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Pages 66-80

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From page 66...
... 66 C H A P T E R   6 The original research plan was to modify and use the updated Roadside Safety Analysis Program (RSAPv3) as the main analysis tool to conduct the risk analysis from which the clear zone guidelines would be developed (25)
From page 67...
... Clear Zone Guideline Assistance Program 67   However, after further analysis, the modification of RSAPv3 was considered inefficient for this project. Most of the RSAPv3 programming was being replaced by the new encroachment models derived from the computer simulation data.
From page 68...
... 68 Development of Clear Recovery Area Guidelines the different encroachment conditions (vehicle type, encroachment speed and angle, and driver input) define different trajectories.
From page 69...
... Clear Zone Guideline Assistance Program 69   Figure 41 shows a mixed distribution for one design scenario at a given lateral offset distance. The distribution provides longitudinal distance versus probability density.
From page 70...
... 70 Development of Clear Recovery Area Guidelines The diameter of the trees and the distance between them are assigned as variables in the program. The probability of impact with each obstacle that intersects the longitudinal distribution is calculated as the area under the distribution with the width of the area equal to the vehicle width, W
From page 71...
... Clear Zone Guideline Assistance Program 71   Figure 44 presents an example of the point of departure (POD) cycling relative to the obstacles (trees)
From page 72...
... 72 Development of Clear Recovery Area Guidelines zone line. This exposure provides a projection or envelope that is mapped onto the longitudinal distance distribution to determine the probability of impact with a given tree at the clear zone line.
From page 73...
... Clear Zone Guideline Assistance Program 73   the right side of Figure 45. erefore, for this project, the adjusted prole width relative to the trajectory was set as given in Eq.
From page 74...
... 74 Development of Clear Recovery Area Guidelines The research team performed a small sensitivity analysis to explore how the separation between trees (closely tied to the tree density in the tree line) relates to the maximum impact angle that would ensure an impact with one tree [i.e., the maximum angle for which P(hit a tree)
From page 75...
... Clear Zone Guideline Assistance Program 75   The design (common) variables are used to fit the impact speed regression models for a given facility type, roadway and roadside terrain configuration, lateral clear zone distance, and longitudinal hazard location.
From page 76...
... 76 Development of Clear Recovery Area Guidelines later combined because the impact speed–injury severity relationship should be independent of facility type. The research team identified at least two possible ways to define the severity of a crash using this database: the AAIS variable and the AINJSER variable.
From page 77...
... Clear Zone Guideline Assistance Program 77   P( K+ A ) Impact Speed (kph)
From page 78...
... 78 Development of Clear Recovery Area Guidelines contained rollover events and fixed-object crashes. Moreover, the vehicle speed at rollover and the impact speed with the fixed objects were available.
From page 79...
... Clear Zone Guideline Assistance Program 79   Figure 53. Comparison of rollover severity with severity of impacting a fixed object.
From page 80...
... 80 Development of Clear Recovery Area Guidelines a rollover crash injury severity based on the relationship derived from the NCHRP Web-Only Document 341 crash database (3)

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