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

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

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

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 : 40 - 90dBA at 10dBA step (6 conditions). Measurement position is 7m from the speaker and 1.2m height.

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

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.

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

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

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.

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 50 - 70dB. This result means TS can be heard clearer than BBS at 50 - 70dB.

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 50 - 70dB. This result means tonal sound is more noticeable at 50 - 70dB.

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 60 - 80dB. This result means BBS is noisier than TS at 60 - 80dB.

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.

　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.

　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

　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 : 50 - 60dB Upper limit value : 70 - 80dB Proposal limit value by Germany and Japan is 58 - 78dB (GRB-66-07). It is confirmed that the proposal value is appropriate by this research.