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Name: Eric S.
Status: student
Age: 14
Location: N/A
Country: N/A
Date: Monday, September 30, 2002

My Mom talks on the cell phone while driving. I want to prove to her that it is dangerous. What is the best way to test reaction times? I want to test her reaction time while driving and again while she is driving and talking. Thank you.

The study of human factors as they relate to driving a car is actually pretty complicated. The first step in any good scientific investigation is a literature search. This helps the researcher avoid repeating work that has already been done. In this case, a number of other researchers have already looked at the effect of mobile phones on reaction time.

The best on-line place to look for transportation-related research is the Transportation Research Information Service (TRIS) database. Go to to perform a search. The report I found is "Cell Phone Use While Driving in North Carolina", which was written by researchers at the Highway Safety Research Center at the University of North Carolina. It is available on-line at and reviews the research conducted on this topic.

In its conclusion, the report says:

"After examining the literature, it has become abundantly clear that talking on a cell phone while driving does elevate the risk of a crash. However, what is far from clear is the extent to which that risk increases. The laboratory simulation studies generally concur that using a cell phone does slow reaction times and degrades tracking abilities. The epidemiological as well as case studies of cell phone-related crashes agree that the risk rises when engaged in cell phone conversation while driving but disagree considerably on the magnitude of that increased risk. And whether hands-free cell phone use is safer than hand-held remains debatable."

So, researchers have pretty well shown in the lab that cell phone usage slows reaction time, but no one has definitively proven if it really makes a significant difference on the road. If the goal is to ban anything that can distract drivers, why not ban radios, CD players, navigation systems, ashtrays, cup holders, and passengers too? (I would have included necking, but the extinction of front bench seats in modern cars has pretty well eliminated that, at least while driving.)

I seem to recall reading a survey somewhere that asked people to rate their own driving skill and the skill of others. Most people rated themselves "good" or better while rating most others "fair" or worse. So, people tend to think they are a better driver than those around them. Obviously, this cannot be true since not everyone can be above average. On my personal 10-mile urban freeway commute, I often see vehicles being driven erratically as their drivers talk on the cell phone. This is especially irksome when their vehicle is 10 feet from my rear bumper, we are going 70 mph, and I can see them talking in my rear view mirror. But then, I use my own cell phone in the car because, hey, I am a good driver and can handle it...

Andy Johnson


Any real-time experiment (one performed while actually driving in traffic) that would convince her of your point would probably be dangerous. As you assert, driving requires concentration and attention on the part of the driver.

The next time your mom attempts to place a call while the car is stationary, immediately engage her in conversation, ask a lot of pesky irrelevant questions while she is attempting to dial, in other words, be a little obnoxious. When she asks you to stop. Ask her why. She is likely to tell you that your chatter is distracting her. Then you can respond that dialing in traffic is an activity that likewise causes her to divide her attention between dialing and driving.

If she sees your point, be polite, thank her, and resist the temptation to be an "I told you so" person. You can undo the lesson if you act impertinent. Good luck.

ProfHoff 490

I totally agree with you but I do not think that it is your responsibility to "test" your mother's reaction times. If they are slowed -- as I suspect they will by -- or if the "voice" on the other end distracts your mother -- doing the test itself could be hazardous. I would think the American Automobile Association (A.A.A.) or a local highway patrol office could provide you with some info. But do not get mom in trouble.

Vince Calder

Hey Eric,

I have a great thing for you to do. Do not do this in the car. It will work just as well in the kitchen. To test reaction time, rest a yardstick, 0 inches down 36 inches up, (vertically), on the end of a table. You are going to hold the yardstick. Mom is going to have the edge of her hand, pinky finger down, palm out ready to grab the yardstick. In other words her hand is resting on the table just behind the yardstick. Tell her that you are going to be sneaky and try to nudge the yardstick off the table. As soon as she senses it is moving she has to grab it. When she grabs it, read how many inches of ruler have slipped through her hand. Read from the bottom of her hand where it was resting on the table. You will have a distance in inches.

Now you have got to get your calculator out for this part. distance / 192 = t2 Distance is in inches where the hand grabbed the ruler. 192 is half of the acceleration due to gravity in inches. Divide distance by 192. This equals her reaction time squared, so you will have to take the square root of that number to get the actual reaction time. Average reaction time is about .33 sec. (As we get older it gets worse, but we do have driving experience on our side.) Give her an opportunity to do this three times and take an average. Then let her get on the phone with someone she enjoys talking to. Do the same thing. Be sneaky with the ruler drop and wait for the moment you think she might be distracted. (Remember, that is the whole point.)

See what the difference is. It might not be a lot but remember, a few seconds at 55 mph you are covering a lot of ground. Do not be snotty or I told you so-ish. Sometimes it is hard for us grown ups to see wisdom in our own kids. Remember, driving a car involves lots of little decisions made many times. If ever anyone is involved in an emotional conversation, they shouldn't be driving. Either stop the car or end the call and call back when you are at your destination. A really great present might a ear piece that mom can use her cell phone hands free. Then at least she will not have to concentrate on holding the phone as well as driving.

Also be aware that anything you do while driving can be a distraction, we have to use our judgement. Heck, I choked on a piece of toast once and almost wrecked the van. I do not eat breakfast in the car anymore either.

Tell mom I am proud that she has a son concerned enough and logical enough to approach this in a scientific way. Congrats to mom and you! It just might be fun to do a little science together in the kitchen.

Have fun. Use this as a learning experience not as a nyah, nyah moment.

Let me know how it all turn out.

Mrs. Croll

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