Debunking the 'science' behind cell phone and driving research

I personally believe that there is a lot of 'junk science' out there about cell phone use and driving.  While I agree that driving while distracted is dangerous, I do not buy into the argument that cell phones are somehow much worse than any of a variety of other activities (changing CDs, dealing with crying babies, talking to a passenger, etc.) that we all engage in everyday.

While I have not read all the articles and literature published on the subject, I have reviewed some of it and I find it less than compelling.  I would like to address what I see as some serious errors in scientific method that have been used to 'prove' that using a cell phone while driving is dangerous.  Rather than make comments about the research in general, I thought it would be more compelling to address the specific issues in one of the touted studies.  However, I believe this is representative of the issues with all the studies in this field of research.

An open letter to Dr. David L. Strayer and William A. Johnston regarding their paper, "Driven to Distraction: Dual-Task Studies of Simulated Driving and Conversing on a Cellular Telephone" (see

I was corresponding with John Ulczycki of the National Safety Council regarding the purported risk of using a cell phone while driving.  I pointed out to him that the real-world numbers do not match what the various studies show.  We went back and forth a few times and he eventually directed me to your study among others.  

After reading your research paper and reviewing other research in the field, I think that I have a handle on why the various studies report a correlation while the real-world numbers (traffic statistics) do not reflect that correlation.  I believe it is the 'human factor' which is frequently, if not always, undermined in the studies.

I'm not a statistician or a think-tank guru but I think I have a handle on this.  Help me understand these two numbers:

1 - Traffic accidents per 100 million vehicle miles traveled are going down at a steady rate and have been for decades (source: Utah Department of Transportation).

2 - Cell phone subscribers and cell phone minutes used are going up at a nearly exponential rate (source: CTIA).

Accidents per 100M vehicle miles traveled vs. Cell minutes used

Accidents per 100M vehicle miles traveled vs. Number of cell subscribers 
What correlation do you see?

It seems to me that if cell phones were actually a major factor in traffic accidents, then the accident rate should at least come close to mirroring the increase in cell phones and minutes used.  Instead, the accident rate continues to fall with no apparent correlation to cell phone usage.

I see two possibilities here.  One is that people don't tend to use their cell phones while driving.  The other is that cell phone usage is not as much of a distraction as the research would suggest.  Either way, cell phone use while driving is simply not that big of an issue.  If it were, the traffic statistics would show some correlation with the massive increase in cell phone usage.

This debate seems to be identical to the debate raised when AM radios were first put in cars ("they are a distraction and millions will die").  Does anyone want to suggest that we try to ban radios, CD players, MP3 players, etc. from cars again?

I agree with general "driving distracted" laws.  I do not agree with vilifying specific devices or technologies that may (or, more likely, do not) have any actual correlation to accidents.

I understand that a cell phone CAN be a distraction, but the video of studies that I've seen (notably on "Scientific American Frontiers", see, specifically the Hold the Phone segment) showed what I consider to be obviously flawed 'science' behind the research.  They put the host (Alan Alda) in unreasonable situations that required things that normal drivers would never do (use their phone while in a difficult driving situation).  I could easily construct similar unreasonable situations that show that any number of things (talking to a passenger, changing CDs, whatever) are equally, or even more, distracting.

I carefully read your article, "Driven to Distraction: Dual-Task Studies of Simulated Driving and Conversing on a Cellular Telephone" at  I am not a researcher nor a think-tank guru, but I see some significant problems with this study.  Let me detail a few of them.

1. Pg. 1 - "One source of evidence concerning the association between cell phone use and motor-vehicle accidents comes from a report by Redelmeier and Tibshirani (1997).  In the study, the cellular-phone records of 699 individuals involved in motor-vehicle accidents were evaluated.  It was found that 24% of these individuals were using their cell phone within the 10-min period preceding the accident."

Yes, and they could easily have been inside their home (and thus not even driving) while doing so since a high percentage of accidents occur within a few miles (and thus the 10 minute window) of one's home.  So, this suggests that you must wait at least 10 minutes after you use a phone before you drive?  Is that like waiting 30 minutes after you eat before you swim?

Just because 1/4 of the accident victims used a phone within 10 minutes of the accident does not establish a causal relationship between the two.  I could rightly say that "It was found that over 99% of these individuals were wearing clothing at the time of the accident."  This does not establish a causal relationship between wearing cloths and traffic accidents.

Further, these statistics come from flawed and clearly biased information gathering mandated by various states and agencies in an effort to 'prove' that cell phones are dangerous.  We force officers to ask "were you using your cell phone" but we don't ask "were you talking to a passenger" or "were you eating, or doing your nails, or reading a book, or changing the radio station, or hunting for a CD, or looking at a map, or paying attention to your crying baby, or breathing, ..." or any number of other activities.  Thus, all these statistics prove is that approximately 1/4 of the population uses a cell phone while driving.  So what?

2. Pg. 2 - Experiment 1 purports to show that cell-phone using drivers missed more traffic signals and had slower reaction times.  While this may be true, it doesn't show any correlation to an increase in traffic accidents.  There are a number of redundant traffic signal alerts (I see the red traffic light, plus I see the brake lights of cars in front of me, plus I see that I am getting closer to the cars in front of me, plus I see the cars around me slowing down, etc.).  If I miss one, I have a significant chance of seeing another.

Figrue 1 - Mean Reaction Time from the study
The reported change in misses and slowed reaction time does not necessarily translate to an accident.  For example, according to figure 1 the change in reaction time was approximately 50 msec which translates to about 4.4 feet if you are traveling at 60 MPH (60 MPH / 60 minutes = 1 mile per minute; 1 mile = 5280 feet; 5280 feet / 60 seconds = 88 feet per second; 88 FPS * 0.050 seconds = 4.4 feet).  Hardly significant.  If you are following so closely that 5 feet makes the difference between an accident or not, you have a much bigger problem (following too closely).

Also, the control group was not doing a task even remotely similar to the test group.  The cell phone users were required to discuss one of two specific topics that were 'hot' subjects at the time.  The control group could listen to a radio station of their choosing.  The assertion of the paper is that "cellular-phone use disrupts performance by diverting attention to an engaging cognitive context other than the one immediately associated with driving" (from pg. 1).  I hardly think that listening to Muzak is an equally "engaging cognitive context" compared to talking about a hotly disputed topic.  Perhaps listening to a talk radio station with an opposing view to your own would be a better choice.  Essentially the control group is doing nothing (certainly nothing cognitively engaging) during the supposed 'dual task' phase and is therefore not an effective control.  They could just as well have not been listening to the radio for all the 'distraction' it offered.

I believe that the detected changes in misses and reaction time are insignificant.  This fails to meet the stated assumption that "slowed reaction time to traffic signals and failure to notice them would contribute significantly to any increase in the risk associated with driving and using a cell phone."  Clearly a 4.4 foot difference in reaction time at 60 MPH would not contribute significantly to accident risk.  Likewise, the doubling of the misses is equally insignificant because both numbers are so small.  This falls into the "twice nothing is still nothing" category.  If I double your wages from $0.01 to $0.02 per hour, even though you got a 100% increase, that's still nothing to write home about.

The experiment may have shown that doing something cognitively engaging measurably distracts drivers.  However, it fails to prove that talking on a cell phone is the only such common activity (e.g. having the same conversation with a passenger).  It also fails to show that the level of distraction of even an engaging cell phone conversation posed a significant increased risk in terms of real-world numbers (e.g. 4.4 feet @ 60 MPH).

3. Pg. 3 - The experiment described under "Additional Control Condition" on pg. 3 contradicts some of the supporting studies cited on pg. 1 - "several studies using cell phones have found that working memory tasks (Alm & Nilsson, 1995; Briem & Hedman, 1995) ... disrupt simulated-driving performance."  You can't have it both ways.  Either the additional control condition was not sufficiently engaging (was not a "working memory task") or this experiment refutes the cited studies and therefore they should be suspect when considering whether memory tasks actually distract drivers.

Also, the additional control condition experiment still fails the "engaging cognitive context" test.  Listening to a book on tape is not cognitively engaging; it is a simple memory exercise, at best.  Something like solving math problems or some other actual thought-provoking process would be a much better control.  My kids routinely watch TV or listen to music while doing homework.  They can tell you what songs were on or what happened on the show, and they still did their homework at the same time.

4. Pg. 3 - Experiment 2 purports to show that "deviations in tracking would contribute significantly to any increase in the risks associated with driving while using a cell phone."  The research shows that the difference between easy and difficult courses (18 to 32) is much greater than the interference of talking on a cell phone (32 to 40).
RMS Tracking Error from the study 
In the case of the easy course the difference between single task, shadowing, and dual tasks is almost not measurable.  In the case of the difficult course, there is a difference, but again one has to ask how significant that difference might be in the real world.  Also, one has to ask if a reasonable driver would continue to talk on the phone (or change CDs, or read the paper, or look at a map, or eat a sandwich, etc.) while in a difficult driving situation (the 'human factor' I mentioned earlier).

Again, this experiment fails to show a significant risk increase while using a cell phone.  I'm not disputing that there is a measurable change, just the significance of the change.  Also, there is no direct causal link to accidents (e.g. the amount of 'drift' could easily be within one's own lane and thus a very low risk).  According to this experiment, we would be much better off to prevent people from driving on the difficult course than we would to discontinue cell phone use.

This experiment also shows that a user can easily carry on a casual conversation (the shadowing task) with little or no change in their ability to stay on course.  If most cell phone conversations do not involve significant cognitive effort, there is no significant risk increase.  The study fails to address whether the level of a typical phone conversation rises to the level necessary to cause even the insignificant change shown in the experiment.

It would be interesting to examine other states/countries that have completely banned cell phone use while driving to see if there is any significant decrease in accident rates pre- and post-ban.  Given that there is no correlation between rising cell phone use and traffic accident rates, I suspect that there is no significant correlation between banning cell phone use and decreased accident rates either.

Based on this particular research paper I maintain that there is no evidence that cell phone use has a significant causal link to increased accident risk while driving.  Further, I assert that even if you believe that this study shows a causal link between engaging cognitive activity and significant increased accident risk; nothing in this study shows that cell phone use is the only (or even a significant percentage of the) engaging cognitive activity commonly performed while driving.

The 'human factor' (to me, at least) explains the difference between studies such as this one, and the real-world traffic statistics.  I believe that the fabricated situations used to get the desired results in the studies are unreasonable.  For example, forcing the driver to continue a phone conversation in a driving situation where they would, in real life, terminate the call or pause the conversation so they could pay attention to the road.

This is akin to saying that freeway speed limits should be 20 MPH anywhere that the temperature ever drops below freezing because, as we all know, driving 65 MPH on an ice-packed road is not safe.  This ignores the human factor where the driver recognizes that the situation is unsafe and, despite the large "SPEED LIMIT 65" sign, elects to drive at a more reasonable 20 MPH given the road conditions.  Are there some idiots that will zoom along at 60 or 70 MPH on the ice?  Sure there are.  But those few idiots should not be the basis for restricting everyone to driving 20 MPH on the freeway all the time "just in case."

Fabricating a test where the driver fails because they are required to drive 65 in icy road conditions is an unfair test.  Likewise, requiring someone to continue a phone conversation under circumstances where they would actually terminate it is equally unfair.  The first test does not show the actual risk from ice on the road just as the second does not demonstrate that cell phone use while driving is dangerous.

I believe that this 'human factor' is actually the explanation for why research shows that cell phone conversations are distracting while the accident statistics do not show an increase.  I believe that the vast majority of people are not idiots.  They do not talk on the phone in hazardous situations.  They either hang up, or they ask the other party to hold for a moment while they extricate themselves from the situation.  I know I've done that on several occasions.

If we really want to 'outlaw' things that are major risk factors, let's start with banning driving anytime there is a heavy storm.  There are orders of magnitude more accidents in a single day caused by icy roads than the number of accidents caused by cell phones in a single day.  For example, in one 6 hour period (4/1/2008, 0600-1200) there were 130 accidents in Utah County alone.  There's no way you can show that many cell related accidents during any 6 hour period.  Cleary icy roads are significantly more dangerous than cell phone use, but we don't see anyone writing special laws to control the weather or ban driving when ice is on the road.

This is really not about safety at all.  It appears to me that this is driven by someone (or some group) who wants to vilify particular technologies.  They have some deep-seated phobia regarding cell phones and they want to ban them regardless of whether it is reasonable or justifiable.  They use studies with fabricated situations to 'prove' their point.  Sorry, but I just don't buy it.  Radios in cars proved not to be the terrible danger they were touted to be and likewise I hope that in a few years we will look back at the cell phone overreaction with the same amusement.

I would enjoy receiving a response to my analysis of your study.  Even more interesting to me would be some explanation of why there is no apparent correlation between the traffic statistics and the explosive growth of cell usage.  I would be happy to meet in person at your convenience to discuss this further if that seems more reasonable.