Medians and Marked Points

It’s a simple situation to model, but help isn’t entirely clear on how to build an assembly with a median.

Start by creating an assembly, and inserting “LinkOffsetAndSlope” on either side.

At first glance, the LinkOffsetAndSlope subassembly requires both a distance and a slope, but an alignment can be substituted for the offset, and a profile for the slope (in the Corridor Properties dialog after the corridor has been modeled), so it’s a great candidate (because of the allowable variations) for a “Marked Point.”

A “Marked Point” (MarkPoint is the actual name of the subassembly) is used to mark an existing point on an assembly with a name. This is usually done so that other subassemblies can later insert links (for example, LinkToMarkedPoint) that attach back to this point. Obviously, quite a few subassemblies lack the ability to tie to a specific location, but by using MarkPoint, you have the ability to tie a subassembly back to almost anything.

Both MedianRaisedConstantSlope and MedianRaisedWithCrown tie to a marked point inherently, as shown (from help).

By defining both the left TC and right TC at the median as alignments, and by setting these alignments as targets (in Corridor Properties) for the LinkOffsetAndSlope subassemblies shown in the figure above – as the alignments meander left and right of the centerline, so will the median. But not until we “mark the point” the subassemblies need (as shown in help above).

In the case of the MedianRaisedConstantSlope, you’ll need to define at least 3 regions along the median shown in the figure below: 1. Where the median occurs to the right of the centerline. 2. Where the median occurs on both sides of the centerline. 3. Where the median occurs to the left of the centerline.

Insert MarkPoint on the center of the assembly as shown. You’ll find the Properties dialog allows you to enter the “Point Name;” simply name it “CL.”

Now insert MedianRaisedConstantSlope, but the placement of the subassembly is key. For the second region, the region in which the median occurs on both sides of the centerline, you want to anchor the median at the location of the left TC alignment – the end of the LinkOffsetAndSlope located at the left of the assembly. Notice in the Properties of the subassembly you have an option to supply the name of the “Mark Point,” you’ll name it “CL,” the name of the marked point you just placed on the assembly. The left side of the median will tie to the TC alignment on the left, and the right side of the median will tie to the marked point at the centerline.

Notice it looks a bit odd, but digitally speaking, it is correct. If we had attached MarkPoint to the end of LinkOffsetAndSlope on the right of the assembly instead, then the right side of the median would effectively tie back to the alignment at the TC on the right side of the median. To complete the median in this region, anchor the median at the location of the right TC alignment – the end of the LinkOffsetAndSlope located at the right of the assembly. Again, it will look odd, but digitally speaking, it’s correct.

To model the median as shown above, you’ll need at least 3 assemblies as shown below (notice the location of the marked point):

In the diagram above, the bottom region is actually “Region 3,” not “Region 2.”

Finish off the roadway by inserting LaneFromTaperedMedian1 or anything else you need. The only trick is that the MarkPoint must always be processed first. You can change the order of processing with a right click in the Assembly Properties (Construction tab) as shown:

Notice a section view:

For more information, check out the webcast done on Friday June 10, 2005 entitled Using Civil 3D 2006 for Road Design with Lane Transitioning and Tapered Medians

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