TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 299—Crash Reduction Factors for Traffic Engineering and Intelligent Transportation System (ITS) Improvements: State-of-Knowledge Report summarizes the current status of crash reduction factors for a variety of treatments and provides a summary of the “best available” crash reduction factors. The report also reviews the relationship between NCHRP Project 17-25, “Crash Reduction Factors for Traffic Engineering and ITS Improvements,” and other ongoing research studies that are either documenting or developing additional crash reduction factors.