Encroachment data sets by Hutchinson and Kennedy and by Cooper, which are used as the foundation for current guardrail design procedures, are compared with each other and with crash databases. Discrepancies between the two data sets are examined and explained. These encroachment data sets are also compared to available real-world crash data, including new crash data from an ongoing study. The encroachment and crash data evaluations clearly indicate that guardrail length calculation procedures developed from the Cooper encroachment data provide more appropriate guardrail run-out length designs for minimizing injuries and fatalities associated with ran-off-road crashes.
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