Simple horizontal curve

[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.

 

[Maury]

The PI Sta. shown on the table of curve data is the PC Sta. plus the tangent length by definition. This has nothing to do with the physical location of the PI relative to the alignment. This is a carryover from the older methods of staking where the PI would be located by chaining (taping) along the alignment. Continuing the stationing would lessen the possibility of error.