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Journal ArticleDOI

A review of transport noise indicators

21 Aug 2012-Transport Reviews (Taylor & Francis)-Vol. 32, Iss: 5, pp 599-628

Abstract: The different approaches to noise impact assessment adopted by the individual countries and the scientific community have led to the development of a certain number of indicators, mainly focused on specific transport modes. However, in practice, technicians and decision-makers alike may fail to identify the most appropriate indicators, if they have no specific expertise on environmental noise. This paper presents a review of the main transport noise indicators, both the general acoustic ones and those used for specific transport modes. A critical analysis of the strengths and weaknesses of these indicators is provided, as well as a section discussing the framework in which they work, and suggestions for their best use, aimed at assisting decision-makers to ascertain their role in the evaluation process of the transport systems. To this extent, a classification is proposed, supplemented by the DPSIR (driving forces, pressures, states, impacts, responses) approach, in an effort to assess the cause–effect re...
Topics: Environmental noise (56%), DPSIR (52%)

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09 August 2022
A review of transport noise indicators / Pronello, Cristina; Camusso, Cristian. - In: TRANSPORT REVIEWS. - ISSN
0144-1647. - STAMPA. - 32:5(2012), pp. 599-628. [10.1080/01441647.2012.706332]
A review of transport noise indicators
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Please cited this article as:
Pronello, C., Camusso, C, (2012): A review of transport noise indicators. Transport Reviews: A
Transnational Transdicsiplinary Journal, volume 32, issue 5, pp. 599-628.
A review of transport noise indicators
Cristina Pronello*(a,b)
(a) Politecnico di Torino.
Interuniversity Department of Regional and Urban Studies and Planning
Viale Mattioli, 39
10125 Torino – ITALY
Phone: +39 011 5645613
Fax: +39 011 5645699
(b) Université Lumiere Lyon2, Laboratoire d’Economie des Transports
14, Avenue Berthelot, 69007 Lyon – FRANCE
Phone: +33 4 72726440
Fax: +33 4 72726448
Cristian Camusso(c)
(c) Politecnico di Torino.
Interuniversity Department of Regional and Urban Studies and Planning
Viale Mattioli, 39
10125 Torino – ITALY
Phone: +39 011 5645640
Fax: +39 011 5645699
* Corresponding author: Cristina Pronello
The different approaches to noise impact assessment adopted by the individual countries and the scientific
community have led to the development of a certain amount of indicators, mainly focused on specific
transport modes. However, in practice, technicians and decision- makers alike may fail to identify the most
appropriate indicators, if they have not a specific expertise on environmental noise.
The paper presents a review of the main transport noise indicators, both the general acoustic ones and
those used for specific transport modes. A critical analysis of the strengths and weaknesses of those
indicators is provided, as well as a section discussing the framework in which they work, and suggestions
for their best use, aimed at assisting decision-makers to ascertain their role in the evaluation process of the
transport systems. To this extent a classification is proposed supplemented by the DPSIR approach (Driving
forces, Pressures, States, Impacts, Responses), in an effort to assess the cause-effect relationship between
society and the environment. Decision-makers will also gain insight in prioritising the use of existing
indicators in accordance to their own needs, as well as advice into the joint use of socio-economic variables
to fully support their decisions.
Noise indicators, transport, sustainability, SEA

1. Introduction
Noise pollution from transport activities is an endemic problem in modern societies and has become a
critical issue in the assessment of transport system sustainability.
Noise induces social and behavioural effects, notably annoyance and sleep disturbance; from a medical
point of view, the effects of noise on human health are also well known: hearing impairment, speech
intelligibility, physiological dis-functions, mental illness, performance reduction, cardiovascular diseases
(WHO, 1999; WHO, 2011). Many of these effects are assumed to result from the interaction of a number of
auditory and non-auditory variables.
The need to safeguard the quality of life and health of the population calls for more efforts for transport
noise abatement as regards to the increasing demand of mobility. To reconcile these conflicting needs, the
EU 6th Action Programme “Environment 2010: Our Future, Our Choice” has set up the target to reduce the
number of people regularly affected by long-term high levels of noise from an estimated 100 million people
in the year 2000 to around 10% reduction in the year 2010 and in the order of 20% by 2020. The difficulty
to attain those targets is that 80% of people live in the urban areas, where transport infrastructures
represent the most important source of noise. In fact, today 115 million people are exposed to noise levels
Lden higher than 55 dB(A), and, at night time, 80 million people are exposed to Lnight higher than 50 dB(A)
(EEA, 2011). All over the world, a total of 2 billion citizens are subject to road traffic Lden of over 55 dB (De
Vos and Van Beek, 2011).
The social costs of rail and road noise in Europe was recently estimated to €40 billion a year (90% related to
passenger cars and goods vehicles) (EC, 2011a). The noise costs, including health care, represent about
0.4% of total EU GDP (den Boer and Schroten, 2007) and, according to the Commission (EC, 2011a; SEC,
2011a,b), the noise-related external costs of transport would increase to roughly 20 billion by 2050
Thence, lawmakers are paying growing attention to adopt reliable and homogeneous instruments for
monitoring and evaluating transport noise emissions. In some cases, the national norms establish rules to
preserve the sound quality of specific areas (e.g. parks, hospitals, schools, etc.) and to reduce people noise
exposure, recommending the adoption of noise indicators and setting the thresholds to be complied with.
In Europe, the need to define guidelines to set common noise legislation led to the Environmental Noise
Directive 2002/49/EC, also known as the “END”. This Directive urges the monitoring of the main European
cities and the biggest transport infrastructures, assessing the number of exposed people and mapping
sound levels, using specific noise indicators.
The study of transport noise emissions kicked off in the 50’s in the United States to tackle the significant
problem of the aircraft emissions (Kryter, 1959), and continued over the years with the research of good
dose-response relationships (FICON, 1992; Miedema and Vos, 1998; Miedema and Oudshoorn, 2001; Fidell,
Various noise indicators have been proposed for different objectives, but, in practice, technicians and
decision-makers alike may fail to identify the most appropriate ones if they lack a specific expertise on
environmental noise.
This paper reviews the main transport noise indicators, proposing a classification of those according to their
nature, to the transport mode to which they are related, and to their field of application. After the review
of the general and mode-related noise indicators, a section is devoted to critically analyse their strengths
and weaknesses. Finally, the framework in which those have to work is discussed, suggesting their best use.
The ultimate goal is to assist decision-makers to distinguish the role of the different indicators in the
evaluation process of the transport systems. However, what it is more significant is to highlight what is
missing today and to propose an operational approach to properly evaluate the impacts of the transport
systems on the exposed population.
2. General acoustic indicators
The general acoustic indicators describe noise emissions in terms of the physical characteristics of the
sound pressure. They represent the physical-mathematical basis on which all the other noise indicators
were developed and are the simplest tools for acoustic noise analysis. Their use in the assessment of
transport noise pollution revealed them inadequate or even useless to describe the phenomenon, for
example when assessing long-term noise impacts. In addition, their relationship with people annoyance has

indeed been challenged. These indicators include the Equivalent Level, the Maximum and Minimum Level,
the Statistical Levels, and the Sound Exposure Level. They were defined in the standard ISO 1990/1-2003.
The best known energy noise indicator is the “Equivalent Level” Leq, used to describe sound fluctuation
over time. It represents the average noise level varying its pressure level during a period T of observation,
expressed in dB(A).
The Maximum and Minimum sound Level, Lmax and Lmin, are, respectively, the highest and the lowest
time-weighted sound level measured expressed in dB(A). These indicators depend on typology and location
of the source. They are generally used to describe the source in terms of acoustic power.
The statistical noise levels Lxx represent the pressure level exceeded the “xx”% of the recording time,
measured in dB(A). The statistical levels usually considered are L5, L10, L50, L90, L95. L90 and L95 are
typically used to describe the “background noise”. Some of those levels are used to calculate other
indicators or in traffic noise models. Well established examples are the models: CSTB (CSTB, 1991), Griffith
and Langdon (Schultz, 1972), Burgess (Burges, 1977), and C.R.T.N. (Department of Transport and the Welsh
Office, 1998).
The “sound exposure level SEL” (or LAEor LAXor SENEL”) is used to describe a single noise event in a
particular context (e.g. a passage of a train or of a single vehicle in an empty street). The evaluation of the
indicator on a base time period of one second (t0) allows to compare SEL values coming from different
sources, where t2 – t1 is the interval of the event where the noise level LA(t) > LAmax -10:
( )
In Italy, this indicator is typically used for railway noise evaluation (D.M., 1998). During an observation time
period (TR) the measure of the SEL of each event allows calculating the corresponding Leq generated by the
In aircraft noise it is common to speak about SENEL for the evaluation of single airplane operations (take-
off and landing). The formulation of SENEL (EPA, 1971) is the same as SEL, but it is generally preferred for
the definition of the integration time (t2-t1) (California Department of Aeronautics, 1971).
3. Road traffic noise indicators
Road traffic is the main responsible for noise in urban areas and is characterized by fluctuations of the
traffic flow during the day, due to the evolution of its kinematic
characteristics, notably speed, acceleration, deceleration. For this reason, road traffic is treated like a
pseudo-casual source, where the energy characteristics of the noise are very important. These noise
indicators are recorded over a long time period to describe the average condition at source, the most
important of those being: the traffic noise index TNI”, the noise pollution level NPL”, the CRTN Indicator
The “traffic noise index TNI” was proposed by Griffiths and Langdon in the 1968 (Schultz, 1972). The index
was developed in the UK using statistical noise levels Lxx:
The indicator takes into account the difference between the noisiest events (L10) and the background noise
(L90); however changes of the base-line sound are weighted with a similar emphasis as those in the noise
peaks (Graf et al., 1980). This is the reason why the indicator is not widely used, since it becomes
representative only when the traffic is flowing, risking to be misinterpreted in a different situation. In fact,
in some cases, when the traffic flow increases, the TNI decreases (Berglund and Lindvall, 1995).
Furthermore, when the difference between the L10 and L90 declines, the attenuation loss over distance
can change significantly (Schultz, 1972).
The “noise pollution level NPL” was developed by Robinson in the late 60´s (Schultz, 1972). The NPL
formulation sums k*σ (constant k = 2.56 and standard deviation) to Leq:
σ+= kLL

When the distribution of the instantaneous A-weighted sound level is Gaussian, the noise pollution level
could be expressed in function of some statistical noise levels:
( )
Like the TNI, the NPL is made up by two terms: the first one is the “average” noise level, or “energy mean”;
the second represents the fluctuation of that level during the emission time.
Moreover, in the first formulation, the parameter σ is influenced by the background noise: for a lower
background noise, the fluctuation and the variability of the events are higher.
The above indicator has not been widely used because of the difficulty to define the parameter σ correctly.
Some examples of its application are presented in Rice (1975) and Langdon (1976, part I and II).
The “CRTN Indicator L10,18h” is the most common indicator of traffic noise used in the UK and in Ireland,
named LA10,18h. It comes from the Calculation of Road Traffic Noise (CRTN) prediction method, and it was
first introduced in the 70’s (Abbott and Nelson, 2002).
This indicator is the arithmetic average of eighteen LA10,1h values (i.e. the noise level exceeded for 10 % of
the hourly period) from 06:00 to midnight:
It does not take into account the noise emission in the night period. When traffic flow is low, the variation
of the LA10,1h depends on the individual passing vehicle and not on the global traffic parameters. In some
cases the indicator shows a high correlation with other statistical indexes and with Leq (Langdon and
Griffiths, 1982).
The indicator is used in the UK in the context of National Insulation Regulations; in that case the value of
noise contains a correction factor of +2.5 dB for the reflection from façades (O’Malley et al., 2009). In
accordance with the END, it is possible to transform the CRTN indicator into Lden (Abbott and Nelson,
4. Railway noise indicators
There are few examples of “noise indicators” specific for rail transport in the state-of-the-art literature. This
may be due to the fact that, historically, railway infrastructure has been perceived as less intrusive than
roads and airports, representing a lower risk and a lower impact on the population.
From an acoustic point of view, railway noise is easier to study: the sound events are better defined and
identifiable, the kinematic characteristics of the traffic being less variable than those of road traffic. Of
course, the individual emissions from each moving train are energetically higher than those from road
vehicles; this issue is acknowledged, in some national legislation, where noise limits are set higher than
those adopted for road traffic.
The best known indicators are the “transit exposure level TEL” and the railway rating levels Lr”. The TEL is
used to describe the noise emitted by railway traffic taking into account the “train pass-by” duration (Tp)
expressed in seconds (train length divided by the train speed). Its formulation is given by the EN ISO
3095:2005 (EN ISO, 2005):
( )

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