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Chapter 4 Working with Cross Sections
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When deciding whether to use the Dynamic or Pinned options, it is usually best
to use the default value of Pinned. The majority of situations work well using
the pinned option.
However, there are a couple of situations where you should use the Dynamic
option. Use the Dynamic option when the transition alignment crosses the
design centerline alignment. If multiple transition alignments cross the design
centerline alignment, then only the first transition region should be defined as
dynamic. All other transition regions following the first transition region should
be defined as pinned regardless of whether they cross the centerline or not.
When you use the Dynamic option, the center portion of the template will be
collapsed or forced to disappear if the two opposing transition region points
have the same horizontal location. This is helpful in situations where a median
island is designed to taper in width and then eventually disappear.
You achieve this by defining opposing transition alignments such as L1 and R1
to follow the proposed edge of median island. If the transition alignments L1
and R1 fall exactly on one another, then the median island is completely
removed from the cross sections at these points. Collapsing template areas only
works between opposing transition regions such as L1 to R1. If R1 and R2 were
defined to fall on top of each other, the template areas do not collapse, but are
stretched together to a single point.
NOTE
The Pinned and Dynamic options only apply to the transition regions
between the innermost left and right transitions where the transition
region surfaces meet at centerline.
10 Specify a transition region type:
n
Type Free to specify a region that can move toward or away from centerline.
n
Type Constrained to specify a region that can only be stretched away from
the center of the template and not towards it. This allows minimum widths
of regions to be maintained.
11 Pick the transition control point from your drawing.
12 Specify the type of transition to hold:
n
Type Grade to hold the grade.
Holding the grade is often used for maintaining the cross slope of the
traveled lane on a road template when that lane is widened. Press ENTER to
select the Grade option.
The following prompt is displayed:
Pick transition reference point:
Pick the transition reference point from your drawing. This point is used to
determine what grade is held by the template segment as it is being
stretched. The transition reference point does not need to reference a point
on the template. It can exist in space. Use AutoCAD object snaps to select
the transition reference point accurately.
n
Type Elevation to hold the elevation that stretches the region horizontally
along the X-axis and changes the grade of the transition region.
When only horizontal transitioning is applied to a template, the elevation of
the control point can be held or the grade of the transition region can be held.