The association between design speed (V) and radius of circular curve (R),
As the R is positively related to V according to the equation (attached), then I expect that the C3D changes R value as the value of V is changed.
For example, on the attached screenshots, the R value of horizontal alignment is built based on a design speed of 100km/hr. Now if the speed is changed to 50km/hr, then why the value of R is not automatically changed to be compatible with the new speed?
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Perhaps you did not understand my last post. C3D does not take V into account when laying out alignments. V is only used when using criteria-based design to flag horizontal curves with a radius too small or vertical curves with insufficient K values to the user can fix them.
It might be possible for a third party developer to build a utility that would check the horizontal and vertical alignment against the design criteria, and change things where possible to fit the design speed. You may want to post this request in the Customization forum and see if anyone can help you.
Personally I don't want the software making changes like that on its own. I can see the error flags and make my own judgement about how to fix them.
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Many thanks Eric and Steve. Now it is much clearer.
I share the idea of “pinwards” to be able to have the minimum value of R that satisfies the design speed instead of just flagging.
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Many thanks troma for the help. The answer you have already provided is very useful.
I got that the value of R can be calculated from two equations
R=1719.74/Da, where Da is the degree of curvature
R=V^2/127(e+f), V: speed, e:superelevation, f: friction
R to be the maximum of these two values.