Max Deflection without Horizontal Curve

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:

  1. arctan(1/design speed)
  2. 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.