The Critical Incident Response Team (CIRT) functions as a subdivision of the Traffic Unit. CIRT members are highly trained in the field of traffic crash reconstruction and are on call 24 hours a day to investigate all crashes involving a fatality or critical injuries.

CIRT members utilize a wide array of equipment and technology to achieve their investigatory objectives. CIRT utilizes state of the art surveying equipment to measure a crash scene. A scale drawing of the crash scene in two or three dimensions can then be created using the data collected. Physical evidence from the crash scene is collected and examined by the CIRT members in order to ascertain the pre-crash state of each vehicle including, for example, whether or not head lights were in use at the time of the crash. CIRT members use advanced crash scene photography techniques to further document short-lived evidence. Pre-crash and post-crash data can also be collected from certain vehicles by using special equipment to interact with a vehicle's crash data recorder.

After the crash scene is thoroughly examined, CIRT members begin the detailed analysis of the data collected. Using mathematical and physical principles, CIRT members are able to use the collected evidence to determine facts such as the pre-impact speed of the vehicles, the vehicles' direction of travel, and a wide variety of other information depending upon available data. CIRT members also investigate alternate scenarios to determine contributing factors to the crash. If, for example, the pre-impact speed of a vehicle is calculated, CIRT members may also calculate the likelihood that the crash would have occurred if the vehicle had been traveling at the posted speed limit.

Because of the complex nature of the crashes investigated, CIRT members participate in monthly training as a team to maintain critical skills. Each team member must have a strong aptitude for mathematics. Team members also attend training on specialized topics, such as commercial vehicle, motorcycle, bicycle, and pedestrian-involved crash reconstruction. This advanced training allows CIRT members to testify as experts in both the criminal and civil courts of Tennessee and to complete a thorough and accurate investigation.

CIRT members are also called upon by the Criminal Investigations Division (CID) to assist with crime scene documentation for major incidents such as homicides or other complex crime scenes. CIRT members use the same equipment to create scale diagrams of the crime scene and to document the precise locations of key evidence.