Blind Pedestrians and Quieter Vehicles: How Adding Artificial Sounds Impacts Travel Decisions
Authors: Wall Emerson Robert , Kim Dae Shik , Naghshineh Koorosh , Myers Kyle 
Published: September 2013

This research examined the influence “quiet” (e.g., hybrid and electric) vehicles may have on the ability of blind pedestrians to perform common orientation and mobility tasks under low vehicle speed conditions. The research involved blind participants detecting forward approaching vehicles and approaching backing vehicles, deciding whether a vehicle coming from behind or from the front but across an intersection would continue to go straight or turn across the intended path of travel of a pedestrian seeking to cross a street (i.e., a pathway discrimination task), and taking parallel and perpendicular alignment from passing traffic. Participants included some with normal hearing and some with impaired hearing.

Testing was conducted on a public roadway and a parking lot in Kalamazoo, Michigan under ambient sound conditions consistent with a typical urban travel environment. Conditions involved evaluating internal combustion engine (ICE) Chevrolet Malibu and a set of hybrid Chevrolet Volts capable of operating in a “quiet” mode (referred to as Electric Mode or EM) or operating in EM but augmented with one of five different artificially-generated sounds emanating out of a front-bumper mounted speaker.

All of the artificial sounds generally performed better against the baseline the Chevrolet Volt EM than the Chevrolet Malibu. This suggests that, to some extent, putting any one of these artificial sounds on a hybrid or electric vehicle may improve pedestrian performance on the measures examined relative to not adding any sound at all. One sound (sound 5) did not outperform against the Chevrolet Malibu in any measure and had the fewest instances of outperforming the Chevrolet Volt EM. Of the remaining 4 sounds, two sounds outperformed both the Chevrolet Malibu and the Chevrolet Volt EM on several measures. Against the Chevrolet Malibu, sound 2 was slightly better in detection distance and crossing margin while sound 4 was better in the path discrimination tasks. The two sounds were equivalent on the alignment tasks.

The pathway discrimination task reflects one of the more potentially threatening situations in which a blind pedestrian might encounter a quiet vehicle (e.g., turning to cross the pedestrian’s path). Sound 4 performed much better than sound 2 on this measure, making it the most effective of all the artificial sounds examined. While these two sounds were equitable in the right-straight task, sound 4 showed almost half as many missed vehicle surges (i.e., forward movement from a stop) and 1/4 the rate of missed paths and incorrect judgments. Vehicle sound condition did not impact participants’ alignment. Normal hearing participants performed significantly better than hearing impaired participants on this task, but not as well as would be expected based on previous data [1].

These results support the potential for artificially-generated sounds to improve the ability of blind pedestrians to detect approaching vehicles relative to what is being achieved with ICE vehicles. Regression analysis of the detection data supports previous results that sound energy in the 500 to 1000 Hz range is important for detection. However, the analysis indicates it is not that energy in this region that makes the signal more noticeable, but that energy in this region in the ambient environment hinders detection. Previous findings in low ambient conditions showing a predictive value for the amplitude modulation of an artificial sound were not supported in these data.