Safety Performance Functions (SPFs) are…

• A. A ratio of the effectiveness of one condition in comparison to another condition
• B. A single crash event
• C. Statistical base models used to estimate the average crash frequency for a facility type with specified base conditions
• D. A calibration method for adjusting forecasts

Answer: (C)

Safety Performance Functions are statistical base models used to estimate the average crash frequency for a facility type with specified base conditions. They come from analyzing crash histories across similar road types and incorporate factors such as traffic exposure, road geometry, and environment to predict how often crashes would occur under those baseline conditions. This baseline estimate is what planners compare against actual crashes and then adjust for changes in conditions using crash modification factors. That combination—a data-derived model that yields expected annual crashes for a given facility type and conditions—is what makes this option the best description.