Horizontal Sightline Offset on a Curve (AASHTO)
AASHTO middle-ordinate clear-zone M = R(1 - cos(28.65 S/R)) an inside obstruction must clear for stopping sight distance.
Formula and source
M = R (1 - cos(28.65 S / R)) [half-angle in degrees]; inverse S = (R/28.65) arccos(1 - M/R); R to the inside-lane centerline.
The AASHTO A Policy on Geometric Design of Highways and Streets (the Green Book) horizontal sightline offset (middle ordinate), by name.
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