Dynamic Parking Lot Design


This is an often asked and misunderstood workflow within Civil 3D.  The general question revolves around what objects should I use and how should I use them to create the finished design. We’ve done this forever using manual calculations and hand drafting.

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Typically, users will opt for feature lines and grading objects first to create their design. And this is my assumption that feature lines closely resemble 3d polylines used in Land Desktop.  Granted, in Civil 3D, if you make a change to the feature line that is a data source for a surface, then the ripple effect happens and the surface will update.

Only, with feature lines, we’re generally hand calculating key points and then possibly using some of the feature line tools to set curb line elevations.  Not a bad tool to use, but a very manual operation in this given scenario.

And, for the most part, you will get a surface. But probably one that you’ll extract the contours and edit them directly.  Again, a very similar mindset used in Land Desktop where at some point you will no longer utilize the LDD design database and rely on the information in the drawing. Pardon my language, but… Yuck!

Wouldn’t it be great if we could make a simple adjustment and have all the islands and curbs update and having a parking lot surface we would he HAPPY to show our boss?

We can do that as a matter of fact.  The basic idea is that we use a reference surface that our corridor object will use for the design profile. Our corridor object will include several baselines for each island. And each baseline will use a simple assembly of just a curb or curb and gutter, much like we do for curb returns in intersections. Once all of that “mapping” is done to connect the various moving parts, then we can make a simple edit to our underlying reference surface and have it ripple through the corridor and out the Finished Grade surface!

Really, that’s it.  There are many ways to define the reference surface.  One way would be to use a single feature line and project a given slope for a distance. Set the grading object to create a surface. Done. {Some may ask, why not paste the grading object surface at all? It is true, this may be an additional step for some.  But I have found that we build many surfaces throughout a design. I like to keep the major surfaces in tact, like EG and FG. That way I can lock down the various data references. But I digress…}

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Next, create an alignment anywhere you want to run a curb or curb and gutter assembly. With LID, LEED, and other environmental requirements, your assembly may be something more like a laid back curb or maybe just an edge between pavement and grass. It really can be anything you need.

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Next , we need to sample the reference surface for each alignment. Typically, surface sampling is meant for existing conditions, but we are using it here for proposed conditions. This leads us to the Corridor object. The corridor object will contain a baseline for each alignment you created earlier. Simply map the reference surface as the profile and the appropriate assembly for each baseline and your basically done on the parameter tab.  Generally speaking, curbs in a parking lot tend to have very small radius values as well as short arc lengths. To accommodate for this, you will need to adjust the curve sampling frequency for certain baselines to a smaller than usual value. Let’s say you have a 10’ wide island with a 5’ radius bullnose. [By the way, does anyone else call them bullnoses or is that just me?] The arc length would be ~15.7’. In order to adequately capture that distance and radius, maybe the curve sampling frequency value might be set to 2’ or 3’.

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Now, within the corridor properties, we still need to have it create a surface. From that point, you could use that as your finished ground or you could paste the corridor surface into an empty finished surface that other objects would be added.

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Initial Design

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Revised Design

Happy Holiday’s!

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About Kevin
Hi… I am a husband, father, brother and neighbor. I am employed as a Civil Engineer and have enjoyed playing the drums for the last 30+ years.

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