Simple Horizontal Curves

[bbagar]

Here is a question about simple horizontal curves:
To calculate PC Sta, subtract T from PI Sta, then add L to PC Sta to get PT Sta. My question is, isn't stationing based on the roadway, that is, on the curve? If this is true, how can you subtract T from PI Sta to get PC Sta? The reason I am saying this is because the length of T and length of one half arc are not the same, therefore I am thinking one has to subtract 1/2L from PI Station.
This is assuming that PI is halfway between PC and PT, which should be correct since T's on both sides are equal to each other and the line from center of arc to PI divides the center angle by two.

 

[CarlB]

If you need to calculate a PC station and are given a PI station, then the alignment is:
1. Stationed along tangents only, not yet stationed along curves; or
2. Dual stationing is being used, and should be somehow identified as such.

I would say that a typical final drawing would be stationed along the centerline alignment only, and the 'tangent' is either given or able to be calculated from other curve parameters.

 

[KRSServices]

If I understand your post correctly (and I must admit that I am not clear on your exact query as to whether you are referencing the drawing details or field layout) your stationing should be along the centerline of the curve. The applicable information on the drawing should be the BC (PC) and EC (PT) stationing, the radius, the arc length and the delta. The labelling of the stationing has nothing to do with the PI, unless of course you were to calculate the stationing from the PI.

If that is the case, there are a series of calculations that can be done. However, it is far easier to calculate from the chord or the BC.

If you would like the development of the formula, I can scan it and email to you.

KRS Services

http://www.krs-services.com