is reasonable for the
(98 99}
latter. ' ' The proposed regulation applies to all interstate motor
carrier vehicles over 10,000 pounds GVWR or GCWR. Additional data will be
obtained in the future so that subcategories of those vehicles, such as
gasoline trucks and buses, may be treated separately in future revisions of
the regulation.
Data on auxiliary equipment of motor vehicles were also limited. Manu-
facturers have submitted some information on the noise emissions from typical
refrigerator units, but additional data will be developed for possible in-
clusion in subsequent revisions of the regulation.
the remainder of this Background Document is based upon an analysis of the
data described in this section.
MEASUREMENT METHODOLOGY DEFINED
The proposed regulation concerns the noise emitted by motor vehicles
engaged in interstate commerce. In order to set a meaningful regulation based
upon specific noise level standards, it is necessary to specify an appropriate
method for characterizing and measuring the noise emission from an individual
vehicle. This entails defining the operation of the vehicle under measurement
as well as the method by which the measurement is conducted.
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In general, there are two main conditions under which motor
vehicles operate, namely
1. Urban driving at low speeds
2. Highway driving at high speeds
In urban areas, the vehicle is seldom allowed to exceed a speed
of 35 miles per hour, except in the western area of the nation where speed
zones of 45 miles per hour are common. On the open highway, and on
urban freeways, vehicle speeds are limited to a range of from about 55 to
70 miles per hour. Subsequent sections of this background document will
show that the noise characteristics of motor vehicles are different
in the two operational conditions. Therefore, the proposed regulation
will include separate noise standards for these two conditions«i.e.,
the two speed ranges. However, if the actual vehicle speed is specified
in the regulation, then subsequent enforcement would require simultaneous
measurement of this speed .along with the noise level produced. 1b remove
this obstacle to enforcement in the proposed regulation, the speed zone
in which the vehicle is operating, rather than the actual speed of the
vehicle under measurement, is specified in the proposed regulation.
For the noise standards to be meaningful it is necessary to
specify the noise level at a given distance produced by a truck when
it is operating under the conditions just discussed. In the proposed
regulation, all references to a quantitative method for specifying the
magnitude of a noise are in terms of the A-weighted noise level scale,
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the units being in dB(A) . A-weighting corresponds
approximately to the way in which a person hears a noise and is effected
by means of a simple electrical circuit contained in most sound
1 ?
level meters. Other scales are available, but they require a more
complex analysis, which is normally not justified by the improved
correlation with human assessment.
The standard measurement distance selected is 50 feet. This is
consistent with current recoimended practice, for the measurement of
both the noise from new vehicles and the operational noise levels
from vehicles on the highway in various states and cities. The
distance of 50 feet is a compromise between 25 feet (the ISO standard
distance), at which slight variations in vehicle distance can lead to
significant errors in the measured noise level, and greater distances
at which background noise and nearby reflecting obstacles can pose a
problem in measurement site selection. Furthermore, almost all of
the data base consists of noise levels measured at this distance. There
may be some occasions when a measurement at 50 feet is not possible or
undesirable; for example, urban or suburban areas with nearby acoustically
reflecting surfaces which could distort the measurement. Alternative
measurement distances together with suitable correction factors to
standardize to a measurement distance of 50 feet can be specified in
the enforcement procedures established for these proposed regulations. The
enforcement procedure should also specify the criteria for selecting
suitable highway measurerrent sites.
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SECTION 4
CATEGORIES OF INTERSTATE M3TOR CARRIER VEHICLES
Interstate motor carriers utilize a broad range of vehicles; from
small two-axle "straight" trucks and buses up to "combination" ( tractor-
(18)
trailer) trucks with 5 or more axles.v ' All of these vehicles contribute to
noise emitted along highways and streets, which sets the ambient noise level in
(19)
most urban communities. But large motor carrier vehicles cause a nod.se
problem that can be separated from the problem of motor vehicls noise
in general. At the present time, diesel trucks emit noise levels
that are so much higher than those emitted by other
motor vehicles that they stand out very noticeably. Ifoise peaks of
12 dB above the ambient noise level from other traffic are common. ^ '
It has been widely acknowledged that such noise peaks are more objectionable
to people than is the ambient noise.'^1)
Trucks weighing less than 10,000 pounds gross vehicle weight rating (GVWR)
typically produce noise levels ranging from 64 to 72 dBA at 35 mph, when measured at
50 feet. This correlates closely to the noise level produced by ordinary
passenger automobiles, which generate up to 68 dB(A) at 50 feet at the
same speed.' ' Such a result is not surprising since the basic noise-
producing components of such small trucks are little different from those
of automobiles. They are powered by gasoline engines similar
in most respects to automobile engines; they have two-axle chassis, and
they usually use rib tires similar to automobile tires.
Trucks of over 10,000 pounds GWR or Gross Combination Weight Rating
(GCWP) for combination vehicles, on the other hand, are different from small
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trucks and automobiles. They can produce noise levels of 95 dB(A) or more at
highways speeds when measured at 50 feet.(23'8' Their hioher noise level can be
accounted for by their canmon use of relatively noisy diesel engines instead of
gasoline engines, their frequent employment of three, four, and five axle designs
using more noise-producing tires, and their occasional use of "pocket retread" tires,
which produce more noise than other tire designs^ ' (see discussion of
tire noise below).
Moreover, trucks of over 10,000 pounds GWR or GCWR are typically
used for long distance intercity and interstate hauling. They are,
therefore, operated many more miles per year on the average than small
trucks, which are usually used for general service and delivery work
(2^
within one relatively small area.v ' Indeed, many small trucks are
devoted to individual uses not unlike private automobiles. The vastly
greater mileage traveled on an average by large trucks than by small
trucks and automobiles causes the former to make up a much larger
percentage of vehicles actually observed on the road than would be
indicated by the percentage they constitute of the total vehicles
registered.* As a result, efforts concentrated on reducing the noise of
large trucks will have a proportionately greater effect than might be
determined from truck registration data.
All of these aspects of large trucks—their relatively high con-
tribution to the noise problem, their design, their typical use, and their
high average mileage—which distinguish them from small trucks and
*See Appendix A.
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automobiles indicate that they should be the focus of EPA efforts under
Section 18 at this time. The problem of noise from small trucks appears
to be more appropriately handled in the same way as the noise from the
automobiles they resemble in design and use; for example, through such, new product
standards as those of Section 6 of the Noise Control Act and through vehicle use
regulations of State and local governments. If in the future it appears
that the operation of smaller vehicles should be regulated under Section
18, the regulations may be revised pursuant to Subsection 18 (a).
The dividing line between large and small trucks has been drawn at
10,000 pounds gross vehicle weight rating or gross conbination weight
rating* because virtually all trucks designed and used much
like passenger cars, are below that weight, while few trucks with signifi-
cantly different characteristics, such as diesel engines, multiple axles, and
significantly higher noise emission levels, are below that weight. Moreover, a
break at 10,000 pounds is convenient because most states use that weight as a
boundary in their vehicle registration categories. In addition it is a
standard weight category distinction used by DOT in their safety regulations.
Compatibility with the present DOT weight categories is advantageous
since DOT is the Federal enforcing agent.
*"Gross vehicle weight rating," GWR, is defined for single vehicles;
whereas "gross combination weight rating," QCWR, is defined for combina-
vehicles such as tractor-trailer trucks.
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The category of interstate motor carrier vehicles over 10,000 pounds
includes many vehicles between 10,000 and 33,000 pounds GVWR or GCWR
powered by large gasoline engines, as well as virtually all of the
interstate motor carrier vehicles powered by diesel engines. As will
be discussed in the section on truck noise characteristics,! diesel
engines are inherently noisier than gasoline engines. In addition, as
a rule, diesel engines are used in heavier trucks that have other more
noisy components, such as a greater number of tires, than trucks powered
by gasoline engines.^ ' Buses, whether diesel or gasoline, are also
inherently quieter than trucks because of design features such as more
fully enclosed engine compartments (see Section 6).
Since large multi-axle diesel trucks pose the roost severe motor
vehicle noise problem, the vast majority of the work done on motor vehicle noise
has been directed at them. Thus, the data discussed in Sections 5 and
6 of this document aro in large part derived from, and specifically
applicable to, large multi-axle diesel trucks. The noise emission
standard based on the analysis of those data is, therefore, one that is
most appropriate for trucks with more than three axles. This is borne out
by the data presented in Appendix A, which show the highest proportion
of vehicles in violation of the proposed standard to be trucks with three
axles or more, which are often diesel powered.
It might be argued that since this is the case, the category of
large motor carrier vehicles should be further subdivided to reflect
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different noise standards for gasoline versus diesel trucks, buses,
and any other relevant categories. Further distinctions could be made
on the basis of the age of trucks, and for new trucks, to reflect the
degree of noise reduction that each class of truck can achieve. This
approach has considerable merit and is being carefully considered
for use in future revisions of the interstate motor carrier noise
regulations. At present, however, the available data on vehicles other
than large multi-axle diesel trucks are not sufficient to permit the
selection of different noise standards for them. Since large multi-
axle trucks are the most severe noise problem, and since much of the
possible noise abatement technology, such as mufflers and cooling fans,
is basically the same for all large vehicles, a standard that is
reasonable for multi-axle trucks can be assumed to be feasible for
other large motor carrier vehicles. (See references 58 and 59) .
Applying the same standard to other large motor carrier vehicles
on an interim basis, while more specific data is gathered for them,
will limit any increase in their noise emissions.
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Section 5
SPECIFIC NOISE SOURCES
This section of the document describes the noise characteristics
of large motor carrier trucks and the methods available for effecting
noise reduction. It specifically discusses trucks because, as indicated
in Section 4, they are the most severe noise problem, most of the available
data concerns trucks, and any regulation that is reasonable for trucks
will be reasonable for other large vehicles. The noise produced by a
truck is dependent on the type and the quality of the component parts.
Large trucks are not standardized as are automobiles. Specialized
user needs result in a greatly varied assembly of truck components,
especially with respect to powertrain and related equipment. As
a result, the noise produced can vary considerably from vehicle to
vehicle. To illustrate the extend of the variation that can exist,
the following discussion of noise sources is preceded by a brief
description of truck components.
C^^ACTERISTICS OF LARGE TRUCKS
Virtually all trucks in excess of 10,000 pounds GWR or QCWR are
powered either by gasoline or diesel engines; those in excess of 33,000
/ 28}
pounds GVWR or GCWR are powered almost exclusively by diesel engines.
Diesel engines may be naturally aspirated (air introduced at atmospheric
pressure), turbocharged ,or supercharged by the engine itself. The engine
is located at the front of the cab in a conventional style (C) and under
the cab in a cab-over-engine (COE) style truck.
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Ihe engine exhaust for both engine types may be routed horizontally
underneath the body of the vehicle or vertically to the rear of the
cab—commonly referred to as a "straight stack." The latter is often
preferred so as to direct exhaust fumes away from motorists and
pedestrians. Single or double exhaust systems may be installed.. The
engine intake may be situated on or under the hood in a conventional
style truck or to the rear of the cab in either style. In the latter
case, it may be on the same or opposite side of the cab as the eshaust
system.
The power-to-weight ratio for a fully laden truck is significantly
less than that for an automobile, with the result that the necessary torque
must be transmitted through a wide range of gears—up to as many as 15.
This torque is usually applied to either one or two drive axles on the
vehicle. The number of axles on the entire vehicle, including the
trailer, depends upon the load to be hauled, and varies according to
State regulations. The result is that the number of tires on a heavy
truck-trailer combination can range from 10 to 42.
TRUCK NOISE CHARACTERISTICS
Many combinations of components exist that affect the total noise
(29)
level of a truck.v ' This is true not only for trucks designed
specifically to perform different tasks, but also for trucks designed to
perform similar tasks. The reason for the variety is the very marked
owner preference in the trucking industry—a preference based on actual
performance, imagined performance, or simply a traditional attachment to
a given model configuration.
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The noise from the propulsion system is not the only contributor
to the overall noise level. At speeds greater than about 45 miles per
hour, additional noise of significant magnitude compared to the propulsion
system noise is produced by the interaction between the tires and the
road surface. ^ ' The relationship between propulsion system noise and
tire noise as a function of vehicle speed is shown in Figure 2. '
In this figure, the noise levels produced by both the propulsion system
and the tires are shewn as functions of vehicle speed. There are 2 fairly
distinct vehicle speed ranges in which the noise level can be characterized.
At speeds less than 45 miles per hour, the overall noise level for a
truck fitted with a typical conbination of tires is determined mainly
by the contribution from the propulsion system, which is independent of
the vehicle speed. At speeds greater than 45 miles per hour, a major
contributor can be tire noise, which increases with vehicle speed.
The vehicle speed at which tire noise begins to dominate depends primarily
on the type and number of tires on the truck, the degree of tire wear,
tire load, type of pavement, and tire inflation pressure.
The effect of vehicle speed on the noise levels produced by one
type of truck operating on the highway is shown in Figure 3. This
Figure presents the cumulative distribution of the noise levels from
tractor-trailer trucks operating at lew and high speeds. These data
were taken in California, where noise regulations are in existence. The
data shown in Figure 3 are therefore not necessarily typical of the nation.
since the Califorina noise regulations may have reduced the number of noisv
trucks in that State. The basic distinction between low and high speeds,
however, is typical. The difference
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Tire Combinations:
Steering Axle Drive Axles
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1/2 Worn X-Bars
Trailer Axles
New Pocket Retread
p New Ribs
New X-Bars
New Rib Retread
A, New Ribs
New Ribs
New Rib Retread
Engine Related Noise Alone
thru 12 Gear Steps
Tire Noise Alone
60
10
20
30
40
50
Vehicle Speed, mph
Figure 2 - Propulsion System and Tire Noise for a
Typical 5 Axle Tractor Trailer
(from reference 31 and 32)
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DATA SOURCE
a CALIFORNIA (1971) 172 TRACTOR-TRAILERS
"OVER 35 MPH"
A CALIFORNIA (1371) 145 TRACTOR-TRAILERS
"35 MPH OR LESS"
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NOISE LEVEL d3 (A) AT 50 FT
Figure 3 . 'Tractor-Trailer Noise Emission Distributions at 35 nph and over 35 irph
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in noise level in the two speed ranges is due mainly to the increased
level of the tire noise contribution.
This completes the summary of overall truck noise characteristics
as a function of operation. Next, the individual truck components that
contribute to the overall noise level are discussed.
TRUCK COMPONENT NOISE SOURCES, ABATEMENT, AND COSTS-
The total noise level produced by a truck is the logarithmic sum
of the individual noise levels produced by several different components.
These component noise sources are as follows ' (not necessarily in
order of importance)—see Figure 4.
Engine system
Engine cooling fan
Engine (mechanical)
Air intake system
Transmission (gearbox, drive shaft, rear axle(s))
Engine auxiliary equipment
Tire/roadway interaction
Aerodynamic flow
Brakes
Of these, the first four sources are of major importance for trucks
of concern here when traveling at low speeds^ ' (less than 45 miles per
hour). At higher speeds (greater than 45 miles per hour) tire noise
assumes a much greater significance. A brief discussion of these major
sources is contained in the following sections.
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Exhaust System
Exhaust noise is created when engine exhaust gases excite oscillations
in the exhaust pipe. These oscillations are radiated to the atmosphere
at the tail pipe. The noise is a function of engine type, induction
system, exhaust system, and other associated parameters. In addi-
tion to the radiation from the end of the tail pipe, noise is also
transmitted through the exhaust pipe and muffler walls. Noise is also
produced by the application of engine brakes (with trucks so equippped)
ti. c, when in use, provide a retarding force on the engine that reduces
the 5eed of the truck. Typical exhaust noise levels range from 77 to
oc; IV ; at 50 feet irrespective of speed ^29^ and are usually greater in
i:ucks that have been poorly maintained.
Although the exhaust system is a major noise source, the associated
,,oiS'_ levels can be reduced fairly easily. A good muffler is mandatory,
and for maximum quieting, a double wall or wrapped muffler can be used
to reduce radiation through the walls. Besides the muffler, considera-
tion can also be given to wrapping the tail and exhaust pipes with insula-
tion. The system must be free from leaks and should be attached by
isolation mounts to the truck frame. The location of the muffler in
the overall system, the exhaust pipe length and diameter and the tail
pipe length and diameter, should be considered although these factors
assume a gradually lessening importance as the insertion loss of the:
muffler is increased. Muffler specification and suggested exhaust system
configurations are currently offered by major muffler manufacturers for
almost every engine, since no universal muffler exists that is the best
for all types of engines.
24
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Major Noise Sources
A. Engine (Mechanical)
B. Engine Cooling Fan
C. Engine Exhaust
D. Air Intake System
Other Sources
e. Transmission
f. Ancillary Equipment
g, Tire/Roadway Interaction
h. Aerodynamic Flow
i. Brakes
Conventional (C) Cab
Cab-Over-Engine (COE)
Figure 4. Truck Noise Sources and Cab Types
-25-
-------
Exhaust noise, using the best available mufflers, typically ranges
fron 72.5 to 80 dB(A) at 50 feet for today's most popular
diesel engines.'36' These mufflers provide insertion losses of from
9.5 to 27 dB, and are of the type installed on new trucks as standard
(36)
equiorent, A good quality muffler typically costs from $35 to $45;
and since the installation is simple, many trucking companies do it
themselves. Installation costs for either single or dual systems are
about $15. ^36' for maximum effect it is necessary to replace existing
flexible exhaust pipes with rigid pipe and slip joints at a cost of about
$45 per side including labor.
A sudden increase in demand for replacement mufflers would not
pose a significant problem to the manufacturers, many of whom are at
present expanding their facilities to increase their output by a. factor
of 1.5 to 2.(38>
"Cooling Fan
Trucks generally use axial fans to draw air through a front-
mounted radiator to provide water ccoling/ which in turn provides engine
cooling. Fan noise is the result of air flow irregularities and is
partially governed by the proximity of shrods, radiators, grills,
(39)
radiator shutters, etc. The noise produced by the fan is related
to fan tip speed. Most diesel engines for heavy trucks are rated for
maximum horsepower at about 2,100 rpm. At this speed, engine cooling
demand is greatest and the fan can very easily be a major contributor
to the overall truck noise level. Typical truck fans usually exhibit
noise levels in the range of 78 to 83 dBA. at 50 feet at rated engine
^ (29)
speed.
26
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Since noise from a cooling fan increases with the rotational
speed, it is possible to reduce the noise while maintaining the same
air flow (to satisfy the same cooling requirement), by using a
larger fan turning at a lower speed. In many cases this may also
require the installation of a larger radiator, which could result
in an expensive modification to the front of the engine compartment.
It is more feasible to install a fan blade that produces less
noise, while at the same time allowing for adequate cooling. Most exist-
ing fans are stamped out of sheet metal with equal spacing between
the blades, and they are driven at a predetermined fixed ratio of fan
to engine speed by a belt-driven pulley. This type of fan was not
originally designed to be quiet nor particularly efficient in perform-
ing its task. In many cases it can be replaced with a more sophisticated
design that affords a noise reduction from the fan alone of from 7 to
12 dB.(4°) The cost is in the range of $30 to $35 installed. ^41^
The overall truck noise can also be reduced by about 1 dB in some cases
by incorporating a venturi-type shroud around the fan with a small
tip clearance at an installed price of about $45.
Trucks are designed to be able to cope with heat rejection of
maximum engine power with little or no ram air. Since ram air increases
with truck speed, fans become proportionally of lesser importance
at higher speeds and could be slowed or stopped in many instances.
The critical condition occurs when — as in pulling a heavy load up
a long grade—the truck is moving slowly in a low gear but the engine
is developing full horsepower. Trucks, unlike automobiles, usually
27
-------
do not have an overheating problem when the vehicle is stopped and
the engine idles at low rpm. As a result of these characteristics,
there are only a limited number of conditions under which additional
cooling is required. When, the fan is needed only a small percentage
of the total engine on-time, there are certain types of fans avail-
able that rotate only when this additional engine cooling is required
and that idle when the cooling due to ram air flow is sufficient.
Typical fans of this type incorporate a thermos tatic clutch or a
viscous fluid drive. Viscous fluid-clutched fans permit the far to
rotate at reduced speeds when not needed. They offer some fan noise
reduction (about 3 to 10 dB) but the on-of f mechanical clutch would be
preferred because of the total elimination of fan noise while the fan is off.
T/pical costs for a viscous clutch are about $225 plus about
$15 for the suggested fan blade. (43) A thermostatically controlled
unit including the necessary fittings costs typically on the order
of $285 to $360, plus $40 to $50 for installation. (37' 43)
Engine(Mechanical)
Engine mechanical noise in internal combustion engines is produced
by the combustion process, which produces the high gas pressures
necessary to force the piston down the cylinder and turn the crankshaft.
The rapid rise in cylinder pressure immediately following combustion
produces mechanical vibrations in the engine structure that are trans-
mitted through the cylinder walls, oil pan, rocker arm, covers, etc.
Some of the vibrational engery is subsequently radiated in the atmosphere
as acoustic energy.
Gasoline engines initiate combustion with a flame that smoothly
28
-------
spreads throughout the cylinder until the fuel-air mixture is
burned. Diesel engines, however, rely on much higher compression
ratios (about 17:1 rather than 9:1) to produce spontaneous combustion.
Ihis causes a more rapid change in pressure in the cylinder, which in
turn results in increased engine vibration and, hence, higher noise
levels than those associated with gasoline engines. ' ' As a result,
noise levels from diesel engines often are as much as 10 dB greater
than those from gasoline engines. (44) rphe engine noise contribution
in typical diesel-powered trucks is on the order of 78-85 dBA. ^ **
Turbochargers are often used to increase the pressure of the intake
air. This reduces the pressure fluctuations in the engine, which in
turn lowers the engine noise level. (44) The devices used to increase
the pressure may in some cases contribute to the overall noise level;
i.e., turbocharger "whine." Retrofit methods of reducing the noise
produced by engines generally fall into one of two categories:
i. Reduction of noise radiated by the engine by
modifying certain exterior surface covers.
2. Installation of acoustic absorption and barriers
in the engine enclosure.
Engine noise reduction kits suitable for retrofit applications to
limited engine models are available from a few major engine manufacturers,
These kits consist of various acoustically treated panels and covers
and provide a reduction of about 3 dB in engine noise only (as opposed
to total vehicle noise level) at a cost of between $50 to $100 for
(45) /-v^
material and, typically, $30 for installation. ^'' Such kits
29
-------
are in limited production at this time and have not undergone
(52)
complete durability testing. They will be considered for
suitability and availability whenever the proposed regulations are
revised.
Air I nduc tion S vs t em
system noise is created by the opening and clos:Lng
of the' intake valve , which causes the volume of air in the system to
pulsate. The associated noise levels are dependent upon the type of
engine, the engine operating conditions, and whether it is turbocharged
or naturally aspirated. ^39' Typical intake noise levels vary from
70 to 80 dBA.
Intake noise reduction technology is very similar to that for
exhaust noise reduction. Major manufacturers are able to provide
assistance in proper selection of air intake systems for all popular
engine models. Retrofitting the intake systems of trucks in
service' consists of replacing older air cleaners with modern quality,
dry element air cleaners. This would result in a cost of $100 - $130,
on the average . Intake cleaners and silencers are manufactured
largely by the major muffler manufacturers, so that the production
could be increased as described in the above discussion of mufflers.
_Tire/Roadway Interaction
Truck tires for highway usage can be classified into two
categories - rib tires and crossbar tires (also known as lug or
cross rib) . Rib tires have the tread principally oriented longitudinally
around the tire (similar to automobile tires) . This is the most
coimon type of truck tire and can be used in all wheel positions;
30
-------
however, they are almost exclusively utilized in steering axle positions
because of their superior lateral traction and uniform we a if characteristics.
Crossbar designs have the tread elements principally arranged laterally
and are popular for use on drive axles. These designs provide for
(47)
up to 60 percent more tread depth due to the rigid cross elements. v '
The physical mechanisms of the production of noise by tires and
tire/roadway interaction are not completely understood. It is known
that the entrapment and release of air from the tire tread cavities
produces noise. ' ' Also, it appears that the vibration of the tire
contributes to the total noise level. * ' However, the effect of
the large lugs on crossbar tires, and the effect of the road surface
on the noise levels produced are not well quantified. The result is
that basically all the noise information available has been obtained
experimentally, and the tire manufacturers do not appear to be
close to any major breakthrough that would result in crossbar tire design
exhibiting significantly lower noise levels.
There seem to be no conclusive data that, indicate any
significant difference between the traction properties of rib and
crossbar tires under dry, wet, or icy conditions. ^49^ Any difference
is possibly in favor of using rib tires because they normally provide
about 5 percent more rubber in contact with the road. However, in
snow, sand, gravel, mud, or loose dirt, where the tire does not come
into contact with a firm surface, there is an advantage to installing
crossbars. ' '
31
-------
There is no conclusive economic preference to the use of crossbar
or rib tires. A rib tire has a tread depth on the order of 17/32
inch and costs about $100. Its life is about 50,000 miles if it is
worn down to 2/32 inch on a drive axle. An equal quality crossbar
tire costing about $130 may have an initial tread depth of 27/32 inch
and last typically 100,000 miles when reduced to 2/32 inch. At this
point, some firms sell the carcasses (the rib possibly being worth more
in this case) and buy new tires. Under this policy it is more
economical (54 percent more mileage per dollar) to use crossbars.
However, other firms choose to spend about $30 to recap the rib tire
with an additional 17/32 inch tread and use it again, obtaining an
overall life of 100,000 miles at a total cost of $140—the same as
the original crossbar type. If the crossbar and rib carcasses (of
equivalent quality) have been subjected to the same abuse, then they
will have essentially the same number of miles left in them. Some
trucking companies will use only new tires on drive axles and when
they are half worn they will be removed and used on a trailer
position until completely worn. They will then be recapped. Rib
tires are thought by some to wear more quickly than crossbars in drive
axle positions.
Extensive measurements of the noise level produced by tires mount-
ed on the drive axle of a truck-tractor have been conducted by the
National Bureau of Standards and the Department of Transportation.
—see figure 5. ^1) Typical values of the noise level measured at
32
-------
50 feet are 68 dBA and 73 dBA at 35 miles per hour for new ribbed
I
(51)
and crossbar tires respectively on a concrete roadway. At 50
miles per hour these levels typically increase to 73 dBA and 80 dBA
respectively, although higher values are by no means uncommon. In
general, ribbed tires produce lower noise levels than crossbar tires.
The noise produced increases with tire wear, reaching a maximum value
when the tread is approximately half worn.
Data indicate that some retread tires that exhibit a tread
design composed largely of pockets that are not vented either around
the tire or to the side produce excessive noise levels by allowing
air to be trapped, compressed, and subsequently released as the
pockets pass through the footprint area of the tire. These pocket
retreads are responsible for noise levels exceeding 90 dBA at highway
speeds. (51)
33
-------
SPEED, KM/HR
50 60 70 80 90 100
NEW TIRES
CONCRETE
LOADED VEHICLE
AT 50 FEET
POCKET
RETREAD
CROSS-BAR
RIB
40 50
SPEED, MPH
60
Figure 5.
Peak A-weighted sound level, as measured at 50
feet, versus speed for a loaded single-chassis
vehicle running on a concrete surface. Various
types of new tires -are represented on the qraph.
These were mounted on the drive axle.
34
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Section 6
NOISE EMISSION STANDARDS
NOISE LEVELS FOR LARGE INTERSTATE M3TOR CARRIER VEHICLES
The noise control information given in the preceding section corresponds
essentially to the state of available knowledge of retrofit technology for
each individual noise source. To reduce the noise level produced by an
existing vehicle, it is necessary to apply one or more of the modifications
outlined—the nurrber or type of modifications, depending upon the
vehicle in question and the overall noise reduction required. For
example, more components of an old or poorly maintained truck would
normally need to be modified than those of one in newer condition.
Similarly, more treatment would be required to reduce the noise level of
a vehicle to 84 dB(A) than would be required to reach 88 dB(A) .
As stated in the discussion of motor carrier vehicle categories, most
cf tfte available data concerns large to'ckr, "-ith Uireo ov -r>rr ax.".o,«r
which are predominately diesel powered. Knowledge of some noise sources,
such as tires, is of course applicable to other vehicles such as gasoline
powered trucks and buses; and it is probable that knowledge of other noise
sources such as cooling fans will prove applicable to all large vehicles.
But the specific information- available at present does not permit an
enumeration of specific treatments, with associated
35
-------
costs, to produce predictable amounts of noise reduction for vehicles
other than large multi-axle trucks. The data nrpsp-ntpd in Tables 1 and
2 and Figures 6, 7, 8, and 9 in this section are based upon studies of
larqe multi-axle trucks t^at ar^ nrimari.lv rh'.efiel nnwprpd. AK discussed in
Section 4, it can be assumed that any noise standard that is reasonable for
such 1araF> trucks is feasible for other rrotor carrier vp>hirlpiQ, -i nr-1 nrl -i nrr
Types of treatment that might be required to reduce noise emissions
(other than noise emissions from the tire/road interaction from trucks
to various levels, and the associated costs per treatment, are listed
in Table 1. The levels indicated correspond to noise emission at maximum
engine speed (where noise other than tire noise is highest) , measured at
50 feet. Since the noise levels of individual existing trucks vary,
not all existing trucks requiring some treatment would require
each of the treatments indicated to reach each noise level indicated.
The percentage of trucks indicated in Table 1 to require each type of
component change is based upon actual experience of a company that has
been extensively engaged in retrofitting trucks to reduce noise emissions.
The average cost per large multi-axle truck that requires treatment to
meet each level is thus the sum of the percentage of trucks that require
each treatment times the cost of that treatment, for each type of
treatment. The average cost of bringing noise levels of existing
multi-axle trucks down to 86 dB(A) is thus $114.
For comparison with the estimated retrofit costs, Figure 6 shows
the typical costs actually incurred in the retrofit of over 7,600 Icirge
multi-axle trucks by that company. The agreement is good with the
36
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TABLE 1 - ESTIMATED COSTS TO RETROFIT TRUCKS TO VARIOUS
NOISE LEVELS (According to SAE J366a)
Noise Level
dBA (? 50'
90
88
86
84
Required
Treatment
Exhaust1
Exhaust
Fan2
Exhaust^
Fan4
IntakeS
Exhaust6
Fan7
Intake5
Engine"
Estimated Cost
Per Item $
50-100
50-100
35
100
80
115
100-200
285-400
115
80-130
% Trucks exceeding
specified noise level
Requiring Pompon p.nf
Change
100%
100%
5%
100%
• 10%
5%
100%
50%
25%
25%
Avg. Cost Per Truck
Requiring Retrofittir
$50 - $100
Total $50 - $100
50 - 100
2 - 2
Total $52 -|102
100
8
6
Total $114
$100 - $200
$143 - $200
$ 29 - $ 29
$ 20 - $ 33
Fotal $292 - $462
1. Muffler and labor—single or dual system
2. Replaced fan blade
3. Mean cost for muffler and labor, plus additional cost for some
trucks requiring replacement of flexible tubing, etc.
4. Replaced fan blade and added shroud
5. Average cost of dry element air cleaner with built-in silencer.
6. Muffler and replacement of feasible pipes—single or dual system
7. Viscous fan clutch and new fan blade in conjunction with shroud.
Thermostatically controlled clutch.
8. Partial engine kit plus installation.
37
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PERCENTAGE OF TRUCKS EXCEEDING A GIVEN
NOISE LEVEL DURING TYPICAL HIGHWAY OPERATION —
CALIFORNIA DATA
Noise Level
dBA
% trucks exceeding
Speeds 33 mph and
less
noise level
Speeds greater than
35 mpn
92
90
88
86
Bk
82
0
5
6
12
19
30
0
10
19
50
78
93
97
38
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exception of the costs to achieve a noise level of 84 dB (A). At this
level, the incurred costs are for a very small number of vehicles and
the estimated costs are approximate. Experience in retrofitting
trucks indicates that the noise level of almost all trucks on the road
today can be reduced to an 86 dB(A) level; however, the noise level of
only about 50 percent of existing multi-axle trucks could be brought down to
84 dB(A) using available hardware. To achieve this level on those trucks on
which it can be achieved, engine enclosures would often be reouirBd.
This type of hardware is not currently available in the large quantities
that would be required by an 84 dB(A) standard, nor has it been fully
tested on in-service trucks. The completion of tests on such hardware
and the establishment of production distribution systems for large quan-
tities of enclosures for specific application will require an inestimable
lead time. The company estimates that from their very limited experience
with engine enclosures in achieving noise levels of 84 dB(A) that it
would cost about $950 per truck to bring large multi-axle diesel trucks
down to that level, if adequate hardware for that purpose were available
and if the safety and maintenance aspects of the enclosure configuration
were established. For application to significant numbers of trucks,
additional lead time would be required to establish a production base
and supply system to retrof itters.
"BEST AVATTARLK TECHNOLOGY, TAKING INTO ACCOUNT THE POST OF COMPLIANCE"
These terms have been defined for purposes of this proposed regulation
as follows:
39
-------
"Best available technology" is that noise abatement
technology available for retrofit application to motor
carriers that produce meaningful reduction in the noise
produced by interstate motor carriers. "Available"
is further defined to include:
1. Technology applications that have been
demonstrated and can be retrofitted on
existing trucks.
2. Technology for which there will be a production
capacity to produce the estimated number
of parts required in reasonable time to
allow for distribution and installation
prior to the effective date of the regulation.
3. Technology that is compatible with all safety
regulations and takes into account opera-
tional considerations, including maintenance,
and other pollution control equipment.
The cost of compliance means the cost of identifying
what action must be taken to meet the specified noise
emission level, and the additional cost of operation
and maintenance. The cost for future replacement parts
was also considered.
Summarizing the discussion of truck noise other than the tire noise leads
to the following major conclusions:
1. Nearly all existing large trucks can be retrofitted to
achieve a noise level of 86 dB(A)« under 35 mph.
2. A large proportion of the trucks that presently exceed 84 dB(A)
under 35 mph could not be brought to this level using current available
hardware or technology without extreme modifications, e.g.,
total encapsulation or replacement of the engine.
40
-------
3. The costs associated with retrofitting large multi-axle
diesel trucks increase greatly between the levels of
86 dB (A) and 84 dB (A) .
4. Large multi-axle diesel trucks constitute the most
severe interstate motor carrier noise problem. Any noise
standard that is reasonable for them to meet can beassumec3 to
be reasible for other interstate motor carrier vehicles to
meet. It is therefore possible to hold all interstate motor carrier
vehicles over 10,000 pounds GVWR or GCWR to the standard set
on the basis of the noisiest trucks for an interim period. When
more information is available on feasible noise standards for
various subcategories of interstate motor carrier vehicles, the
proposed regulation can be revised to incorporate such information.
Accordingly, the conclusion can be reached that the noise emission
level that existing trucks can be expected to achieve, exclusive of
tire noise, after the application of the best available technology,
taking into account the cost of compliance, is 86 dB(A), for speeds
less than 35 miles per hour. Based on the truck survey data from Calif-
ornia in 1965 discussed earlier in this section (see Table 2), 19 percent
of the large multi-axle diesel trucks in operation today will not initially
comply with the noise standard. Non-diesel trucks and other vehicles
will generally require much less treatment to meet the standard than
diesel trucks and, consequently, will incur much smaller average costs.
Most of them meet the proposed standard now, and those that do not will
41
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rarely require more than a new muffler to meet the proposed low speed
standard.
Since the noise characteristics of large vehicles differ at low
and high speeds—the propulsion system noise dominating the former and
the tire noise the latter—it is necessary to set different noise standards
for low and high speed operation so that both major noise sources will
be covered. At speeds greater than 35 miles per hour, the noise levels
produced by trucks complying with the 86 dB(A) low speed standard will
normally exceed 86 dB(A) because of the increase in the tire noise
contribution. Examination of the noise distribution of trucks operating
on the highway—see Figure 3—shows that the same number of trucks that
exceed 86 dB(A) at speeds less than 35 miles per hour exceed 90 dB(A) at
speeds greater than 35 miles per hour. In most cases, trucks that can
comply with the low speed noise standard can also comply with a 90 dB(A)
noise level at high speeds. Some trucks equipped with the noisier types
of cross-bar tires will exhibit higher noise levels and would be required
to install alternative cross-bar or rib tires, particularly on the drive
axles. Trucks equipped with pocket retread tires will normally exceed
the proposed regulation of 90 dB(A) at speeds in excess of 35 miles per
hour—see Figure 2. The 90 dB(A) high speed standard will therefore
effectively remove this type of tire from highway use. It is therefore
42
-------
appropriate to incorporate into the regulation a visual inspection clause
to restrict the use of pocket retread tires.
In many cases, trucks will exceed the proposed noise standards
because of poorly maintained exhaust systems. Accordingly, it is con-
sidered that the proposed regulation should contain a clause allowing
for a visual inspection of the exhaust system.
When heavy trucks are operated at speeds of 35 miles per hour or
less, they are often in urban or suburban areas. It is during this phase
of their operation that truck noise emissions can have a major impact
on the public due to the large population densities in these areas.
Under certain conditions of highway grade and constant speed less than
35 miles per hour, trucks can be operated in a manner that will miniinize
exterior noise emissions. The principal variable in attaining these
lower levels is operator technique.
Trucks designed or retrofitted to the recommended 35 miles per hour
all-conditions pass-by test level of 86 dB (A), if operated in a quiet
manner,would emit exterior sound levels of 80 dB(A) or less. As shown
in Figure 9, the percentage of vehicles that could not comply with a
level of 80 dB(A) on level roadways is approximately the same as the
percentage of vehicles not complying with the two recommended noise
emission standards at 86 and 90 dB(A) discussed earlier.
43
-------
An 80 dB(A) level does not impose an additional cost to the
industry above that which is required to meet the other reconmendai noise control
levels, but it does require quiet operation in areas where population
densities are generally high.
STATIONARY RUN-UP,TEST
The Federal enforcement of the proposed noise regulation will be
undertaken by inspectors from the Bureau of MDtor Carrier Safety (BMCS)
of the Department of Transportation (DOT). Four possible enforcement
strategies were considered.. These are:
!• Enforcement at the time the owner first receives the vehicle
2. Enforcement at random times at the vehicle depot
3. Enforcement during normal operation on the highway
4. Enforcement at specific roadside locations, such as weigh
stations.
Enforcing the noise regulation at the time of initial (or subsequent)
sale would not take into consideration that the noise level produced by
a motor vehicle may increase with age as a result of poor maintenance or
improper selection or replacement of parts. Enforcement at the vehicle
depots would lead to significant logistic problems due to the wide
dispersion of depots. The noise regulation could be enforced by setting
up measurement locations alongside major highways and monitoring the
noise produced by each vehicle as it passes through the site. This is the
method adopted by the California Highway Patrol and other enforcement
agencies who have "curbing" power, or , the ability to pursue and
apprehend offending operators. The DOT inspectors do not have this
power, but they do have the power to inspect vehicles at roadside weighing
44
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stations. This form of enforcement requires a method of measuring the
noise produced by the vehicle while in the weighing station such that
the noise levels correlate well with those measured for typical opera-
tion on the highway. Lack of space at the weighing station indicates
that this should be a test conducted with a stationary vehicle. Such
a stationary test procedure has been developed by the motor vehicle
manufacturers through the Society of Automotive Engineers. Though the
test procedure has only been documented on 877 trucks, the results
indicate a close relationship with the SAE J366a test, and it is considered
acceptable by DOT. It consists of running the engine from idle to
stabilized governed engine speed with rapid application of the throttle.
The noise level measured is the maximum value observed during the test.
No such stationary test is recommended for vehicles that use
engines without engine speed governors (ungoverned engines) for
the following reasons:
1. The operator variability (including tachometer error) in
achieving horsepower rated rpm.
2. Tte variability of manufacturer specified horsepower
rated rpm.
3. The likelihood of catastrophic engine failure when an
ungoverned engine is rapidly accelerated to such high speeds .
None of these drawbacks exists for governed truck engines. Since it
is the diesels and big gasoline engines that normally produce the highest
noise levels (exclusive of purposefully modified exhaust systems) and
45
-------
since these engines are normally equipped with engine speed governors,
the fact that this test procedure is limited to such vehicles will not
reduce the effectiveness of the overall regulation.
The noise level of a truck measured according to the above stationary
procedure is about 2 dB greater than the noise level produced in the
course of typical acceleration at low speeds (less than 35 miles; per hour).
Therefore, a noise level of 88 dB(A) measured according to the stationary
test procedure is considered approximately equivalent to a level of
86 dB(A) measured on the highway during acceleration at speeds less than
35 miles per hour.
TIME FOR COMPLIANCE
In determining the amount of time required for trucks to apply
some retrofit solution—if they exceed the proposed noise emission
standards—the following factors must be taken into account:
1- The availability of replacement hardware—mainly mufflers
and quiet tires.
2. The replacement cycle for items that need to be replaced .
In many cases, the action required to bring a noisy truck into
compliance with a proposed noise emission regulation would be the
replacement or installation of a suitable muffler. Replacement mufflers
are provided by the original equipment manufacturers as well as by the
replacement equipment manufacturers. In general, the industry is capable
of increasing its output of mufflers, probably by a factor of two,
because it has the additional facilities and material necessary.
46
-------
The life of a muffler depends greatly on the actual truck operation, but
is on the order of one to two years. Therefore, to a first approximation,
one-half of the trucks will install new mufflers every year.
In contrast, the tire industry is at present striving just to
maintain a sufficient supply for the demands of the trucking companies.
The life of a cross-bar tire as installed on a "line-haul" truck is not
usually greater than 100,000 miles, which corresponds to a tire tread
life of approximately one year.
Considering all of the information given leads to the conclusion
that the majority of trucks can be modified to comply with the
proposed noise emission standards within one year from promulgation of
the regulation. It should be noted that the estimated costs for
compliance do not take into account the normal replacement cycle for
mufflers, since such repalceraents are not related to these costs.
-47-
-------
1000
900
800
700
CO
rH
S 600
8
500
400
300
200
100
0
estimated
cost of retrofitting
range based on actual
cost of retrofitting
Total Sanple 7/600 trucks
a
94 93
92
91 90
89
88 87 86 85
84
Attained Noise Level, dBA @ 50'
(Low Speed, Full Throttle)
Figure 6, Estimated and Actual Cost Incurred in Retrofitting
Trucks to Various Noise Levels
48
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DATA SOURCE
° CALIFORNIA (1971) 172 TRACTOR-TRAILERS
"OVER 35 MPH"
A CALIFORNIA (1371) 145 TRACTOR-TRAILERS
"35 MPH OR LESS"
100
LU
_J
( jj
100
J10
70 80 90
NOISE LEVEL dB (A) AT 50 FT
Figure 7 - Tractor-Trailer Noise Emission Distributions at 35 mph and over 35 ir
-------
99.8
99.5
99
98
95
M 90
3
0 80
(0
I 70
o
03 50
tn
£ 40
1 30
X
w
w 20
"v
1 10
o
c*= 5
2
1.0
0.5
0.2
0.1
0.05
0.01
8
(V/'v
N/\
^X
\~\
"^
>
!
*
DATA SOURCE - i
0 CALIFORNIA (1971) 172 COMBINATION VEHICLES 1 -
A CALIFORNIA (1965) 5,838 DIESEL TRUCKS jj
0 WASHINGTON (1972) 531 TRUCKS, jl
3 OR MORE AXLES .J
A NEW JERSEY (1972) 1000 TRUCKS 1
3 OR MORE AXLES J
SPEED ZONES OVER 35 MPH |
\
^J
0 82 84
•
K
\.R\
1 \~\V~\
^
^Sk
%.
^
•
^x_
v^
"\
^\
^§x
s \
i
1
I
i
^3x"
r\
^-
\
\
86 68 90 92 94 96 98
Noise Level dBA at 50 Feet
Figure 8«. Truck Noise Emission Road Side Survey Data for Soeeds Ov^er
35 nph.
50
-------
A CALIFORNIA (1971) 105 COMBINATION VEHICLES
"LEVEL ROADWAY" (CORRECTED)
SPEED ZONES 35 MPH OR LESS
£3
9
1UU
50
0
6
j i i i ri ! i s
~! 1 I I 1.1.!.!.!.
I'M.ri Jill
\
V
*<
1 I 1 I ' I M i
i II I I I I I 1
^
Sj.
.a^M_LLJ_Ll_
i i 1 1 I 1 I ) I
1 ! 1 I 1.1 ! I !.
1 ! I ! I 1 1 i L_j
*
jj i i .' u ) n
0 70 80 90 TOO 110
ENFORCEMENT LIMIT, dB(A) AT 50 FT
FIGURE 9. Tractor-Trailer Noise Emission Distribution at 35 mph
or Less on Level Roadways.
51
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Section 7
ECONOMIC IMPACT OF THE PROPOSED REGULATIONS
DIRECT RETROFIT COST
In order to relate individual truck
retrofit costs to the total impact on the industry, the
number of trucks engaged in interstate commerce over
10,000 pounds GVWR must be determined. There is no
direct method for making this determination. A reasoned
judgement was made based on truck population statistics,
industry information, and inputs to the Advance Notice
of Proposed Rule Making Dofefeet that approximately
1 million trucks over 10,000 Ib GVWR or GCWR were engaged in
55 54 12
interstate commerce. ' ' '
As discussed in Section 6, the primary impact of the
proposed regulation will be on large multiaxle trucks,
which are primarily powered by diesel engines. Section 6
shows an estimated average cost of $114 (with a range of $50
to $200) to bring into compliance those trucks with 3 or more
axles that are not presently in compliance with the proposed
regulation. Figure 8, a survey of diesel
trucks in California in 1965 (before that state had any
noise regulation that might influence the data), shows that
19% of those trucks would be in violation of the proposed
standard. Data from New Jersey and Washington (figure
8), support this figure of about 19% of multi-axle diesel
trucks that would be in violation of the proposed standard.
(See Appendix A for data on the percentage of vehicles
52
-------
that might initially be in violation of the proposed
standards that" have been accumulated for EPA since
the date of publication of the proposed regulation).
The $114 average cost per truck shown in Section 6
is for those approximately 19% of the trucks (3 axles
and over) that are expected initially to be in violation
of the proposed standard. The mean direct retrofit cost
to the industry is therefore $22 million dollars, with
a range of $10 to $38 million dollars.
For a truck running 50,000 revenue miles per year,
a $114 retrofit cost represents an increased expense of
$0.002 Per revenue mile when amortezed over a single
year. When this increase is compared with current
average expenses of $1.20 per revenue mile (see Section
2), it can be seen that cost is not an obstacle to
lower noise emission standards.
OTHER COST CONSIDERATIONS
Additional costs include loss of revenue resulting
from trucks being out of service during retrofit. The
installation of a suitable muffler may increase the back
pressure on the engine and in turn increase the fuel
consumption. Considering the wide variety of mufflers
available for different types of engines, a significant
increase in back pressure is avoidable.
53
-------
There are also some factors that reduce the
total cost. First, the muffler on a line-haul truck
is normally replaced at 1-1/2'to 2 year intervals.
Thus, of those trucks that require a replacement
muffler about one-half will be installing a new
muffler even in the absence of the regulations. In
these cases, the cost incurred will be the difference
between that for the required muffler and that for the
one that would have been installed, the difference in
cost being in the range of a few dollars.
Secondly, for those trucks requiring installations
of a more efficient fan, the amount of engine power wasted
in driving the fan will be reduced. Standard diesel fans
typically consume 15-25 horsepower. In particular,
the addition of a thermostatically controlled fan clutch
can decrease the fuel consumption by 1 to 1.5% and can
reduce operating cost for the life of the truck. With
these considerations, the long term cost of compliance
with the noise regulations may be less than that given
above.
54
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Section 8
ENVIRONMENTAL IMPACT OF PROPOSED REGULATION
POSITIVE EFFECTS
The proposed regulation impacts directly on those
trucks that presently make the most noise and requires that
they be quieted to levels that are feasible from a cost and
technology standpoint within one year of final promulgation.
The principal noise reduction will be of the intrusive "noise
peaks", which have been widely acknowledged as more objec-
tionable to people than much lower levels of continous noise.
These peaks can be 12 dB or more above ambient highway noise
level. The benefit of noise reduction is to be realized in
1 year or less.
A significant increase in truck fuel economy will also
be realized for those trucks that require installation of
more efficient fans to meet the proposed noise emission
standard. As described in Section 7, thermostatically controlled
fan clutches that engage the fan only on engine cooling
demand can decrease fuel consumption throughout the life of
the truck.
NEGATIVE EFFECTS
There may be a slight increase in the number of older
trucks retired from service? and that would therefore suddenly
increase the solid waste disposal problem by the number of
55
-------
trucks scrapped. Following this, the scrappage rate would
decrease as a result of the younger population of trucks.
However, a small net increase on total trucks scrapped would
be obtained - an increase related to the number of truck years
lost from service. Because the net increase in scrappage
would be small, and because of the ready market for steel,
adverse environmental effects would be minimal.
There will be no anticipated increase in scrap tires
resulting from these regulations. The pocket tread design
tire that the regulation excludes from highway use is not in
wide use, and those currently installed and in stock would
wear out prior to the effective date of the regulation. In
some installations of a quieter muffler, there may be an
increase in back pressure on the engine and a resulting
decrease in fuel economy. As discussed in Section 6, a
significant increase in back pressure is avoidable in almost
all cases by a muffler matched to a particular engine.
56
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APPENDIX A
TRUCK NOISE EMISSION DATA AND ANALYSIS
Sijbsequent to the issuance of the proposed regulation, a substantial
additional body of recent vehicle noise survey data has now been analyzed.
This body of data was obtained in 10 states, in which approximately
39 percent of all U.S. trucks and buses are registered. For 9* of
these 10 states, the data permitted an assessment of the percentages of
various types of trucks that would exceed the proposed standards. From
the analysis, it was concluded that:
1. An average of 23 percent of all observed trucks above 10,000 pounds
GVWR or QCWR exceeded the proposed standards (Table A-l).
2. The mean percentage of observed trucks exceeding the proposed
standards varied significantly by type of truck: 1.9 percent for two-
axle straight trucks, 10.8 percent for three-axle combination trucks,
15.0 percent for four-axle combination trucks and 36.1% for 5-axle
combination trucks (Table A-2).
3. The range of percentages of trucks observed in the nine states
that exceeded the proposed limits was substantial: 0.6 to 3.5 percent
for two-axle straight trucks above 10,000 pounds GVWR, 1.2 to 26.0
percent for three-axle straight trucks,
*California, Colorado, Illinois, Kentucky, Maryland, New Jersey,
New York, Pennsylvania, Texas
**The average of 23.1 percent calculated in Table A-l is an
arithmetic mean of percentages exceeding the proposed standards in
various states, unweighted by sample size.
-57-
-------
1.0 to 26.0 percent for three-axle combination trucks,
3.0 to 26.0 percent for four-axle conbination trucks,
and 7.0 to 74.0 percent for five-axle conbination trucks (Table A-2)
4j According to the 1972 Census of Transportation - Truck
Inventory and Use Survey (Department of Commerce, Bureau
of the Census)/the total population of registered trucks
above 10,000 Ibs. GVWR or GCWR is distributed approximately
as follows:
72.1 percent two-axle straight trucks,
10.3 percent three-axle straight trucks,
2.4 percent three-axle conbination trucks,
5.5 percent four-axle conbination trucks,
8.0 percent five-axle conbination trucks, and
1.7 percent other or unspecified types.
9. Multiplying these percentages by the mean percentage of
each type exceeding the proposed standards reveals that
approximately 7 percent of all registered trucks above
10,000 Ibs. GVWR or GCWR exceed the proposed standards (Table A-3).
61 The apparent discrepancy between the 23 percent of trucks
observed on the road and the 7 percent of all registered
trucks above 10,000 Ibs. GVWR or GCWR that exceed the proposed
standards results from the fact that conbination trucks
travel many more road miles per vehicle per year than straight
-58-
-------
trucks do. For example, five-axle examination trucks
constitute approximately 50 percent * of the trucks observed
on a typical interstate highway, even though they represent
only 8 percent of all registered trucks in the weight class
under consideration.
3For the nine of ten States represented in the new data base where
the data allow for a breakdown by axle category, of the 6,875 total
trucks over 10,000 pounds GVWIV'GCWR, 4,098 or 59.5 percent were 5-axle
trucks.
-59-
-------
Table A-l
SUMMARY OATH FOR ALL TRUCKS ABOVE 10, "D00 LBS GVWR OR GCWR
Mean Noise % Ab°Yg.
State Source Level Mean Speed 90.0 dB(A) 91.0 dB(A) 92.0 dB(A)
CA W.L. 85.4dB(A)(a) - 5.0% 3.0% 1.5%
CO BBN 84.6 51.7mph 10.0 4.5 2.0
IL BBN 89.1 57.2 42.0 21.0 15.0
KY BBN 88.8 61.3 40.0 30.0 21.0
MD Md.DOT 88.1 - 30;0 21.0 14.5
NJ BBN 87.2 56.5 20.0 12.0 7.0
NY BBN 88.8 60.0 43.0 30.0 18.0
PA W.L. 86.2 (a) - 13.0 8.0 5.0
TX BBN 83.7 56.1 12.5 7.5 4.0
WA WA-72 86.6 (a) , - 16.0 9.0 6.0
mean percentage exceeding given noise level:
23.1% 14.6% 9.4%
(a) median
-60-
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Table A-2
SUMMARY OF TRUCK NOISE EMISSIONS BY TYPE OF TRUCK
Mean Noise % Above
State Sourc^ Level Mean Speed 90.0 dB(A) 91.0 dB(A) 92.0 dB(A
CA W.L. ^81.0dB(A)(a) - 1.2% 0.6% 0.3%
. CO BBN 80.4 50.9mph 1.9 1.0 0.5
IL BBN 83.1 55.7 1.0 0.3 0.1
KY BBN 82.9 57.7 1.0 0.3 0.1
- MD Md.DOT 83.9 - 3.5 1.6 0.8
NJ BBN 82.3 55.7 0.6 0.2 0.1
NY BBN 85.1 59.4 6.0 3.3 1.9
PA W.L. 81.2(a) - 0.9 0.4 0.2
TX BBN 78.6 54.6 0.6 0.3 0.1
mean percentage exceeding given
noise level: 1.9% 0.9% 0.5%
3 AXLE STRAIGHT TRUCK
CA W.L. 85.2(a)(b) - 8.0 4.0 2.0
CO ^ BBN 84.1 47.7 1.2 0.4 0.1
IL BBN 85.8 54.5 9.0 4.5 2.0
KY BBN 87.7 59.9 * * *
MD Md.DOT 87.5 - * * *
NJ BBN 84.7 57.4 * * *
NY W.L. 88.0(a)(b) - 26.0 17.0 11.0
PA W.L. 84.5(a)(b) - 2.0 0.9 0.3
TX BBN 84.8 50.6 * * *
mean percentage exceeding given
noise level: 9.3% 5.4% 2.7%
3 AXLE COMBINATION TRUCK
CA W.L. 85.2(a)(b) - 8.0 4.0 2.0
CO BBN 83.8 51.9 * * *
IL BBN 86.0 55.7 * * * •
KY BBN 87.8 59.0 * * *
MD Md.DOT 86.6 - 17.0 11.0 7.0
NJ BBN 85.7 57.2 1.0 0.3 0.1
NY W.L. 88.0(a)(b) - 26.0 17.0 11.0
PA W.L. 84.5(a)(b) - 2.0 0.9 0.3
TX BBN 83.0 56.5 * * *
mean percentage exceeding given
noise level: 10.8% 6.6% 4.1%
(a) median
(b) all 3 axle trucks
* insufficient data
-61-
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Table A-2 (Continued)
State Source
4 AXLE COMBINATION TRUCK
Mean Noise
Level
% Above
CA
CO
IL
KY
MD
NJ
NY
PA
TX
W.L.
BBN
BBN
BBN
Md.DOT
BBN
BBN
W.L.
BBN
84.2(a)
84.8
87.1
88.0
87.9
86.7
88.8
85.7(a)
83.9
wean speed
49.0
55.4
61.0
57.7
58.8
56.4
90.0 dB(A)
3.0%
9.0
22.0
24.0
26.0
11.0
26.0
.0
4 5
91.0 dB(A)
2.0%
4.0
15.0
13.0
19.0
6.0
13.0
3.5
. 0
2. U dB (A)
1.2%
1.4 '
9.0
6.0
12.5
2.5
7.0
2.0
1.0
mean percentage exceeding
noise level:
15.0%
8.6%
4.7%
5 AXLE COMBINATION TRUCK
CA ^
CO
IL
KY
MD
NJ
NY
PA
TX
W.L.
BBN
BBN
BBN
Md.DOT
BBN
BBN
W.L.
BBN
85.9(a)
87.0
90.2
90.6
89.7
88.3
91.2
87. 6 (a)
87.5
53.7
57.7
62.6
58.7
61.6
57.9
7.0
18.0
-51.0
56.0
42.0
32.0
74.0
22.0
23.0
mean percentage exceeding given
noise level:
36.1%
3.5
8.0
38.0
42.0
31.0
20.0
56.0
14.0
14.0
24.9%
1.6
3.0
26.0
30.0
21.0
12.0
34.0
9.0
8.0
16.0%
(a) median
-62-
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Table -A-3
ESTIMATED NUMBER OF TRUCKS AFFECTED
2 axle straight truck
3 axle straight truck
3 axle combination
4 axle combination
5 axle combination
All other (a)
% of all
trucks above
10,000 Ibs
72.1%
10.3
2.4
5.5
8.0
1.7
% of type
exceeding
90.0 dB(A)
1.9%
9.3
10.8
15.0
36.1
36.l(b)
% of all trucks
above 10,000 Ibs
affected
1.37%
0.96
0.26
0.83
2.90
0.61
2 axle straight truck
3 axle straight truck
3 axle combination
4 axle combination
5 axle combination
All other (a)
% of all
trucks above
10,000 Ibs
72.1%
10.3
2.4
5.5
8.0
1.7
% of type
exceeding
91.0 dB(A)
0.9%
5.4
6.6
8.6
24.9
24.9(b)
% of all trucks
above 10,000 Ibs
affected
0.65%
0.56
0.16
0.47
1.99
0.42
4.25%
2 axle straight truck
3 axle straight truck
3 axle combination
4 axle combination
5 axle combination
All other (a)
% of all
trucks above
10,000 Ibs
72.1%
10.3
2.4
5.5
8.0
1.7
% of type
exceeding
92.0 dB(A)
0.5%
2.7
4.1
4.7
16.0
16.0(b)
% of all trucks
above 10,000 Ibs
affected
(a) "All other" includes straight truck with trailer, combinations
with 6 or more axles, and unspecified combinations.
(b) No data available. Percentages exceeding various noise
levels assumed to be the same as for 5 axle combinations.
-63-
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References
1, American Trucking. Trends, 1972, by the American Trucking
Association, Inc., Washington, D.C.
2. 1973 Motor Truck Facts, by the Motor Vehicle Manufacturer
Association, Detroit, Michigan
3. Advance Notice of Proposed Rule Making, Federal Register,
Vol. 33, No. 21, P. 3087, Feb. 1, 1971
4. EPA Public Hearing on Noise Abatement and Control-
Manufacturing and Transportation Noise, Chicago, Illinois, July
28-29, 1971
5. "Transportation Noise and Noise from Equipment Powered by
Internal Combustion Engines," U.S. Environmental Protection Agency,
Report NTID 300-13, Dec. 31, 1971
6. "Use of Motor Vehicle Noise Measuring Instruments,"
California Highway Patrol Report, 1965
7. Foss, R.N., "Vehicle Noise Study - Final Report," Applied
Physics Laboratory, University of Washington, Report for Wash-
ington State Highway Commission, Department of Highway, June, 1972
8. Unpublished data, Bolt, Beranek and Newman
9. "California's Experience in Vehicle Noise Enforcement,"
California Highway Patrol (Exhibit G, ONAC Docket M07O)
10 . Personal Communication with W.H. Close, Department of
Transportation
64
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11. Unpublished data, Bolt, Beranek and Newman, Memorandum to
EPA, June 1, 1973
12. "Community Noise" U.S. Environmental Protection Agency, Report
NTID 300-3, Dec. 31, 1971, p.4.
13. Ibid., p.5
14. "Exterior Sound Level for Heavy Trucks and Buses -
Recommended Practice SAE J366a," Society of Automotive Engineers,
New York, New York, 1971
15. "Vehicle Noise Measurement," California Administrative
Code, Title 13, Chapter 2, Subchapter 4, Article 10, February
1968
16- "Measurement of Noise Emitted by Vehicles," 3362, International
Organization for Standardization, 1964.
17* "Research on Highway Noise Measurement Sites," Wyle Labor-
atories Report for California Highway Patrol, March 1972
18. Op Cit., 1973 Motor Truck Facts
19. Report to the President and Congress on Noise, February,
1972, p.p. 2-73
20. Op Cit, NTID 300.3 pp A-S, A-7
21. Effects of Noise on People, NTID 300.7
22. Op Cit., NTID 300.13 p. 92-95
23. Op Cit., NTID 300.13 p. 92-93
24. "Truck Noise I - Peak A - Weighted Sound Levels Due to
Truck Tires," National Bureau of Standards Report by Department
of Transportation, Report No. OST-ONA 71-9, Sept., 1970
65
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25. Op Cit., 1973 Motor Truck Facts
26. Op Cit., 1973 Motor Truck Facts
27. Op Cit., NTID 300.13 pp 96-106
28. Op Cit., 1973 Motor Truck Facts
29- Op Cit., NTID 300.13, p. 102
30. Alexandra, A., "Motor Vehicle Noise," O.E.C.D. Report, Novem-
ber, 1971
31. Op Cit., "Truck Noise I11 Sept. 1970
32- Personal communication with W.H. Close, Department of
Transportation
33' Op Cit., DOT Report No. OST-ONA 71-9, p. 3-4
34- Op Cit., NTID 300.13, P. 94
35. Op Cit., NTID 300.13, P. 100
36- "Diesel Exhaust and Air Intake Noise," Stemco Manufacturing
Company for Department of Transportation, Report No. DOT-TSC-OST-73,
March 1973.
37. Data from Service Engine Company, Cicero, Illinois
38. Wyle Laboratories personal cortnunication with three major
muffler manufacturers (Donaldson Company, Riker, and Stemcoj.
39. Op Cit., NTID 300.13, P. 103
40. Wyle Laboratories, personal communication with Flesc-A-Lite
Corp., Tacoma, Washington
41. Wyle Laboratories, personal communication with Advanced
Products Group, White Motor Company, Torrance, California
66
-------
42. Shipe, M.D., "Operating Principles of the Schwitzer Viscous
Fan Drive," Schwitzer Division of the Wallace-Murray Corp.,
Indianapolis, Indiana, March, 1971
43. Published literature from Schwitzer Division of the Wallace-
Murray Corp., Indianapolis, Indiana
44. Op Cit., NTID 300.13, P. 104
45. Law, R.M., "Diesel Engine and Highway Truck Noise Reduction,"
Society of Automotive Engineers (SAE) Report 730240, Jan., 1973
46. Literature from Donaldson Company, Minneapolis, Minnesota
47. Davisson, J-A., "Design and Application of Commercial Type
Tires," SAE Paper SP 344, Jan., 1969
48. Wik, T.R., and Miller, R.F., Mechanisms of Tire Sound
Generation," SAE Paper SP373, Oct., 1972
49. Wyle Laboratories, personal communication with major
tire companies
50. Wyle Laboratories personal communication with W.H. Close,
Department of Transportation
51. Op Cit., DOT Report OST-ONA 71-9, P. 42
52. Op Cit., NTID 300.13 P. 7
53. Personal communication with Ben Sharp of Wyle Laboratories
54. 1972 Census of transportation -Truck Inventory and Use
Survey, Dept. of Commerce, Bureau of the Census
55. Response from American Trucking Association, April 2, 1973, Docket
Serial No. M042
56. Wyle Laboratories communications with the Schwitzer Division of
Wallace-Murray Corporation and the Flex-a-lite Corporation, 1973.
67
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57. Bolt, Beranek and Newman, Inc. Report No. 2563, The Cost of Quieting
Heavy Cab-Over Engine Diesel Tractors, July 1973
58. Transportation Noise and its Control, p. 10, DOT publication
P5630.1, June 1972.
59. Op. cit., p. 96, p. 101, NTID 300.13.
68
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