Understanding Alignments
You can think of the basic road geometry discussed in the chapter introduction as a single-line form of the roads, as shown in Figure 5.1. The lines you draw will typically represent the centerlines of the roads, and eventually, you’ll build the rest of each road around those centerlines.
Civil 3D Alignments
Civil 3D alignments are designed specifically for representing the initial single-line version of a linear design feature. They are also used to establish the backbone of linear designs such as roads, railroads, channels, and pipelines. The lines, arcs, and spirals that make up an alignment can interact with one another. This allows you to edit part of the alignment and have the other parts adjust automatically. Additionally, other design objects such as profiles, sections, and corridors can be built around alignments. You’ll learn more about these design objects later in this course.
Creating Alignments from Objects
A common way to create an alignment is by using basic AutoCAD® software geometry already present in the drawing. You might be working with someone’s “sketch,” or perhaps you’ve chosen to draw the initial layout this way due to the simplicity of AutoCAD tools. Whatever the case, Civil 3D makes it easy to convert simple AutoCAD entities into alignments.
Exercise 5.1: Create Alignments from Objects
In this exercise, you’ll create alignments from polylines in the drawing that represent road centerlines.
- Open the Drawing
Open the drawing named Alignment from Objects.dwg which you can download from Youtube Video description below.
Since alignment design is strictly a 2D process, the drawings in this chapter do not use multiple viewports. - Access the Alignment Creation Tool
On the Home tab of the ribbon, click Alignment ➢ Create Alignment From Objects. - Select the Polyline
When prompted to select an object, click the longest magenta polyline labeled Jordan Court. - Confirm Selection
Press Enter. A black arrow should appear on the polyline, indicating the program’s guess at the alignment’s direction. - Set the Alignment Direction
- If the arrow points south, press Enter.
- If it points north, press R and then press Enter.
The alignment direction is critical as it affects the configuration and labeling of many design components.
- Configure the Alignment
In the Create Alignment From Objects dialog box:- For Name, enter Jordan Court.
- For Type, verify that Centerline is selected.
- For Site, verify that <None> is selected.
- For Alignment Style, verify that Proposed is selected.
- For Alignment Label Set, verify that _No Labels is selected.
- Uncheck the box next to Add Curves Between Tangents.
- Verify that the box next to Erase Existing Entities is checked.
- Click OK.
- Inspect the Alignment
Click the newly created alignment and then click one of the magenta polylines.
Notice how the polyline grips differ from the alignment grips (see Figure 5.2).
- Experiment with Grips
Move the grips on both the Civil 3D alignment and the polyline to compare their behavior. Notice how Civil 3D alignments allow for more dynamic adjustments compared to polylines. - Create Additional Alignments
Repeat steps 2 through 6 to create the Madison Lane and Logan Court alignments. - Save and Close the Drawing
Save your progress and close the drawing.
You can verify the results of this exercise by opening the Alignment from Objects – Complete.dwg file.
https://www.mediafire.com/file/6u3npxtcegb8h09/Alignment+from+Objects+-+Complete.dwg/file
Watch Complete video here for this Exercise:
Alignments Are Smarter
When investigating the grip-editing behavior of an alignment versus a polyline, you’ll notice a key difference: the alignment follows a basic geometric rule that the polyline doesn’t—maintaining tangency. Whether you move or stretch a straight line (tangent) or modify a curve, the adjacent lines and curves adjust themselves to remain tangent. This ensures smooth transitions, which is critical because driving on a road without tangent curves and lines could be hazardous.
Creating Alignments Using the Alignment Creation Tools
Sometimes, you may not have existing geometry in the drawing to convert into an alignment. In such cases, you can use the Civil 3D Alignment Creation Tools to create alignments from scratch. These tools are accessible through Civil 3D’s toolbar and provide a comprehensive set of commands for creating and editing the lines, curves, and spirals that form an alignment.
Alignment Terminology
Before proceeding with the next exercise, familiarize yourself with the following terms commonly used in the Alignment Creation Tools and throughout Civil 3D:
- Tangents (Alignment Segments): The straight-line portions of an alignment.
- Tangent (Geometric Condition):
- Touching or passing through at a single point.
- For a line and arc: perpendicular to a line drawn from the intersection point to the center of the arc.
- For two arcs: intersecting such that a line drawn between their centers passes through the intersection point.
- Curves: Curved portions of an alignment with a constant radius.
- Spiral: Curved portions of an alignment that vary in radius from one end to the other.
- PI (Point of Intersection): The location where two tangents intersect or would intersect if extended.
- PC (Point of Curvature): The point where a curve begins.
- PT (Point of Tangency): The point where a curve ends.
- Free: A line, curve, or spiral dependent on alignment segments at both ends.
- Floating: A line, curve, or spiral dependent on an alignment segment at one end.
- Fixed: A line, curve, or spiral not dependent on other alignment components
Exercise 5.2: Create Alignments Using the Alignment Creation Tools
In this exercise, you’ll use the Alignment Creation Tools to draw alignments based on the provided reference geometry, dimensions, and notes.
- Open the Drawing
Open the drawing named Alignment Creation Tools.dwg which you can download from the Youtube video description below. - Review the Reference Geometry
Examine the blue geometry, dimensions, and accompanying notes. Details about this geometry are provided in the sidebar titled Using Temporary Geometry. - Access the Alignment Creation Tools
On the Home tab of the ribbon, click Alignment ➢ Alignment Creation Tools. - Set Alignment Name
In the Create Alignment – Layout dialog box:- For Name, enter Jordan Court.
- Click OK.
- Select Tangent-Tangent (With Curves)
On the Alignment Creation Tools toolbar:- Click the black triangle on the first button on the left to expand the options.
- Select Tangent-Tangent (With Curves) (see Figure 5.3).
- Snap to Center of Circle A
Snap to the center of the circle marked A. - Snap to Other Circle Centers
Snap to the centers of circles B through E (skip circles F and I), and press Enter. The Jordan Court alignment is created. - Create Madison Lane Alignment
To create the Madison Lane alignment, repeat steps 3 through 7:- Enter Madison Lane for Name.
- Use circles F through H.
- Create Logan Court Alignment
To create the Logan Court alignment, repeat steps 3 through 7:- Enter Logan Court for Name.
- Draw the alignment from circle I, perpendicular to the Madison Lane alignment.
- Save and Close the Drawing
Save your work and close the drawing.
You can view the results of successfully completing this exercise by opening the Alignment Creation Tools – Complete.dwg file.
https://www.mediafire.com/file/m3kyg4rxkhbd8g2/Alignment+Creation+Tools+-+Complete.dwg/file
Watch complete video here for this exercise:
Using Temporary Geometry
Existing physical and legal boundary features almost always influence the layout of any land-development design. In a residential project such as the example in this book, the goal is to create as many optimally sized lots as possible within the available area. Every lot must also be accessible from roads built through the site. With these things in mind, along with the geometry of the existing property boundaries, terrain, and other constraints, it’s frequently helpful to create some temporary geometry to guide you in the creation of the alignments.
In the drawing for this exercise, the blue linework is provided for you and represents geometry that references existing features of the site. Dimensions and notes have also been provided to help explain the reasoning behind this geometry. The following list represents key points to consider when you’re creating this temporary geometry:
▶ ▶ 150′ (45-m) offset from the road centerline to the backs of the lots to accommodate a 50′ (15-m) right-of-way, an adequate front yard, a single-family residence, and an adequate rear yard.
▶ ▶ Perpendicular intersection with the existing road that is ideal for safety and accessibility.
▶ ▶ Avoidance of the steep area to the south.
▶ ▶ Uniform geometric properties where possible, such as 90° angles, parallel lines, and so on. This is recommended for simpler, more efficient stake-out and construction.
▶ ▶ Avoidance of the farmhouse and buildings, because that part of the property will be deeded back to the original owner.
In the real world, you’ll need to come up with this temporary geometry on your own. In fact, this is what design is all about: using your knowledge and creativity to come up with a technical solution to a need or problem. Creating the alignment is the easy part. Coming up with the temporary geometry as described here is the real challenge.
Editing Alignments
Of course, nobody gets it right the first time. As a general rule, you’ll find yourself laying things out about 10 percent of the time and spending the remaining 90 percent making edits. That’s totally OK; it’s the way Civil 3D was designed to be used. In fact, it’s highly recommended that you do a rough layout of the basic design elements at the beginning of a project and then spend the rest of the time adjusting, refining, and improving that initial layout until it’s the way it needs to be. This is also a great approach because it matches up with the general nature of land-development designs, which typically change frequently throughout the life of the project.
Editing Alignments with Grips
As you learned in the first section of this chapter, alignments are different. They’re smarter and more sophisticated than basic AutoCAD entities. They have more types of grips, and the way they respond to geometric changes is more intelligent. You can leverage this to make quick visual edits to your alignment without ever typing a number or entering a command.
Exercise 5.3: Experiment with Alignment Grips
In this exercise, you’ll experiment with the different grips that can be used for editing alignments.
- Open the drawing named Graphical Editing.dwg which you can download from Youtube video description below.
- Click the Jordan Court alignment to display its grips. Click the upright triangular grip on the second curve, and move your cursor to a new location without clicking the new location.
This grip is located at the PI. As you move it, the curve always remains tangent and the radius of the curve remains constant (see Figure 5.4).
3: Press Esc, and click the circular grip at either end of the curve. Move your cursor to a different location without clicking.
These grips are located at the PC and PT. As you move them, the radius changes and tangency is maintained at both ends of the curve (see Figure 5.5). They can be used to graphically set the exact beginning point or ending point of a curve.
4: Press Esc, and click the circular grip at the midpoint of the curve.
Move your cursor to a different location without clicking.
This grip is located at a pass-through point, and it forces the curve to pass through that point while maintaining tangency at both ends. This is accomplished by changing the radius of the curve (see Figure 5.6). You can use this grip to make the curve pass through a specific point.
5: Press Esc, and click the triangular grip located near the midpoint of the curve. Move your cursor to a different location without clicking.
This grip controls the radius of the curve while maintaining tangency at both ends of the curve (see Figure 5.7).
6: Press Esc, and click the square grip at the end of the Jordan Court alignment. Move your cursor to a different location without clicking.
This type of grip is located at either the beginning or the end of the alignment. As it’s moved, the geometry adjacent to it responds. In the case of this alignment, the curve just before the endpoint changes the locations of its beginning and ending points to remain tangent at both ends (see Figure 5.8).
7: Press Esc, and click the square grip located at the midpoint of the last tangent in the alignment. Move your cursor to a new location without clicking.
This grip moves the tangent while maintaining its orientation in the drawing. Adjacent geometry responds as needed to meet its geometric rules. In the case of this alignment, the PI to the left of this grip changes location, and the curve to the right changes its beginning and ending points to remain tangent (see Figure 5.9).
8: Close the drawing without saving.
Because this drawing was not changed, there is no “completed” version of the drawing.
Watch Complete video here for this exercise:
Editing Alignments using the Alignment Layout Tools
Grips are wonderful tools to edit geometry that is already there, but what if you need to add a PI or draw a curve? For that, you need the Alignment Layout Tools toolbar (see Figure 5.10). This toolbar is the same one you used initially to lay out the alignment.
Exercise 5.4: Apply the Alignment Editing Tools
In this exercise, you’ll edit the Jordan Court alignment using the Alignment Editing Tools. The goal is to create a perpendicular intersection where Jordan Court meets Emerson Road.
- Open the drawing named Editing Tools.dwg which you can download from Youtube video description below.
- Click the Jordan Court alignment, and then click Geometry Editor on the ribbon.
This opens the Alignment Layout Tools toolbar. - On the Alignment Layout Tools toolbar, click Insert PI. Then snap to the center of the circle marked A.
- Click Delete Sub-entity, and then click the curve at the PI marked B.
- Click the tangent between A and B to remove it as well. The alignment should now look like Figure 5.11.
6: Expand the curve button, and click More Floating Curves ➢ Floating Curve (From Entity End, Radius, Length).
7: Click the tangent near point A.
8: Type O and press Enter to indicate a counterclockwise direction.
9: Type 100 (30) and press Enter to provide the radius.
10: Type 100 (30) and press Enter to provide the curve length.
A short curve is placed at the end of the tangent.
11: On the Alignment Layout Tools toolbar, expand the curves button, and select Free Curve Fillet (Between Two Entities, Radius).
12: Click the curve you just created in the previous steps.
13: Click the red tangent that begins at point B.
14: Press Enter to indicate that the solution is less than 180 degrees.
15: Type R and then press Enter to indicate that it’s a reverse curve.
16: Type 100 (30) and press Enter to provide the radius. Press Enter to end the command.
The new curve is created in the drawing, as shown in Figure 5.12.
17: Save and close the drawing.
You can view the results of successfully completing this exercise by opening Editing Tools – Complete.dwg.
https://www.mediafire.com/file/o175lnw0c6jjmsh/Editing+Tools+-+Complete.dwg/file
Watch Complete video here from this Exercise:
Editing Alignments Numerically
At times, you may want to adjust your design by telling Civil 3D the exact dimension of a portion of the alignment. This can be done in one of two different ways. The first is Alignment Grid View, which opens a tab in Panorama. This tab shows the geometry of the alignment in table form and enables you to edit some of the values to adjust the design.
Exercise 5.5: Edit Alignments using Alignment Grid View
In this exercise, you’ll edit the Jordan Court alignment using the Alignment Grid View command.
- Open the drawing named Alignment Grid View.dwg which you can download from Youtube video description below.
- Click the Jordan Court alignment, and then click Geometry Editor on the ribbon.
- Click Alignment Grid View to open the Alignment Entities tab and display the tabular version of the alignment geometry, as shown in Figure 5.13.
- For the Radius values for items 2 and 3, type 150 (45) and press Enter.
Notice that the alignment updates automatically in the drawing. - Save and close the drawing.
You can view the results of successfully completing this exercise by opening Alignment Grid View – Complete.dwg.
https://www.mediafire.com/file/i9oah50o0svweqk/Alignment+Grid+View+-+Complete.dwg/file
Watch Complete video here for this Exercise:
Another method for editing the alignment design numerically is referred to as component-level editing. With this approach, you open the numerical data for a piece of the alignment (such as a line, curve, or spiral) in a separate window. You do so by clicking the Sub-entity Editor button on the Alignment Layout Tools toolbar and then using the Pick Sub-entity tool to choose the part of the alignment you want to edit.
Exercise 5.6: Edit Alignments using Component-level Editing
In this exercise, you’ll edit the Jordan Court alignment using component-level editing.
- Open the drawing named Component Level Editing.dwg which you can download from Youtube video description below.
- Close Panorama if it’s open. Click the Jordan Court alignment, and then click Geometry Editor on the ribbon.
- Click Sub-entity Editor on the Alignment Layout Tools toolbar to display the Alignment Layout Parameters dialog box. (This dialog box is blank when it first appears.)
4: Click Pick Sub-entity (see Figure 5.14), and then click the curve at the 90° bend on Jordan Court.
5: Type 50 (15) for Radius, and press Enter.
The curve in the drawing updates automatically.
6: Close the Alignment Layout Parameters dialog box and the Alignment Layout Tools toolbar.
7: Save and close the drawing.
You can view the results of successfully completing this exercise by opening Component Level Editing – Complete.dwg.
https://www.mediafire.com/file/kf640uyehnbbtln/Component+Level+Editing+-+Complete.dwg/file
Applying Design Criteria Files and Check Sets
When you’re laying out a design, how do you know whether you’re doing it right? What should the curve radii be? Should there be a minimum tangent length between curves, or is it OK to have back-to-back curves? How does the expected speed of traffic affect the answers to these questions?
The answers to these types of questions can differ, depending on the project. For road design, the government entity that accepts responsibility for the road is most likely calling the shots when it comes to design standards. That may be the state Department of Transportation (DOT), county planning commission, or even the community homeowners association. In other cases, you may be designing roads or other linear features on private property that isn’t governed by any official design standards. In this case, you’ll have to utilize your knowledge and experience to create the best design. Whether the design standards come from you or someone else, it’s helpful to have tools that ensure that your design meets the requirements assigned to it.
Design criteria and check sets are two ways of telling Civil 3D what your design standards are and asking Civil 3D to tell you when you’ve violated those standards by displaying a warning symbol (see Figure 5.15). These two features are customizable, so you can use them to represent any standard or combination of standards that is necessary.
Applying Design Check Sets
A design check set is a collection of one or more design checks. There are four types of design checks: line, curve, spiral, and tangent intersection. When a design check set is applied to an alignment, Civil 3D flags any violations with a triangular yellow shield marked with an exclamation point. You can hover over the shield to get more information about the violation, as shown previously in Figure 5.15.
Preloading Your Design Standards
If you work for a company that does projects in different jurisdictions with different design requirements, it would be a good idea to talk with your CAD manager about separate templates, one for each jurisdiction. Not only can these templates establish graphical standards as discussed previously, but they also can be set up with preloaded design-criteria files and design check sets that represent applicable design standards. With this type of setup, you can simply choose the right template before starting your design and proceed with confidence that a warning symbol will pop up if you have not met a requirement of the county, state, or client for whom you’re designing.
Exercise 5.7: Apply a Design Check Set
In this exercise, you’ll apply a design check set to the Jordan Court alignment and then make edits based on the results.
- Open the drawing named Design Check Set.dwg which you can download from Youtube video description below.
- Click the Jordan Court alignment, and then click Alignment Properties on the ribbon.
- In the Alignment Properties dialog box, click the Design Criteria tab.
- For Design Seed, type 25 (40), and press Enter.
- Check the box next to Use Criteria-Based Design.
- Uncheck the box next to Use Design Criteria File.
- Verify that Use Design Check Set is checked, and select Subdivision.
- Click OK to close the Alignment Properties dialog box. Press Esc to clear the grips on the alignment. You should see three yellow warning symbols in the drawing, as shown in Figure 5.16.
9. Zoom in to the curve farthest to the south. Hover your cursor over the yellow shield. A tooltip should appear, indicating that the Subdivision Curve design check has been violated.
10. Click the alignment to display its grips; then click the circular grip at the midpoint of the curve, and drag it northward to increase the radius of the curve. Repeat as necessary until the shield disappears.
11. Click the Jordan Court alignment, and then click Geometry Editor on the ribbon.
12. On the Alignment Layout Tools toolbar, click Alignment Grid View. Notice the yellow shields in the No. column as well as the bold values in the Radius column and several other columns (see Figure 5.17). This tells you which items have violations as well as which specific values are causing them.
13. For the Radius value of item 3, type 150 (45), and press Enter. The shield should disappear, and the bold values for item 3 should now show in normal print. The Radius value for item 5 will remain at 50′ (15 m).
14. Save and close the drawing. You can view the results of successfully completing this exercise by opening Design Check Set – Complete.dwg.
https://www.mediafire.com/file/i9l9pmd1g49jnpc/Design+Check+Set+-+Complete.dwg/file
Watch Complete video here for this exercise:
Applying Design Criteria Files
Exercise 5.8: Apply a Design Criteria File
In this exercise, you’ll apply a design criteria file to the Jordan Court alignment and then make edits based on the results.
- Open the drawing named Design Criteria Files.dwg which you can download from Youtube video description below.
Note that currently only one warning symbol is shown for the Jordan Court alignment. - Click the Jordan Court alignment, and select Alignment Properties on the ribbon.
- Click the Design Criteria tab. Check the box next to Use Design Criteria File.
- Click the button to the right of the file path, and select the file named Autodesk Civil 3D Imperial (2011) Roadway Design Standards.xml (or Autodesk Civil 3D Metric (2011) Roadway Design Standards.xml). Click Open.
- Uncheck the box next to Use Design Check Set.
- Click OK, and press Esc to clear the grips.
New warning symbols appear on the first, second, and fourth curves (the one on the third curve was there previously). As you can see, the design criteria file is a bit more stringent than the design check set of the previous exercise. - Hover your cursor over the warning symbol farthest to the north.
- Select the alignment, and click Geometry Editor on the ribbon.
- Click Alignment Grid View on the Alignment Layout Tools toolbar.
- Note that the minimum radius is listed in Panorama. Change the radius of items 2, 3, and 7 to 155 (48).
Do not edit item 5; it should remain set to 50′ (15 m). - Close Panorama, and observe the change to the alignment.
- Save and close the drawing. You can view the results of successfully completing this exercise by opening Design Criteria Files – Complete.dwg.
https://www.mediafire.com/file/pisobouqe9lawjj/Design+Criteria+Files+-+Complete.dwg/file
Watch Complete video here for this exercise:
You have the Power
Design check sets and design criteria files don’t change your design. They simply tell you when one of the rules has been broken. Depending on many factors, there will be times when you fix the issue to satisfy the rule and times when you don’t. In the previous case of the 50′ (15 m) radius, you know that Phase II of the project will create a T intersection at this location, which makes the sharp turn acceptable.
Now You Know
Now that you have completed this chapter, you have an understanding of alignments: their purpose, how to create them, and how to modify them. You’re able to create alignments from objects already in the drawing or create them from scratch using the Alignment Creation Tools. You can edit alignments graphically and numerically using a number of approaches. These include grips, Alignment Editing Tools, Alignment Grid View, and component-level editing. You now know how to apply design check sets and design criteria files to enable Civil 3D to keep track of how well your design adheres to your standards. Generally speaking, having completed this chapter, you’re ready to begin working with alignments in a production environment.
Watch All videos for this Chapter: