This does not seem to be covered in AASHTO, but I’ve seen two equations used to determine the max deflection that can be used without a horizontal curve:
- arctan(1/design speed)
- arctan(60/design speed^2)
What is the appropriate criteria & reference to use for this situation? My application is a 4-lane local road with 35mph design speed.
You could use the MUTCD taper equations
V > 45 mph L = WS2/60
V >= 45 mph L = WS
and plug 1 in for W to give you a rate.
Above is a snippet.