Table 1 Rationale for TTF suggestions based on Lee et al. [17], Schoettle and Sivak [23]

Adopted in this study

No system problems occurred in automated mode

Lack of information^a (TTF1)

Anxiety about interacting with pedestrians and cyclists^b and anxiety about interacting with non-self-driving vehicles^b

Distrust due to lack of information about the surroundings and performance of automated system

Out of control^a (TTF2)

–

Distrust because the system assesses and functions on its own during operation without providing users with a choice

Unpredictability^a (TTF3)

Lack of confidence^a, anxiety about self-driving vehicles getting confused by unexpected situations^b and anxiety about system performance in poor weather^b

Distrust due to suspicions about the ability of the automated system to respond to its surroundings

Value incongruence^a (TTF4)

Machine-like^a and anxiety about self-driving vehicles not driving as well as human drivers in general^b

Distrust due to differences in driving styles between an automated system and human users in normal scenarios

Excluded from this study due to our study scope

Automated system problems during automated mode

Functional incompetence^a

Anxiety about safety consequences of system failure^b

Distrust due to system and vehicle problems

Anxiety about system security^b

Anxiety about vehicle security^b and anxiety about data privacy^b

Distrust due to security failure of the system

Automated system not in use

Fiduciary irresponsibility^a

Legal liability of users^b

Distrust due to the lack of clarity on the assignment of responsibility for an accident during automated driving

Anxiety about learning to use self-driving vehicles^b

–

Distrust due to problems caused by the user’s poor use of the system’s functions