Version 2 of the Needs-Based Assessment of Trauma Systems (NBATS) tool quantifies the impact of an additional trauma center on a region. This study applies NBATS-2 to a system where an additional trauma center was added to compare the tool's predictions to actual patient volumes. Injury data were collected from the trauma registry of the initial (legacy) center and analyzed geographically using ArcGIS. From 2012 to 2014 ("pre-"period), one Level 1 trauma center existed. From 2016 to 2018 ("post-"period), an additional Level 2 center existed. Emergency medical service (EMS) destination guidelines did not change and favored the legacy center for severely injured patients (Injury Severity Score (ISS) >15). NBATS-2 predicted volume was compared to the actual volume received at the legacy center in the post-period. 4068 patients were identified across 14 counties. In the pre-period, 72% of the population and 90% of injuries were within a 45-minute drive of the legacy trauma center. In the post-period, 75% of the total population and 90% of injuries were within 45 minutes of either trauma center. The post-predicted volume of severely injured patients at the legacy center was 434, but the actual number was 809. For minor injuries (ISS £15), NBATS-2 predicted 581 vs. 1677 actual. NBATS-2 failed to predict the post-period volume changes. Without a change in EMS destination guidelines, this finding was not surprising for severely injured patients. However, the 288% increase in volume of minor injuries was unexpected. NBATS-2 must be refined to assess the impact of local factors on patient volume.