FWIW Semi truck m/t going down hill pulling 70 feet of m/t double flatbed trailer is silent until it is next to you. BTDT. To rely on hearing alone is foolhardy. BTW every time I get my hearing checked it is fine. I'm guessing that unless you have a tailwind equal to your speed then the wind whistling in your ears due to your speed somewhat deafens you. RIP Professor! My guess is also that the motorist, unless a repeat offender will not even get a written warning. So sad.
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Sir Mark, Knight of Sufferlandria