Traffic Incident Management Performance Measures

Overall, the greatest benefits to an effective TIM program result from reduced incident duration, which is achieved through (1) reducing the time to detect incidents, (2) initiating an expedient and appropriate response, and (3) clearing the incident as quickly as possible.  TIM activities supporting the overall reduction of the incident timeframe directly affect safety, including secondary crashes and responder safety.

The figure below illustrates the incident management timeline from the Transportation Management Center: Data Capture for Performance and Mobility Measures Guidebook with specific points identified on the timeline (3).

View of Incident Timeline

Visually Understanding Clearance Times

One purpose for TIM performance measurement is to work to shorten the time expended between T0 and T7, thereby shortening the duration of the entire incident.  The table below identifies the key incident characteristics or “times” that can be obtained from the incident timeline (3). Overall, each minute of reduction in the incident response timeline has been statistically shown to reduce the occurrence of secondary crashes by 2.8 percent (4). Reductions to the overall duration of an incident can come from any of the five timeframes identified below.

Key Incident Characteristics from Incident Timeline

Measure Calculation Definition
Detection Time T1 – T0 Time between the incident occurring and the incident being reported. Detection time is not typically reported due the fact that the actual time the incident occurred is often unknown.
Verification Time T2 – T1 Time between incident being reported and the incident being verified. TMCs can typically assist with verification through use of their CCTV cameras
Response Time T4 – T2 Time between the incident being verified and the first responder arriving on scene. Law enforcement may not always be the first party to arrive on scene.
Roadway Clearance Time (RCT) T5 – T1 Time between the first recordable awareness of the incident by a responsible agency and the first confirmation that all lanes are available for traffic flow.
Incident Clearance Time (ICT) T6 – T1 Time between the first recordable awareness of the incident by a responsible agency and the time at which the last responder has left the scene.
Time to Return to Normal Flow T7 – T0 Time between the incident occurring and the traffic has returned to normal flow after all clearance activities are complete.