The first point to note is that in any pair of reverse
or compound curves the EC (or ETC) of the first curve
must fall before the BC (or BTC) of the second curve.
The separation can be as little as 1mm, but it must be
there. Use the Review Alignment menu option and check
the calculated chainages for the curves to ensure that
the separation exists. In the following example curves
1 and 2 form a reverse curve pair while curves 3 and 4
form a compound curve pair.
Once you have the horizontal alignment defined you
must generate the coordinated chainage points using
the Coordinate menu option.
The vertical alignment is handled normally as the
reverse or compound curves have no effect here, other
than the fact that you might not want your vertical
curves to fall within the horizontal curves.
Edge Levels is however the function with which most
people trying to design reverse or compound curves
have a problem.
If you enter your superelevation details by hand then
you should have no problem in defining the details
around the reverse or compound curves.
The other method of defining superelevation details,
Slave Super, requires more work to handle the reverse
or compound curves.
Before starting Slave Super take careful note of the
PI numbers, BC and EC chainages of the reverse and
compound curves in the horizontal design. When you
start running Slave Super you are asked for some
general information on road widths, crossfalls and
templates.
Enter this information and click the OK button to
continue.
From this point on Slave Super will present a dialog
for each of the PI's in the horizontal alignment. This
dialog will show the PI number being processed, the BC
and the EC chainages. You will need to fill in the
lengths over which superelevation should be applied,
the percentage of superelevation before the BCC or
after the ECC, and the super elevation to applied
through the curve.
Proceed normally until you reach the first PI of a
reverse or compound curve pair. Enter the BCC details
normally. For the ECC of this PI enter the runout
length and percentage development after the ECC as 0
and click the OK button to continue.
For the BCC of the second PI of the pair enter the
development length in and the percentage development
before the BCC as 0. Enter the ECC details normally
and click the OK button to continue.
Carry on in this fashion until the Edge Level details
are fully defined. You will now need to edit the Edge
Level spreadsheet.
Looking through the spreadsheet you will find two
pairs of entries for the ECC of the first PI of a
reverse or compound curve pair and the BCC of the
second PI. The chainage entries for the ECC of the
first curve should be identical, as should those for
the BCC of the second curve. In the following example
lines 4 and 5 are for the ECC of the first curve of a
reverse curve pair, lines 6 and 7 are for the BCC of
the second curve of the pair, lines 12 and 13 are for
the ECC of the first curve of a compound curve pair,
and lines 14 and 15 are for the BCC of the second
curve of the pair.
To set up for a reverse curve simply delete the first
duplicate entry for the ECC, the second duplicate
entry for the BCC, and set the left and right
crossfalls to 0 for the remaining two lines. This will
allow the development to pick up into the first curve,
return to a neutral position at the end of this curve,
continue the neutral line on into the second curve,
and then reverse the superelevation in the second
curve before returning to normal. In the case of a
compound curve simply delete all four of the entries
(two for the ECC of the first PI and two for the BCC
of the second PI). This will allow the development to
pick up into the first curve, continue the maximum
development through into the second curve, and then
drop down out of the second curve.
After carrying out the required operations on the Edge
Levels spreadsheet, it will now look like this.
The reverse curve details are now on lines 2 to 7 and
the compound curve details are now on lines 8 to 11.
All relevant details have been handled and you can now
continue on as per usual.
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