A two-lane highway (two 12-ft lanes) has a posted speed limit of 45 mi/h and one section has both horizontal and vertical curves, as shown in the figure below. A recent daytime crash (driver traveling eastbound and striking a stationary roadway object) resulted in a fatality and a lawsuit alleging that the 45 mi/h posted speed limit is an unsafe speed for the curves in question and was a major cause of the crash. Evaluate and comment on the roadway design if superelevation and radius, as well as SSD and K (rate of curvature) values of the road was adequate in safety provisions. Use g = 32.2 ft/sec2. Use 1.47 as conversion factor from mi/h to ft/s. Formula of rate of curvature is K = L/A hint: compare values of fs, SSD, and K with allowable values listed below allowable fs for 45 mi/h at e = 7.0%: 0.15 allowable SSD for 45 mi/h = 360 ft allowable K at 45 mi/h = 79
A two-lane highway (two 12-ft lanes) has a posted speed limit of 45 mi/h and one section has both horizontal and vertical curves, as shown in the figure below. A recent daytime crash (driver traveling eastbound and striking a stationary roadway object) resulted in a fatality and a lawsuit alleging that the 45 mi/h posted speed limit is an unsafe speed for the curves in question and was a major cause of the crash. Evaluate and comment on the roadway design if superelevation and radius, as well as SSD and K (rate of curvature) values of the road was adequate in safety provisions.
Use g = 32.2 ft/sec2. Use 1.47 as conversion factor from mi/h to ft/s.
Formula of rate of curvature is K = L/A
hint: compare values of fs, SSD, and K with allowable values listed below
allowable fs for 45 mi/h at e = 7.0%: 0.15
allowable SSD for 45 mi/h = 360 ft
allowable K at 45 mi/h = 79
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