This study presents an on-road evaluation of driver performance
when controlling in-car technology via a handheld or
voice-controlled interface. Participants drove with an experimenter
on public roads while making mobile phone calls, having brief phone
conversations, and playing tracks from a portable music player
using both types of interface. The test vehicle was an instrumented
2010 Mercury Mariner equipped with the Ford SYNC® system, which
allows for voice control of mobile phones and portable music
devices. Twenty-one participants were tested, including 12 younger
(19-34) and 9 older (39-51). All participants were owners of a
vehicle equipped with the voice-control system, and all used the
system regularly for phone calls and music playback.
Results indicated that handheld dialing and music track
selection tasks were of longer duration and were associated with
more frequent and longer glances to the interior of the vehicle,
more total glance time to the interior of the vehicle, higher
steering variance and maximum steering wheel velocity, and higher
subjective mental demand than when using voice control for the same
tasks. These differences were not found for conversation tasks. All
tasks had higher mental demand than baseline driving. Further,
older drivers had more difficulty maintaining vehicle tracking when
dialing and playing tracks using handheld controls, as seen in
steering variance and maximum steering velocity data. These
findings suggest that voice control of in-vehicle devices may allow
drivers to keep their eyes on the road longer, track their course
more consistently, and have lower mental demand than when these
devices are controlled manually.
