Difference in r value and K value equations

Kevin McDonald — Fri, 12 Sep 2014 20:41:43 GMT

Current Revision posted to OpenRoads | OpenSite Wiki by Kevin McDonald on 9/12/2014 8:41:43 PM


	Applies To

	Product(s):	InRoads, GEOPAK, MX
	Version(s):	08.11.09.493+
	Environment:	N/A
	Area:	Vertical Geometry
	Subarea:
	Original Author:	Kevin McDonald, Bentley Technical Support Group

Problem:

We (Technical Support) are sometimes asked why the r value for a vertical parabolic curve is off by a factor of 100, when it appears (by looking at the equations) to be the reciprocal of the K value.

Solution:

The difference between the two equations is the length value used in each.

For K value: K = l / (g2 - g1) where l = length of curve

For r value: r = (g2 - g1) / L where L = length of curve in stations

Therefore, with a unit station length = 100, r = 100 * ( 1 / K )

Tags: K Value, Vertical, r value