# Surveying - Horizontal curve



## cantaloup (Jul 22, 2007)

Question 115 of the Morning Sample Questions (page 27) in the "NCEES Sample Questions &amp; Solutions" book. Why the solution (p. 140) states that the station of the PI is equal to station PC plus the distance T (tangent) ? Why not equal to station PC plus half of the length of curve L ?

I also see the CERM equation 79-11 states:

Sta PT = sta PC + L ; this is correct

But then equation 79-12 states :

Sta PC = sta PI - T

Why not Sta PC = sta PI - L/2 . Anybody has an explanation?

Thanks.


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## Snappy (Jul 23, 2007)

Hi cantaloup,

The PI is *not* located on the actual curve; it's located along a tangent from the PC. The PC and PT are along the curve, and therefore Sta PT = Sta PC + L applies, whereas Sta PI = Sta PC + T because it's separated by a tangent distance.


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