Noise Pollution

Noise Impacts are an important consideration of the Environmental Review Process. State, Federal and international standards establish acceptable levels of noise in various contexts. There are guidelines for measuring noise from train systems and various strategies used to mitigate its impacts.  Schools, hospitals , environmental groups and residential neighborhoods are among the stakeholders who should pay particular attention to the impacts of noise.

Critical Health Effects

Noise pollution can result in adverse impacts on health and well-being. The impacts on humans of noises above the acceptable range have been studied extensively.   At extreme levels, hearing itself can be impacted.   Other problems related to noise include compromised learning, stress, high blood pressure, sleep loss, distraction and lost productivity, and a general reduction in the quality of life and opportunities for tranquility.1 Fewer studies have been done on impacts to wild and domesticated animals, but environmentalists are concerned with  impacts such as interference with communication, masking predation, startle and fright.2

Studies indicate that children are more sensitive than adults to loud noise.  Humans (and animals) are more sensitive to noise when they are sleeping.  More than 30 years ago a researcher, Dr. Arline Bronzaft, found that students in a school next to a elevated train in NYC were one year behind in reading ability if they had been on the noisy side of the school. That same researcher found that a couple years after the noise was reduced, the reading abilities of students on the formerly noisy side of school improved.3

The community, train riders, and train operators & employees have different types of exposure to the “noise climate” and the climate will be different after build out than during construction.   During construction, the noise levels are typically greater.  Workers constructing the train, as well as members of the community adjacent to the tracks, must be protected from the adverse impacts of excessive noise.

The HSRA is obligated to mitigate noise issues that excede the current situation.  However, the EIR might not address specific concerns in your community unless members of your community provide very specific comments to the HSRA detailing areas of concern (e.g., schools, hospitals, etc.), location, details of land use (e.g., hours of use, typical ages), desired dB levels (see chart below), accepted standards, etc.

Please note:  we are not experts on Noise Pollution.  The following is an attempt to synthesize the available HSRA reports as well as current literature to provide some suggestions for how stakeholders can effectively provide input into the EIR process.  An extensive list of Reference links is provided at the bottom of this page and we encourage anyone who is interested in diving into the originals to do so.

Suggested Comments from Community Members

The goal is to identify all the areas that might be impacted by noise,  specify concerns about potential adverse effects and ensure that the appropriate analyses are conducted.  Do not assume that the HSRA knows all the schools, libraries, parks, etc in your community.  As an example, in the Program Level EIR for the Bay Area,  only two schools were identified on the entire corridor from San Francisco to San Jose.4 You know your own community, so it is helpful to provide as detailed an inventory as possible.

The What

Until the vertical alignment of the train is known, it is safest to assume a conservative band for potential impact area:  900 feet on either side of the corridor and within a 1/4 mile radius from stations.

Various stakeholders may wish concentrate on different community assets (eg a school board may only wish to comment on the schools, a particular organization might simply want to document its particulars).  Don’t feel overwhelmed by this list, it is meant as a guide for the community as a whole.

  • schools & pre-schools – name, location, age range of students, school hours
  • libraries – name, location, hours of operation
  • parks – name, location, size, amenities
  • hospital and other medical and mental health facilities
  • courtrooms
  • childcare facilities
  • faith communities (churches, temples, etc) – name, location, hours of operation
  • funeral homes, cemeteries, etc.
  • wild animal habitats
  • livestock areas
  • other community assets you think might be impacted by sound
The Why

In your comment, it is most effective to indicate why you are concerned and cite the relevant critical effects and Standards. Specifying studies, established standards, and scientific reports is the best way to ensure that the Authority will study your concern, rather than just “note” it.  See the sections on Standards and Critical Effects for ideas.

The How

It is entirely appropriate for the public to comment on the actual methodology used to study noise impacts.  The HSRA’s analysis is heavily weighted towards establishing and mitigating average noise levels.  This is a useful and standard practice.  However, there are additional analyses that do not seem to currently be under consideration, which may indeed be relevant in getting a full picture of the impacts.  These include analysis of the following:

  • Wind, rain, relative humidity, temperature and other meteorological effects have a strong influence on noise measurements. In order to fully understand noise events and conditions, weather and noise measurements should be combined.
  • Rapid onset of noise generated by a fast moving train has a different effect than traditional trains and should be studied in addition to the average noise levels.



Sound is measured in decibels (dB), which uses a logarithmic scale (it is not linear).   Each increase of 10 dB means twice the perceived “loudness”.

Environmental noise fluctuates over time, so the Sound Level is used to describe the “noise climate” in a particular location.  The standard is the “Equivalent Sound Level” (Leq).  It is formulated in terms of “the equivalent steady noise level which in a stated period of time would contain the same noise energy as the time-varying noise during the same time period”.5 That basically means that a series of noise measurements are taken over time (eg. one hour) and then entered into a mathematical equation to figure out what the “average” sound is (Note: because it is a logarithmic scale, you cannot use simple arithmetic to calculate the sound level.) Various sound level measurements exist:  day-night sound level (LAdn) is measured for a 24 hour period, an Hourly Equivalent Sound Level (LAeq) is measured over an hour, and a maximum level, LAmax.

HSRA uses day-night sound level (LAdn) in dBA for residential areas, and an hourly equivalent sound level (LAeq) in dBA is applied during hours of active use in parks, churches, libraries, schools.6

Regulations & Standards

A host of laws and guidelines have been established by various agencies, including the FRA (Federal Rail Administration), FTA (Federal Transportation Administration), EPA, OSHA.  See the reference section for a full list.

The acceptable level of noise varies by the context.  The World Health Organization has established standards for maximum acceptable noise levels, which the following table summarizes.7

Specific environment Critical health effect(s) LAeq [dB] Time base [hours] LAmax, fast[dB]
Outdoor living area Serious annoyance, daytime and evening
Moderate annoyance, daytime and evening
Dwelling, indoors
Inside bedrooms
Speech intelligibility and moderate annoyance, daytime and evening
Sleep disturbance, night-time
Outside bedrooms Sleep disturbance, window open (outdoor values) 45 8 60
School class rooms and pre-schools, indoors Speech intelligibility, disturbance of information extraction, message communication 35 during class
Pre-school Bedrooms, indoors Sleep disturbance 30 sleeping-time 45
School, playground outdoor Annoyance (external source) 55 during play
Hospital, ward rooms, indoors Sleep disturbance, night-time Sleep disturbance, daytime and evenings 30
Hospitals, treatment rooms, indoors Interference with rest and recoverya
Industrial, commercial, shopping and traffic areas, indoors and Outdoors Hearing impairment 70 24 110
Ceremonies, festivals and entertainment events Hearing impairment (patrons:<5 times/year) 100 4 110
Public addresses, indoors and outdoors Hearing impairment 85 1 110
Music through headphones/Earphones Hearing impairment (free-field value) 85d 1 110
Impulse sounds from toys, fireworks and firearms Hearing impairment (adults)
Hearing impairment (children)

Outdoors in parkland and conservation areas Disruption of tranquility c

a as low as possible; b peak sound pressure (not LAmax, fast), measured 100 mm from the ear;
c existing quiet outdoor areas should be preserved and the ratio of intruding noise to natural background sound should be kept low;
d under headphones, adapted to free-field values

High Speed Rail Implications

We need to consider the change in noise pollution between High Speed Rail and the existing situation.  Some of these changes are positive and others need to be mitigated.

According to the HSRA, High Speed trains “generate lower noise levels than conventional trains at speeds with which most people are familiar [under 125 mph]. At higher speeds, however, HST shows a noise increase over conventional trains due to aerodynamic effects. A mitigating factor is that the high speeds enable HST noise to occur for a relatively short duration (a few seconds at the highest speeds).”

In addition, “the total noise generated by a train is the combination of sounds from several individual noise generating mechanisms, each with its own characteristics, including location, intensity, frequency content, directivity, and speed dependence… These noise sources can be grouped into three categories according to the speed of the train.”8

For low speeds, below about 40 mph (64 kph), noise emissions are dominated by the propulsion units, cooling fans, and under-car and top-of-car auxiliary equipment, such as compressors and air conditioning units. The HST would be electrically powered and considerable quieter at low speeds than conventional trains, which are usually diesel powered.

In the speed range from 60 mph to about 150 mph (98–241 kph), mechanical noise resulting from wheel-rail interactions and structural vibrations dominate the noise emission from trains. In the existing rail corridors in California, conventional trains seldom exceed 79 mph (127 kph), so this speed range, which represents a medium range for HST, is the top end of noise characteristics for trains with which most people are familiar. Speed has a strong influence on noise in the medium speed range.

Above approximately 170 mph (274 kph), aerodynamic noise sources tend to dominate the radiated noise from the HST. Conventional trains are not capable of attaining such speeds. HST noise in the transition speeds between each of the three foregoing ranges is a combination of the sources in each range.

In addition, the noise onset is very rapid with higher speeds. Instead of a slowly approaching noise that gradually gets louder as the train approaches and then dissipates as it leaves, the velocity of a high speed train means that the noise is more sudden.  Typically, rapid onset noise is considered more disruptive. The following graph demonstrates the areas of impact of rapid noise onset as a function of distance and train speed.

In areas where HSR will share an existing rail corridor (e.g. Caltrain, Metrolink), grade separations should eliminate noise from horns at the existing grade crossings as well as the warning bells of the crossing guards. (Note: horns may still be used at stations.)  HSR found that these sources currently dominate the noise climate in areas within a .25 mi radius of the grade crossings.9 However, they appear to have assumed in their analysis that this benefit would outweigh all other impacts:

the potential noise impact ratings from screening were adjusted to account for segments where at-grade crossings would be eliminated for existing passenger and freight trains as part of the implementation of HST service along that alignment. A reduction in one impact rating level (high to medium or medium to low) was made only for alignments where HST speeds would be less than 150 mph (241 kph)

Train operations have an impact on noise pollution as well.  Obviously, the frequency of trains increases the cumulative impact of noise. The HSR anticipates running 19 trains per hour (tph)  at peak service.10 In addition, for corridors with existing commuter trains, it is important to understand the future plans for those services as well. For example, Caltrain 2025 anticipates an increase to 12 tph during peak hours.11 (Note: the rail documentation usually talks about a tph number in each direction: eg. 6 tph in each direction.  The numbers here are for both directions because that seems to make more sense to the average person.)

Vertical Alignments

According to HSRA, the vertical alignment of the train has an effect.  “Noise from elevated trains travels twice as far as noise from trains that are ‘at grade’ (at ground level).  The noise of underground alignment is concentrated at tunnel entrances and at vent locations.”12

The FRA provides a useful diagram that shows comparisons of the shielding corrections associated with various types of track geometries (alignments).
[insert image pg 56,]

Power Stations

In addition to noise of the trains themselves, other operational structures should also be considered, such as the electric substations, venting of tunnels, transformers and catenary lines.

Construction Noise

Noise during construction includes similar factors as any heavy construction site.  Trucks, heavy equipment, etc. will all create noise pollution as the train system is built. Early morning and nightime operations could impact community sleep, and loud construction in sensitive areas (eg around schools) can impact the learning environment.  OSHA regulations are expected to protect the people working on construction.


There are three basic approaches to mitigating noise pollution: quieting the source, interrupting the path, and quieting the receiver

Quiet the Source

The design and proper maintenance of the train systems and tracks have an impact on noise and various strategies can be used to reduce noise at the source.  Designing for a system that is as quiet as possible is the first step in mitigating against noise pollution.

The times of operation are another factor.  Many jurisdictions institute “quiet hours” on air traffic since sleep-time is more sensitive.  The current operational plans for High Speed Train systems does not call for nighttime operations, but the exact operational hours have not been solidified, so it is important for the public to document current standards in their communities.

Interrupt the Path

Of course, no train system can be designed to be completely quiet, so the next step is to try to limit the impact of the noise by interrupting the path of the sound waves, typically with sound walls.  HSRA plans to mitigate noise impacts with physical barriers in areas where there is noise impact.  “Noise walls constructed approximately 30 to 50 feet from the centerline of the nearest track to the sensitive land use. The wall height necessary to mitigate these situations would normally be in the range of 8 to 12 feet high and would depend on the particular circumstances of each situation requiring noise mitigation.”13

“In general, the rules of thumb for sound barriers are easy to remember and fairly accurate: Up to 10 dB of sound reduction is fairly straightforward to obtain. A range of 15-17 dB is practical to obtain. But more than 20 dB of reduction is difficult to obtain, and more than 25 dB is impossible to obtain.”14

Quiet the Receiver

Finally, if the noise continues to be an issue, attempts can be made to quiet the receiving end.  One strategy used by airports is to apply sound-proofing treatments to nearby buildings (homes, schools, medical facilities), by augmenting insulation, installing double-pane windows, etc. Of course, if window treatments are applied a side effect to consider is summer cooling costs if air conditioning is not already in place.

Further Reading

HSRA documents on noise

Other Train/Transit references

On noise pollution and its effects

On measuring noise and basic science of sound

  • Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Safety Margin, U.S. Environmental Protection Agency, 1974 (EPA/ONAC 550/9-74-004). Appendix A
  • Sound Pressure Levels,
  • What is a Decible?, Department of Physics, University of New South Wales

On Federal and State regulations and laws guiding noise pollution and mitigation

On Noise Mitigation

Please email to correct inaccuracies, omissions or broken links. Thanks!


  1. Noise Pollution Clearninghouse
  2. High Speed Train Noise Effects on Wildlife and Domestic Livestock, C.E. Hanson
  3. A Quieter School: An Enriched Learning Environment, Quite Classrooms
  4. Bay Area to Central Valley Final [Decertified] Program EIR/EIS Volume1, Section 3.4
  5. Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Safety Margin, EPA.
  6. HST Noise and Vibration Technical Evaluation, Bay Area to Merced; and Los Angeles, Orange County and San Diego
  7. Guidelines for Community Sounds, WHO.
  8. Bay Area to Central Valley Final [Decertified] Program EIR/EIS Volume1, Section 3.4
  9. ibid
  10. HST Noise and Vibration Technical Evaluation, Bay Area to Merced
  11. HSRA Report to the Legislature, Dec 2009 (aka 2009 Business Plan) Ridership, Revenue & Operations Chapter (p 66)
    “This peak schematic pattern provides 57 trains in each direction in 6 hours, for an average of just under 10 trains per hour. The off-peak for the initial phase of service provides 71 trains in each direction over a 10-hour period, for an average of 7 trains an hour.”
  12. Caltrain Electrification Newsletter, Summer 2009 (here)
  13. HST Noise and Vibration Technical Evaluation, Bay Area to Merced
  14. Sound Walls: Absorptive versus reflective design and effectiveness