The objective of the research carried out by MB and TUD is to determine the effect of different sound characteristics in a situation where a stopped vehicle near a pedestrian resumes motion. It intends to clarify the necessity for having sound at idle. So to ensure for a visually impaired pedestrian to quickly recognize vehicle has started its movement.

The following basic variances in sound of the quiet vehicle were compared:

  • Vehicle with sound at idle
  • Vehicle without sound at idle
  • Vehicle without sound at idle but with commencing motion sound (CMS)

In all cases the sound of vehicles when driving complied with the NPRM.

In a testing arrangement, the subject should signal the approach of a vehicle that was original stopped at a distance of 10m. The a.m. variances of vehicle sound where overlaid by different types of ambient noise. Test is carried in the TUB sound using recordings taken in the MB indoor test rack. 30 subject (25 sighted/5 visually impaired or blind) were exposed to. Test conditions differing not only in the a.m. variances but also in randomized starting time of the vehicle. It was their task to signal. The average results:

  • Stationary sound 1.43s delay after start of vehicle
  • No station sound: 1,12 s
  • CMS +6 dB(A): 1,02
  • CMS +12 dB(A): 0,84s

In summary it can be concluded that the capability of detecting a starting vehicle w/o sound at idle is bigger (1.12 s) compared to a vehicle with stationary sound (1.43 s) and the application of a CMS accelerates detection even further (0.84 s – 1.02 s). The different ambient didn’t not result a significant difference in detection time.

These test results suggest that the sound change (contrast) transitioning from no sound while stationary to alert sound active in motion has a measurable effect on detectability.

The results are in line with the joint demonstration conducted by Nissan, Toyota, Honda and Mitsubishi, showing that sound level of sound at idle as proposed by NHTSA can mask the sound of an approaching vehicle. A vehicle poses a danger to a visually impaired person only as it starts to move. Therefore, quick detection of a vehicle approaching is paramount to the detection of a stationary vehicle. For this situation the study shows that CMS is more effective than sound at idle. It is therefore proposed to allow CMS as an alternative to stationary sound.

NFB: What would be the result in the case of sound at idle and CMS?

OICA this risk to result in a vicious circle as it would always request in CMS to be louder than the sound at idle with all its negative impact on the environment.

NFB: The concern of no sound at idle is that a blind would not know of the presence of a vehicle at all and can therefore not take any appropriate action. A vehicle would only be recognisable when in motion, but not earlier. Also, hearing a vehicle would not only give information about the vehicle itself but also about the presence of a street and can therefore increase the orientation.

OICA: from a safety aspect, it may be important to have as much information available as possible. We must prioritize, which information is of higher value: a vehicle in standstill which in this condition does not pose a risk or a moving vehicle.

NFB: blind unions and associated institutions have all expressed their preference for sound at idle over CMS.

EU: Isn’t there a risk of masking of vehicles behind vehicles with sound at idle?

NFB: the risk is minor as once you hear one vehicle, you are aware, that a second one might be masked so that you can take appropriate action.

OICA: In terms of improved orientation, there are other items that better serve, such as house wall and curb stones

NFB: in a residential area this may be true, but in normal urban traffic with multilane roads, any acoustical info is very helpful. Start/Stop systems of ICEV risk posing a similar concern.

OICA: For an engineer it is important to collect data that can be analysed. It was not the intention of this presentation to argue against navigation aids, but some of the mentioned arguments are difficult to measurement and with it difficult to evaluate. The presentation intended to show that there is a risk of masking other potential risk. So we must balance our knowledge between safety aspects, but also we must consider the environmental aspect in parallel.

EU: we support the OICA position and are interested in learning about the NFB’s attitude towards the potential lowering of environmental noise from EVs.

NFB agrees overall sound level going down is beneficial. The final solution will have to be determined based on a concerted compromise between safety and environmental aspects.

The Chairman concluded that there is a general conflict in approaching the subject of the necessity of a sound at idle. While a sound at idle may be used for general navigation purposes as it includes the information about the location of a nearby road, it is not supportive for the cognition of a vehicle that changes its condition from standstill to move.