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HOW many different things can you do at once?

One American president supposedly couldn’t walk and chew gum at the same
time, but we all have our limits. One of the few things that cognitive
psychologists agree on is that human information processing capacity is tightly
constrained. The brain is not incapable of doing two things at once, but if they
both require conscious attention there will be a price: you won’t do them as
well together as you would separately.

So why do so many people think that it is safe to conduct a telephone
conversation while driving a car? Great play has been made of the idea that
“hands-free” phones allow drivers to safely use a mobile phone. This argument is
literally brainless, because it completely ignores the fact that it is not just
your hands that are involved in these activities. You use your brain both to
control a car and to conduct a telephone conversation. What is needed is a
“brain-free” phone—though to judge from some inanities I have overheard
this may not be entirely unrealistic.

Another specious argument is that phoning can be no more distracting to
drivers than listening to the radio or talking to a passenger. This completely
ignores differences in the mental demands of these activities. Listening to the
radio doesn’t require me to participate in conversation when I need to attend to
a road hazard. And most car passengers will pause in their speech—or their
demands for a response—when they see that the driver needs all their
attention.

The caller at the other end of the phone, however, who is cheerfully
oblivious of the driver’s situation, might well make demands on the limited
attention of the driver at a critical moment. Telephone protocol also obliges
drivers not to pause for thought. While you can think and drive, explaining
Fermat’s last theorem as you negotiate a difficult junction is not
recommended.

Strong evidence that phoning while driving is dangerous comes from Donald
Redelmeier and Robert Tibshirani at the University of Toronto. They studied 699
car drivers who had been involved in a collisions and who also owned a mobile
phone. By scrutinising their phone bills, the drivers’ statements and police
records, they established that the risk of a collision when you’re using a
mobile phone is more than four times as high as when you’re not (The New
England Journal of Medicine, vol 336, p 453). For users of hands-free
phones, the risk of collision appears, if anything, higher than for hand-held
phones—nearly six times the level when not using a phone. Who knows,
perhaps hands-free phones enable drivers to risk more difficult manoeuvres?

The debilitating mental costs of telephoning will also be obvious to anyone
who’s tried making their way along a crowded pavement. Those with a phone
clapped firmly to their ear are rendered effectively decorticate by the demands
of the conversation. On they march, zomboidally failing to emit or respond to
the usual cues by which pedestrians avert collisions. I’m reminded of my travels
in Costa Rica, where drivers have to weave their way around huge potholes, many
large enough for a person to hide in. There, local wisdom has it that the police
detect drunks because they drive in a straight line.

No one wants pothole-bound drunks or gum-chewing presidents behind any wheel.
It’s simple: drive, don’t phone.