Acoustic Data for Hybrid and Electric Heavy-Duty Vehicles and Electric Motorcycles

Hastings, Aaron; Shumway, Meghan Ahearn; Guthy-McInnis, Catherine; Garrott, Riley; Garay-Vega, Lisandra · 2015 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This report addresses the acoustic characteristics of hybrid and electric heavy-duty vehicles and electric motorcycles to support the National Highway Traffic Safety Administration’s (NHTSA) rulemaking under the Pedestrian Safety Enhancement Act (PSEA) of 2010. The PSEA mandates the establishment of a Federal Motor Vehicle Safety Standard requiring alert sounds for electric and hybrid vehicles to enhance pedestrian safety, particularly for blind individuals. The study was motivated by the need to determine if existing vehicle noise levels meet minimum detection thresholds and to gather data for regulatory standards. The report also analyzes crash data to contextualize pedestrian risks associated with these vehicle types. The methodology involved acoustic measurements conducted on ISO 10844 certified test surfaces, following general procedures outlined in SAE J 2889/1. Two electric motorcycles (2012 Brammo Enertia and 2012 Zero S) were tested at the Transportation Research Center in Columbus, Ohio, while one electric heavy-duty delivery truck (Navistar eStar) was tested at Navistar’s proving grounds in Fort Wayne, Indiana. Test scenarios included start-up, stationary, constant speed pass-by (10, 20, and 30 km/h), acceleration, and deceleration. Additionally, screening tests were performed on four other hybrid and electric heavy-duty vehicles (including buses and trolleys) at various urban locations. These screening tests did not fully comply with SAE J 2889/1 parameters due to environmental and operational constraints, yielding illustrative rather than definitive results. The findings indicate significant variability in acoustic emissions. The 2012 Zero S motorcycle failed to meet minimum detection levels in any of the 13 one-third octave bands (315–5000 Hz) across all tested speeds. The Brammo Enertia met detection thresholds in only two to three bands at 10 and 20 km/h, but failed at 30 km/h. In contrast, the Navistar eStar heavy-duty vehicle generally exceeded minimum detection levels in seven to nine of the 13 bands across stationary and pass-by scenarios. Screening data for other heavy-duty vehicles showed mixed results, with measured levels meeting detection thresholds in two to eight bands depending on speed and vehicle type. Crash data analysis revealed that while passenger cars are involved in the majority of pedestrian injuries, low-speed pedestrian crash rates are higher for light-duty vehicles than for motorcycles or heavy-duty vehicles. The significance of this research lies in its contribution to the development of federal safety standards for quiet vehicles. The data demonstrate that electric motorcycles often emit sound levels below human detection thresholds, highlighting a critical safety gap that necessitates artificial alert sounds. Conversely, electric heavy-duty vehicles often produce sufficient noise for detection, though variability exists. The report confirms that the proposed test protocols are applicable to these vehicle classes, despite minor adjustments required for motorcycles, such as lane positioning to avoid painted center lines. These findings provide the empirical basis for NHTSA to define performance requirements for alert sounds, ensuring that pedestrians can reasonably detect approaching electric and hybrid vehicles.

Key finding

The Navistar eStar electric heavy-duty vehicle met minimum pedestrian detection sound levels in 7 to 9 of 13 frequency bands across stationary and pass-by scenarios, whereas the two tested electric motorcycles failed to meet these levels in most bands, especially at 30 km/h.

Methodology

lab_experiment

Sample size: 7

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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• auditory warnings