The massive flows of containers through seaport terminals create bottlenecks and long total truck turnaround times (TTTTs). Because long TTTTs adversely affect terminal operators and road hauliers alike, the purpose of this study is to evaluate how automated gate services (AGSs) affect TTTTs using data from the real-world implementation of AGSs in a seaport terminal. Data were analysed using an innovative application of queuing theory. Following implementation, the overall mean TTTT decreased by 17% and the overall mean queuing time by 38%, and variation in queuing time during peak hours also decreased. For theory, our study has shown how queuing theory can be applied in capacity analyses and contributed a new understanding of how AGSs can decrease queuing time and TTTTs in a seaport terminal. For practice, our findings provide decision-makers with evidence of how AGSs decrease TTTTs and consequently reduce stress, reduce idling, and increase profit.