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Today’s vehicles are becoming highly automated, however, if the automation fails, drivers must take over control of the vehicle. Automation may fail as a result of known system limits (system-limit failure) or of malfunctions that are unforeseen by system designers (system-malfunction failure). The aim of this research was to quantify the differences between how these two failure types influence driver takeover performance and monitoring behaviors. In a simulator with SAE Level 2 driving automation, 18 drivers experienced both a system-limit and system-malfunction failure while engaging in a secondary task. Results show that drivers put their hands on the wheel 0.62 s sooner and took over 0.51 s faster for the system-limit failure compared with the system-malfunction failure. Eye tracking data revealed that the percent of time looking at the secondary task display was 12.7% lower and the percent of time looking at the roadway was 11.2% higher before the system-limit failure compared with before the system-malfunction failure. Given that takeover performance and monitoring behavior differ significantly based on failure type, a distinction should be made in the literature between system-limit and system-malfunction failures, and comparisons between previous studies using these failures should not be done without considering this distinction. Furthermore, as SAE Level 2 vehicles are currently available to consumers, efforts should be focused on supporting drivers’ mental models of automated systems, so that drivers are able to successfully predict system-limit failures.

Much of the existing research on drivers’ understanding of adaptive cruise control (ACC), a type of advanced driver assistance system, was conducted several years ago. Through an online survey, this study aimed to assess ACC knowledge among ACC owners and non-owners now that this system is more widely available. Along with knowledge of ACC features and limitations, demographic information, experience with technology, and experience with ACC (for owners) were also collected to investigate which factors predicted knowledge of ACC features and limitations. Results showed that owners today may have a better understanding of some of the main limitations of ACC compared with research conducted over 10 years ago. However, a large percentage of owners still had misperceptions about their ACC system. While owners had a slightly higher percentage of correct answers overall, they did not differ from non-owners in their knowledge of limitations. As this technology is becoming more common, even non-owners may be becoming aware of common limitations; owning and using ACC does not seem to result in a better system understanding. Higher income was associated with a higher percentage of correct responses on the ACC knowledge questionnaire for both owners and non-owners, and for non-owners, higher education level was also significantly associated with a higher percentage of correct responses. Future research should focus on developing training materials that are accessible to all drivers, so that drivers in lower education and income groups are also supported to understand how advanced driver assistance systems work and benefit from these technologies.