1. JASIC National Traffic Safety and Environment Laboratory
Research on detectability and acceptability of reverse warning sound by evaluation test
JASIC
National Traffic Safety and Environment Laboratory

2. 　The aim
The aim of this study is to decide limitation value considering environment friendly (less complaints) and pedestrian's safety (detectability).

3. Heavy duty vehicle with idling (about 60dB)
　Scene of evaluation test
Layout of the test
Speaker for BGN
Heavy duty vehicle with idling (about 60dB)
Test participant :
The ear position is set at 1.2 m height
Speaker for warning sound

4. Test method Test target : 30 people (All of them are Japanese).
Warning Sound Quality :
2.1 kHz tonal sound (TS) and broad band sound (BBS) are used.
TS is created by computer.
BBS is recorded in anechoic chamber.
BBS generator is made by Yamaguchi Electric Ind. Co, Ltd.
Duty ratio of both sounds is about 50%.
All of warning sounds are emitted by speaker.
Warning Sound level :
dBA at 10dBA step (6 conditions).
Measurement position is 7m from the speaker and 1.2m height.

5. Test method -con't BGN level: 35 - 65dBA at 10dBA step (4 conditions)
BGN type:
NHTSA NPRM
Image of BGN level:

6. Question 1 : Intelligibility Score
As a pedestrian, can you hear warning sound well?
Can't hear at all
Hear well
TS (2.1kHz)
BBS
Scores at 40dB is less than 2. Scores at 80dB is more than 6.
The results of BGN 45dB and BGN 55dB are similar, because vehicle idling noise level is about 60dB.
Vehicle engine is stopped at the test of BGN 35dB.
There is small score difference among BGN levels above 80 dB warning sounds.

7. Question 2 : Noticeability Score
As a pedestrian, do you feel that you have to do something after hearing this warning sound?
I don’t think so
I think so
TS (2.1kHz)
BBS
The result shows a similar tendency as Q1

8. Question 3 : Noisiness Score
Suppose you were in your house and hear this sound, do you feel this warning sound noisy?
Not at all
Noisy
TS (2.1kHz)
BBS
The result shows a similar tendency as Q1

9. Question 4 : Integrated Evaluation Score
Please evaluate the total impression of the warning sound in nine stages
TS (2.1kHz)
BBS
At 40dB, the score is about "1 - 2". This sound level is too small to hear.
At 90db, the score is about "8 - 9". This sound level is noisy.
From 40dB results, TS can be heard clearer than BBS.
From 90dB results, BBS is noisier than TS.

10. TS vs BBS : Q1 - Intelligibility Score
The average of 30 people’s evaluation at each sound level is shown in the graph below.
4 plots exist at same sound level due to 4 different BGN levels.
SPL
Can't hear at all
Hear well
TS scores are higher than BBS scores at dB.
This result means TS can be heard clearer than BBS at dB.

11. TS vs BBS : Q2 - Noticeability Score
The average of 30 people’s evaluation at each sound level is shown in the graph below.
4 plots exist at same sound level due to 4 different BGN levels.
I don't think so
I think so
TS scores are higher than BBS scores at dB.
This result means tonal sound is more noticeable at dB.

12. TS vs BBS : Q3 - Noisiness Score
The average of 30 people’s evaluation at each sound level is shown in the graph below.
4 plots exist at same sound level due to 4 different BGN levels.
noisy
Not
at all
BBS scores is higher than TS at dB.
This result means BBS is noisier than TS at dB.

13. TS vs BBS : Q4 - Integrated Evaluation Score
The average of 30 people’s evaluation at each sound level is shown in the graph below.
4 plots exist at same sound level due to 4 different BGN levels. 1 2 3 4 5 6 7 8 9
The sound is too small to hear
The sound is hearable, but it is hard to recognize due to ambient noise
The sound can be heard clearly, and its volume is appropriate as a warning sound
The sound can be heard clearly, but a little bit loud
The sound is too loud and noisy
BBS score is higher than BBS above 80dB.
This means BBS is recognized as a noisy sound above 80dB.

14. 　Question 5
Do you think tonal sound/broad band sound is an appropriate sound for warning of vehicle approaching? 7 6 5 4 3 2 1
I think so 6 5 4 7 1 5 4 3 6 2
I don't think so TS
BBS
Almost all of the people answered TS is an appropriate sound.
The scores of BBS for this question is not positive because BBS is not widely used in Japan.

15. 　Other questions
After evaluation test, we asked 2 questions to the test participants.
How do you think about volume of reverse warning sound?
・Louder is better ：1 person
・A certain level of the volume is preferable ：15 persons
・Appropriate volume is preferable ：14 persons
・Smaller is better　　　　　 ：0 person
・Reverse warning sound is not necessary ：0 person
This result shows that the participants tend to think safety is more important than environment.
The scores of this research might be larger value.
Do you think "Low mode" is necessary for the revers warning device?
・Absolutely necessary ：3 persons
・Preferable ：22 persons
・Not sure ：4 persons
・Not preferable ：1 person
・Not necessary at all ：0 person

16. 　Conclusion
The score become larger depending on the warning sound volume at each questions.
BBS is not recognized as reverse warning sound in Japan.
To decide lower/upper limit value of “normal mode” from results of Q4,
　 Lower limit value is appropriate above score 3.
(Score 3 : The sound is hearable, but it is hard to recognize due to ambient noise)
　 Upper limit value is appropriate under score 7.
(Score 7 : The sound can be heard clearly, but a little bit loud)
From this research, appropriate limit values are as follows.
　 Lower limit value : dB
Upper limit value : dB
Proposal limit value by Germany and Japan is dB (GRB-66-07).
It is confirmed that the proposal value is appropriate by this research.