The following outlines the Inverse Gamma thresholds set in WisDOT’s instance to determine LOSS categories.
Injury/Fatal:
High Threshold: 75%
Low Threshold: 10%
All crashes:
High Threshold: 90%
Low Threshold: 10%
No injury crashes:
High Threshold: 90%
Low Threshold: 10%
WisDOT chose to use the inverse gamma distribution, which uses percentage-based thresholds. This decision was made due to the following advantages of inverse gamma thresholds:
Removes the possibility of negative crashes in rural low-AADT locations.
Produces thresholds that are easily interpreted and communicated to professionals, the public, and elected officials.
Allows for more flexible and fine-tuned threshold setting.