Automotive User Interfaces and Interactive Vehicular Applications

incorporate natural breakpoints will only influence performance
when users set appropriate priorities (i.e., “safety first”).
A second problem is to choose the right amount of breakpoints. In
a study where multiple breakpoints were provided we again found
that people use these breakpoints [12]. However, they did not use
all of them. This was probably because additional interleaving did
not improve performance strongly. Future work should point out
to what extent people can be guided in other ways (for example
using feedback [13]) in how they make performance trade-offs.
3. GENERAL DISCUSSION
In this paper we have taken the position that considering natural
breakpoints when designing in-car devices can be beneficial.
Interleaving at natural breakpoints offers users many advantages,
and people show a tendency to interleave here. Good design might
therefore encourage how frequent people interleave between tasks
by providing sufficient breakpoints. In the context of in-car
systems this might make the difference between a driver that
checks the road frequently and one that ignores the road
altogether. However, there are limitations to this approach. Most
importantly, drivers who don’t set safety as their priority tend to
ignore cues for interleaving. It is therefore important to make
them aware of the impact of multitasking on safety [see also 19].
A limitation of our studies is that they were conducted in a lab
setting. Surely in the real-world people’s priority is always to
drive safely? Unfortunately this doesn’t seem to be the case.
Closed test track studies have shown that people multitask in the
car, even when they have full knowledge about future safer (nonmultitask)
opportunities to perform a secondary task [8].
Similarly, in-car phone use is still observed frequently [18].
A complementary design solution to our work is to reduce drivers’
need to make performance trade-offs altogether. For example,
phones that have speech interfaces reduce the need to share visual
and manual resources between the phone and the road. However,
this approach also has limitations. First, the reduction of visualmanual
interaction does not necessarily make it safe to make a
phone call while driving (e.g., [10]). Second, even when “safer”
interfaces are available, users might not always choose to use
them, if the interaction style does not serve their objective. For
example, audio interfaces might reduce visual distraction, but can
also be slow to use compared to visual interfaces. Users might
therefore choose to use a visual interface over an audio interface if
they want to complete a task quickly [5]. Due to these limitations
it is still worthwhile to think about natural breakpoints in tasks.
4. ACKNOWLEDGMENTS
This work was sponsored by EPSRC grant EP ⁄ G043507 ⁄ 1.
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