Heavy vehicle traffic and vehicle mix have a substantial impact on crash frequency and severity. The consideration of vehicle mix would improve predictive methods for crash frequency and severity. Improved methods will result in better use of the limited funds and resources available for improving the safety of the highway system and supporting performance-based approaches. NCHRP Web-Only Document 393: User’s Guide for Quantifying the Effects of Vehicle Mix on Crash Frequency and Crash Severity , from TR…