Civil 3D Turn Lane and Median Corridors

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Multiple Baseline Corridors are a powerful design and deliverables documentation tools in Autodesk Civil 3D. The Multiple Baseline Corridor (MBC) or the Complex Corridor is one of my favorite things in Civil 3D. Why? Project-based and better managed design in Civil 3D is what I tend to rave about in this blog.

The folks out in Civil 3D Land will laugh and point out that I appear to appreciate all the complicated, integrated, and managed detail we must plan and execute well to get that MBC work done in Civil 3D.

It’s true. I’m spoiled. The many Civil 3D resources in the Framework for Civil 3D do make the iterative design and development of the MBC more approachable. The Power of Choice does make that not-so-simple Complex Corridor challenge more possible.

Truly, the Framework for Civil 3D is affordable for all civil engineering and survey professionals. That speaks volumes about the real liberty to work in Civil 3D. We recently released huge new Updates of the Framework for multiple releases of Civil 3D. See the Release 8 page for links and details.

Civil 3D Turns and Medians

The path to faster and improved roadway Corridors with intersections, medians, and turn lanes is a meat and potatoes problem in Civil 3D. If you’ve already mastered the Art of Medians, Hoorah - You own a significant Civil 3D skill set.

Public help on this intricate set of topics is difficult to find. There are reasons for that.
Register and visit the Autodesk Civil 3D Videos page for some other older video training approaches to the problem. The WISDOT and FDOT training sites include public videos with highly structured and standardized DOT approaches.

Based on popular customer requests we now include some basic Sandbox Project example drawings of an approach to get basic Medians with Turn Lanes done in Civil 3D.

Framework Sandbox Project Examples

To keep things realistic, the latest Framework Sandbox Projects example drawings employ some complex Alignment and Profile design geometry for the Civil 3D horizontal and vertical design control in one drawing. A second example drawing employs that copied design control to produce a resolved Multiple Baseline Corridor and the typical Corridor engine output produced with the supplied Civil 3D stock Subassemblies.

The intentional work in progress result is an Undivided Crown roadway and intersection with a curbed Medians and left turn lanes without Superelevation. This represents a common suburban AASHTO Collector or Arterial design construction specification condition perhaps better suited for dryer climates. The example as constructed employs curbed structures.

See the recent Manage Sets of Assemblies in Civil 3D post and video for how we might update the cross section Assemblies with a new Set of Assemblies resource and those workflow mechanics.

To employ new Superelevation design details in the examples would require a modified Set of Assemblies (to employ Superelevation parameters in some Subassemblies) and changes to a promoted west to east horizontal design control and/or manual edits to the Superelevation tables.

The Framework Sandbox Projects in their multiple flavors do include project-based Alignment and Profile design control examples without the above complications. There is room to play in the sandboxes.

The Civil 3D Diva in the Details

Whether the Civil 3D Diva is a devil is a matter of perspective.

The latest Civil 3D 2022.1 Update includes some serious, behind the scenes Data Reference, Corridor performance, Corridor tool, and Corridor targeting interface enhancements. Those changes generally make a Complex Corridors for Medians and Turn Lane designs easier to build and manage.

We do call it a Complex Corridor for a reason. There are, as always in Civil 3D, some nuances and default behaviors to be aware of.

That’s worth a video review to examine some of that.


Median and Turn Lane Corridors in Civil 3D

Clearly, a Multiple Baseline Corridor that constructs Medians with Turn Lanes is a complex beast.

MBC construction is certainly a Civil 3D skill set worth the time and practice investments to master.

To construct and publish a Complex Corridors effectively we must learn how to employ much of the capability that Autodesk has built into the herd of Alignment related Civil 3D Features and the mission critical Corridor engine improvement made in over a decade of intense product development.
See the Civil 3D Alignment post and linked in-depth series of posts and videos.

The Principles of the Separation of Powers

It is readily apparent that we must learn to employ classic Separation of Powers methodologies to create, edit, and manage all the interrelated data complexities of a Complex Corridor.

To summarize some of the Multiple Baseline Corridor Best Practices:

  • Project DREF management of the design control is essential
  • Plan and Manage the creation of the Baselines and the Regions
  • Know Thy Subassemblies and their codes
  • Employ Sets of Assemblies to manage the cross section design control and Property details
  • Master the Region Create and Edit Tools and Master the Corridor Targeting Tools 
  • Corridor Surfaces are and are not generic Civil 3D Surfaces

In upcoming posts we’ll discuss these principal Multiple Baseline Corridor Best Practices in more detail and include more linked references and help.

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Complex Corridor Posts