RELATIONSHIP BETWEEN V/C RATIOS AND ACCIDENT RATES. FINAL REPORT

This project sought to establish if there is a relationship between accident rates and volume to capacity ratios on rural highways. The data base for this study consisted of traffic volume data from 44 permanent count stations and traffic accident data in the vicinity of these stations. The study found that the highest accident rates occurred at nighttime during hours with the lowest traffic volumes. As volumes increased, up to V/C ratios of approximately 0.2, accident rates tended to decrease. The major component of the hourly variation was found to be the much higher single vehicle accident rates at night. The sites studied in this project did not have sufficiently high traffic volumes to permit an examination of the full range of V/C ratios. Preliminary studies of several urban intersections and sections of urban freeways suggest that accident rates may begin to increase when the V/C ratios exceed 0.7. The study found that V/C ratios may be a useful safety analysis tool, especially at higher volume levels.