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You are here: Home > Environmental issues > Noise > Rail noise > Rail infrastructure project noise > Noise and vibration trigger levels

2. Noise and vibration trigger levels

This guideline addresses two types of noise and vibration impacts:

• Airborne noise from the operation of a surface rail line that is heard at, and within, noise-sensitive premises
• Ground-borne noise generated inside a building by ground-borne vibration generated from the pass-by of a vehicle on rail: These noise trigger levels apply at receiver locations above rail operations in tunnels where ground-borne noise levels from rail transport are likely to be greater than airborne noise levels.

Vibration that can be created by rolling stock movements also requires appropriate assessment and mitigation. Rail infrastructure proponents are directed to Assessing vibration: A technical guideline (DEC 2006) for methods of assessing potential impacts and ways to manage vibration from rail operations.

The noise trigger levels for airborne noise and ground-borne noise differentiate between noise impacts during the day and night. It is widely accepted that noise is generally more disturbing at night because of the more noise-sensitive activities occurring at that time of the day (e.g. listening activities and sleep); the large numbers of residents that are at home; and the increased intrusiveness of noise due to lower background levels at night.

Most European countries with criteria for rail noise apply separate noise levels for day and night. In the United States the night-time period is also given special attention by use of a noise descriptor that applies an acoustic penalty to night movements to account for increased annoyance of noise at night (see Appendix I for details).

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2.1 Airborne noise trigger levels for heavy rail

The noise trigger levels address:

• An increase in rail noise due to rail infrastructure projects
• Absolute levels of rail noise: For residential receivers the noise trigger levels for absolute levels of rail noise have two components, L_Aeq and L_Amax. This combination addresses both the average level of noise (L_Aeq) over the day or night period and the maximum noise level (L_Amax) from pass-by events. The application of the L_Amax descriptor for residential land uses recognises that rail events are not adequately described solely by the L_Aeq descriptor when preservation of residential amenity and wellbeing are considered.

For other noise-sensitive land uses, only L_Aeq is applied, as the focus is on speech interference and providing adequate acoustic protection to conduct the activities associated with those land uses.

An increase in both rail noise and the absolute level of rail noise at the trigger values in Tables 1 and 2 must be met to initiate an assessment of rail noise impacts.

The increases in rail noise trigger levels for L_Aeq and L_Amax are set at levels where an increase in rail noise may become perceptible.

Table 1: Airborne rail traffic noise trigger levels for residential land uses

Type of development	Noise trigger levels dB(A)
	Day(7 am–10 pm)	Night (10 pm–7 am)	Comment
New rail line development	Development increases existing rail noise levels and resulting rail noise levels exceed:		These numbers represent external levels of noise that trigger the need for an assessment of the potential noise impacts from a rail infrastructure project. An 'increase' in existing rail noise levels is taken to be an increase of 2 dB(A) or more in LAeqin any hour or an increase of 3 dB(A) or more in LAmax.
	60 LAeq(15h) 80 LAmax	55 LAeq(9h) 80 LAmax
Redevelopment of existing rail line	Development increases existing rail noise levels and resulting rail noise levels exceed:
	65 LAeq(15h) 85 LAmax	60 LAeq(9h) 85 LAmax

Table 2: Airborne rail traffic noise trigger levels for sensitive land uses other than residential

Sensitive land use	Noise trigger levels dB(A)
	New rail line development	Redevelopment of existing rail line
	Development increases existing rail noise levels by 2 dB(A) or more in LAeq in any hour and resulting rail noise levels exceed:
Schools, educational institutions – internal	40 LAeq(1h)	45 LAeq(1h)
Places of worship – internal	40 LAeq(1h)	45 LAeq(1h)
Hospitals	60 LAeq(1h)	60 LAeq(1h)
Hospitals – internal	35 LAeq(1h)	35 LAeq(1h)
Passive recreation	LAeq as per residential noise level values in Table 1 (does not include maximum noise level component)
Active recreation (e.g. golf course)	65 LAeq(24 h)	65 LAeq(24 h)

Technical notes to Tables 1 and 2

1. Specified noise trigger levels refer to noise from rail transportation only and do not include ambient noise from other sources. However, they refer to noise from all rail traffic at the receiver location, not only noise due to the specific rail project under consideration.
2. The noise level values represent external levels except where otherwise stated.
3. 'Residential' typically means any residential premises located in a zone as defined in a planning instrument that permits new residential land use as a primary use. Where there is doubt as to the status of the residential land use, the relevant planning authority should be consulted.
4. L_Aeq(T) (where T is the relevant time period) refers to the equivalent continuous noise level from all train movements (excluding shunting activities in designated shunting areas) occurring during the assessment time period.
5.  L_Amax refers to the maximum noise level not exceeded for 95% of rail pass-by events and is measured using the 'fast' response setting on a sound-level meter.
6. Noise levels at residences are assessed 1 metre in front of the most affected building façade. Where only free-field measurements can be made, the measured noise level is corrected (generally by + 2.5 dB(A)) to account for the façade reflection effect. In the case of multi-level residential buildings, the external point of reference for measurement for the trigger is the two floors of the building that are most exposed to rail noise, usually the ground and first floors. On other floors, an internal noise level value 10 dB(A) below the relevant external noise level value applies on the basis that openable windows are opened sufficiently to provide adequate ventilation (refer to minimum ventilation requirements in the Building Code of Australia).
7. Internal noise level values refer to the noise level at the centre of the habitable room that is most exposed to the noise source and are applied with windows opened sufficiently to provide adequate ventilation. In cases where gaining internal access for monitoring is difficult, external noise level values 10 dB(A) above the internal level values apply.
8. The noise level values for sensitive land uses apply for the periods when the premises are in use.
9. In assessing noise levels at passive and active recreational areas as well as in hospital grounds, the noise level is assessed at the most affected point within 50 metres of the area boundary.
10. For external activities associated with schools, educational institutions and places of worship, the relevant passive or active recreation categories apply.
11. Where the category of the premises is not clear, seek advice from the relevant planning authority.
12. For sensitive land uses, L_Aeq(1h) means the highest 10th-percentile hourly A-weighted L_eq during the period when the particular class of receiver building/place is in use. Alternatively, the highest measured L_Aeq(1h) value can be used where insufficient measurements have been made to provide a valid 10th-percentile level and it can be demonstrated that the measured values are representative.
13. For new and redeveloped rail projects, the noise trigger levels apply both immediately after operations commence and for projected traffic volumes over an indicative period into the future that represents the expected typical level of rail traffic usage (e.g. 10 years or a similar period into the future).
14. Where noise above the noise trigger levels continues even after all feasible and reasonable mitigation measures have been applied to a project, other long-term strategies need to be applied to minimise impacts. These include reducing noise emissions from rolling stock by applying noise standards to new rolling stock; managing noise emissions from rolling stock already in use; and improved planning, design and construction of adjoining land-use developments.
15. There may be situations where it is reasonable to vary the standard time periods applied to the day and night periods. For example, there may be instances where the noise levels in an area begin to rise quickly before 7 am (the standard cut-off point between day and night) because of normal early morning activity by the general community. In these cases it is reasonable to consider varying the standard day- and night-time periods to better reflect the actual temporal changes in noise for that location. Appropriate noise level values for these shoulder periods where night-time noise levels rise quickly to daytime noise levels may be negotiated with the determining or regulatory authority on a case-by-case basis.

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The absolute L_Aeq rail noise trigger levels for heavy rail are based on social survey research and international and national practices. Research by Miedema and Oudshoorn (2001) and illustrated in Figure 1 provides the basis for considering the levels at which noise creates community annoyance and informs the airborne noise trigger levels in Table 1. The noise trigger levels are aligned with what is applied for road traffic noise by aiming to protect 90% of the population from being highly annoyed.

Because noise descriptors (such as L_Aeq(24h), L_Aeq(night) and L_DN) vary between different countries and jurisdictions, it is difficult to make a direct comparison between the trigger levels in this guideline and those used elsewhere. However reference to Appendix I, which outlines the noise levels set in other countries, indicates the noise trigger levels in this guideline are consistent with the range of levels adopted internationally.

The L_DN (Day-Night) shown in Figure 1 is L_Aeq-based and is measured over a 24-hour period that includes daytime noise and applies a 10-dB penalty to night-time noise.

Figure 1: Percentage highly annoyed vs L_DN for rail noise (Miedema and Oudshoorn 2001)

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2.2 Ground-borne noise trigger levels

Ground-borne noise is defined in ISO 14837 Mechanical vibration – Ground-borne noise and vibration arising from rail systems as noise generated inside a building by ground-borne vibration generated from the pass-by of a vehicle on rail.

Ground-borne noise level values are relevant only where they are higher than the airborne noise from railways (such as in the case of an underground railway) and where the ground-borne noise levels are expected to be, or are, audible within habitable rooms.

Ground-borne noise differs from airborne noise because the actions available to anyone affected by the noise to reduce or avoid it are more limited. For example, airborne noise can often be reduced by actions such as closing windows, improving the acoustic insulation of the building façade, or relocating noise-sensitive activities in the building to a location more remote from the noise source. These actions are likely to be relatively ineffective against ground-borne noise, because the noise is emitted by the building structure itself.

Retrofitting mitigation measures to rail infrastructure to reduce ground-borne noise may also be more difficult and expensive than for airborne noise. This is because the ability to apply these measures can be restricted by the amount of head-room available in a tunnel or the ability of the track-bed to accommodate additional mitigation. It is therefore important to ensure that an adequate level of mitigation is applied during the design and construction of underground rail projects.

Only limited research into the impacts of ground-borne noise is available, and information on practices applied overseas is also scarce. From a review of what is available it appears that the factors that can affect reaction to ground-borne noise include:

• the level of the noise
• how often it occurs
• whether an area is already exposed to rail noise
• whether the area affected has a low density of development (e.g. low-density residential) with associated low levels of ambient noise.

It appears reasonable to conclude that ground-borne noise at or below 30 dB L_Amax will not result in adverse reactions, even where the source of noise is new and occurs in areas with low ambient noise levels. Levels of 35–40 L_Amax are more typically applied and likely to be sufficient for most urban residential situations, even where there are large numbers of noisy events.

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For a good night's sleep, the World Health Organization (WHO) recommends that individual noise events exceeding 45 dB L_Amax indoors (measured on 'fast' response setting) should be avoided. However, WHO (Berglund, Lindvall and Schwela 1999) also notes that the effects of noise may be greater:

• in areas with low background sound levels
• for sources with combinations of noise and vibrations
• for noise sources with low-frequency components

all of which may be present in ground-borne noise. It is also possible to conclude that the WHO level is based on airborne noise events. Hence, levels for ground-borne noise lower than 45 dB L_Amax (indoors) appear desirable.

The noise trigger levels in Table 3 for ground-borne noise and the associated measurement methodology described in Section 3 of this guideline are aimed at providing a reasonable basis for triggering the assessment of impacts from ground-borne noise. They are necessarily set to the lower end of the range of possible trigger values so that potential impacts on quieter suburban locations are addressed. In practice, higher levels of ground-borne noise than the trigger level for assessing impacts may be suitable for urban areas where background noise levels are relatively high.

Table 3: Ground-borne (internal) noise trigger levels

Receiver	Time of day	Noise trigger levels dB(A)
		Development increases existing rail noise levels by 3 dB(A) or more and resulting rail noise levels exceed:
Residential	Day (7 am–10 pm)	40 LAmax (slow)
	Night (10 pm–7 am)	35 LAmax (slow)
Schools, educational institutions, places of worship	When in use	40–45 LAmax (slow)

Technical notes to Table 3

1. Specified noise levels refer to noise from rail transportation only and do not include ambient noise from other sources.
2. The noise level values represent internal noise levels and are to be assessed at the centre of the most affected habitable room. For example, at night this may be the bedroom experiencing the highest levels of ground-borne noise, while during the day this might be another habitable room experiencing the highest levels of ground-borne noise. They are relevant only where ground-borne noise levels are audible and are of a higher level than airborne noise levels from rail operations.
3. 'Residential' typically means any residential premises located in a zone as defined in a planning instrument that permits new residential land use as a primary use. Where there is doubt as to the status of the residential land use, the relevant planning authority should be consulted.
4. L_Amax refers to the maximum noise level not exceeded for 95% of rail pass-by events and is measured using the 'slow' response setting on a sound-level meter.
5. For schools, educational institutions and places of worship, the lower value of the range is most applicable where low internal noise levels are expected, such as in areas assigned to studying, listening and praying.

2.3 Vibration trigger levels

Vibration associated with movements on a rail network can cause disturbance and complaint in a similar fashion to noise.

A separate guideline, Assessing vibration: A technical guideline (DEC 2006), contains information on trigger levels for vibration covering continuous, impulsive and transient vibration. Train movements on a rail network can cause vibration of a transient type.

 

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