Some regions only record and track incidents above a certain threshold, such as those lasting longer than 30 minutes or those resulting in an injury. As Birenbaum (14) notes, the Manual on Uniform Traffic Control Devices(15) classifies incidents as “major,” “intermediate,” or “minor” based upon incident duration and other incident characteristics as noted below. These classifications could be used to calculate TIM performance more specifically for incidents based on their severity, duration, or overall impact.
Major incidents–traffic incidents involving hazardous materials, numerous vehicles, fatal crashes, and other natural or man-made disasters. These traffic incidents typically involve closing all or part of a roadway facility for a period exceeding 2 hours. Traffic control is implemented.
Intermediate incidents–affecting travel lanes for a time period of 30 minutes to 2 hours and usually require traffic control on the scene to divert road users past the blockage. Full roadway closures might be needed for short periods during incident clearance to allow incident responders to accomplish their tasks. Traffic control is implemented.
Minor incidents – disabled vehicles and minor crashes that result in lane closures of less than 30 minutes. On-scene responders are typically law enforcement and towing companies and occasionally highway agency service patrol vehicles. Diversion of traffic into other lanes is often not needed or is needed only briefly. It is not generally possible or practical to set up a lane closure with traffic control devices for a minor traffic incident (15).
In addition, classifications for injury severity could be similarly used to assess TIM performance. Injury severity classifications might include:
- Property Damage Only