OBJECTIVE: The goal of this meta-analysis is to investigate the effect of partial automation on mental workload, visual behavior, and engagement in nondriving-related tasks. BACKGROUND: The literature on the human factors of operating partially automated driving offers mixed findings. While some studies show partial driving automation to result in suboptimal mental workload, others found it to impose similar levels of workload to the ones observed during manual driving. Likewise, while some studies evidence a marked increase in off-road glances when the automated system was engaged, other work has failed to replicate this pattern. METHOD: 41 studies involving 1482 participants were analyzed using the PRISMA approach. RESULTS: No significant differences in mental workload were found between manual and partially automated driving, indicating no changes in mental workload between the two driving modes. A higher likelihood of glancing away from the forward roadway and engaging in nondriving-related tasks was found when the partially automated system was engaged. CONCLUSION: Although the adoption of partial driving automation comes with some intended safety benefits, its use is also associated with an increased engagement in nondriving-related activities. APPLICATION: These findings add to our understanding of the safety of partial automation and provide valuable information to Human Factors practitioners and regulators about the use and potential safety risks of using these systems in the real-world.