We all know that cell phones are a distraction in cars. It is annoying—and downright frightening–to see people talking on their hand-held phones while driving especially when their behavior creates a hazardous situation for everyone on the road. In 2009 the National Safety Council (a non-profit) recommended banning all cell phone use. In December 2011 the National Transportation Safety Board also recommended banning all cell phone use in cars.
Pragmatically, banning cell phones use in cars is like stuffing a genie back into the bottle. There are certain obvious cases where cell phone use truly should be banned, such as teenage drivers and bus drivers, but there are a lot of people who depend on communicating while driving.
However, the research shows that most hazardous usage of a cell phone are for operations that have little to do with actually talking on a cell phone.
There is considerable research that shows that merely talking on a cell phone, whether hands-free or handheld is a hazard. At the same time, talking to a person in the front seat is a distraction, yet nobody is suggesting banning passengers from talking to the driver.
Two recent studies providedmuch needed insight to the subject of distractions and driver safety related to using cell phones. One is a study, sponsored by AAA, was conducted to rate the different forms of distraction. Another is a study performed by the Virginia Tech Transportation Institute for the National Highway Traffic Safety Administration. This last study evaluated the risk of different tasks related to cell phone use.
The AAA study put drivers in car simulators as well as actual cars to measure the effect of different types of distractions on reaction times and peripheral vision. This study is one of many that show that any form of talking puts a cognitive load on the brain and causes a degree of distraction. Also, anything that puts a load on the brain also tends to narrow our peripheral vision. That is, we literally see less when we are distracted.
Greatly distilling down the information obtained, this study showed the rank of distractions and gave the distraction level a score from 1.0 to 5.0. Here are the results:
- No distractions 1.0
- Radio On 1.21
- Audio Book 1.75
- Hands-Free Cell Phone 2.27 (talking only, not looking at the cell phone)
- Talking to Passenger 2.33 (passenger unaware of surroundings)
- Hand-Held Cell Phone 2.45
- Speech-to-Text 3.06 (dictating a text message)
- Operational Span Task 5.0 (solving a math problem while trying to remember a fact)
The remarkable fact of the study was that the concentration level for a hands-free, speech-to-text operation was higher than expected. Just because a task is hands-free does not mean that it is not dangerous.
This test did not measure the ability to do accident avoidance, so the fact that a hand-held cell phone user only has one hand on the steering wheel was not part of the “distraction.” Obviously, it is less safe to drive with one hand on the wheel than two.
The score is a figure of merit that roughly represents the probability of having an accident.
Virginia Tech & NHTSA Study
The study by Virginia Tech is quite interesting because it was a “naturalistic” study. They actually tracked real users–about 200 drivers–over the span of one month, who were monitored while driving to see which tasks were resulting in collisions, near collisions, and collision avoidance maneuvers.
Prior to this study, there were many studies that relied on statistical extrapolation, or highly controlled lab scenarios. The trouble with statistical extrapolation is that an accident is a relatively rare event that has only a loose correlation with any particular behavior. The reliability of the statistical extrapolation relies on a lot of assumptions. The results of previous tests pegged the risk of a crash while talking on a cell phone at anywhere between no effect to about 4X increased risk. The trouble with the lab scenarios is that it did not take into account the ability of the driver to modulate their concentration depending on the driving conditions. In real life, a driver with good judgment will tell the caller that they cannot talk, or they will wait until it is safe, or simply ignore the talker on the other end when there is a challenging driving situation.
The Virginia Tech study found that the risk of an accident depended on the specific task associated with the cell phone. Again, greatly distilling down the results, here is the relative risk of cell phone related tasks relative to just driving:
Task Risk Range (with 95% confidence)
- Hand-Held Cell Phone Use 1.20 – 2.49
- Portable Hands-free Cell Phone Use 0.49 – 2.30
- Integrated Hands-free Cell Phone Use 0.25 – 1.31
- Visual and Manual Subtask 1.91 – 4.51
There are variations for more subtasks, but the main conclusion corresponds to common sense. Without a doubt, hand-held cell phone use will increase your risk of a crash. Without a doubt, any task involves touching the phone and taking your eyes off the road will greatly increase your risk of an accident.
One very important point to note is that this naturalistic test allowed the drivers to pick when they chose to take on a task. They can use their judgment when it is relatively safer to do a task. From prior studies, and the AAA study, there is no doubt that any task other than driving raises the risk of an accident. If you attempt to execute a visual and manual task while in an intense driving situation, then your risk goes up dramatically. Even talking hands-free is a distraction, so the driver must exercise good judgment when they choose to do any task other than driving.
Putting things in perspective, accident risk depends on a number of other factors.
Each 1 MPH faster raises the risk by 5%. This is compounded, like interest rate, so driving 10 MPH faster raises your risk by a factor of 1.62. Driving 20 MPH faster raises your risk by a factor of 2.65.  However, if you are driving about 5 MPH faster than the prevailing speed of traffic then the risk goes up much more steeply.
Choice of Roads
There is huge variation in accident risk depending on the choice of road. The accident rate on a complex urban arterial road is about 10 times higher than a freeway.
Drivers under 25 years old are at 3X risk of having an accident. Old age is not a big problem until the driver gets quite old – around 70 years old.
Men get in more fatal accidents. Women get in slightly more fender benders.
In California, a blood alcohol concentration of 0.08 is the legal limit, but any amount of alcohol is dangerous. A legally drunk driver, about two drinks for most people, is about equal to a teenage driver.
BAC Relative Risk
- 0.00 1.0
- 0.05 1.8
- 0.08 3.2
- 0.12 7.1
- 0.21 30.5
All drivers think they are better drivers than they really are.
Some driver’s have mental deficits and anger issues that make them far more dangerous than the rest of the population. 
Citations for moving violations predict how likely you will be to get in an accident. 
When you look at the risks and the carnage on the roads, it is questionable whether humans should be driving cars at all. Talking on cell phones is about the same cognitive load as talking to someone in the front seat. Should talking to a passenger be banned? Listing to an audio book is slightly less cognitive load as a conversation, but the driver might be listening to the audio book close to 100% of the time. Should audio books be banned from cars? A teenage driver is about the same risk as a legally drunk driver. Yet, a young driver has to actually drive in order to learn how.
Here is what we know: Hands-free is better than hand-held and hand-held usage is easier to enforce. Texting while driving is dangerous, worse than driving drunk. That should be banned. Trying to find your cell phone to answer a call is dangerous, but if the driver uses good judgment, then it is a limited hazard. The Virginia Tech study shows that driver judgment is a big factor, but even with typical driver judgment, visual and manual tasks will cause more accidents. We also know that talking hands-free is not as safe as driving without distractions, so a driver should never assume that a hands-free task is risk-free. Just because it is not illegal does not mean it is safe. A hands-free task is merely less distracting than a visual task.
Until we have self-driving cars, it is reasonable to ban the worst offenders: hand-held phones and texting.
 http://www.vtti.vt.edu/featured/052913-cellphone.html Fitch, G. A., Soccolich, S. A., Guo, F., McClafferty, J., Fang, Y., Olson, R. L., Perez, M. A., Hanowski, R. J., Hankey, J. M., & Dingus, T. A. (2013, April). The impact of hand-held and hands-free cell phone use on driving performance and safety-critical event risk. (Report No. DOT HS 811 757). Washington, DC: National Highway Traffic Safety Administration
 https://www.aaafoundation.org/sites/default/files/MeasuringCognitiveDistractions.pdf Measuring Cognitive Distraction in the Automobile, June 2013, AAA Foundation for Traffic Safety
http://ec.europa.eu/transport/wcm/road_safety/erso/knowledge/Content/20_speed/speed_and_accident_risk.htm European Road Safety Observatory
 http://onlinepubs.trb.org/onlinepubs/ctbssp/ctbssp_syn_4.pdf Commercial Truck and Bus Safety, Individual Differences and the High Risk Commerial Driver, Synthesis 4, TRANSPORTATION RESEARCH BOARD, 2004