[csense]

Both common sense and personal experience tell me that talking to a passenger while driving also decreases the driver's attention to the road and increases the risk of an accident.

Having a conversation with someone in the car, who is within your frame of reference, is not the same as having a conversation with someone on the phone, who is in a completely different frame of reference. That's why it doesn't matter whether your system is "hands free" or not. The distinction isn't where your hands are or what they are doing, it's where your mind is, what it's aware of, and what it's focusing on, etc.

[AnotherUnixGeek]

Having a conversation with someone in the car, who is within your frame of reference, is not the same as having a conversation with someone on the phone, who is in a completely different frame of reference.

Hmm. I can believe that phone conversations might be more distracting than conversations with passengers, though I don't know if anyone has run any studies, but that's not to say that conversations with passengers aren't also distracting.

That's why it doesn't matter whether your system is "hands free" or not. The distinction isn't where your hands are or what they are doing, it's where your mind is, what it's aware of, and what it's focusing on, etc.

I agree - the distinction is indeed where your mind is, what it's aware of and what it's focusing on. For this reason, I'm pretty sure that a conversation with a passenger to the side or behind you can be every bit as distracting and detrimental to driving safety as talking on a cell phone. I was in a car pool for a while and I saw examples of this repeatedly. Other activities such as listening to talk radio or good music could be distracting as well.

The point is that many things people do while driving decrease safety and can be rated as being equivalent to some level of intoxication, as cell phone use is. The real difference is that when we see someone using a cell phone while driving we know their first priority is not driving. But this is true of many or most of the other drivers on the road - we just don't get obvious visual evidence in the form of cell phones. Personally I think bans on cell phone use while driving are unnecessary.