What is the purpose of the Calibration Factor (C) in safety analysis?

• A. Determine road geometry
• B. Adjust crash frequency predicted by SPF to account for spatial and temporal differences
• C. Predict weather
• D. Rank countermeasures

Answer: (B)

The Calibration Factor C is used to tune the predicted crash frequency from the Safety Performance Function to fit the local crash experience. The SPF provides a baseline forecast based on exposure and road characteristics, but real-world crash counts vary by location and time due to factors the model doesn’t capture. C scales the SPF output so predictions reflect those spatial and temporal differences. For example, if the SPF estimates 10 crashes for a site over a period but observed data show 15, applying the calibration factor increases the forecast to align with the actual level. This keeps the analysis grounded in local data. The other options don’t fit because determining road geometry, predicting weather, or ranking countermeasures aren’t the purposes of this calibration part of the safety analysis.