Unfortunatey, ppl don`t use mirrors enough to observe traffic around them and don`t look ahead for possible dangerous situations.
I use IEMs while driving all the time and can`t really see difference with ppl turning their stereo system loud (also can`t hear much) but they still do drive (a LOT of ppl do that and even dancing/singing behind wheel!).
IMHO, it`s all about driving skills (mirrors,observing, proper speed etc.) and adequate behaviour behind wheel
Also, imho, most dangerous drivers are SMOKERS, SMARTPHONE & CONSOLE USERS!
With latter ones ppl lose contact/eyesight with traffic competely for seconds while I with my IEMs still have eyes 100% on the road/traffic/mirros with both hands on wheel!
Ps, I don`t change tracks, playlist etc. while driving - just put it on play before moving and stop when my car is parked and off.