Minimum Vertical Curve Length

[maximus808]

In doing some practice problems, I had a question, would there ever be a time where both equations are fulfilled for SSD given a velocity. If so, which answer is more correct, the shorter curve length? I suppose if the questions is asking that is the required length of curve given down and upgrade and velocity. Do I use the smaller length of curve?

 

[sac_engineer]

In doing some practice problems, I had a question, would there ever be a time where both equations are fulfilled for SSD given a velocity. If so, which answer is more correct, the shorter curve length? I suppose if the questions is asking that is the required length of curve given down and upgrade and velocity. Do I use the smaller length of curve?

It's not clear what you're asking but let me know if the following resolves your inquiry:

For vertical curves (sag vs crest), you need to compute the length of travel along the curve (i.e. "L") and compare that to the SSD with the same initial velocity along a horizontal (i.e. zero slope) condition (i.e. "S"). "S" needs to be calculated first since it's one of the variables used to solve for "L". There are always 2 equations associated with the sag and crest scenario; one equation applies when S is less than or equal L and the other is for the opposite (i.e. S > L). Initially assume S is less than L, use the appropriate equation, and verify the assumption.

I highly doubt you'd find a scenario where both equations are fulfilled for a given velocity. However, solving SSDs for vertical curves isn't necessarily about the shortest length, but more about using the proper equation.