For years I thought Robert Johnson’s Crossroads was an autobiagraphical tune about deals with the Devil and trading his soul for a song.  I had this picture in my mind of a road-weary guitar slinger, standing at a desolate intersection, struggling with an epic moral conflict.  What a choice.  One path leads to righteousness and salvation – the other straight to the fiery halls of Hell. 

I wasn’t even close.  It’s a great blues standard but not nearly as dramatic as all that.  I heard it on XM radio this morning and I guess it set me off.  I actually do like Robert Johnson but I don’t walk to talk about crossroads, at least not in that sense.  I want to talk about intersections. 

AutoCAD Civil 3D 2010 introduces automated Intersection Modeling.  This is a long awaited step for Civil 3D.  The new Create Intersection wizard automates the process by creating dynamic offset alignments and profiles; dynamic curb return alignments and profiles; and an intersection model using a corridor. 

By now we all should know what dynamic means.  Change something over here and associated elements update over there.  Some of you may be strangers, however, to the term simple but Autodesk certainly nailed it: pick the alignment intersection and step through the wizard.  I like simple.

The wizard offers two grading options: to maintain the primary road crown; or to maintain both primary and secondary crowns. The first option gives priority to the crown of the primary road and warps the surface of the side road. The second option preserves the crown of both center lines and warps the grade of all the road surfaces that meet at the intersection.

The intersection object can be used to create a new corridor or added to a corridor that already exists.  The creative part of the process is how these assemblies are managed. Fully constructed assemblies are stored as individual drawings in a folder along with an XML file identifying them.  The Corridors page of the wizard displays a list of the required intersection corridor regions and their assigned default assemblies.  Assemblies can still be created in the drawing and substituted for ones in the default list.

A fast favorite new feature of mine is the visual cues displayed when creating or editing these objects.  Conceptual graphics are displayed in key dialog boxes to indicate the element you are creating.  A good name and description is hard to beat but a picture is worth…well, you know. 

It gets better.  Temporary graphics display in the drawing area when you edit intersection elements.  Pick a region in the corridor parameters dialog and the region is highlighted in the drawing.  I promise you will love this feature and the depth of your love will grow in direct proportion to the size of your corridor. 

Another related feature is the Edit Region… command from the popup menu.  Pick a region, right-click, and be whisked directly to that region in the corridor properties.  You can call me fickle but I love this feature too.

So how does it work?  Some preparation is required but not as much as you might think. The basic assemblies necessary to create an intersection are a full section (1), half-sections (1+), and quadrant sections (1+) for the curb returns.  The obligatory EG and FG profiles are needed for both the primary and secondary alignments but that is about it.  The road offset alignments are created automatically as are the curb return offset alignments and profiles.

My personal belief is that our language has become infested with superlatives.  Everything can’t possibly be awesome or excellent but I will say this: Create Intersections is very good.  The Create Intersection wizard is fairly simple and intuitive.  The default assembly concept is creative, easy to implement, and ideal for a network environment.  It’s also simple to override.  Creating turn lanes and acceleration lanes is a snap.  The visual cues are a tremendous help.  Somebody stop me when I say something bad.  

Whew!  This is exciting stuff but let’s take a moment here to catch our breaths.  Very good does not mean perfect and there are a few things you need to know.

  1. It doesn’t always work.  The function occasionally balks at intersections on a curve.  I logged the incident with Autodesk but I don’t expect a solution short of a service pack or new release.
  2. A separate baseline is required to connect intersections.  What a perfect place to take advantage of another great new feature – grip editing regions.  I grabbed a full section region grip on my intersection and with trembling hands stretched it to the next intersection.  I was excited. It was a special moment – connected intersections.  I collapsed in my chair and imagined a chorus of angels singing the praises of what I had just created but, alas, my heavenly host was quickly replaced by a demon choir.  When I created the next intersection, all intersections in that corridor were rebuilt and my edits were lost.
  3. Corridors are so bloated.  I set out to create a mass grading plan for Section 1 of my infamous Lakewood Heights data set.  My corridor for fifteen 3-way intersections with connectors has 75 baselines with 90 regions.   I reduced some of the intersection regions by replacing the full section region at each intersection end with a new full-section baseline connecting the intersections.
  4. Many, many, many alignments are created.  The same data set produced 16 primary alignments, 30 offset alignments and 30 curb return alignments.  

So, what does this mean to us in production?  The failed intersection was an inconvenience but not to the extent that it would halt production.  I would skip the failed intersection and continue to the next.  Once the remaining intersections were complete I would return to the failed one(s) and use the method we employed in the 09 version and create it manually. 

Losing intersection edits from the corridor rebuild was a big disappointment and what a waste of a new feature (grip editing regions).  It’s a shame because many of the intersection full assembly regions could be eliminated making the corridor easier to work with.  A simple corridor is a happy corridor.  The solution may be to simply create all the intersections first although that may require a change in work flow.

I went to great effort to name the corridor baselines and regions.  I also renamed alignments, offset alignments, curb return alignments, and profiles according to a reasonable, consistent standard on the Prospector tab of the Toolspace.  Although not critical to the construction of my corridor, easily identifying the various corridor elements was a big benefit when editing from the corridor properties dialog.  I cannot emphasize enough what a tremendous help the highlighted drawing graphics were in the editing process.

I was shocked by the number of alignments created but it could have been worse.  When creating offset alignments there is an option to create new offsets from start to end of centerlines.  It’s a necessary option but if left on, new offset alignments are created – one on top of the other – for every new intersection created along the primary alignment and the user is not warned a duplicate alignment is being created. (For example, 6 intersections along Main Street would result in 12 offset alignments – 6 left and 6 right.) 

Oddly enough, managing the corridor properties and alignment collections may not be an issue.  The program doesn’t have a problem with it so unless someone decides to clean house and delete duplicate alignments life will go on as usual.

In summary, I like the ease of execution, grip editing regions, and especially the highlighted drawing graphics.  Without the graphics this task would have been much more difficult.  Being able to grip edit regions without losing the changes would have made it much simpler.

I’m on the fence about the logistics of managing the mountain of data that’s created and, trust me, it is a mountain.  There was so much data that it was tedious to meet what I consider to be good CAD practice regarding naming and managing alignment, profile, and corridor elements.  It didn’t seem to matter to the program but it does to me. 

I definitely don’t like losing edits or failed functions.  That makes me sing the blues.  Certainly not the Crossroad blues because I created 15 connected intersections dramatically faster than I ever could before.


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