PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Acoustic Vehicle Alerting Systems (AVAS) of electric cars and its
possible inﬂuence on urban soundscapeFelix LAIB1;2; J. Alexander SCHMIDT1
1

University of Duisburg-Essen, City Planning and Urban Design, Germany
2

Consulting Engineers Dr. Droescher, Germany

ABSTRACT
Starting July 1, 2019, all new types of hybrid electric and pure electric vehicles in the EU must be equippedwith an Acoustic Vehicle Alerting System (AVAS), in particular to warn pedestrians at low driving speed. Ina case study, comprehensive measurements of the pass-by levels on 7 current electric vehicles were carriedout at constant pass-by speeds of 10 km/h to 50 km/h. This involved recording the sound pressure level
including and without AVAS. The results show that in some cases the pass-by level is considerablyincreased by the AVAS. Due to the frequently low speeds in urban traffic, the AVAS will play a relevantrole for the future acoustics and soundscape of cities. On the one hand, electric vehicles generally induce
less noise in urban traffic than vehicles with combustion engines – a chance to reduce health threatening
urban environmental noise. However, since the AVAS of electric vehicles is intended to attract attention forsafety reasons, it can on the other hand also generate additional noise annoyance. Considering an increasing
share of electric vehicles in urban traffic in the future, the effects on urban soundscape and the quality oflife are investigated.
Keywords: Electric vehicles, Acoustic Vehicle Alerting Systems (AVAS), Soundscape, Quality of life

1. INTRODUCTION
Road traffic is the main source of noise, especially in urban areas, and often exposes people tohigh noise levels. In the European Union by itself, an estimated 125 million people are exposed toroad traffic noise levels above 55 dB(A) Lden (day-evening-night level) (1), which, according to thecurrent Environmental Noise Guidelines of the World Health Organization, can increase
noise-induced health impairments, such as the risk of ischemic heart disease (2). According to theguidelines, the risk of adverse health effects is even increased from a level of road traffic above
53 dB(A) Lden. Noise pollution and the associated impairment of quality of life cannot be ruled out
even far below these levels (2). In a survey on quality of life with around 37,000 participants in
33 European countries, around a third of respondents felt annoyed by noise in their neighborhood. In
cities and urban areas, up to half of the respondents reported noise problems impairing their qualityof life (3).
Since the actual noise impact and annoyance cannot be fully explained by physical measurement
and forecasting techniques, an integrated approach to noise assessment is often called for (4). The
soundscape approach provides an opportunity to extend the classical noise assessment methods byfocusing on the perception of the acoustic environment by the exposed persons (5). In recent years, astandardized framework has been developed to support a general understanding of soundscape andthe practical application of the concept (6, 7).
Since vehicles with electric motors are generally much quieter at low speed than vehicles withcombustion engines (8, 9), there is a relevant noise reduction potential, especially in urban traffic.
The low noise emissions from electric vehicles can, however, endanger the safety of pedestrians andcyclists, especially at low speed, as the vehicles are less well perceived. This can be dangerous forexample for blind people (10, 11).

1
2

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felix.laib@stud.uni-due.de; alexander.schmidt@uni-due.delaib@dr-droescher.deFor this reason, in accordance with the ECE regulations (for the European Union and othercountries) as well as the technical regulations of the NHTSA (USA) for hybrid electric and purely
electric passenger cars, there will be a requirement to install an Acoustic Vehicle Alerting System(AVAS) in the future (12, 13). Differences in the regulations of the NHTSA and the ECE arecompiled in a publication by Wagner and Gajda (14). According to ECE Regulation No. 138,
vehicles must emit a minimum sound level from motion up to a speed of 20 km/h. A frequency shiftmust take place to make the acceleration and deceleration of the vehicle audible . The AVAS must notexceed a defined maximum level. Thus the vehicle may only be as loud as the lowest permissible
limit value for vehicles with combustion engine (12). Many e-vehicles currently have the option of
temporarily switching off the AVAS via a switch in the interior of the vehicle (pause function). Whenthe vehicle is restarted, the AVAS is automatically reactivated. This option will no longer beavailable in the future (15).
At present, there are many e-vehicles that are already equipped with an AVAS. The AVAS causes
additional noise emissions that can change the acoustic environment. There is a dilemma here
between the perceptibility of warning signals to ensure safety and potential annoyance from artificial
sounds.

2. INVESTIGATION OF NOISE EMISSIONS FROM ELECTRIC CARS
So far, there are only a limited number of studies that address the noise emissions of electric cars
at low speed and the possible effects on urban soundscape and quality of life. There are certainly
many studies that investigate the noise emissions of electric cars in comparison to cars with internal
combustion engines (9, 10, 16, 17). However, the effect of acoustic warning systems on theenvironment was still not the focus of these studies.
In general, the total noise of passing vehicles in city traffic is composed of the powertrain andtire/road noise. In theory, at low speed the noise of the powertrain dominates, while at higher speed
the tire/road noise is decisive (18). For electric cars, the powertrain noise contributes only slightly tothe total noise level. In a study investigating the rolling noise of electric car tires, the rolling noise
was the main sound source even at a low speed of only 20 km/h (19). Here, however, there was noinfluence from AVAS.
We assume that the AVAS will significantly increase the noise emissions of electric cars at low
speeds and that this will have an impact on the urban soundscape and the quality of life. The present
study therefore examines the pass-by levels of electric cars at low speeds. The noise emissions ofpassing vehicles at constant speed with and without AVAS are compared and evaluated. The firstquestion here is to what extent the AVAS increases the pass-by level of vehicles. Subsequently,
possible effects of AVAS on noise pollution, urban soundscape and quality of life will be discussed.
Based on the previous knowledge and the factual context, findings on the possible influence of
AVAS on urban soundscape and quality of life conveyed by noise pollution are finally derived.

3. METHODOLOGY
3.1 Sound measurements on electric cars
In order to investigate the noise emissions of electric cars, noise measurements were carried out
on 7 pure electric cars. The noise measurements on the vehicles were carried out during pass -by at aconstant speed between 10 km/h and 50 km/h. Since the AVAS only generates noise in the speed
range from the movement of the vehicle up to a maximum of 30 km/h, in the present case a focus
was placed on driving speeds up to 30 km/h. Almost all the studied cars were already equipped withan AVAS. If the AVAS could be switched off by the driver in the vehicles, the pass-by levels
including and without an AVAS were recorded. In this way, the acoustic contribution of the AVAS to
the overall noise level can be determined. Table 1 below lists the electric cars that were studied. In
addition, it is described whether the vehicle is equipped with an AVAS and whether the AVAS ca n be
manually switched off by the driver.

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Table 1 – Studied electric cars
Studied vehicle

Vehicle equipped

AVAS in operation (from the

AVAS can be(manufacturer and model)

with AVAS

movement of the vehicle to aswitched off byspeed of approximately)

the driver

Hyundai Ioniq

yes

25 km/hyesOpel Ampera

yes

23 km/hyes

Nissan Leafyes

30 km/hyesTesla Model S

no

-

-

Smart Forfour

yes

30 km/hnoRenault Zoe

yes

30 km/hyes

VW e-Golf

yes

30 km/hyes

The e-cars were mainly current models (first registration in 2016 to 2018), with a low mileage(average approx. 16,000 km). With the exception of the VW e-Golf, which was fitted with wintertires, all of the other cars were fitted with summer tires. The tires of the vehicles (nominal
width/height to width in mm) ranged from 185/60 mm (Smart Forfour) to 245/45 mm (Tesla
Model S).
3.2 Conducting and analyzing the sound measurements
The measuring arrangement for the recording of the pass-by levels was carried out in accordancewith the requirements of Regulation (EU) No. 540/2014 (20). The sound pressure level (L AFmax) at a
distance of 7.5 m from the center axis of the vehicle was measured at constant speeds of 10 km/h,
20 km/h and 30 km/h on the left and right sides of the vehicles. The sound measurements per speed
and situation were carried out for at least 6 vehicle passes, so that at least 12 sound measurements
were carried out for each speed.
The measurements were carried out on a minor road with a low background noise level in Augustand November 2018. The pass-by levels of the vehicles studied (L AFmax) were at least 10 dB(A)above the background noise level (L AF95% ) on each of the measurement dates. A relevant influence of
background noise on the sound measurements can be excluded in this case. The noise measurementson the vehicles at a constant speed of 10 km/h represented an exception. In this case, the pass-by
levels of the studied vehicles were still at least 7 dB(A) above the background noise level, so that norelevant influence on the pass-by level can be expected in this case as well. However, this is anacceptable value for sound measurements on electric cars. In comparable studies, the noise
measurements on electric vehicles at low speeds were only rejected if the noise level during pass-by
was less than 3 dB(A) above the background noise level. (17). No background noise correction was
performed.
The surface course of the road at the measuring site consisted of asphalt concrete (AC) with agrain size of 0/11 mm. All measured values were used in the evaluation of the measurements. Only
measurements that were obviously influenced by disturbances (levels not caus ed by the passing of
the vehicle) were not taken into account for the evaluation. For each vehicle and speed, thearithmetic mean of the pass-by levels was calculated. In the evaluation of the measured values(LAFmax), the variance per vehicle and speed was usually approximately 1 dB(A), in rare cases up to
2 dB(A).

4. RESULTS
The following table compares the sound pressure levels (SPL) during pass -by of the electric cars
examined at 10 km/h, 20 km/h and 30 km/h with and without AVAS. For the sake of clarity, thevalues listed in the table were rounded off to whole numbers. The differences of the pass-by levels
including and without AVAS were, however, calculated from the non-rounded arithmetic mean of themeasured values.

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Table 2 – 7.5 m pass-by level (LAFmax) of the e-vehicles including and without AVAS in dB(A)Studied vehicle

SPL including AVAS

SPL without AVAS

Difference in SPL
including and without AVAS

(manufacturer
and model)(at 10/20/30 km/h)(at 10/20/30 km/h)(at 10/20/30 km/h)

Hyundai Ioniq

49/56/60

43/54/60

6/2/0

Opel Ampera

49/52/57

42/51/58

7/1/0

Nissan Leaf

47/52/58

44/52/58

3/0/0

Tesla Model S-

46/56/62-

Smart Forfour

45/53/59--

Renault Zoe

54/58/60

43/53/60

11/5/0VW e-Golf

50/57/62

50/56/62

1/1/0

It can be seen that the pass-by levels of electric cars caused by the AVAS sometimes increasesignificantly, especially when passing by at 10 km/h. When driving past at 20 km/h, the level
increase is less distinct, but is still present, whereas when driving past at 30 km/h, no relevant level
increase is detected by the acoustic warning system in any of the studied vehicles. The level increase
due to the AVAS is very variable. While the acoustic warning system increases the pass -by level ofthe Renault Zoe by 11 dB(A), the AVAS only increases the level of the VW e-Golf by 1 dB(A).
Correspondingly, the acoustic warning system of the vehicles is designed very differently by the
manufacturers.
The pass-by levels including AVAS were sometimes very different on the left and right side of thevehicle. The investigated Renault Zoe represents an extreme case. Here, differe nces in the pass-by
levels of 7 dB(A) and 4 dB(A) were determined between the left and right sides of the vehicle at
10 km/h and 20 km/h, respectively. Wagner and Gajda suspect that higher levels than necessary will
be induced on certain sides of the vehicle if only one speaker is installed for the warning signal andmanufacturers are required to comply with the AVAS minimum sound pressure level on all sides ofthe vehicle (14).
In addition to the increase in the sound pressure level, the evaluation of artificial noise by otherroad users such as pedestrians or residents plays a decisive role. In order to investigate the possible
effect of AVAS on urban soundscape and quality of life, existing studies on the perception of
acoustic warning systems will be summarized in the following. Based on the previous knowledge
and the factual context, findings on the possible influence of AVAS on urban soundscape and qualityof life conveyed by noise pollution are finally derived.

5. DISCUSSION
5.1 AVAS - potential conflict between safety and annoyance
The measurements on the sample of electric cars show that the AVAS can significantly increase
the pass-by level in certain cases. Basically, this leads to a conflict between the desired traffic safety
and a possible noise annoyance caused by artificially generated sounds.
Already in 2010, Giudice et al. pointed out that artificial sound from electric vehicles could beannoying, impair the soundscape and quality of outdoor living (21). According to Genuit and Fiebig,
noise can be particularly annoying if it is perceived as unnecessary. Especially in the case of
artificially generated warning signals from electric vehicles, noises might find little acceptance. In
addition, the overlaying of warning noises could create an annoying acoustic environment (22). Thus
Genuit and Fiebig describe that the influence on environmental noise is often not fully taken into
account in the development of warning signals for electric vehicles. In particular, aspects ofperception and annoyance caused by multiple vehicles with warning signals are generally not taken
into account (23).

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A study on the annoyance of AVAS showed that both the individual pass-by of an electric car with
AVAS and the pass-by of several electric cars with AVAS were perceived by the study participants inlistening experiments as being considerably more annoying than the pass-by of cars with a
combustion engine. Steinbach and Altinsoy suspect that this may be due to the fact that participants
are familiar with the sound of cars with internal combustion engines, while the artificial warning
signals of e-cars were probably previously unknown among the participants (24). Similar findings
were obtained in a listening experiment study on the detectability and annoyance of various warning
signals from Parizet et al. Some warning signals were perceived as annoying as the noise of a diesel
car passing by. Here it was also shown that the recognition of a warning signal strongly depends on
the timbre, but not on the total sound pressure level (25).
In addition to the annoyance for the environment, the warning signals, according to Wagner andGajda, can also be perceived as annoying by the driver, since the vehicle can no longer be moved
silently and the artificial noise is added inappropriately to the vehicle's own noise. The driver often
has reservations about disturbing the quiet environment with artificial noise, which is why the noise
is often paused manually by the driver directly after starting the vehicle (14).
5.2 Possible consequences for urban soundscape and quality of life
The described studies on the perception of AVAS in electric vehicles suggest that artificial soundsof electric vehicles may influence the soundscape in cities and consequently may become a noise
annoyance in the future. The much-discussed and aspired urban quality of life could thus be further
restricted. The soundscape concept represents an interdisciplinary, holistic approach in which theperception of the acoustic environment by the exposed is the main focus. Basically, a distinction ismade between the perceptual construct (soundscape) and the physical phenomenon (acoustic
environment). The soundscape is (only) created by the human perception of the acoustic
environment (6). For example, the effect of an acoustic environment on well-being and quality of life
can also be addressed. Data acquisition in soundscape studies should take place, for example,
through sound walks, questionnaires, guideline-based interviews and binaural measurements. Ideally,
the data should be collected on site. According to ISO/TS 12913 -2:2018, each soundscape study
should always consider the key components of the user, acoustic environment and context (7).
Since the share of e-cars with AVAS in total traffic is still relatively low at the moment and thetotal noise level in cities is usually dominated by the noise of vehicles with combustion engines, it iscurrently difficult to conduct soundscape studies in an acoustic environment that is influenced to a
sufficient extent by AVAS. In soundscape studies with the simulation of acoustic environments andthe execution of listening experiments, immersive methods should be taken into consideration whenplaying back via speakers or headphones (7).
When considering the influence of AVAS on the acoustic environment and the soundscape, it istherefore inappropriate to derive generally valid conclusions, since the individual situation should betaken into account with the involvement of the exposed. From the previous knowledge and thefactual context, however, the following findings can be derived on the possible influence of AVAS on
soundscape and quality of life conveyed by noise pollution.
Since the AVAS is only operated at low driving speeds up to a maximum of 30 km/h, an influenceon the urban soundscape can be assumed, especially in certain traffic situations such as stop-and-go
traffic, in residential areas or on minor roads. However, the possible influence is essentially limited
to these situations, as the AVAS is masked by tire-road noise at higher driving speeds (14). Basically,
however, it is precisely these traffic situations and the acoustic environments in which e -vehicles
offer the greatest noise reduction potential compared to vehicles with internal combustion enginesthat are affected by potential noise pollution from the AVAS.
A possible influence on the urban soundscape and an annoyance potential by the AVAS is given if
the total noise level (from other road traffic or other sound sources) is particularly low.
The personal attitude of the exposed to the sound source is relevant for the perception andevaluation of sound effects and should be considered in AVAS soundscape studies. One study, forexample, found that people with a positive attitude towards air traffic (objectively) had less sleep
disturbances caused by aircraft noise (26). It can be assumed that a generally positive attitude of
exposed persons towards e-mobility influences the evaluation of the sound effects from the AVAS. In
addition, noise annoyance and disturbance assessments may be influence d by other factors related toroad traffic, such as traffic-related air pollution (27). Furthermore, changes in the assessment ofvehicles as status symbols can play a special role, especially for the younger generation (28).

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If the exposed are not familiar with the noises of the AVAS, it is possible that the noises of the
AVAS are perceived as equivalent (25) or more annoying (24) compared to the noises of vehicles
with combustion engines.
An exclusion of vehicles with combustion engines in a city distric t or the redesign of a city
district in which only e-vehicles are allowed to drive can represent a targeted design of an acoustic
environment characterized by noises from AVAS. It can be assumed that the inclusion andinformation of the exposed increases the acceptance of the sounds.
Soundscape studies on the effects of AVAS can provide in-depth knowledge on potential effects
on the quality of life conveyed by noise pollution, particularly as there is a continuing need forin-depth research in this area. In a systematic review, Clark and Paunovic examined 14 quantitative
studies on the link between road traffic noise and self-reported quality of life or health. Clark andPaunovic concluded that there is a very low evidence that road traffic noise has no relevant effect on
the self-reported limitation of quality of life or health. The very low evidence of the assessment canbe explained by the fact that there are too few studies in this field of research and that, in particular,
suitable intervention and cross-sectional studies are lacking. The lack of evidence, however, does notnecessarily mean that there are no effects, but that the complex interrelationships have not yet been
investigated sufficiently (29).
Should it turn out in the future that the acoustic warning systems of electric vehicles have anegative impact on urban soundscape and quality of life, the question arises whether road safety
cannot be ensured in another way. There may also be other appropriate methods to warn the blind
about quiet electric vehicles. Thus, according to Yamauchi, the problem is defined less by the silenceof the e-vehicles than by the existing environmental noise. Forcing a quieter urban environment
would make it easier to hear the quiet vehicles better. Enforcing stricter noise emission standards forvehicles would be beneficial not only for the visually impaired or the elderly with impaired hearing,
but also for residents (30).

6. CONCLUSIONSIn the present study, the pass-by levels of a sample of electric cars including and without AVAS
were recorded and the potential effects on urban soundscape and quality of life were discussed. The
results of the case study show that the acoustic warning system can considerably increase the pass-by
level of e-cars, especially at low speeds, but that the AVAS level increase varies considerably
depending on the vehicle. The AVAS increased the pass-by level from 1 dB(A) to 11 dB(A)depending on the vehicle. When passing electric cars at 30 km/h with and without AVAS, no level
difference anymore was determined.
Regarding the possible influence of AVAS on urban soundscape and quality of life conveyed bynoise pollution, it can be stated that it is precisely the traffi c situations and acoustic environments inwhich electric vehicles have the greatest noise reduction potential compared to vehicles with internal
combustion engines (low driving speeds and low background noise levels) that are affected by apossible noise annoyance by AVAS. It cannot be excluded that the sounds of AVAS will be perceived
to be more annoying than those of vehicles with combustion engines. Ultimately, it is conceivablethat the overlay of AVAS by varying tone pitches and tone durations can lead to a cacophony that
leads to a disharmonic urban soundscape that disregards listening habits.
The urban soundscape approach provides a suitable tool to gain basic knowledge for planning anddesigning acoustic environments and to improve the quality of life. With a fundamental change intransport systems expected in the future, the opportunity should be seized to actively design acoustic
environments. Urban soundscape approaches are conceivable, whose basic considerations also
include a still to be determined harmony of the AVAS in concept and planning.
Should there be more evidence in the future that the acoustic warning systems of e -vehicles canbe expected to have relevant negative effects on urban soundscape and quality of life, the question
arises whether road safety cannot be ensured by other means. In the targeted design of acoustic
environments, it is of particular relevance how the noises of electric vehicles harmonize with theenvironment (28) without endangering road safety and impairing the quali ty of life of residents. The
proportion of electrically powered vehicles could rise significantly in many parts of the world in the
coming years. Accordingly, the acoustic effects of an increasing share of electric vehicles in total
traffic must also be investigated.

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ACKNOWLEDGEMENTS
The present study was supported by Consulting Engineers Dr. Droescher, including the provisionof technical equipment to carry out sound measurements.

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