> Effective Noise Control During Nighttime Construction

# Introduction

In recent years there have been fundamental changes in the types of
projects that Departments of Transportation (DOT) are constructing.
Today a significant number of projects are urban widening/rehabilitation
work where daylight construction closures of the routes cause
unacceptable congestion problems. Therefore, because of the high traffic
volumes during the normal workday on these major urban transportation
corridors, it is usually only possible to perform construction
operations during the nighttime.

Departments of Transportation are writing into the specifications for
these projects severe restrictions on when a contractor can execute the
work. Typically the work must be performed at night. In turn, these
nighttime work requirements precipitated disturbances to adjacent
property owners'. When residents complain the path of their complaints
is often through their local government. Additionally, the resulting
complaints are coming during a climate of national concern about the
adverse effects of environmental noise.

In the conduct of their construction and rehabilitation programs
agencies struggle with three interested and impacted parties that must
be satisfied.

-   The driving public both commercial and private

-   The community through which the transportation corridor traverses

-   The construction contractors

This is a compilation of methods and techniques for mitigating nighttime
construction nuisances. Mitigation is a critical requirement for serving
the traveling public, for conducting DOT business in a responsible
manner, and for preparing valid contract documents.

# PROBLEMS

The major nuisances associated with the nighttime construction are
noise, vibration, and illumination. Noise problems are normally caused
by the operation of heavy equipment and specifically by vehicle and
machine backup-alarms, Table 1. Vibration problems are primarily a
result of pile driving, blasting operations, or the use of vibratory
rollers. While good illumination is necessary for the work to proceed at
night and for the safety of the traveling public, proper work zone
illumination can be very intrusive to project neighbors. There is also
concern by Departments about exposure to possible contractor claims if
noise objectives are not properly presented in the contract documents.

A telephone survey of state DOTs found that many require adherence to
certain noise (decibel) limits during nighttime construction. In many
cases these limits are the consequence of specific local ordinances.
Some Departments indicated that they could receive local ordinance
waivers rather easily. Other Departments stated that they had
jurisdiction over the local municipalities in these matters, but they
tried to abide by the local ordinances.

#### TABLE 1. Critical Nighttime Construction Noise Generators  {#table-1.-critical-nighttime-construction-noise-generators .unnumbered}

  -------------------------------- --------------------------------------
  **Noise Generator**              **Percent of DOTs identifying as Cause
                                   of Problems\***

  **Back-up Alarms**               **41%**

  **Slamming Tailgates**           **27%**

  **Hoe Rams**                     **24%**

  **Milling/Grinding Machines**    **16%**

  **Earthmoving Equipment**        **14%**

  **Crushers**                     **6%**
  -------------------------------- --------------------------------------

\*As rated by the 50 State DOTs

# SOUND

The human ear does not judge sound in absolute terms, but instead senses
the intensity of how many times greater one sound is to another. A
decibel is the basic unit of sound level; it denotes a ratio of
intensity to a reference sound. Most sounds that humans are capable of
hearing have a decibel (dB) range of 0 to 140. A whisper is about 30 dB,
conversational speech 60 dB, and 130 dB is the threshold of physical
pain, Fig. 1.

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#### Figure 1. Representative Noise Levels {#figure-1.-representative-noise-levels .unnumbered}

*Noise levels tested (in increasing decibel level) include: sound studio
(20 dB), quiet office (40 dB), conversation (60 dB), noisy restaurant
(75 dB), chain saw (120 dB), jet plane (148 dB), and saturn rocket (200
dB).*

Sound and noise are not the same thing, but sound becomes noise when:

-   It is too loud

-   It is unexpected

-   It is uncontrollable

-   It occurs unexpectedly

-   It has *pure tone components*

Noise is any sound that has the potential to annoy or disturb humans, or
cause an adverse psychological or physiological effect on humans. In the
case of the general population a 5 dBA change is required before most
people realize there is a perceptible sound difference.

The noise levels generated during the construction process vary
depending on the type of equipment and the nature of the work being
performed. It should be recognized that noise impacts can be severe,
especially during nighttime activities, and that in many cases simple
noise mitigation strategies will not suffice.

Noise generation on most construction projects is the result of
equipment operation with diesel engines being the primary generators.
Equipment components that generate noise include: the engine, cooling
fan, air intake, exhaust, transmission, and tires. In assessing noise
generation, construction equipment can be grouped into two categories,
stationary and mobile. Equipment noise can also be categorized as being
either continuous or impulse in nature. Stationary equipment is
considered to operate in one location for one or more days at a time;
pumps, generators, compressors, screens, are typical examples of
stationary equipment. In addition, pile drivers and pavement breakers
are sometimes categorized as stationary equipment. Mobile equipment
includes machinery that performs cyclic processes such as: bulldozers,
scrapers, loaders, and haul trucks.

# EQUIPMENT NOISE

Construction equipment is a major noise generator on nearly all
nighttime construction projects. The equipment type, specific model,
equipment condition and the operation performed influence equipment
noise. Equipment manufacturers began attacking machine noise problems in
the late '60s and today because of design improvements and technological
advances new machines have been quieted to an acceptable level for
almost every situation. *Newer equipment is noticeably quieter than
older models* due primarily to better engine mufflers, refinements in
fan design and improved hydraulic systems. Noise levels as generated by
typical equipment are shown in Table 2.

How equipment noise will be perceived is also a function of use
duration. On a monitored project in New Jersey the highest noise levels
resulted from pile driving; but, because the driving was completed in a
short period of time, the activity did not draw any complaints.

One of the conclusions from the U.S. Department of Transportation's 1979
construction equipment noise study was that 88 dBA is a reasonable noise
level to expect for *used* equipment with an engine horsepower of 400 or
less. It should be noted that the USDOT tests were made in the field
under actual operating conditions at road construction sites, mines and
quarries.

In 1994 and 1995 Harris Miller Miller & Hanson Inc. performed noise
studies for the Central Artery/Tunnel project in Boston. The first study
sought to quantify an *average* noise level while the second defined a
*typical* noise level. It would seem that a typical value is better to
use in developing specifications or project restrictions. That data
delineates the most commonly occurring level.

#### Table 2. Construction Equipment Noise Emission Levels {#table-2.-construction-equipment-noise-emission-levels .unnumbered}

+----------------+------------+------------+------------+------------+
| **Equipment**  | Typical    | Average    | Typical    | Lmax Noise |
|                | Noise      | Noise      | Noise      | (dBA)      |
|                | Level      | Level      | Level      |            |
|                | (dBA)      | (dBA)      | (dBA)      | 50 ft.,    |
|                |            |            |            | CA/T       |
|                | 50 ft., U. | 50 ft.,    | 50 ft., U. | Project    |
|                | S. Dept.   | CA/T       | S. Dept.   | Spec.      |
|                | of Trans.  | Project    | of Trans.  | 721.560    |
|                | study 1979 | study 1994 | study 1995 |            |
+----------------+------------+------------+------------+------------+
| Air Compressor |            | 85         | 81         | 80         |
+----------------+------------+------------+------------+------------+
| Backhoe        | 84         | 83         | 80         | 80         |
+----------------+------------+------------+------------+------------+
| Chain Saw      |            |            |            | 85         |
+----------------+------------+------------+------------+------------+
| Compactor      | 82         |            | 82         | 80         |
+----------------+------------+------------+------------+------------+
| Compressor     | 90         | 85         |            | 80         |
+----------------+------------+------------+------------+------------+
| Concrete Truck |            | 81         |            | 85         |
+----------------+------------+------------+------------+------------+
| Concrete Mixer |            |            | 85         | 85         |
+----------------+------------+------------+------------+------------+
| Concrete Pump  |            |            | 82         | 82         |
+----------------+------------+------------+------------+------------+
| Concrete       |            |            | 76         | 80         |
| Vibrator       |            |            |            |            |
+----------------+------------+------------+------------+------------+
| Crane, Derrick | 86         | 87         | 88         | 85         |
+----------------+------------+------------+------------+------------+
| Crane, Mobile  |            | 87         | 83         | 85         |
+----------------+------------+------------+------------+------------+
| Dozer          | 88         | 84         | 85         | 85         |
+----------------+------------+------------+------------+------------+
| Drill Rig      |            | 88         |            | 85         |
+----------------+------------+------------+------------+------------+
| Dump Truck     |            | 84         |            | 84         |
+----------------+------------+------------+------------+------------+
| Excavator      |            |            |            | 85         |
+----------------+------------+------------+------------+------------+
| Generator      | 84         | 78         | 81         | 82         |
+----------------+------------+------------+------------+------------+
| Gradall        |            | 86         |            | 85         |
+----------------+------------+------------+------------+------------+
| Grader         | 83         |            | 85         | 85         |
+----------------+------------+------------+------------+------------+
| Hoe Ram        |            | 85         |            | 90         |
+----------------+------------+------------+------------+------------+
| Impact Wrench  |            |            | 85         | 85         |
+----------------+------------+------------+------------+------------+
| Jackhammer\*   |            | 89         | 88         | 85         |
+----------------+------------+------------+------------+------------+
| Loader         | 87         | 86         | 85         | 80         |
+----------------+------------+------------+------------+------------+
| Paver          | 80         |            | 89         | 85         |
+----------------+------------+------------+------------+------------+
| Pile Driver,   |            | 101        | 101        | 95         |
| Impact         |            |            |            |            |
+----------------+------------+------------+------------+------------+
| Pile Driver,   |            |            | 96         | 95         |
| Sonic          |            |            |            |            |
+----------------+------------+------------+------------+------------+
| Pump           | 80         |            | 85         | 77         |
+----------------+------------+------------+------------+------------+
| Rock Drill     |            |            | 98         | 85         |
+----------------+------------+------------+------------+------------+
| Roller         |            |            | 74         | 80         |
+----------------+------------+------------+------------+------------+
| Scraper        | 89         |            | 89         | 85         |
+----------------+------------+------------+------------+------------+
| Slurry Machine |            | 91         |            | 82         |
+----------------+------------+------------+------------+------------+
| Slurry Plant   |            |            |            | 78         |
+----------------+------------+------------+------------+------------+
| Truck          | 89         | 85         | 88         | 84         |
+----------------+------------+------------+------------+------------+
| Vacuum         |            |            |            | 85         |
| Excavator      |            |            |            |            |
+----------------+------------+------------+------------+------------+

\* There are 82 dBA @ 7 meter rated jackhammers (90 lb. class)
available. This would be equivalent to 74 dBA @ 50 ft. These are
silenced with molded intricate muffler tools.

## Equipment Noise Control Options {#equipment-noise-control-options .unnumbered}

Listed in Table 3 are the major sources of equipment noise that cause
complaints. The Table also lists specific methods for controlling the
identified noise problem.

#### Table 3. Construction Equipment Noise Control Options {#table-3.-construction-equipment-noise-control-options .unnumbered}

+---------------------+------------------------------------------------+
| ##### **Nois        | **Control**                                    |
| e Source** {#noise- |                                                |
| source .unnumbered} |                                                |
+---------------------+------------------------------------------------+
| **Backup alarms**   | Use manually-adjustable alarms                 |
|                     |                                                |
|                     | Use self adjusting alarms                      |
|                     |                                                |
|                     | Use an observer                                |
|                     |                                                |
|                     | Configure traffic pattern to minimize backing  |
|                     | movement                                       |
+---------------------+------------------------------------------------+
| **Slamming          | Establish truck cleanout staging areas         |
| tailgates**         |                                                |
|                     | Use rubber gaskets                             |
|                     |                                                |
|                     | Decrease speed of closure                      |
|                     |                                                |
|                     | Use bottom dump trucks                         |
+---------------------+------------------------------------------------+
| **Pavement breakers | Fit with manufacturer approved exhaust muffler |
| (jackhammers)**     |                                                |
|                     | Prohibit within 200 ft. of a noise sensitive   |
|                     | location during nighttime hours                |
|                     |                                                |
|                     | Enclose with a noise tent                      |
+---------------------+------------------------------------------------+
| **Prolonged idling  | Reduce idling                                  |
| of equipment**      |                                                |
|                     | Locate equipment away from noise sensitive     |
|                     | areas                                          |
+---------------------+------------------------------------------------+

**Ambient-sensitive self-adjusting backup alarms** increase or decrease
their volume based on background noise levels. These alarms work best on
smaller equipment such as backhoes and trucks. The alarm self-adjusts to
produce a tone that is readily noticeable over ambient noise levels (a
minimum increment of 5 decibels is typically considered readily
noticeable), but not so loud as to be a constant annoyance to neighbors.
The typical alarm adjustment is 82 or 107 dBA. Close attention must be
give to the alarm's mounting location on the machine in order to
minimize engine noise interference, which can be sensed by the alarm as
the ambient noise level. These alarms should be mounted as far to the
rear of the machine as possible. An alarm mounted directly behind a
machine's radiator will sense the cooling fan's noise and adjust
accordingly, Figure 2. Such a mounting will **negate the purpose of the
device.**

**Manually**-adjustable alarms are effective in reducing backup alarm
noise nuisance but their use requires that each alarm be set at the
beginning of each day and night shift. The manual setting feature
eliminates the machine mounting location problem of the
ambient-sensitive self-adjusting backup alarms. The manually adjustable
alarms typically have an 87 and 107 dBA setting range, with the 87 dBA
setting used for nighttime operations.

# NOISE MITIGATION

Of interest in terms of community noise impact is the overall noise
resulting from a construction site. The noise of each individual piece
of equipment and sometimes the highest noise source is not always the
number one priority. Noise control is directed toward modification of a
perceived sound field. It strives to change the impact at the receiver
so that the sounds conform to a desired level. Mitigation of undesired
sounds should consider source control, path control, and receptor
control Figure 3.

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#### Figure 2. A Self-Adjusting Backup Alarm Mounted in the Wrong Position {#figure-2.-a-self-adjusting-backup-alarm-mounted-in-the-wrong-position .unnumbered}

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#### Figure 3. Noise Transfer Situation  {#figure-3.-noise-transfer-situation .unnumbered}

*The Noise Transfer Situation shows the relation between sources, such
as a pile driver, loader and truck, and their paths, groundborne
vibration and direct sound (which includes a reverberant field) to the
receiver. The relation is detailed below.*

*The Pile Driver creates a groundborne vibration path to the receiver.
The loader and truck create a direct sound (reverberant field) path to
the receiver.*

## Source Controls {#source-controls .unnumbered}

Source control is the most effective method of eliminating noise
problems. It is a cardinal rule that, where possible, noises control
should occur at the source. Source controls, which limit noise
emissions, are the easiest to oversee on a construction project. Source
mitigation reduces the noise problem everywhere not just along a single
path or for one receiver. Consequently, a project's noise mitigation
strategy should emphasize noise control at the source.

### Require Construction Operations Planning {#require-construction-operations-planning .unnumbered}

Restrict the movement of equipment into and through the construction
site. Long-term impacts are generated along haul routes when there are
large quantities of materials to be moved. Reroute truck traffic away
from residential streets. Impose seasonal limitations on construction
noise, the spring or fall are critical times in residential areas
because windows are usually open at night.

### Example Specifications {#example-specifications .unnumbered}

> *Where practical and feasible, construction sites shall be configured
> to minimize back-up alarm noise. For example, construction site access
> should be designed such that delivery trucks move through the site in
> a circular manner without the need to back up.*

### Require Modern Equipment {#require-modern-equipment .unnumbered}

Unions recognize construction noise as a hazard to workers and the first
of five things suggested to workers to address the problem is that they
"Ask contractors to buy quieter equipment when they buy new equipment."
DOT specification of equipment noise emission limits forces the use of
modern equipment having better engine insulation and mufflers. The
emission levels specified should reflect levels that can reasonably be
achieved with well-maintained equipment, see Table 3.

### Equipment Restrictions {#equipment-restrictions .unnumbered}

Restrict the type of equipment used.

### Example Specifications {#example-specifications-1 .unnumbered}

> *The use of impact pile drivers shall be prohibited during evening and
> nighttime hours.*
>
> *All jackhammers and pavement breakers used on the construction site
> shall be fitted with manufacturer's approved exhaust mufflers.*
>
> *The use of pneumatic impact equipment (i.e. pavement breakers,
> jackhammers) shall be prohibited within 200 feet of a noise-sensitive
> location during nighttime hours.*
>
> *The local power grid shall be used wherever feasible to limit
> generator noise. No generators larger than 25 KVA shall be used and,
> where a generator is necessary, it shall have a maximum noise muffling
> capacity.*

Call the contractor's attention to the back-up alarm noise problem and
require measures to address the issue.

By specification direct the use of only power grid connected or solar
powered traffic control devices, Figure 4.

### Example Specifications {#example-specifications-2 .unnumbered}

> All variable message/sign boards shall be solar powered or connected
> to the local power grid.

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#### Figure 4. Solar Powered Traffic Control Devices {#figure-4.-solar-powered-traffic-control-devices .unnumbered}

### Operate at Minimum Power {#operate-at-minimum-power .unnumbered}

Noise emission levels tend to increase with equipment operating power.
This is a critical issue with older street sweepers, demolition work
using a hoe-ram, and equipment such as vac-trucks, Figure 5. Require
that such equipment operate at the lowest possible power levels.

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#### Figure 5. vac-truck working at night {#figure-5.-vac-truck-working-at-night .unnumbered}

### Use Quieter Alternate Equipment {#use-quieter-alternate-equipment .unnumbered}

Electric or hydraulic powered equipment is usually quieter than a
diesel-powered machine. Encourage contractors to use alternate
equipment. Use electric tower cranes, Fig. 6, instead of diesel power
mobile cranes

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#### Figure 6. Electric Tower Cranes for Bridge Construction  {#figure-6.-electric-tower-cranes-for-bridge-construction .unnumbered}

## Path Controls {#path-controls .unnumbered}

Alone, source noise controls are frequently inadequate at adequately
minimizing noise impacts on abutting sensitive receptors because of the
close proximity to residences and businesses in urban areas and because
of the very nature of the construction work. Thus, having exhausted all
possible mitigation methods of controlling noise at the source, the
second line of attack is controlling noise radiation along its
transmission path. Noise path barriers should provide a substantial
reduction in noise levels, should be cost effective, and should be
implementable in a practical manner without limiting accessibility.
Barriers can increase a project's visual impact. This visual change can
have either a positive or negative impact. Therefore, aesthetic effects
must be considered when designing barrier systems.

### Path Mitigation Techniques {#path-mitigation-techniques .unnumbered}

Once established, only reflection, diffraction insulation or dissipation
can modify an airborne sound field. In other words, it is necessary to
increase the distance from the source or to use some form of solid
object to either destroy part of the sound energy by absorption, or to
redirect part of the energy by wave deflection. The three techniques for
path mitigation are therefore:

-   Distance

-   Reflection

-   Absorption

### Enclose especially Noisy Activities or Stationary Equipment  {#enclose-especially-noisy-activities-or-stationary-equipment .unnumbered}

Enclosures can provide a 10 to 20 dBA sound reduction. Additionally the
visual impact of roadwork activities has an affect on how construction
sounds are perceived. An important noise mitigation issue, therefore, is
the audio-visual sensing factor. Enclosures address both the absolute
audio and the visual perception issue, Figure 7.

### Example Specifications {#example-specifications-3 .unnumbered}

> All jackhammers and pavement breakers used at the construction site
> shall be enclosed with shields, acoustical barrier enclosures, or
> noise barriers.

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#### Figure 7. Slurry Plant Enclosure for Audio-Visual and Dust Control {#figure-7.-slurry-plant-enclosure-for-audio-visual-and-dust-control .unnumbered}

# CONCLUSIONS

A significant number of future construction projects will involve urban
work. Therefore, it is important that before contracts are advertised
and bid that there be an objective assessment as to the magnitude of
noise nuisances. Noise problems are normally caused by the operation of
heavy equipment. The identification of methods and techniques for
mitigating such nuisances is a critical planning requirement for both
owners and contractors.

**Source control** is the most effective method of controlling
construction noise. Source controls, which limit noise, are the easiest
to oversee on a construction project. Mitigation at the source reduces
the problem everywhere not just along one single path or for one
receiver. The specification of equipment *noise emission limits* forces
the use of modern equipment having better engine insulation and
mufflers.

**Path Controls** are the second line of attack in controlling noise.
Barriers can provide a substantial reduction in the nuisance effect in
some cases. The use of barriers should be examined against other
possible measures to prove that they are cost effective. Further,
aesthetic effects must be considered when designing barrier systems.
Path control measures include:

-   Move equipment farther away from the receiver

-   Enclose especially noisy activities or stationary equipment

-   Erect noise barriers or curtains

-   Use landscaping as a shield and dissipater