keep an eye on the driving environment (Safety Science, 2014).
That extra pressure might increase stress and error.
“You remove some of the physical and mental tasks, but load
up a bunch of other mental tasks,” Stanton says. “What is the
trade that’s being made?”
Given a nearly infinite combination of driver personalities,
road conditions and vehicle technologies, the answer is anything
but straightforward. In a study using a driving simulator, for
example, Stanton found that adaptive cruise control — in
which a car maintains a safe following distance from the vehicle
ahead of it — can reduce a driver’s mental workload and stress
levels (Ergonomics, 2005). However, that technology also caused
a reduction in drivers’ situational awareness. And while a lower
mental workload may be a good thing in tricky traffic jams, it
could cause problems if drivers totally tune out.
Indeed, driver disengagement is a serious concern for
automated-car designers. Users in such vehicles are expected
to tune out. After all, the appeal of such cars is that they can
transport us to and fro without our having to do the hard work.
But that presents a problem for our busy brains.
“You change from being an active ‘doer’ to being a monitor,”
Strayer says. “And that turns out to not be one of our best skills.”
Detached from the activity of driving, most people soon
begin to experience “passive fatigue,” says Gerald Matthews,
PhD, a psychologist at the Applied Cognition and Training
in Immersive Virtual Environments Lab at the University of
Central Florida. That cognitive muddling can be a big problem,
Matthews says, if the driver has to take back control of the
vehicle (when leaving a highway “platoon” of automated cars to
re-enter city streets, for instance — or, in a worst-case scenario,
if automated systems fail).
In a series of studies using driving simulators, Matthews and
his colleagues have induced passive fatigue in volunteers as they
experience a ride in an automated car. When control is suddenly
handed back to the volunteer, people with passive fatigue react
more slowly when they have to brake or swerve to avoid a crash.
Worse, Matthews says, passive fatigue kicks in alarmingly
quickly. “We can see signs of it after only 10 minutes,” he says.
In a fully automated system, the car itself does all the
work and passive fatigue poses little problem. But right now,
automakers are developing systems in which drivers handle
some, but not all, of the driving duties, such as navigating
city streets while allowing the car to deal with a long, boring
stretch of open highway. Such partially automated systems are
precisely the ones in which passive fatigue is most dangerous,
many experts say. “Our biggest concern is that we’ll end up with
clumsy automation that solves the easy problems but leaves us
responsible for the hard problems,” Strayer says.
The weakest link
Researchers are still puzzling over the best ways to keep drivers
engaged when they use features such as automated braking and
The 2014 Mercedes Benz S-Class has technology that helps
drivers to automatically stay in their lane and adjusts speed to
maintain a safe following distance.