• use a more realistic view of the simulated scenario
external to the vehicle. For example, instead of the
radar grid, consider to use a lanes representation,
which is more familiar to drivers’ mental model
and creates less visual cluttering;
• reduce the latency time in s1 sector of the HMI to
avoid the perception of a delay in the system’s
ability to detect obstacles;
• Avoid flickering in the graphical elements, which
can be annoying and distracting.
Area C (s4)
Evaluate moving the indication of position into
Area A, to be more consistent with the navigator
mental model users have
Area D
Regarding this area the following changes were
identified:
• do more to differentiate the signs of different
domains to minimize issues with signs
comprehension, for example road signs, weather
conditions, road types;
• associate relevant events occurring in the external
scenario with the displayed signs. For example,
when there is a crossroad in the external scenario,
display the crossroad sign on the SUaaVE HMI
prototype in the proper road sign dedicated sector.
5 GENERAL DISCUSSION
The SUaaVE first loop user test was fundamental to
understand if the methodology was adequate and
could provide sufficient feedback to redesign the
HMI for the second loop test.
The mixed (physical and virtual) apparatus used
to evaluate the usability of the HMI first version had
pros and cons.
In fact, it allowed participants to experience the
sensation of the automated driving of an AV and the
HMI, even if on a video basis. The displayed scenario
(e.g., urban, highway) and the relative use cases (e.g.,
crossroads, pedestrians, other vehicles manoeuvres,
traffic lights, roundabouts, road signs, vehicle
overtaking) were adequate for participants to project
themselves in the use of an automated vehicle, and to
collect very interesting data on the usability interface
issues.
On the other side though, it was not easy for
participants to fully experience the role of HMI in the
automated vehicle and express a preference without
interacting with a real HMI prototype.
In the second test loop, the HMI will be integrated
on the vehicle physical mock-up, positioning the
tablet (visualising the HMI) in the central upper part
of the dashboard, where a real central head-unit
typically is. This way participants will have the
opportunity to interact with the HMI.
Moreover, to enhance the fidelity of the
simulation, the second loop test will be performed
with the low level VHCD, and the participants will be
able to interact with the simulator, instead of
watching a video only and three 55” screens will be
used to create an immersive external environment.
This testing method (video based) remains
interesting at the beginning of the design process, as
in this instance for the SUaavE project and in such
situations where there is a need to conduct tests with
users remotely (e.g., working on international
projects, or realized by remote teams, or to test with
users who stay at home). In fact, although participants
were exposed to a video, from their subjective
comments, it was derived they felt immersed in this
low-fidelity virtual environment. They felt they were
able to appreciate the driving style of the reproduced
automated vehicle or to experience anxiety while
testing this AV and appreciate with the usage the
novelty of the automated driving.
The psychometric instruments and the Thinking
Aloud method were easily understood by participants
and did not cause any issues during testing or data
analysis. These instruments will be used again in the
next experiments.
The duration of the test was found to be long
enough to collect the data and not annoying
participants, so the next experiment will be designed
taking into account this duration as a reference.
6 CONCLUSIONS
Using a mixed-reality method, valuable insights on
participants’ evaluation of the usability of the first
cognitive SUaaVE HMI prototype were obtained.
The first loop test allowed highlighting pros and
cons of the HMI prototype.
Thanks to the identification of aspects considered
‘not intuitive’ or ‘less useful’, etc., recommendations
to enhance the usability of the HMI, were suggested.
The results will be useful to the redesign of the
SUaaVE HMI, as stated in the Human-Centered
Design process (ISO 9241-210:2010).
Moreover, the interesting lesson learned on the
methodological side on the video-based experiment
will be useful for possible next usability remote
evaluation needs it might occur in the future.