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Disclaimer:  The information provided in this blog post is intended for educational purposes and not legal advice. For specific legal inquiries, please consult an attorney. The information provided is intended for the sole purpose of reconstructing accidents and injuries and not for serving as a risk management resource. 

LISKE Human Factors Expert, Dr. Miao Song who has conducted research projects on issues related to automobiles, drivers, and road users, including vulnerable ones, in his peer-reviewed paper ^[1] undertook an effort to evaluate UNECE’s proposed evaluation method for quiet road vehicles, as well as to assess performance between two additive noise approaches. His study also evaluated the detectability of an EV with no additive noise versus a traditional internal combustion engine (ICE) vehicle.  The following is an abstract of his paper.

As the adoption of hybrid and electric vehicles (HVs and EVs) increases, concerns have emerged regarding their relative quietness with respect to pedestrian detectability. Although all pedestrians face a possible increase in risk due to lower operating noise associated with HVs and EVs, the visually impaired and blind community faces an even greater potential for risk due to their reliance on hearing as an assessment for when it is safe to cross a roadway.

Vehicle manufacturers have started implementing additive noise solutions designed to increase vehicle detectability while in electric mode and/or traveling below certain speeds. Over the course of three phases of research beginning in 2013, the National Highway Traffic Safety Administration (NHTSA) determined that adding synthetic sounds of combustion noise to EVs and HVs was relatively ineffective and that the ability to detect approaching vehicles was not significantly impacted by visual impairment. Moreover, NHTSA’s research ultimately recommended minimum additive sound requirements designed to improve the detection and recognition of EVs and HVs as motor vehicles. NHTSA stated that international guidelines addressing the issue namely the United Nations Economic Commission of Europe (UNECE) fell short of the level of detail typically found in a Federal Motor Vehicle Safety Standard (FMVSS). Notably, NHTSA clarified that some test standards had failed to account for psychoacoustic factors.

To this end, four vehicles, specifically a 2011 Chevrolet Volt (EV, no additive sound), a 2014 Cadillac ELR (EV, GM production additive sound), a 2013 Toyota Prius (HV, competitor additive sound under electric mode), and a 2013 Cadillac SRX (ICE) were chosen to benchmark noise tests and listener evaluations. Twenty-four legally blind participants were engaged in a full-day session evaluating their ability to detect approaching vehicles in controlled scenarios, including different speeds and complete stops.

The findings reveal that, in diverse conditions, average detection distances exceed NHTSA thresholds, with differences among vehicle types. ICE vehicles generally detect better, but EVs and HVs perform adequately. Instances of detections below NHTSA criteria signal collision risks, especially with the Chevrolet Volt having a higher proportion. Despite slight disparities in average detection distances, potential collision cases suggest an advantage from an additive noise component.

Moreover, the results demonstrate significant variations in detection distances based on vehicle type, approach speed, and background noise levels. At a consistent approach speed of 20 kph (12 mph), detection distances notably increase compared to 10 kph (6 mph), mainly due to amplified road noise at higher speeds. However, the detection advantage of ICE vehicles diminishes, except for the Prius, which displays notably shorter mean detection distances compared to others.

Increased background noise negatively impacts detection ranges, resulting in a proportional decline across various approach speeds. However, mean detection distances still surpass NHTSA standards. Higher noise levels lead to more cases nearing potential collision, notably with quieter vehicles like the Prius. Importantly, safe-to-cross points are often identified before a vehicle stops, potentially posing safety risks. In addition, higher ambient noise levels and faster approach speeds reduce detection distances and heighten the risk of missed or premature responses, underscoring the importance of considering environmental factors in pedestrian safety design.

In conclusion, although average detection distances tend to be higher for vehicles equipped with an added noise feature, they are not significantly different from conventional electric vehicles (EVs) at speeds of 10 kph (6 mph). Moreover, all-electric and hybrid vehicles (EV/HVs) were detected at notably shorter distances compared to internal combustion engine (ICE) vehicles. At a speed of 20 kph (12 mph), these distinctions became less discernible, likely due to the increased road noise generated by tires at higher speeds.

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Reference:

[1] Neurauter, M. L., Roan, M., Song, M., Harwood, L., Moore, D., & Glaser, D. (2017). Electric vehicle detectability by the vision impaired: Quantifying impact of vehicle generated acoustic signatures on minimum detection distances. In 25th International Technical Conference on the Enhanced Safety of Vehicles (ESV) National Highway Traffic Safety Administration.

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