The research showed that the reduction was greater for cars.wouldn't it depend considerably on the earphones? Some keep out outside noise, and some don't.
I guess ditto the car - with say, a near silent Rolls keeping out most outside noise, or far that matter an old Landy drowning out most outside noise.
Still 20dB difference - with cars letting in more outside noise (if I've understood figures right)
The difference between a cyclist's ability to hear ambient noise with headphones an a moderate volume was less than the difference betwen open and closed car windows.
Why should one group be criticised and the other allowed to perform the same ambient noise reduction as a standard practice?