HIGHWAY GUARDRAILS: SAFETY FEATURE OR ROADSIDE HAZARD?

On the basis of reported accident data, from 50 to 60% of guardrail accidents involve an injury or a fatality. From this highway engineers have concluded that guardrail installations are a roadside hazard and should be used only when absolutely necessary. On the other hand, by using a more in-depth study of accident data and estimates of the frequency of unreported accidents, a more positive view of guardrail performance is projected. Specifically, unreported guardrail impacts represent approximately 90% of the total impacts, with the other 10% being reported. Assuming no injuries or fatalities in the unreported drive-away accidents, only 6% of all guardrail impacts involve any injury or fatality. Furthermore, analysis reveals that terminals, as opposed to segments of typical lengths, are overrepresented in the accident data, comprising up to 40% of the guardrail accidents resulting in fatalities or injuries. Also, clinical data indicate that many of the 6 percentile accidents resulting in injuries or fatalities involve (a) guardrail installations that are obsolete, improperly constructed, or inadequately maintained, (b) noncrashworthy ends, or (c) collisions that are outside the practical design range of modern guardrail systems. It is concluded that properly installed and maintained longitudinal barriers may be successfully performing in 97 to 98% of all design range length-of-need impacts, with only 2 to 3% of the impacts causing occupant injuries or fatalities, a stark contrast to the erroneous 50 to 60% based on only reported accidents.