Vehicles operating in electric mode can be particularly hard to hear below 20mph (32kph), according to experiments by Lawrence Rosenblum and his colleagues at the University of California, Riverside.

• 根据美国加州大学河滨分校劳伦斯.；罗森布拉姆及其同事所做的实验结果，电动模式的车辆如果驾驶速度低于20英里/时（32千米/时）很难听见。