Want to drive safely? Talking to passengers may be okay, but talking on the phone isn't

[This article was originally published in January of 2007]

ResearchBlogging.orgMany many studies have repeatedly shown the dangers of driving while using a cell phone. Yesterday, while discussing a new law in Britain imposing heavy penalties not only for driving using a handheld phone, but also while using phones with hands-free kits, commenter Jan claimed that talking to a passenger was less dangerous than talking on a phone. I replied that I hadn't seen a study demonstrating that talking with passengers was any different from talking on a phone, and Jan provided a link to one such study.

Greta and I have both read over the study, and while we can't say from these results that talking with a passenger is unequivocally safer than talking on a phone, the research is impressive. The study comes from David Strayer's laboratory, the same group that has conducted a number of studies demonstrating the danger of driving while talking on the phone.

The researchers, led by Frank Drews, recruited 48 pairs of licensed drivers to participate in a driving / talking task. Drivers were selected randomly, and were paired with people they were friends with outside of the study. Each pair was told to talk about about a "close call" -- a time when their life was threatened -- either on a cell phone or in person, while one of the people drove an eight-mile course on a driving simulator.

The conversation topic was the critical portion of the task, because previous studies comparing conversations with passengers versus on cell phones have found driving ability to be equally impaired. In these tasks, typically the passenger and driver had to complete a difficult task such as thinking of a word that starts with the last letter of the word their partner said, often under competitive circumstances: arguably this is not analogous to a real conversation in a car. The "close calls" topic was chosen because other studies had revealed that it leads to naturalistic conversations.

Drivers were instructed to drive down a busy simulated highway and take the next exit -- a rest area 8 miles away. Half the drivers were told to lead the conversation (tell their own close call story) and half were told to respond to the passenger / cell phone's lead. Every driver also drove the course conversation-free. Here are the results:


Fifty percent of the drivers who were talking on the cell phone missed the exit, while only 13 percent of the drivers talking to the passengers did, a number not significantly different from the control condition with no conversation. What's more, the researchers analyzed the substances of the conversations, and found that in conversations with passengers, the discussion shifted to the traffic / driving situation nearly twice as often than in conversations on the cell phone.

The study appears to be a clear indication that conversations with passengers are safer than conversations on cell phones. Certainly the sort of casual conversation proscribed in this study appears to be less distracting to drivers talking to passengers rather than on phones.

That said, the study has some significant limitations. Arguably, the topic of the conversation -- a life-threatening situation -- is one that primes participants to be looking for danger. I'd be interested to see additional studies with different, more benign conversation topics. Also, since both participants were licensed drivers, these passengers might be more likely to alert drivers to dangers than, say, a child might. The study also doesn't address hands-free cell phone use. Perhaps this is just as safe as conversing with the passenger for this type of conversation. Finally, the study doesn't directly address driving safety, just the ability to complete a driving task.

Despite these limitations, it's the first study I've seen that demonstrates that passengers really do help drivers, and for that, it should be commended. A word of warning: this study is most certainly not an open ticket to gab away in any traffic circumstance. Any distraction will shift attention away from driving and can potentially be dangerous, and this study does nothing to refute earlier claims that the more difficult the conversation topic, the less safe it is for drivers.

Drews, F.A., Pasupathi, M., & Strayer, D.L. (2004). Passenger and cell-phone conversations in simulated driving. Proceedings of the Human Factors and Ergonomics Society, 2210-2212.


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By Ken Shabby (not verified) on 26 Mar 2008 #permalink

I wonder if it takes more attention to communicate without the nonverbal cues you get when talking in person; and this is why the phone is more attention-grabbing.

I wonder if this is because it takes more attention to communicate without the nonverbal cues you get from in-person chat.

Re: ...passengers really do help drivers, and for that, it should be commended.

Teenagers should be studied as a separate group in this regard. From my recollection, and supported by teenage driving statistics, a teenaged driver + talking on cell phone + increased number of passengers = increased chances of a fatal accident.

I think many drivers are still going to use cell phones regardless of known risks and laws. What would be interesting is a study that illustrates what can be done to reduce this risk with drivers that persist on celling and driving. Identifying what specifically about the introduction of the graduated licensed program that has reduced teenaged driving fatalities might point to a solution.

By Tony Jeremiah (not verified) on 26 Mar 2008 #permalink

what if the study participants are acting to a certain degree how they are expected to act?

I know I would be tempted to sway a study about cellphone usage by acting impaired, because I have this inbuilt bias against people who do it. How does one control for such biases?


I assume the control condition in the study somewhat addresses that. But probably something like administering a questionnaire about expected driving habits about various drivers and comparing them with their performance in the course would do the trick.

By Tony Jeremiah (not verified) on 26 Mar 2008 #permalink

I think another limitation is that the study was done on a simulator which may or may not reproduce behavior of a real-life driving environment. There is, after all, no actual risk in driving a simulator.

There was an exchange over at Island of Doubt on this subject a few days ago in which I expressed some reservations about studies that purport to show equal risk from using hands-free cell phones and just holding the phone up to your ear. That seemed counterintuitive, since driving one handed (or even no handed!) seems to me to add additional risk, over and above that of talking on the cell phone. That degenerated into a "you-must-be-an-idiot-cell-phone-user" type of exchange. I may, indeed, be guilty as charged, but that doesn't really answer all the questions about these studies. Of course I, too, have witnessed idiots doing stupid things with their cars while talking on cell phones, so I am not (repeat:not) defending the practice.

I wonder how much of this has to do with visualization? I know that when I'm talking to someone on the phone, I tend to be visualizing the person I'm talking to and am less aware of my surroundings. It's like I'm watching them and/or the conversation topic in a corner of my brain instead of in front of me. When I'm talking with someone in person, I don't need to do this since I can see the surroundings and the person I'm talking to. Could visualization be big competition for vision, hence the larger problem while driving?

My guess is that there is increased cognitive load associated with the poor quality and reduced acoustic bandwidth of phones.

I seem to remember someone putting forward the possibility that fellow passengers are to some extent also monitoring traffic and may pause during high risk traffic situations or may otherwise assist the driver in maintaining their awareness during the conversation.

I think I'd have to agree with comment #8. I think a good part of your brain is taken up with visualizing the person you're talking with, when talking on the phone. I'd like to see a study of the different patterns in a person's brain when they're talking with someone they can see versus talking to someone they can't see. I'd bet more of the visual center is taken up when talking to someone you can't see, and thus you're more oblivious to what's happening around you.

I've always wondered if the fact that a passenger in the car can see the traffic situation from moment to moment, and even if not actively helping the driver will naturally (and probably unconciously) pause for situations requiring more driver concentration is a part of this equation.

I think it would be interesting to see what the relative accident rate is when the non-driver is on a video phone to the driver - but with a view not of the driver's face but of the road ahead, with a fairly wide angle lens.

If my (very fuzzy) theory is correct, then for safe driving conversations the driver should NOT have a video feed, but the one they are talking to MUST. This also naturally precluded driver-to-driver phonve conversations.

This is a bit to the side of the topic, but...

I've seen countless articles/news stories on how cell phones cause lots of accidents. Given that millions of people today are using cell phones and that no one was using cell phones twenty years ago (or so), shouldn't that mean that the accident rate has increased significantly?? Has It??

Or is it the case that the same people that are distracted overly much by the cell phone would have been distracted by something else (I once saw a driver in traffic with a plate of food on their lap and a fork in their hand).

By Rich Beckman (not verified) on 26 Mar 2008 #permalink

Good points. I think there is social cueing and imitation as to 'what is important here for us to pay attention to', a shared consensus of focus in many situations, a matching-of-steps-as-we-walk-together, so to speak; and so the continual verbal input from someone to whom the traffic is simply not perceptually real may subliminally de-prioritize that too for the driver, unless the driver deliberately puts traffic references into the conversation so there can be a shared perception of it as real and pertinent.

We all have known people who annoy us by 'hogging' the focus of conversation to their own world, or who skip about from subject to subject leaving us behind: people who do not bother to 'walk in step'.

When, as here, one person has ONLY the conversation to attend to, and the other has to drive TOO while conversing, they have discrepant attention-focussing within their now-linked perceptual worlds, and a compromise must somehow (often not overtly) be negotiated. Any such compromise here is likely to reduce the driver's focus on traffic.

By Graham King (not verified) on 26 Mar 2008 #permalink

The results of the study make sense to me. When you have a passenger you have someone else with you who is able to point out potential problems with traffic, missing an exit, etc. Also, there may be other social factors at play. When a passenger is in the car the driver may feel some level of social evaluation, prompting him/her to be a better driver to demonstrate competence. Additionally, the driver may feel responsibility for the safety of the passenger, causing them to be more vigilant than they might when alone.
I intuitively agree with some of the statements above about talking on the phone being more attention-demanding due to the lack of nonverbal cues. I notice this effect in myself. One other thing: when having an in-person conversation with someone there seems to be less pressure to continue a constant conversation (quiet moments are not uncomfortable). When on the phone, however, there is more pressure to keep up a conversation, which may demand more attention.

Comments #8 and #11 are interesting, regarding the role of visual perception.

I would also suggest their concerns are also valid when the passenger is not in sight, but is in a position obvious to the driver (e.g. hidden behind the driver's seat). This would imply that it is easier to talk to the passenger who is within the driver's (perceived) spatial locality, whereas talking to on a phone is more difficult involving perception of a distinct spatial locality.

Thus it becomes a question of competing spatial maps.

I wonder if this is because it takes more attention to communicate without the nonverbal cues you get from in-person chat.

Posted by: mdreyer | March 26, 2008 11:30 AM

I think this is probably the case, plus the concentration it takes is more likely to over ride and blank out stimuli in the environment that would normally draw our attention.
Dave Briggs :~)

Cell phones contributing to visual interference in the form of change blindness is probably another potential source of accidents. One study did find differences in visual attention for person talking and not talking on mobile phones but rather than the conclusion of simply not detecting these hazards visually, they concluded that the difference is due to greater demands on the attention system. For example, one result showed that persons talking on the cell phone visually detected hazards to the same degree as persons who were simply driving, but time spent attending to these hazards (as measured by eye fixations) was less.

I really think that driver characteristics is a more important variable to consider though. Specifically as it concerns individual differences in information processing and driver experience.

Some people process information more verbally than visually; others more visually than verbally. Going solely by the nature of the input, cell phone talking is primarily a verbal task; driving is primarily a visual task. Cell phone users who are primarily verbal processors potentially represent a smaller percentage of cell users involved in car accidents, because talking on the phone doesn't place as much attentional demand on what is their dominant processing mode. Since most people are right handers that process language in their left-hemisphere (language-dominant hemisphere), and left handers process language in the right-hemisphere (visual-dominance hemisphere), there's some suggestion that at a proportion higher than the general population of left-handers, left-handed cell phone users may represent a disproportionate percentage of persons in accidents involving cell phones.

But on top of all these common cognitive processes, experience must play a role. As an example, its possible that professionals used to and/or trained for two-way communication while operating vehicles
(e.g., pilots, police officers, truck drivers), might have less difficulty in using cell phones while driving.

So most of these accidents may not be primarily a problem with cell phones, per se, but the result of persons who are attempting to perform a new skill (talking on cell phone) in the context of an older one (driving) that may or may not have already been acquired.

By Tony Jeremiah (not verified) on 27 Mar 2008 #permalink

I agree with JD.

There is another common (though less life-threatening) example:
You are talking to someone in the room with your kids making a lot of noise in the room. You can probably carry on the conversation.

Now put yourself on the phone: You almost always have to quiet the kids to understand the caller.