This was the most interesting bit of what Dr. Novella had to say:
What this all might mean is that there is something about talking on a cell phone that is particularly demanding of our attention – more so than listening to music or talking with someone who is physically present. These results also support the hypothesis that talking with a passenger is not as dangerous because the extra pair of eyes increases the chance that someone will notice a sudden obstacle or unexpected traffic pattern.
Anecdotally, I would certainly agree. I notice things just fine walking down the street when I'm listening to my iPod or walking to the bus station with Mike. If I'm having to return a phone call while I'm walking, I wouldn't even notice a full marching band unless they were making enough noise to keep me from hearing the person on the other end of the phone. I once dropped my USB drive and walked off, and a really nice guy had to chase me half a block to give it back to me because I was talking on my phone and didn't notice someone shouting to get my attention.
I've pretty much thought hands-free laws were crap from the beginning. It doesn't help if you've only got one hand on the wheel when it comes to maneuvering, but frankly I'd bet that most people only keep one hand on the wheel unless they're turning anyway. (On a side note, I don't know how people who drive manuals can manage to talk on a cell phone like that anyway, unless they're on the highway and don't have to shift.) It really is the distraction that causes accidents and kills.
In my opinion, even freakier: people who text and drive. Actually, I'll own up. The only car accident I've been in since becoming a driver was my own fault, and caused by me attempting to text and drive. (This was seven or eight years ago when it happened.) I rear ended someone at about five miles an hour on the highway when we were in complete gridlock. At that point, I realized how I literally had not seen it coming, and since then I refuse to even touch my cell phone when I'm in the driver's seat. If someone calls me, I toss it to my passenger and make them check it. (Another reason not to drive with me?)
So we know it's dangerous to be on a cell phone and drive, particularly now whether it's hands free or not. I don't know if there's really anything you could do about it. Sure, you can make laws, but enforcing them is another matter. The biggest problem is that if it were just people deciding they'd rather take the risk than be separated from their precious cell phone for the duration of a drive, fine. But they're on the road with everyone else, including people who probably aren't happy accepting that risk since they're the ones that will get rear-ended by the jackass that won't just hang up and drive.
When I put it like that... well. Driving while on a cell phone: the new driving while intoxicated.
One thing I'd like to see more on scientifically is why talking on a cell phone is more distracting than talking to someone else while walking. I don't know if I buy that it's just the other pair of eyes that makes the difference, since I'd think both people would be distracted by the conversation. If we assume that one conversation is as distracting as the other, then you'd expect that people in pairs would still pay attention better, but I don't know if it would be as much better as it was.
Only 25% of the cell phone users had noticed the clown and many turned around at that point to see what they had missed. In essence, 75% of the cell phone users experienced inattentional blindness to the unicycling clown. In contrast, over half of the people in the other conditions reported seeing the clown (51% of single individuals, 61% of music player users, and 71% of people in pairs).
(Note: the clown thing was testing for inattention blindness by putting a clown on a unicycle very visibly along the path and seeing who noticed him.) The gap here is 25% as compared to 71% - that's a difference of 46%. That's pretty impressive. Maybe cell phones are more distracting because you're missing out on most of the nonverbal side of the conversation?
Also, I wonder why people listening to music did better than people just walking along. That seems odd, but very interesting.