SEP File Equations

I'm developing a company standard SEP file.  I'm having difficulty with the equations for Superelevation Runoff and Tangent Runout.  I'm wondering where the equations came from?  They're not familiar to me and do not match AASHTO GDHS Equations 3-23 & 3-24.  I'm trying to validate the provided equations and without knowing where it came from, it is difficult.  I think I can use the intrinsic variables to come up with an appropriate value.  When I calculate with the current equations, I am not getting the desired results.

The SEP Preference File Settings Manual indicates the equations are as follows:

RUNOFF LENGTH

= (0.24 * ((0.0571 * (Vd * Vd)) - (4.84 * Vd) + 306.74)) + ((Wn * 2) * ((e - 2)/100) * ((0.0571 * (Vd * Vd)) - (4.84 * Vd) + 306.74))

RUNOUT LENGTH

= (0.24 * ((0.0571 * (Vd * Vd)) - (4.84 * Vd) + 306.74))

WITH INTRINSIC VARIABLES

  • e = Superelevation Rate
  • Vd = Design Speed
  • NL = Number of Lanes
  • Wa = Actual Roadway Width
  • Wn = Nominal Lane Width
  • NC = Normal Crown (in percent)
  • Xm = Maximum Cross Slope (in percent)
  • La = Adjusted Runoff Length
  • Lu = Unadjusted Runoff Length
  • LR = Length Adjustment Ratio
    • Adjusted Runoff Length
    • Unadjusted Runoff Length
  • RG = Relative Gradient of Runoff Portion of the Transition

PowerGEOPAK V8i (SELECTseries4) Version 08.11.09.878

Thank you for your help,

Joe