We report results from two experiments that examined the time course of vigilance decrements during a demanding multitasking scenario. Specifically, we implemented a novel paradigm in two experiments in which a total of 123 participants performed a go-no-go target detection continuous performance test (CPT) task simultaneously with a driving-based tracking task. Growth curve analyses of the temporal trajectories of performance of both tasks revealed vigilance decrement effects that varied across CPT and tracking measures, and between different target presentation rate conditions. Our findings highlight the importance of executive function, arousal, and motivation in such dual-task performance and support a multifaceted approach combining elements from the cognitive overload, cognitive underload, and opportunity-cost models of vigilance decrements. Insights from this work can inform the design and development of complex operator--system interfaces and thus increase safety and effectiveness for operators during mission-critical situations.