Fred T. et al --
I don't measure length for spiral easements. I use a three-foot length of .172
rail. I spike one end to the straight centerline in three places. Then I
spike
the other end to the curved centerline in three places. The unspiked portion
takes on a least-energy shape. If the unspiked portion exhibits a reverse
curve, the curved and straight spiked locations are too close to each other.
Remove the closest ones, and add spike pairs beyond the next closest spike
pairs.
Rules of thumb: For curves less than 33", use a 3/4" offset. The spiral
easement will be long. For curves greater than 48", use a 3/8" offset. The
spiral easement will be relatively short. For curves in between these radii,
use a 1/2" offset.
You can pretty much judge for yourself how much free distance to leave between
the spiked portions by flexing the rail by hand while holding it against the
centerlines. If you need to exert like-direction twisting forces with your
hands (e.g., both hands twisting to the right or to the left, creating a
reverse
curve, rather than each hand twisting in an opposite direction), you need to
spread your hands further apart until the twisting forces are opposite. The
locations of your hands correspond approximately to the locations of the
closest
of the three spike locations.
There are of course equations for easements that are well known to land
surveyors. Feel free to use these if you must. But the approximate method is
quick and easy and requires no math.
Dick Karnes
[Non-text portions of this message have been removed]
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