Guidelines for Guardrail Implementation (2009) / Chapter Skim
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Pages 2-10
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From page 2... ...
2Ideally, highway designers would be provided with detailed guidance for determining when guardrail is needed and the barrier performance level appropriate for any highway route. This sort of guidance must be based upon an economic analysis of guardrail implementation.
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From page 3... ...
3formation for supporting an economic analysis of proposed safety improvements. Note that the lack of crash history at a site does not mean there is no risk of future crashes.
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4A vehicle leaving the roadway within the hazard envelope will strike the hazard, provided that lateral extent of encroachment is sufficient to reach the hazard. The effective lateral offset of the hazard is different, depending on the zone within which a vehicle encroaches, as shown in Figure 1.
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From page 5... ...
where CC = Estimated annual crash cost; Ef = Annual encroachment frequency; and AC(C wv θψ ) = Crash cost of a collision involving a given vehicle type w, speed v, angle θ, and vehicle orientation Ψ.
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From page 6... ...
6median shoulders included in the Hutchinson and Kennedy study were on the order of 4 to 6 ft (1.2192 to 1.8288 m) , while outside shoulders on the highways studied by Cooper ranged from 0 to 13 ft (0 to 3.9624 m)
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From page 7... ...
for adjustment of encroachment rates for horizontal curvature and vertical grade is a study by Wright and Robertson (10)
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for encroachment frequency to correct for under-reporting can be obtained by multiplying the Y-intercept by the fraction of observed encroachments that were in excess of 13.2 ft (4 m)
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From page 9... ...
probability of injury produces a nonlinear relationship between crash severity and impact speed. The severity of a crash must be linked to the object struck, as well as the speed, angle, orientation, and vehicle size involved in the crash.
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From page 10... ...
initiated. As a result, the Monte Carlo procedure will normally give slightly different answers as a run is initiated even though the input may be unchanged.
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