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• AV disengagement on public roads dominated by causes due to a planning issue. • AV disengagement induced by lacking certain numbers of radar and LiDAR sensors. • Drivers' take-over time impacted by disengagement cause and roadway characteristics. • To improve AV disengagements five or more radar sensors are needed. • Optimal number of LiDAR sensors to be installed is 3 or 4. Automated vehicles (AV) testing on the public roads is ongoing in several states in the US as well as in Europe and Asia. As long as the automated vehicle technology has not achieved full automation (Level 5), human drivers are still expected to take over the steering wheel and throttles when there is an automated vehicle disengagement. However, contributing factors and the mechanism about automated vehicle-initiated disengagement has not been quantitatively and comprehensively explored and investigated due to the lack of field test data. Besides, understanding human drivers' perception and promptness of reaction to the AV disengagement is essential to ensure safety transition between automated and manual driving. By harnessing California's Autonomous Vehicle Disengagement Report Database, which includes the AV disengagement data from field tests in 2016–2017, this paper quantitatively investigated the AV disengagement using multiple statistical modeling approaches that involve statistical modeling and classification tree. Specifically, the paper identifies the contributing factors impacting human drivers' promptness to AV disengagements, and quantitatively investigates the underlying causes to AV disengagements. Results indicate that current AV disengagement on public roads is dominated by causes due to a planning issue. The cause of an AV disengagement is significantly induced by lacking certain numbers of radar and LiDAR sensors installed on the automated vehicles. These thresholds of these sensors needed are revealed. Cause of disengagement and roadway characteristics significantly impact drivers' take-over time when facing an AV disengagement. AV perception or control issue-based disengagement can significantly extend drivers' perception-reaction time to take over the driving. The quantitative knowledge obtained ultimately facilitates revealing the mechanisms of the automated vehicle disengagements to ensure safe AV operations on public roads. [ABSTRACT FROM AUTHOR]

• Perceptions of AV safety were surveyed across 41,932 individuals in 51 countries. • Young, high-income, employed, and highly-educated males are the most optimistic about AV safety. • Western European countries are aware of AV technology, but are pessimistic about its safety. • Conversely, developing countries in Asia are the most optimistic about current and future AV safety. • AV safety optimism in risk-taking individuals and developing countries may reduce global disparity in road safety. Autonomous vehicles (AVs) are envisioned to reduce road fatalities by switching control of safety-critical tasks from humans to machines. Realizing safety benefits on the ground depends on technological advancement as well as the scale and rate of AV adoption, which are influenced by public perceptions. Employing multilevel structural equation modeling, this paper explores differences in perceptions of AV safety across 33,958 individuals in 51 countries. At the individual level, young males report higher perceptions of current AV safety and predict fewer years until AVs are safe enough for them to use. Since young males are more likely to undertake risky driving behavior, their positivity towards AV safety could lead to more rapid manifestations of safety benefits. Urban, fully employed individuals with higher incomes and education levels also report fewer years until AVs are safe to use. The multilevel model identifies country-level effects after controlling for individual characteristics. Developed countries with greater motorization rates and lower road death rates tend to have greater awareness of AVs but are more pessimistic about their present and future safety. Individuals in developing countries that face greater road safety challenges, particularly involving 2- and 3-wheeled vehicles, predict fewer years until AVs will be safe enough for them to use. Higher AV safety perception among the most risk-taking road users and in developing countries coincide with sociodemographic groups and geographic areas facing the greatest road safety challenges and most in need of improvement, highlighting a potential opportunity to reduce the global disparity in road safety. [ABSTRACT FROM AUTHOR]