Civil 3D Alignment Types

Tags alignment, alignment type, Alignment Style, intersection, connected alignment, Project Explorer

Alignments in Autodesk Civil 3D have Types. Whoopie. No Biggie. If we get the Type wrong when we create the Alignment, we can change the Type? Errr. Well sort of and it depends. This is Civil 3D. Some Civil 3D Feature Properties and Parent and Child relationship properties only can be built on creation. Some may be destroyed by a manual change of Alignment Type.

Recall that an Alignment Feature in Civil 3D is a Parent collector of buckets of Properties as we discussed in the earlier Civil 3D Alignment post. It pays to align our thinking with the Civil 3D realities. The different Types of Alignments have different editable property buckets. The specific Alignment Type Property differences have significant ramifications.

We may consider Alignment Types as related solely our design purpose – a roadway centerline for example. We may create confusion for ourselves if we think that way.

The formal Civil 3D Alignment Types are about specific forms of Managed Design Control - a somewhat subtle but significant difference in perspective from the intended purpose for any particular Alignment.

This post remains a work in progress. Significant updates and changes have been made to the original.

Dumb and Dumber

The Alignment Types are all about the Alignment’s property buckets. The property buckets are reflected in the changing tabs we see in the Alignment Properties box. The contents of these tabs are more important than what we draw or what we see on the screen. In Civil 3D, it’s about the data, Baby. Actually, it’s about the managed design control of the property data.

“Honey, I know your type.”

Inside Civil 3D Alignments and Profiles work in pairs (or couples) most of the time. In other words, the horizontal and vertical control are often best developed and maintained together. We find this to be pretty apparent when we talk about Civil 3D Alignment Type design control and the practical use of the Civil 3D tool and mechanics.

Centerline Alignments are the most frequent Type choice we make. The Centerline Type allows us to employ Design Criteria (aka rules) to all the geometry collected in the Alignment’s property buckets or not. The management tools of Design Criteria (DC) require a Design Speed - a Station controlled property(s) to turn the DC on. Be careful – It is possible to delete the Design Speed settings of an Alignment after the fact by moving the Alignment’s Reference Point for example.
The Civil 3D Diva will squeal at you.

It is worth a mention that we can copy, create, and edit the supplied Civil 3D Alignment Design Criteria and tables. Roadways and Rail systems are not the only civil engineered structure systems that can benefit from custom applied Design Criteria.

The Miscellaneous Alignment Type is dumber – no Design Criteria properties or rules can be added or applied to the collected data. Everything else stays the same. Oh, goody.
We can work without inappropriate Design Criteria.

If we create an Alignment as Centerline Type, add some DC, and then change the Type to Miscellaneous, the Alignment keeps the Design Criteria properties, but the Civil 3D interface hides and ignores them.
The Alignment collector doesn’t forget. This can be good news or bad news and may depend on the release or update of Civil 3D. Not so good.
As a Miscellaneous Type, the DC no longer manages the geometry relationships. If you change the Type back again to Centerline, the Diva may start to scream.

The Rail Alignment Type has it’s own specialty Design Criteria files and definitions and an added Track width property coupled with Design Speed and Station control properties. Switching between Centerline and Rail Types and vice versa is destructive to the Design Criteria specifics. Civil 3D warns you.

Offset and Widening Support By Type

The Centerline, Rail, Miscellaneous, Curb Return, and the Offset Alignment Types all support Offset and Widening functionality.

An Offset Alignment Type is connected at birth to the Parent Centerline, Miscellaneous, Rail, Curb Return, or even another Offset Alignment. Key on-create aspects of Offset Alignment functionality depend on the existence of previous related child Profiles. Offset Profiles adhere to these same Parent and Child relationships.

Most of the time we want to consider the basis of a new Offset Alignment to be an Alignment and Profile pair.

The Offset Alignment Type is a hierarchical property. If we change the Alignment Type of an Offset Alignment, we destroy the Parent Child geometric relationship. Undo, reconstruction or replacement are the only way back.
We can, of course, Type an Alignment this way to keep track for it by “purpose”. That will probably confuse you and others later. Planned Alignment Names and Descriptions work better in Civil 3D to track our design intent.

The Curb Return Alignment Type and the kissing cousin Connected Alignments is about the link properties of Pairs of Features. The Curb Return Alignment Type’s design control connects two separate Alignments, and hopefully at the same time, their related Profiles together.
We can Type an Alignment this way to keep track for it by “purpose”. That will probably confuse you and others later. Planned Alignment Names and Descriptions work better in Civil 3D to track our design intent.

The available Civil 3D construction tools for the Curb Return Alignments deserve some discussion.

The Civil 3D Intersection Wizard

The Civil 3D Intersection Wizard can automatically create Curb Return Alignments and/or their related Profiles. It is important to recognize that the Intersection Wizard is not an all or nothing tool.
We can employ a few steps in the Wizard to only build the horizontal and/or vertical design control for collections of intersecting Alignment and Profile pairs and choose not to create or add the Civil 3D Corridor components when we do.

Do only the Horizontal control. Stop on page two. Connect up the right pieces and clean up the unneeded.
Intersections require that we understand Offset Alignments, Offset Profiles, Alignment Widenings, Curb Return Alignments, Connected Alignments, and the various edit interfaces to manage and maintain all of the above.
See the Stop the Wizard video and post.

All Those Other Design Intersections

If we believe the Civil 3D Intersection Wizard and the Civil 3D Corridor engine are only all about roadway design, we clearly miss the point that there usually a lot more ditch and utility trench infrastructure intersections in all forms of civil engineering design than pavement intersections. That is something to consider seriously.

If we don’t like the Intersection Wizard functionality, we have manual options.

Connected Alignments

Since the 2018+ version of Civil 3D, we can manually create individual Curb Return Alignments and related Profiles with the Connected Alignments tool. Until the 2022 Civil 3D release added new multi-segment and significant new design control properties to Connected Alignments, a single Curve and simple Profile was the supplied design control solution available.

Nothing says we cannot mix together the Intersection Wizard functionality with the Connected Alignments tool use in our design workflows.

The Most Common Dumbest

In the previous Civil 3D Alignment post, we talked about many recognition steps we need to accept about the properties of Alignment Features in Civil 3D. Before we ever enter the Alignment Create box, we need to consider something else – our old CAD drafting construction habits.

If we create Alignments from Objects, we significantly restrict what we can do with an Alignment. This is less problematic in more recent releases, but it still remains an issue. AutoCAD line, curve, and polyline primitives are dumb. They obey no rules. They do not recognize tangency for example.

To create Alignment geometry, constraints, and parameters with the Alignment Layout Tools takes only  moments longer. To habitually employ the Alignment and Profile Layout tools significantly increases our design control capabilities and the depth of our Civil 3D create and edit skill.

Put another way – An Alignment in Civil 3D does not need all the segments to be connected together all the time. Disparate and separated segments can be collected into an Alignment. These separate segments may be going in different directions as well. The creation of some complex geometry control is not possible without this malleable Civil 3D Alignment capability.
Sorry. We cannot do either of those things with an AutoCAD polyline.

In project management terms, it is also very significant that an Alignment need contain no segments at all. We can create named Alignment placeholders in our Civil 3D Project Templates to optimize our project workflow for our typical design tasks in Civil 3D.

Drawing Focus or Project Think

The other serious bad CAD habit is not separating our QAQC’d design control from the resolved design results. We want our Alignment and Profile pair’s Design Control to become a shared project-based resource and not be confined to a single design drawing.

There is nothing particularly difficult about creating the fixing the Data References (DREF) problem.
We can all learn to employ, clean, and maintain Civil 3D DREFs more effectively.
See the Civil 3D Styleless DREF Mechanics post and series.

With the Data Shortcut Manage tool (DSM) we can replace one set of project-based Alignment and Profile Data Referenced design control with another in a few seconds.
See The Data Shortcut Manager and DREF Replacement video and post.

A solid practical understanding of the nuances and mechanics of the Civil 3D Alignment Types helps us reduce the total amount of time and energy we invest in our project development and final deliverables production.

The Liberty to Make Civil 3D Work
Get the Framework for Civil 3D Release 8


The Book of Alignments Posts