Curve length 1

[nervous79]

What is the best way to compute curve length? The knowns are PI, PT and Radius.

 

[aas1]

The formulas for horizontal curves (English units) are:

R = 5729.578/D T = Rtan(delta/2) and L = 100(delta/D)

R = radius (ft.)
D = degree of curve (DMS)
T = tangent length (ft.)
delta = angle between forward and back tangents (DMS)
L = length of curve (ft.)

Find T by subtracting the station of PT from station of PI.

 

[adamsw1]

If you have a PDA and you don't want to mess around with locating the curve equations or don't want to have to solve them for the specific variables you could download the shareware program "Curves" from

http://www.handango.com.

Justin Adams

 

[Bayou]

the curve length is equal to the angle(radians) * radius

 

[bbagar]

Here is a question about simple horizontal curves:
aas1, you are saying that "Find T by subtracting the station of PT from station of PI." which is something that I see in every surveying book. What they do is, they subtract T from PI Sta to get PC Sta. Then they 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.

 

[KRSServices]

You need to know the radius and delta angle.

L = (delta/180) * pi * Radius



KRS Services

http://www.krs-services.com

 

[MrGriz]

For BBagar:

AAS1 is incorrect. To find the T, you subtract the PC station from the PI station, not from the PT station. The formulas that AAS1 gives are for an arc definition too.

You're right, it seems that the 1/2L should have the same stationing as the PI but of course it doesn't. If you were to draw a line from the center of the curve to the PI, it will interesect the curve at the 1/2L point. Adding the T to the PC station is meant to give you the PI stationing only, not the station of the 1/2L.

As far as the original question, how do you find the curve length from the PI, PT and radius, you can't do it with that information only.