An advanced automatic collision notification system (AACN) called “D-Call Net” started operation in Japan at the end of 2015. D-Call Net reports both the location of the accident and the probability of serious and fatal injuries calculated based on event data recorder (EDR) information such as the collision direction, delta-V, seatbelt usage, and whether multiple impacts occurred. This information is sent simultaneously to fire departments and emergency responders at hospitals operating air ambulances to shorten the duration before a doctor reaches the injured as much as possible. The probability of serious or fatal injury used by D-Call Net was calculated by Toyota Motor Corporation and Nihon University based on 2.8 million items of crash data in Japan. This probability was developed using only driver side data, and is also applied to the passenger side. The recommended threshold for dispatching a doctor to an accident site is currently set to a 5% probability of serious or fatal injury, which means that the under-triage (UT) rate does not exceed 10%. This research investigated 374 accidents notified via D-Call Net to determine whether the current threshold of 5% is appropriate. This investigation found that the UT rate was 0%, the over-triage (OT) rate was 29%, and that the correct judgment was made in 71% of cases. These results satisfy the targets set when operation of the system started (UT: 10%, OT: 61%). This paper also discusses the appropriate threshold for dispatching doctors via D-Call Net to further reduce the rate of unnecessary emergency dispatches.