“Research shows that motorists talking on a phone are four times as likely to crash as other drivers, and are as likely to cause an accident as someone with a .08 blood alcohol content.”
Driven to Distraction – NYTimes.com
And the research also shows that it’s the conversation, not the phone, that takes a driver’s mind off the road.
Your last sentence implies that even those of us who responsibly use a headset so as to be able to keep both hands free are still at risk of becoming dangerously distracted.
It seems to follow that listening to speech while driving – whether books on “tape” or talk shows – would be more of a distraction than listening to music.