Technical information

Calculating Vertical Curve Length | 167
In the geometric calculator section of the curve calculator, you can review
information about crest and sag vertical curves for a selected PVI. For crest
curves, the calculated K value, as well as passing and stopping sight distances,
are shown for a specified curve length. For sag curves, the headlight sight
distance is shown. You can enter a value for a stopping or passing sight
distance and a K value, and the program calculates a corresponding curve
length.
The lookup table section of the calculator uses a series of separate ASCII text
files, which you can edit, to compare vertical curve design information
regarding the current finished ground PVI against the associated alignment-
based speed values. From these lookup tables, a list of minimum and maxi-
mum curve lengths are shown for the currently selected PVI.
Key Concepts
■ The geometric calculator section of the curve calculator calculates vertical
curve length based on empirical values.
■ If you know the intended design speed for the alignment, you can assign
design speed values to the alignment and then use the lookup table
section of the calculator to calculate curve length.
■ To select a curve length that was calculated using a lookup table, double-
click the value in the Length column. This sends the value to the Curve
Length box in the geometric calculator section of the calculator, where
you can round the value up or down and then commit the value to the
vertical alignment.
Click this
button to
commit the
curve
length
value to the
vertical
alignment.
Double-click
a length
value to send
it to the
geometric
calculator on
the left.
Geometric calculator
section
Lookup table
section