I was on vacation in Scotland recently with some friends and we piled into a van for a road trip from Edinburgh to Loch Lomond. One of my friends — a well-known theater producer in London — got behind the wheel and put on her Bluetooth hands-free mobile phone earpiece, so that she could conduct some business calls along the way.

I protested that phoning while driving was as bad as climbing behind the wheel with a gin and tonic, but I was shouted down by my mates. It's just talking, and everyone talks while driving.

I thought everyone knew that talking on the phone is as bad, maybe worse, than drunk driving. But it turns out I'm in a minority — while everyone knows that texting while driving leads to accidents, most people believe that talking on a hands-free cellphone device is no different than chatting to the person next to you in the shotgun seat.

Most people, however, are wrong.

The available studies so far suggest that talking on the phone while driving, even hands-free, is as bad or worse than driving drunk. Indeed, hands-free talking may be worse than drunk-driving precisely because so many people are lulled into thinking it's safer.

Here's the research:

It is, therefore, especially scary that the Bluetooth company web site actively encourages hands-free talking-while-driving as a safety measure (because they are not hand-held devices).

It's not clear why talking on a hands-free is worse than chatting with a passenger. Theories floated so far suggest that talking to a person remotely requires greater cognitive effort than talking to a person sitting next to you. (Think about how much more effort you have to put into a cellphone conversation than a face to face one.)  Also, the person next to you can respond to your driving cues and alter the workload of the conversation based on the difficulty of driving conditions — the person on the other end of the cellphone can't help you with any of that.

My friend didn't crash our van in Scotland, luckily. She did, however, take directions from a person using a GPS app on a cellphone in the passenger seat — and she blew right through a "Dead End" sign within five minutes of setting off, forcing her into an embarrassing three-point turn at the end of a cul-de-sac.

Perhaps her performance would have been better if she had been drinking and driving alone.