Presentation on investigations into response times to vehicle sounds under various scenarios, including assessment of sound levels proposed in the NHTSA NPRM.
5.2 ACEA Study on detection distances
On order of ACEA, the Technical University of Dresden (TUD) has carried out a study intended to assess the detection distance of various types of propulsion. The preliminary results of that study were presented by OICA. More details, such as frequency spectrum specification, will be shown at the next official meeting of the IWG in Tokyo.
One part of study consisted on a jury testing of various artificial sounds emitted by HEV/EV as well as ICE-V and recorded during outdoor testing of approaching vehicles. Those recordings were mixed with a standardised 55 dB(A) ‘Pederson’ background noise and presented to probands at the TUD Acoustic test lab. All of the presented sounds were detected earlier than 1.8sec before the vehicle would have passed in front of the microphone line. With that, the basic requirement contained in the US NPRM for sufficient detection distance is fulfilled (page 17 of presentation). It was noted that most of the sounds did not meet the NHTSA proposed specification for sound composition. It was concluded that 2 1/3rd octave bands are sufficient to make a vehicle detectable and that detection distance is not a function of SPL. CLEPA (Brigade) emphasized that beside a pure ability for detection, also locatibility is important and that from internal experience, four 3rd octave bands would probably be sufficient to add that attribute to the AVAS signal.