Does a Confidence Level for Automated Driving Time Estimations Improve the Subjective Evaluation of an Automation HMI?

Hecht, Tobias; Danner, Simon; Feierle, Alexander; Bengler, Klaus · 2020 · Crossref

DOI: 10.3390/mti4030036

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Summary

This study investigates whether adding a confidence display to time budget estimations in Level 3 automated driving improves the subjective evaluation of the human–machine interface (HMI). As automated driving systems often have limited availability, users engage in non-driving related activities (NDRA) and require predictable information about remaining automated driving time to manage interruptions. However, these time estimations are prone to errors due to changing traffic conditions. The authors aimed to determine if displaying the confidence level of these estimations enhances usability, trust, and acceptance, and whether this effect differs between urban and highway scenarios. The research employed a mixed-design driving simulator study with 32 participants. The within-subject factor was the HMI concept: a baseline version showing only the time budget versus an advanced version including a confidence symbol. The between-subject factor was the driving scenario, with participants randomly assigned to either city or highway routes. The confidence display was developed based on a preliminary study and resembled a horizontal mobile phone connectivity bar, chosen for its familiarity and discrete steps. During automated driving sections, participants engaged in naturalistic visual NDRA. The experimental design included four automated driving periods per drive, with three featuring time leaps where the confidence level was reset to 100% after an adjustment. The results indicated significant effects based on the driving scenario: participants in the city scenario reported higher levels of frustration compared to those in the highway scenario. However, the presence of the confidence display had no significant impact on subjective evaluations, including usability, frustration, trust, or acceptance. Furthermore, most participants preferred the baseline HMI without the confidence symbol. The study found that while predictive time budgets are a user need, adding confidence information did not improve the user experience and was generally not favored by participants. The findings suggest that confidence displays for time budget estimations do not necessarily enhance the subjective evaluation of automation HMIs in Level 3 automated driving. The lack of positive impact may stem from the specific design or the nature of the information provided. The higher frustration in city scenarios highlights the challenges of complex urban infrastructure on user experience. These results imply that while predictive HMIs are beneficial, the addition of confidence indicators requires careful design consideration, as they may not provide the expected benefits in terms of user acceptance or trust. Future research may need to explore alternative visualizations or contexts where confidence information is more effectively utilized.

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Topics

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• automation
• trust calibration
• ehmi external hmi
• automation surprise
• acceptance adoption

Information type

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• Applied Guidance: design guidelines
• Empirical Findings: self report data