Are hands-free cell phones safer to use in cars than non-hands-free
phones?

Specifically, compare the number of serious accidents and fatalities
of two groups: accidents where driver hands-free cell-phone usage was
determined to be at least a contributing factor vs. driver
non-hands-free cell phone usage being determined to be at least a
contributing factor.

There is lots of general advice on this subject floating around mainly
advocating hands-free and "abstinence", but my initial research has
yet to find that hands-free cell phones are any safer.

Thanks!

The trouble is that very few dead people will own up to using a phone
at the time of their accident

>The trouble is that very few dead people will own up to using a phone
>at the time of their accident

You bring up 2 important issues:
- People are reluctant to admit inattention due to cell phone usage.
- Dead men tell no tales.

On the first point, hopefully the question, a comparison between
non-hands-free and hands-free will get past that. The educated guess
is that the two groups would be about as likely to admit cell-phone
inattention. For example, if both groups admitted inattention (or the
inattention was somehow found out) only 30% of the time, the
comparison would still be valid; we could still determine which mode
is more dangerous.

On the second point, there will still be a decent amount of reporting.
Actually, it's likely that this reporting would be higher, since the
person that was on the line with the now deceased person has less
incentive to hide the inattention, and this person will also be likely
to come forward, wanting to relay their story about their last minutes
with the deceased to family and emergency personnel. Similar to my
first point, it's probably reasonable to assume that an equal
percentage of both groups would be represented.

So all we're missing now are the reporting statistics from both
groups.

I have not found recent accident statistics comparing the two groups.

Here you will find some related information that may be useful:

"In sum, we found that conversing on either a hand-held or hands-free
cell phone led to significant decrements in simulated driving
performance. We suggest that the cellular phone use disrupts
performance by diverting attention to an engaging cognitive context
other than the one immediately associated with driving.

Our data suggest that legislative initiatives that restrict hand-held
devices but permit hands-free devices are not likely to reduce
interference from the phone conversation, because the interference is,
in this case, due to central attentional processes."

National Safety Council
http://www.nationalsafetycouncil.org/library/shelf/inincell.htm

Here is an excerpt from a 1997 study that found no significant safety
advantage for hands-free car phones:

"A total of 26,798 cellular-telephone calls were made during the
14-month study period. The risk of a collision when using a cellular
telephone was four times higher than the risk when a cellular
telephone was not being used (relative risk, 4.3; 95 percent
confidence interval, 3.0 to 6.5). The relative risk was similar for
drivers who differed in personal characteristics such as age and
driving experience; calls close to the time of the collision were
particularly hazardous (relative risk, 4.8 for calls placed within 5
minutes of the collision, as compared with 1.3 for calls placed more
than 15 minutes before the collision; P<0.001); and units that allowed
the hands to be free (relative risk, 5.9) offered no safety advantage
over hand-held units (relative risk, 3.9; P not significant)."

New England Journal of Medicine
http://content.nejm.org/cgi/content/short/336/7/453

There have been numerous studies done on the effect of mobile phone
use on driver performance.  Most have shown that there is a negative
effect on decision making performance when doing complex driving tasks
such as left-turning and weaving.  It is more the fact that your
attention is taken away from driving than the physical holding of the
phone. Therefore phones of any kind are a distraction to driving. The
journal "Accident Analysis and Prevention" has published quite a few
studies on this subject that are worth looking at.  The one I have in
front of me at the moment is by Cooper et al Called "The impact of
hands-free message reception/response on driving task performance" in
Accident Analysis and Prevention vol 35 issue 1 Jan 2003.