The National Highway Traffic Safety Administration recognizes that quieter cars such as hybrid-electric vehicles in low-speed operation using their electric motors, may introduce a safety issue for pedestrians who are blind. This study documents the overall sound levels and general spectral content for a selection of hybrid-electric and internal combustion vehicles in different operating conditions, evaluates vehicle detectability for two ambient sound levels, and considers countermeasure concepts that are categorized as vehicle-based, infrastructure-based, and systems requiring...