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

Pedestrian awareness of the approach of quiet vehicles: Effect ofapproach informing sound and designing awarenessTakahiro KOSUGE1; Tomoya TSUJINAGA2; Toki KOBAYASHI3;
Mariko TSURUTA-HAMAMURA4; Hiroshi HASEGAWA5
1–5

Graduate School of Engineering, Utsunomiya University, Japan

ABSTRACT
Hybrid and electric vehicles are quieter than combustion-engine vehicles. To prevent accidents resulting fromsuch quietness, an acoustic vehicle alerting system generates an approach informing sound (AIS). However,
the recognition rate of the AIS is not high (~40%) and it might be difficult for pedestrians and others to notice
the approach of quiet vehicles via hearing alone. To improve AIS recognition, we designed an AIS based on
onomatopoeic sounds. A subjective evaluation experiment using these sounds revealed that people tended toevaluate noisy and rough sounds, such as those similar to the sound of a car traveling or an engine, as a good
indication of a car traveling. Another experiment investigated the sounds that pedestrians actually use torecognize the approach of quiet vehicles. It was found that most participants recognized the approach of aquiet vehicle not by AIS but by sounds emitted from the vehicle, such as road and wind noise. This tendency
was also observed after participants correctly recognized the AIS. However, some participants reported that
their awareness of AIS changed and they became more aware of AIS in daily life after the experiments.
Designing awareness is effective and necessary for the design of AIS.
Keywords: Quiet vehicles, Approach informing sound, Designing awareness

1. INTRODUCTION
Quiet vehicles such as hybrid vehicles and electric vehicles emit less noise than vehicles having
internal-combustion engines, particularly when traveling at low speed. Although such quietness
results in less environmental noise, it may cause accidents in which pedestrians are unaware of
approaching vehicles. To address this issue, the Ministry of Land, Infra-structure, Transport andTourism in 2011 established for the first time in Japan guidelines for the installation of acoustic
vehicle alerting system (AVAS) in quiet vehicles. An international standard was established on thebasis of these guidelines (1). However, the recognition rate of the AVAS has not been high (i.e.,
approximately 40% (2)). To improve the recognition of the AVAS, studies on designing an approach
informing sound (AIS) have been conducted (3–6). In a previous study, we proposed a method ofdesigning an AIS based on onomatopoeia sound that reflects the pedestrians’ image of AIS (7). In
addition, to reveal factors affecting the evaluation of “the sound indicates a car traveling”, a subjective
experiment was conducted using sound stimuli designed according to provided onomatopoeic soundand an evaluation grid method (8). This experiment revealed that “engine sound”, “wind noise”, and“road noise” remain dominant in the evaluation of sound that indicates a car traveling while quiet
vehicles have been widespread.
The above results suggest that pedestrians might become aware of the approach of quiet vehicles
by listening to the sound emitted from the road or car body rather than the AIS. A previous study (7)reported that it is difficult for pedestrians to notice the AIS without recognizing the sound, whereas
providing the opportunity to hear the AIS helped pedestrians notice the sound. This approach ofproviding the opportunity to recognize the AIS is referred to as the design of awareness. On that basis,the present paper reports an experiment aimed at clarifying the sounds that pedestrians actually use in1

mt186515@cc.utsunomiya-u.ac.jp
mc196852@cc.utsunomiya-u.ac.jp
2
tk.piratwo@gmail.com
4
mariko@is.utsunomiya-u.ac.jp
5hasegawa@is.utsunomiya-u.ac.jp
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noticing the approach of quiet vehicles. In addition, a survey was conducted to examine the long-term
effect of designing awareness according to a previous study (7).

2. EXPERIMENT 1: SOUND USED IN RECOGNIZING THE APPROACH OF AQUIET VEHICLE
An experiment was conducted to clarify the sound that pedestrians actually use in noticing theapproach of quiet vehicles. Participants were required to report the sound that they heard and used innoticing the approach of a quiet vehicle.

2.1 Experimental conditions
The experiment was conducted on a traffic comprehensive test road at Nihon University on 16
October 2017 using a Prius (TOYOTA) as an example of a quiet vehicle. The positions of the quiet
vehicle and participants are shown in Fig. 1. The quiet vehicle traveled from line AA′ to line BB′ at aconstant speed of 15 km/h, which was within the operational speed range of the AVAS and ensured
the safety of participants. The vehicle speed was measured using a speed gun.
The participants stood 2 m from the center line of the quiet vehicle near line PP′ in Fig. 1, forming
a line with 1-m intervals. The experimental scene is shown in Fig. 2. So that the participants paid
attention to the sound emitted from the quiet vehicle, the participants stood with their backs to thevehicle and closed their eyes during the experiment. The quiet vehicle passed behind the participants
three times. The participants were 11 male students and one female student attending Nihon University
and having an average age of 21.7 years. The experiment was recorded using a video camera.

Figure 1 – Positions of participants and the quiet vehicle

Figure 2 – Experimental scene7181

2.2 Experimental method
To avoid the participants intentionally directing their attention to the AIS, the experimenters
explained that “This experiment aims to measure the distance at which pedestrians sense the dangerof an approaching vehicle”. The participants were required to raise their hand when they felt they
were in danger from the approaching vehicle. The experiment was conducted twice with the emittingof AIS. The experimenter then conducted an interview in which participants were asked what soundthey used in noticing the approach of the vehicle and feeling danger.
2.3 Experimental results
Experimental results obtained from the interview are given in Table 1. Each participant is indicatedby a letter. Those who knew about AIS before participating in the experiment are indicated by coloredcells. Table 1 shows that no participant answered that he or she noticed the approach of the quiet
vehicle and felt danger because of the AIS, and rather, they used other sounds, such as the sound of
the motor, road noise, and wind noise. One participant referred to an “engine sound” even though thequiet vehicle did not drive with an engine. The sounds listed by participants are emitted from not only
quiet vehicles but also vehicles with internal-combustion engines. The results suggest that theparticipants might use these familiar sounds as clues to the approach of the quiet vehicle.
Participants who did not notice the AIS reported that “I did not recognize the sound as a notification
sound” and “I noticed sounds such as road noise and running noise other that the AIS”. As reported
in a previous study (7), it might be difficult for people to notice the AIS without recognizing the sound.
However, participants who knew about AIS before participating in the experiment also reported thatthey did not use AIS in noticing the approach of the quiet vehicle but other sound emitted by thevehicle. The recognition of the AIS might not affect the use of sound in noticing the approach ofvehicles and feeling the danger posed by vehicles. To address this point, the same experiment was
conducted after providing the opportunity for participants to recognize and hear the AIS as Experiment
2.
Table 1 – Results of an interview conducted after the experimentA

What sound did you use in noticing theapproach of the vehicle and feelingdanger?
Sound like that of a motor and road noise

Yes

B

Sound pressure of soundYes

CSound unique to the PRIUS

No

It needs a louder volume to be
noticedIt hardly induces a feeling of
danger–

D

Road noise and sound of a motor

Yes

It is difficult to notice

E

Driving noise

No

–

F

Driving noiseNo–

What did you feel about AIS(if you noticed AIS)G

Car approaching sound and wind sound

No

–

H

No

–

No

–

J

Increasing in the sound pressure level,low- and high-frequency soundEngine sound and sound emitted fromtires
Increasing sound pressure level

Yes

K

Increasing soundNo

It can be heard in a quiet area
but might be difficult to hear ina noisy area–

L

Driving noise

No

–

I

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Did you notice AIS?
(Yes/ No)

3. EXPERIMENT 2: EFFECT OF DESINGING AWARENESS
3.1 Experimental conditions and method
The experimental conditions and method were the same as those in Experiment 1. The
experimenters explained the AIS to the participants and the participants heard the AIS repeatedly until
they could recognize it before the experiment began.
3.2

Experimental results
Experimental results are given in Table 2. As in Table 1, each participant is assigned a letter andthose who knew about the AIS before participating in the study are indicated by colored cells. Half ofthe participants answered that they used the AIS in noticing the approach of the quiet vehicle andfeeling danger, and three of them (participants G, H, and I) did not know about the AIS before
participating in the study. This result suggests that providing the opportunity to hear and recognize
the AIS (referred to as the design of awareness in a previous study (7)) can contribute to the use of
the AIS in noticing the approach of a vehicle. In Experiment 1, physical quantities such as the volume
of sound and abstract sounds such as driving noise were reported as factors used in recognizing theapproach of a quiet vehicle and feeling danger. Meanwhile, specific sounds such as the AIS and soundof tires were reported as factors in Experiment 2.
As observed in Experiment 1, other participants in Experiment 2 did not use the AIS. These
participants reported that the AIS did not notify them of the approach of a vehicle enough to feel
danger. They therefore use familiar sounds such as road noise rather than the AIS in noticing theapproach of a quiet vehicle. Further studies on various aspects of the design of AIS are required.
Table 2 – Sounds that participants used to notice the approach of a quiet vehicle

A

What sound did you use in noticing the approach of
the vehicle and feeling danger?
AIS and road noise

B

AIS

C

Rubbing noise of tires

D

Road noiseESounds other than AISFSound of tire slippingG

AIS or the sound of tires

H

AIS and the sound of tires

I

AIS

J

Sound of tires

K

Rubbing noise of tires

LSounds other than AIS

4. SURVEY FOLLOWING EXPERIMENTS 1 AND 2
The results of Experiments 1 and 2 reveal that the design of awareness is effective in improving
the recognition of AIS and changing pedestrians’ attitude toward sound. To discuss the long-term
effect of this design of awareness, the following survey was conducted 1 and 3 months after theexperiments.
4.1

MethodThe questionnaire survey was conducted using Google Form provided by Google. The
experimenters sent the URL of the Google Form by e-mail and required participants to complete thequestionnaire survey via the Internet. The survey questions are given in Table 3. Up to nine questions

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were asked according to the answers given.
Table 3 – Questions asked in the follow-up survey
Question
1

4.2

1-1

Did you notice the AIS in daily life after participating in
the experiments?
How many times did you notice AIS?

1-2

What were the road conditions when you noticed AIS?

1-3

Where did you notice AIS?

2
3

Did your attitude toward AIS change after participating in
the experiments?
Did you talk to someone about AIS?

3-1

Who did you talk about AIS?

3-2

Why did you talk about AIS to someone?

3-3What content did you discuss when talking about AIS?

Results
Results of the questionnaire survey completed 1 month after the experiments are given in Table 4.
Each participant is indicated by a letter and those who knew about the AIS before participating in the
study are indicated by colored cells. The table shows that six participants (A, B, C, D, K, and L)
noticed and heard the AIS in daily life (i.e., under noisy conditions), whereas the experiment was
conducted under quiet conditions. However, only some reported that their attitude toward the AISchanged and that they consciously listened to the sound. A change in attitude toward the AIS might
not necessarily affect the participants’ awareness of the AIS. Meanwhile, participants who were notaware of the AIS in daily life reported that their attitude toward the AIS changed after participatingin the experiment (participants E, G, H, and J). Their participation in the experiment and opportunity
to recognize and hear the AIS affected the participants’ attitude toward the AIS. Furthermore, threeparticipants (B, E, and H) reported that they had talked to friends or someone about AIS afterparticipating in the experiment. A previous study (7) showed that information from other people ismost effective in terms of recognizing AIS. Therefore, participating in the experiment and the effectof designing awareness could improve the recognition of AIS. These results again confirm the effectof designing awareness on AIS reported in a previous study (7). The design of awareness contributed
to improving the recognition of and changing the attitude toward AIS.
Results of the questionnaire survey completed 3 months after the experiments are given in Table
5. Again, each participant is indicated by a letter and those who knew about the AIS before
participating in the study are indicated by colored cells. Three participants (E, H, and J) reported thatthey noticed AIS in daily life even though they did not 1 month after the experiments. The number oftimes that five participants (C, E, H, J, and K) noticed AIS increased from that reported 1 month after
the experiment. As observed in Table 4, more than half the participants stated that their attitudechanged in that they consciously heard AIS. The design of awareness thus has a long-term effect.
In the interview conducted after Experiment 2 and described in Chapter 3, few participants
answered that they noticed the approach of the quiet vehicle and felt danger through AIS. However,six participants (C, D, E, J, K, and L) reported that they noticed AIS in daily life 1 or 3 months afterparticipating in the experiment. Two of them (participants C and E), who did not know about AIS
before participating in the study, also reported that their attitude toward AIS changed after theexperiments. The results show that providing the opportunity to recognize and hear AIS, or in otherwords, the design of awareness, can change the participants’ recognition of and attitude toward AIS
over the long term and contribute to improving others' recognition of AIS.

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Table 4 – Results of the follow-up questionnaire survey: 1 month after the experiment
Did you notice AIS in
How many times did Did your attitude toward Did you talkdaily life after
you notice AIS?
AIS change after
to someone
participating in theparticipating in theabout AIS?
experiments? (Yes/No)
experiment?
(Yes/No)A
Yes
No
More than 10 times
I think neither
BYes
5 or 6 times
I think somewhat so
Yes
C
D
E
F
G
H
I
J
K
L

Yes
Yes
No
No
No
No
No
No
Yes
Yes

1 or 2 times

I think so

No

1 or 2 times

I think neitherNo–

I think somewhat soYes–

I don't think so much

No–

I think somewhat soNo–

I think somewhat soYes–

I don't think so much

No–

I think somewhat so

No

1 or 2 times

I don't think so muchNo

5 or 6 times

I think somewhat so

No

Table 5 – Results of the follow-up questionnaire survey: 3 months after the experiment
Did you notice AIS in
How many times did Did your attitude toward Did you talkdaily life after
you notice AIS?
AIS change after
to someone
participating in theparticipating in theabout AIS?
experiments? (Yes/No)
experiment?
(Yes/No)A
Yes
No
More than 10 times
I think somewhat so
B
C
D
E
F
G
H
I
J
K
L

Yes
Yes
No
Yes
No
No
Yes
No
Yes
Yes
Yes

1 or 2 times

I think soYes

5 or 6 times

I think soNo–

I think soNo

I think neitherNo–

I don't think so much

No–

I think neitherNo

1 or 2 times

I don't think so muchYes–

I think somewhat so

No

5 or 6 times

I think somewhat so

No

5 or 6 times

I don't think so muchNo

3 or 4 times

I think somewhat so

No

1 or 2 times

5. CONCLUSIONSThe two experiments conducted in this study revealed that pedestrians who did not recognize AIS
noticed the approach of a quiet vehicle and felt danger not through AIS but through other, familiarsounds, such as wind noise and road noise, which are also emitted by vehicles having internalcombustion engines. After providing the opportunity to hear and recognize AIS (in the design ofawareness), half the participants began using AIS in noticing the approach of quiet vehicles. However,others reported that AIS was not enough to inform them of the approach of quiet vehicles, and they
thus did not use it. Further studies on the design of a more noticeable AIS are needed. Surveys
conducted 1 and 3 months after the experiments showed the long-term effect of designing awareness.
About a half of participants noticed AIS in daily life and recognized that their attitude toward AIS
had changed such that they listened to the sound consciously after participating in the experiments.
Further studies on the design of AIS, including designing awareness, would contribute to and improve7185

the recognition of AIS.

AKNOWLEDGEMENTS
This research was partially supported by a Grant-in-Aid for Scientific Researchers B (16H03021)
from the Japan Science and Technology Agency (JST), Japan.

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