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3. Assessment of noise and vibration impacts

An assessment of rail noise and vibration impacts may be needed as part of an environmental assessment, environmental impact assessment or review of environmental factors required under the EP&A Act, or under the provisions of the POEO Act.

3.1 Applying noise and vibration level values and determining feasible and reasonable mitigation measures

The noise and vibration trigger levels identified in this guideline and the associated guideline Assessing vibration: A technical guideline (DEC 2006) are used as indicators or trigger levels for when a noise and vibration assessment needs to be conducted for a project

Figure 2 outlines the process of using the noise and vibration trigger levels contained in this guideline. The trigger values indicate when an assessment of noise and vibration impacts is needed to develop any project-specific noise and vibration levels and any feasible and reasonable mitigation measures that may need to be implemented. Figure 2 also highlights the need for community involvement throughout the process.

As a guide, 'feasible' and 'reasonable' mitigation measures can be defined as follows:

'Feasibility' relates to engineering considerations and what can practically be built or modified, given the opportunities and constraints of a particular site.

'Reasonableness' relates to a judgement which takes into account the following factors:

• noise-mitigation benefits – noise reduction provided, number of people protected
• cost of mitigation – total cost and cost variation with level of benefit provided
• community views
• aesthetic impacts
• noise levels for affected land uses – existing and future levels, and expected changes in noise levels
• benefits arising from the development or its modification.

In practice, the detail of the mitigation measures applied will depend to a large extent on project-specific factors. The outcome that is aimed for in this process is to balance the benefits for the wider community arising from the project and the costs and benefits of project-related mitigation measures which aim to minimise (as far as practicable) the local impacts. Conditions that flow from this process will be achievable and will provide clarity and confidence for the proponent, local community, regulators and the ultimate operator that the proposed mitigation measures can achieve the predicted level of environmental protection.

Note that an assessment of vibration or ground-borne noise may not always be required. These should be assessed only where they are likely to be an issue (e.g. in the case of an underground tunnel or where past experience indicates that the proposal may result in vibration or structure-borne noise).

Figure 2: Typical noise and vibration impact assessment process for a rail project

Planning focus phase
Determine the environmental noise and vibration values that need to be protected and where, through discussions with the community and relevant agencies in planning focus meetings and by referring to this guideline.

Use the noise and vibration trigger levels in Tables 1, 2 and 3 to decide if an assessment of impacts is needed.

Step 1
If an assessment is needed, determine if the selected noise and vibration trigger levels are exceeded through a noise impact assessment as part of the environmental impact assessment process under the EP&A Act.

Planning approval
Achievable noise and vibration levels and/or mitigation measures for the project are included in the approval conditions.

Achievable noise and vibration levels and/or mitigation measures for the project are included in the approval conditions.

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3.2 Shared rail corridor

Some sections of rail corridor have shared usages (i.e. passengers and freight) and some have shared ownership. in some cases there are dedicated freight lines, but in most cases these are the same tracks with shared usage.

Both situations add complexity to assessing the possible noise levels from the corridor and also may restrict the potential range of mitigation measures. In particular, the large number of freight operators and different types of freight rolling stock increase the need to consider alternative options, such as control of noise at its source.

Where a noise assessment needs to be carried out for a rail project in a shared rail corridor, these steps should be followed:

• identify the existing levels of rail noise
• report separately on the contribution to existing rail noise from each of the different usages (in the case of shared usage, freight compared with passengers) or from each of the different rail infrastructure owners (in the case of multiple owners)
• predict noise from the construction and operation of the rail project
• report both contributed noise levels (distinguishing between shared usage or shared ownership) and the cumulative levels of rail noise, thus allowing relative noise contributions from usage type or owner to be identified.

The process from here on is as described below for any other rail project. However, the range of feasible and reasonable mitigation measures considered needs to be appropriate for these operations.

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3.3 Areas to cover in a noise and vibration impact assessment report

This section outlines the areas to be covered in an assessment report into the noise and vibration impacts from a rail project. Note that the extent of work and information required for each step will depend on the expected level of impact: the more significant the likely impact, the more detailed the assessment will need to be.

Industrial developments which need to report on off-site noise and vibration impacts from rail traffic might also be able to use this as a guide.

Describe the track layout, sensitive development locations and proposed operations

1. Describe the alignment of the proposed track, including gradient and heights of cuttings and fill and other track features, such as turnouts or crossovers, that may increase or decrease noise levels. include diagrams showing the track alignment, land uses along the proposed development, and noise measurement locations. These should be at a scale large enough to delineate individual residential blocks.
2. Estimate rail traffic speeds and operating conditions, such as use of horns, locomotive throttle settings, braking locations, shunting and signalling.
3. Estimate rail traffic volumes immediately after commencement of operations and at a point 10 years after commencement. Break this at least into the periods 7 am–10 pm and 10 pm–7 am, and specify the proportion of freight trains for each period. Preferably, obtain projected volumes for each hour and use average weekday volumes.
4. Provide details of assumed data for the new development, including rail traffic volumes and speeds, operating conditions and percentage of freight trains by time of day; and details of the calculation process, including assumed noise source heights for rail vehicles.

Determine the appropriate noise and vibration trigger levels

1. Identify affected land uses adjacent to the proposed rail project. For tunnels, this is the land use above the tunnel.
2. Determine the appropriate airborne noise trigger levels (and if relevant, ground-borne noise and vibration trigger levels) for each section of track. An assessment of vibration or ground-borne noise may not always be required. These should be assessed only where they are likely to be an issue. Where the assessment has rejected certain noise and/or vibration trigger levels as not appropriate to the project, the reason should be made clear in the assessment report.

Establish the level of existing rail noise and vibration (if present)

1. Monitor noise in the vicinity of the proposed rail project or land-use development using the measurement procedures described in Section 3.4 to determine existing rail noise levels. in cases where non-rail noise makes a major contribution to ambient noise in the area, monitoring may be supplemented by calculation of the rail noise component. Note that all noise descriptors that will be used in the assessment should be monitored. These may include L_Aeq(1h), L_Aeq(15h), L_Aeq(9h), L_Amax, sound exposure level (SEL) and root mean square (rms) acceleration in m/s².
2. Provide details of noise monitoring procedures and/or calculations of existing noise levels. This should include noise-measurement data from each site and rail traffic volumes and speeds, operating conditions and proportions of freight trains. Where estimates of existing levels of rail noise are made, include information on the calculation procedure, including the assumptions used.

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Predict the impacts of the rail infrastructure proposal

1. Impact predictions should be conducted for three scenarios: duration of construction; the proposed commencement date; and an indicative period into the future (e.g. 10 years or a similar period). These should be an estimate of projected traffic volumes that represent the expected future typical level of rail traffic usage. if mitigation measures are being proposed, the predictions should be for both the before- and after-mitigation periods.
2. The contribution of noise and (if relevant) vibration levels from different types of use (e.g. freight or passenger) should be calculated and reported separately. The total or combined noise and (if relevant) vibration levels should also be reported.
3. All assumptions used in the prediction should be clearly stated, and the expected accuracy should be quoted along with the final predicted levels.
4. 12 Calculate noise levels (including ground-borne noise and/or vibration where relevant), expressed in terms of the required descriptors, for each receiver (or representative group of receivers), assuming that no noise amelioration measures are introduced. Calculated levels should include noise from rail traffic on the new development and on any other track, which may influence the total rail traffic noise level at the receiver.
5. Noise level contributions from freight and passenger rail traffic should be reported separately along with the total rail noise. The increase in rail noise due to the project should also be reported.

Identify potential mitigation measures

1. Where the predicted noise and/or vibration levels exceed the trigger levels selected to protect the local environment resulting in environmental harm or community concern, ameliorative measures should be investigated. Examples of these include:
   • alternative track alignments
   • control of rail traffic (e.g. limiting times or speed)
   • use of track measures (e.g. special track forms, rail fasteners and potential operational measures such as rail grinding)
   • identification of the rolling stock producing the highest levels of noise or vibration and management to rectify this
   • construction of noise barriers or bunds
   • treatment of the façade of residential buildings where night-time noise levels are the major concern to reduce internal noise levels in sleeping areas
   • restricting the type of rolling stock (e.g. based on noise emission levels)
   • use of rolling stock measures (e.g. noise treatment of rolling stock)
2. Provide a description of all mitigation measures proposed and the reasons for the particular mitigation measures selected.
3. For the mitigation measures selected, recalculate noise levels to take into account the effect of the proposed mitigation measures.
4. Provide a diagram showing noise level contours, or other methods of presenting the calculated noise level at each receiver, both with and without ameliorative measures.
5. Report the noise and vibration levels that the project can achieve after the application of all feasible and reasonable mitigation measures. These are the project-specific levels that may be considered for inclusion in conditions.
6. Where the relevant noise and vibration trigger levels will not be met after applying all feasible and reasonable mitigation measures, quantify the residual level of noise and vibration impacts.
7. In cases where (after the levels are calculated as set out above and ameliorative measures evaluated) it is considered impractical to meet the noise trigger levels, provide an assessment that justifies how all feasible and reasonable measures have been considered and recommend actions that could further ameliorate the residual level of noise impact in the long term.

Develop a monitoring regime

Select representative locations along the length of the new or modified railway at which it is appropriate to later assess compliance, and present these along with the expected noise and vibration levels (from steps 7, 8 and 9 above) in tabulated form.

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3.4 Measuring existing levels of rail noise and vibration

The existing levels of rail noise and vibration will need to be measured when an assessment of the noise and vibration impacts from a rail project is carried out. All measurements undertaken as part of a rail noise assessment should be accompanied by at least the following information:

• details of the equipment used (including last date of calibration) and equipment settings
• relevant standards
• details of the location of measurement and the positioning of equipment
• details of operations and activities being measured, including the actual monitored train speeds
• where internal levels – noise and vibration – have been determined on the basis of external measurements, the method used, the accuracy of the method and all assumptions made
• a description of the dominant and background noise and vibration sources at the site.

Airborne noise

Procedures for measuring rail noise levels at receivers in terms of L_Amax, L_Aeq and third-octave band L_max levels are set out in AS2377: Acoustics – Methods for the measurement of railbound vehicle noise (Standards Australia 2002). Note that this Standard requires free-field rather than façade measurements of receptor impact. The noise trigger levels in Tables 1 and 2 apply at the façade, and an appropriate adjustment (see footnotes to the tables) will need to be applied.

AS2377 outlines the meteorological conditions suitable for measuring rail noise. However, note that, following periods of inclement weather, wheel rail discontinuities promoted by wheel and track slippage may be created, potentially leading to higher noise levels than would otherwise be the case.

The principal impacts of rail noise will be experienced relatively close to the rail line, although meteorological effects (e.g. winds and temperature inversions) promoting the propagation of noise should be taken into account when considering receivers at distances greater than 300 metres. This is typically only an issue in rural areas where there are no residents in the near vicinity of the line.

Determining the L_Aeq(T) of rail vehicle movements

L_Aeq(T) over the relevant time period T (e.g. day, night) is generally determined on the basis of measurements of individual movements in terms of L_Aeq(i) or SEL_i and solution of the relevant equation below. it is important to obtain a representative L_Aeq(i) or SEL_i measurement at the location of the most-affected receiver for each type of rail pass-by event likely to occur at the section of track measured. A rail pass-by event is defined by the type of vehicle and track, such as near and far track. This would involve first determining the types of vehicles likely to use the section of track and then taking sufficient measurements of each type of rail event. A representative L_Aeq(i) or SEL_i may then be determined by logarithmically averaging the individual measurements. Other information required before L_Aeq(T) can be determined includes the number of each type of pass-by event likely to occur at the site over time period T and, if L_Aeq(i) is used, the average time period of each type of event.

Equation using SEL_i

where:
T is the total time in the relevant period in seconds (i.e. hours x 60 x 60)
n_i is the number of each type of event
SEL_i is the representative event SEL of each type of event as measured at the most-affected receiver and is summed over the different type of events occurring at the site.

Equation using L_Aeq(i)

where:
T is the total time in the relevant period in seconds (i.e. hours x 60 x 60)
t_i is the average time of each type of event in seconds
n_i is the number of each type of event
L_Aeq(i) is the representative L_Aeq level for each type of event as measured at the most-affected receiver and is summed over the different type of events occurring at the site

Accompanying information in support of a quoted L_Aeq(T) should include the general measurement and equipment information described earlier in this section, as well as:

• justification that sufficient measurements have been undertaken for each type of event
• justification of the number of each type of event used based on the types of vehicles likely to be used on the section of track. This could include evidence that the infrastructure owner/operator and rail vehicle operators have been consulted with regard to the typical or expected use of the railway section.

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Determining L_Amax at a site

L_Amax measurements are required when assessing airborne levels and are measured by using the 'fast' response setting on a sound-level meter.

Noise from individual trains can vary for a number of reasons, including the condition of the wheels. When L_Amax levels are reported under this guideline, the noise levels from rail pass-bys equivalent to the L_Amax levels from the 50th and 95th percentiles of rail pass-bys should be reported. in determining the 50th and 95th percentile L_Amax levels, sufficient sample measurements to ensure a robust statistical analysis are required. Similarly, where measurement is not feasible and predictive modelling is used, the modelling must be shown to be sufficiently rigorous to provide a reliable result.

Ground-borne noise

For the purposes of this guideline, ground-borne noise levels should be measured (or determined) at the centre of the most-affected noise-sensitive room by using the L_Amax noise descriptor and the 'slow' time response setting on the sound-level meter. The 'most-affected noise-sensitive room' means the room where the structure-borne noise is the most significant, either in overall level, frequency spectrum, or the time at which it occurs.

Ground-borne noise from individual trains can vary for a number of reasons including the condition of the wheels. When ground-borne L_Amax levels are reported under this guideline, the ground-borne noise levels from rail pass-bys equivalent to the ground-borne L_Amax levels from the 50th and 95th percentiles of rail pass-bys should be reported. in determining the 50th and 95th percentile ground-borne L_Amax levels, sufficient sample measurements to ensure a robust statistical analysis are required. Similarly, where measurement is not feasible and predictive modelling is used, the modelling must be shown to be sufficiently rigorous to provide a reliable result.

Further information on measuring ground-borne noise is contained in ISO 14837 Mechanical vibration – Ground-borne noise and vibration arising from rail systems (International Organization for Standardization 2005). Another useful reference is the US Federal Transit Administration's Transit noise and vibration impact assessment manual (FTA 2006).

Vibration

Methods for measuring vibration from rail operations are covered in a separate DECC guideline Assessing vibration: A technical guideline (DEC 2006).

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3.5 Mitigating noise from railways

This section gives a broad overview of ways to mitigate noise from rail operations. it also provides useful guidance to developers of rail infrastructure in the early stages of planning and design.

Types of mitigation measures

Measures for reducing noise and vibration impacts from railway operations follow three main control strategies:

• controlling noise and vibration at the source
• controlling the transmission of noise and vibration
• controlling noise and vibration at the receiver.

The scope for applying feasible and reasonable mitigation measures to existing railway operations is generally more limited than for new rail developments, and this step is almost inevitably far more costly. This underscores the importance of effective noise management strategies as an integral part of the planning for new rail projects.

Controlling noise and vibration at the source

For new rail line developments it is important that the route is carefully selected to avoid creating noise impacts. in particular, attention should be paid to the location of the proposed rail line in relation to existing and planned residential areas and the possibility of using existing topographical features to mitigate noise.

Keeping rail vehicles and tracks well maintained is important (Hemsworth and Hubner 1999) and this should be given high priority in any mitigation strategy. Other types of sources that should be given high priority are those with annoying characteristics (e.g. tonality, impulsiveness), such as wheel squeal, brake squeal, and the noise from track joints and turnouts as they generally evoke a strong community reaction. Noise mitigation that reduces these annoying characteristics would provide a benefit to the community, even where there may be no measurable changes in measured noise levels.

Examples of mitigation measures at the source include:

• track measures: rail grinding, welding to smooth discontinuities, lubrication, use of soft rail pads, and relocation of signals or turnouts
• rolling stock measures: effective muffling of diesel locomotive exhaust noise, wheel truing, on-board wheel lubrication, use of disc brakes, dampening of wheels, and use of resilient wheels, wheel vibration absorbers and low-squeal brake blocks.

in applying mitigation measures at the source it is recommended that the principles of 'best management practice' (BMP) and 'best available technology economically achievable' (BATEA) be followed.

BMP: This is the adoption of particular operational procedures that minimise noise while retaining efficient operations. When a mitigation strategy that incorporates expensive engineering solutions is being considered, the extent to which cheaper, non-engineering-oriented BMP can contribute to the required reduction of noise should be taken into account. Application of BMP includes the scheduling of noisy operations at least-sensitive times, selective use of certain tracks, keeping equipment well maintained, siting noisy operations behind structures, employing 'quiet' practices when operating equipment, and running staff-education programs.

BATEA: This involves ensuring operations incorporate the most advanced and affordable technology to minimise noise output. Affordability is not necessarily determined by the price of technology alone. increased productivity may also result from using more advanced technology offsetting the initial outlay: for example, 'quieter' trains can be operated over extended hours without causing impact. Where BMP fails to achieve the required noise reduction by itself, the BATEA approach should then be considered.

As both track and rolling stock factors contribute to rolling noise, mitigation needs to address both to be effective. For example, the noise control achieved by just applying track mitigation measures is only as effective as the condition of the rolling stock that is using the track. Vincent (2000) provides a useful analysis on the differing contributions of track and rolling stock measures in reducing overall emissions.

Reducing vibration levels and ground-borne noise can be achieved by including resilient elements in the tracks, such as rail pads or rubber mats inserted between the ballast and tunnel floor, or on other types of sufficiently rigid supporting structures, such as steel bridges.

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Controlling noise and vibration in transmission

This involves restricting the propagation of noise and/or vibration. Such measures include the use of noise barriers, installation of resilient baseplates and ballast mats, and noise treatment of bridges.

Barriers should be used selectively. They are a high-cost approach, and their effectiveness in controlling impacts will depend on the situation. Barriers are more effective if they are near the source or the receiver. Their effectiveness is also determined by their height, the material used (absorptive or reflective), and their density. The relationship of these design features to attenuation is well documented.

Barriers can take a number of forms, including freestanding walls, grass or earth mounds or bunds, and trenches or cuttings within which noise sources are sited.

Controlling noise and vibration at the receiver

Rail lines are an essential part of our urban infrastructure. Even after the application of BMP and BATEA, the closeness of affected premises and the physical, operational and economic constraints may be such that measures to manage the problems at source or to intercept noise in transmission may need to be complemented by management at the point of impact. Where new residential development is planned to occur around a rail line, appropriate building design, layout and construction techniques should be applied to minimise noise intrusion and provide suitable internal noise levels for sleeping and external areas shielded from high levels of noise.

More details on mitigation measures for new residential developments may be available from the relevant local council, and extra details can also be found in Section 3.4 of Environmental criteria for road traffic noise (EPA 1999). The Rail infrastructure Corporation (2003) has also produced interim guidelines, Consideration of rail noise and vibration in the planning process.

Where a proposed rail development will affect an existing development, acoustic treatment of buildings (e.g. insulation, double-glazing, upgrading construction) can be considered as an option to mitigate noise. For this to be effective, an appropriate ventilation system that does not compromise the effect of noise insulation, such as air conditioning, often needs to be incorporated into the design.

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Page last updated: 21 February 2008