Improving Usefulness of Automated Driving by Lowering Primary Task Interference through HMI Design

Table 2

Dependent measures and description of categories/questions.

Measure	Description	Range
Level of interference with nondriving related task	Coding during automated manoeuvres; (i) Not distracted: driver does not perform task (1); (ii) Continuation of NDRT; (a) No reaction, continuation of NDRT (2); (b) Short glance ahead, continuation of NDRT (3); (iii) Alternating of NDRT and looking ahead (4); (iv) Interruption of NDRT until situation is completed; (a) Interruption of NDRT and looking ahead, magazine in hand (5); (b) Interruption of NDRT and looking ahead, putting magazine aside (6)
Monitoring ratio	The total duration of glances towards the HMI scaled to the duration of the automated manoeuvre.
Assessment of usefulness	How helpful was the HUD?; How helpful was the auditory output?
Visual workload	How much attention did you pay to the HUD?
Acceptance	Which system do you prefer?	—