In the field of emergency medicine and trauma, accurately assessing and classifying the severity of injuries to optimize patient treatment and management is recognized as an important task. Therefore, this study conducted a comparative analysis of the Injury Severity Score (ISS) and the New Injury Severity Score (NISS) used to measure the severity of injuries in trauma patients. The ISS, introduced in 1974, is a widely used scale for assessing the severity of injuries in trauma patients. It evaluates the three most severe injuries across six body regions to determine overall injury severity. Despite its effectiveness, the ISS has a limitation in that it does not adequately emphasize multiple severe injuries within a single body region. To address this, the NISS was developed, focusing on the most severe injuries regardless of their location. Numerous studies are currently comparing ISS and NISS situationally to determine the appropriate scale for evaluating patient injuries. Therefore, as part of relevant research, this study utilized passenger injury data provided by the National Highway Traffic Safety Administration to derive ISS and NISS and analyzed their agreement using Cohen’s Kappa analysis. The analysis revealed a high level of agreement between the two scales regarding driver injuries, indicating minimal differences between them. The results of this study provide a reliable indicator of the agreement between ISS and NISS in evaluating patient injuries, which can serve as fundamental data for evaluating injury severity and establishing treatment plans in the fields of emergency and trauma medicine.