Accident records involving guardrails were analyzed and summarized.

Guardrail-related accidents comprised a significant percentage of interstate and parkway accidents, particularly those resulting in fatalities. Guardrail involvement in accidents was much less on primary and secondary highways than on interstates and parkways.

The severity of guardrail-related accidents was higher than the average severity of all accidents. The severity of guardrail-related accidents was higher on the primary and secondary system than on the interstate and parkway system.

Guardrails have not been very successful in redirecting vehicles parallel to traffic. The largest number of severe injuries involved vehicles vaulting over the guardrail Increased angles of impact with the W-beam guardrail resulted in accidents of higher severity due to a higher percentage of vehicles vaulting the guardrail. Vehicle penetration through the W-beam guardrail was limited mostly to heavy trucks.

The W-beam guardrail as railing on short bridges on primary and secondary highways is another problem area which may be minimized with the use of the Thrie beam guardrail.

Collisions with the guardrail end had a much higher severity than collisions downstream from the leading end. The buried end treatment provided a significant improvement over the blunt guardrail end; ramping and subsequent rollover remain as the major cause of high severity accidents with the buried guardrail end.

No accident experience is available for the new breakaway cable terminal.

The severity of collisions with concrete median barriers has been considerably less than with W-beam barriers; this is true primarily because vaulting or breaking through the barrier has been eliminated by the concrete type of barrier.

Guardpost-type barriers, remaining from previous times, do not provide effective protection. Guardposts connected with cables were not effective because vehicles tended to go over or through the barrier.

Report Date


Report Number

No. 442

Digital Object Identifier



The contents of this report reflect the views of the author who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Bureau of Highways. This report does not constitute a standard, specification, or regulation.