DOI: 10.4121/de7105b7-6200-4e9b-bc17-db3613bef6a7.v1
title: Supplementary material for paper: "Passengers Perceive more Uncertainty in Fully Automated Cars than in Manually Driven cars : An Online Crowd-sourced Animation study under Mixed Traffic Conditions"

description: <strong>Abstract</strong>Automated cars have the potential to improve road safety and reduce traffic congestion. Not all objective benefits are perceived this way by society. Passengers may feel uncertain about the behavior, reliability, and intentions of fully automated cars, which can affect their overall experience. This study investigates the amount of psychological uncertainty that passengers perceive in fully automated and in manually driven cars. Using a crowd-sourced approach, participants reviewed scenarios in which the only difference was whether they were passenger in a fully automated car or in a manually driven car. Participants rated their perceived uncertainty after each scenario. The results show that passengers generally perceive higher psychological uncertainty in fully automated cars. The passenger's trust in the capabilities of a fully automated car seems to influence the psychological uncertainty that they perceive. Furthermore, the psychological uncertainty scores for different scenarios indicate a link between perceived risk and psychological uncertainty.<br><strong>Procedure & Participants</strong>To study perceived psychological uncertainty, we chose to let the participants use their own understanding of what they perceive as the feeling of uncertainty, in order to measure it in its purest form as it would be experienced by passengers under those conditions. We clearly defined the action that the passenger could be uncertain about, by asking: "At the end of the scenario, the fully automated car (/the driver of your car) changes to the left lane. How uncertain would you feel?". Perceived psychological uncertainty was measured using a subjective rating scale. After viewing each scenario, participants were instructed to use a slider scale ranging from "Absolutely not uncertain" to "Absolutely uncertain", but were not shown numerical values to minimize anchoring bias. The slider ranged from 0 ("Absolutely not uncertain") to 100 ("Absolutely uncertain"), keeping track of a numerical value in the back end. To understand and control individual differences, participants were also asked to rate their attitudes toward fully automated cars at the beginning of the experiment and to give an indication of how much day-to-day uncertainty they think they experience. This additional data helped assess whether people with a prejudice towards fully automated cars were more likely to feel uncertain about being a passenger in a fully automated car.<br>A total of 1437 people (Valid N) (M = 705, F = 718, Other = 8, Prefer not to respond = 6) from 84 countries participated in the study. We allowed contributors from all countries to participate except Venezuela (after a ban), as there were serious cheating incidents as identified by the researchers. All participants were 18 years or older (M = 35.55, STD = 11.00) and digitally provided their informed consent prior to participation. Participants were recruited through the crowd-sourcing service Appen (https://appen.com) and were later redirected to Heroku (https://www.heroku.com) to review the stimuli.