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TrainingRoads
DifficultyadvancedAdded2027.0Statusdraft

Roundabout Design (advanced training)

The image below shows a cross intersection with road descriptions. The roundabout will be designed where Road 1 and Road 2 are intersecting.

The workflow below assumes that the corridors, profille views as well as the corridor top surface are already created. In this workflow the Corridor Wizard was used. The veritcal alignment of Road 1 and Road 2 have been adjusted as shown in the images below:

An auxiliary corridor and surface must be created over the region where the roundabout will be situated. In the image below, the region from chainage 220m to 280m will be the start and end station of the auxiliary corridor.

  1. Go to the profile view of Road 1 and draw two vertical construction lines at chainage 220m and 280m. The keyboard shortcut, "XL – Enter", can be used to draw the construction lines as shown in the image below:

  2. Go to Home – Profile – Profile Creation Tools and select the profile view:

  3. Specify the profile Name as VA Auxiliary Corridor, Profile style and the Profile label set:

  4. Select the first dropdown and select Draw Tangents:

  5. Specify the start and end station of the profile:

  6. Go to Corridors in the menu bar and select Create Assembly:

  7. Specify the assembly Name and click OK:

  8. Specify the assembly insertion point. In the Home tab of the ribbon go to the Subassembly Tool Palette:

  9. Select the LinkWidthAndSlope subassembly in the Generic tab of the tool palette:

  10. Select the right-hand side of the assembly marker to add the subassembly to:

  11. Select the LinkWidthAndSlope subassembly and change the width to 11m and the slope to 2.5%. The width of the link needs to be wide enough to cover the entire intersection, including the radii of the curves. The Properties window can be accessed by pressing Ctrl – 1 on the keyboard. The slope of the link matches the slope of Road 1 in this example:

  12. Select the LinkWidthAndSlope subassembly, right- click and select mirror:

  13. Select the left-hand side of the assembly marker and change the slope of the link to -2.5%. It is critical to never use keyboard shortcuts or the Civil 3D modify commands to copy, move or mirror a subassembly in an assembly. Always use the available right-click options.

  14. Go to the Home tab – Corridor:

  15. Specify the corridor Name, Alignment, Profile and Assembly. Tick the option to Set baseline and region parameters. Click OK:

  16. Change the corridor region start station to 221m and end station to 279m. It is important to make sure the corridor doesn't start at a station before a chainage of 220m or end after a chainage of 280m because the vertical alignment does not extend beyond those stations and would result in a surface targeting a zero elevation. This is sometimes referred to as a waterfall:

  17. Click OK and rebuild the corridor:

  18. Select the Auxiliary Corridor – right-click and go to the Corridor Properties. In the Surface tab, click on the left icon to create a corridor surface. Click on the plus icon to add the Top links to the surface. Click OK and rebuild the corridor. The surface style will be switched to No Display for clarity.

  19. Go to the Home tab – Alignment – Alignment Creation Tools:

  20. Specify the alignment Name, Alignment type, Alignment style and the Alignment lable set. Click OK:

  21. In the Alignment Layout Tools, select the curve dropdown – More Fixed Curves – Fixed Curve (Centre point and radius):

  22. Specify the intersection point between the horizontal alignment of Road 1 and Road 2, choose a clockwise direction and specify the radius of the circle:

  23. In the Home tab, go to Profile – Create Surface Profile:

  24. Select the Roundabout Outer Edge alignment and the Auxiliary Corridor surface. Click on the Add button to add the surface to the profile and select Draw in profile view:

  25. Specify the Profile view name and Pofile view style:

  26. Specify the profile view band set and click on Create Profile View:

  27. Specify the profile view location. This surface profile is created to have the ability to target the surface profile when setting the width and elevation targets of the corridor.

  28. Draw the roundabout bellmouth alignments. Go to the Home tab – Alignment – Alignment Creation Tools:

  29. Specify the alignment Name (in this example the quadrant direction NW for North West is used). For the alignment Type use Curb Return (Civil 3D term for bellmouth). All the bellmouth alignments will be listed under Curb Retun alignments in the Prospector of the Toolspace. For the Alignment Style use No Plot Style | Curb Return which is automatically in the C3D-No Plot Objects layer, this style also shows the alignment direction. For the the Alignment label set use _No Labels, there is no need to display the chainage labels:

  30. For the bellmouth alignment tangents, use Fixed Line (Two points):

  31. Draw tagents on top of the Road 1 and Road 2 edge of traveled ways (ETW). For the NW quadrant bellmouth alignment, draw the alignment from Road 1 to Road 2. The direction of the two fixed tangent lines must be the same:

  32. For the curved alignment along the roundabout outer edge, use Fixed Curve (Three point):

  33. The midpoint can be adjusted manually if necessary, and the snap overrides (Shift – Enter) can be used to snap to a specific point.

  34. For the bellmouth alignment curves, use Free Curve Fillet (Between two entities, radius):

  35. Follow the command line prompts. When selecting the First Entity, select the first tangent in the chainage direction. Click on a direction arrow to select the tangent:

  36. For the Next Entity select the start station of the curve:

  37. For a curve solution angle use the Lessthan180 option:

  38. Specify that the curve is a Reverse curve:

  39. Specify the curve radius and press Enter. In this example a 10m radius was used:

  40. For the second bellmouth alignment curve, use Free Curve Fillet (Between two entities, radius):

  41. Follow the command line prompts. When selecting the First Entity, select the end station of the curve:

  42. For the Next Entity select the second tangent in the chainage direction:

  43. For a curve solution angle use the Lessthan180 option:

  44. Specify that the curve is a Reverse curve:

  45. Specify the curve radius and press Enter. In this example a 10m radius was used:

The created horizontal alignment:

  1. Create the bellmouth alignments for the remaining quadrants. Use the same steps as described for the Roundabout NW Quadrant alignment. Use the same directions as indicated in the image below, it will allow the use of only one assembly for the bellmouth alignments and one assembly for the transition regions between the bellmouth curves on the roundabout outer edge. The follwing alignment names can be used:

  2. The Road 1 and Road 2 corridors should not extend through the roundabout, therefore the corridor region can be removed in the region where the roundabout is situated. Select the Road 1 Corridor – right-click and select Corridor Properties:

  3. In the Corridor Properties, Parameters tab, right-click on Region 1 and select Split Region:

  4. Specify the start and end split region of the corridor and select the middle region where the roundabout is located. Right-click on the middle region and select Remove Region:

  5. Click OK and rebuild the corridor. Select the Road 1 Corridor – right-click and select Corridor Properties:

  6. In the Corridor Properties, Surfaces tab, change the surface style of Road 01 Top and Road 01 Datum to Triangles, and click OK:

  7. The triangulation across the roundabout region from the Road 01 Top and Road 01 Datum surface can be deleted by selecting the surface and in the Contextual Ribbon, go to Edit Surface – Delete Line:

  8. Select the surface lines across the roundabout region and press Enter. This can be done for both the Road 01 Top and Road 01 Datum surface:

  9. The above steps can be repeated for the Road 2 Corridor:

  10. Create an assembly for the Roundabout. Go to Corridor in the menu bar and select Create Assembly:

  11. Specify the assembly Name and click OK:

  12. Specify the insertion point of the assembly. The Roundabout assembly will follow the Roundabout Outer Edge alignment and therefore nothing will be added to the left of the assembly centreline. In the Home tab of the ribbon, go to the Subassembly Tool Palette:

  13. In the Tool Palette, Basic or Lanes tab, select the GernericPavementStructure subassembly:

  14. Add the GenericPavementStructure subassembly to the right-hand side of the assembly centreline:

  15. Select the GenericPavementStructure subassembly and modify its properties as shown in the image below:

  16. Select the GernericPavementStructure subassembly in the Basic or Lanes tab of the Tool Palette and add the GenericPavementStructure subassembly to the bottom-left circle (point code) of the first layer:

  17. Select the second layer (Layer 2) or bottom GenericPavementStructure subassembly and modify its properties as shown in the image below:

Note: The Width and Default Cross Slope of Layer 2 has not been adjusted because the layerworks can be linked together in terms of width and slope through the assembly properties. The default depth of 0.2m will be used in this example:

  1. Select the Roundabout assembly centreline, right-click and select Assembly Properties:

  2. In the Construction tab of the Assembly Properties, select the RB Layer 2. For the Width input value in the Get Value From column, tick the option to use a parameter reference and specify RB Layer 1.BottomWidth. For the Default Cross Slope input value in the Get Value From column, tick the option to use a parameter reference and specify RB Layer 1.CrossSlope:

The width and the slope of the RB Layer 2 is now driven through the width and slope of the RB Layer 1, therefore only the RB Layer 1 needs to be used when targeting widths and elevations through the Corridor Properties:

  1. A barrier kerb can be copied from the Devotech Assemblies Drawing into the current design drawing. Go to the iDAS tab, Resources and select the Assemblies Drawing.

  2. In the Devotech Assemblies Drawing, go to the Home tab and open the Subassembly Tool Palette:

  3. Right-click on any of the subassembly tabs and select New Palette:

  4. Give the New Palette a name for instance Devotech Assemblies. Select the centreline of the assembly to be copied, hover with the mouse over the centreline, left-click and hold the left mouse button to drag and drop the assembly to the Devotech Assemblies tab in the tool palette:

  5. The barrier kerb assembly can now be used in the design drawing. Select the Barrier Kerb SABS (Fig 3) subassembly and choose the insertion point of the assembly in the roundabout design drawing. Select the barrier kerb on the right hand side of the assembly centreline, right- click and select Copy to:

  6. Select the ETW point code of the first Layer as the insertion point of the barrier kerb:

  7. The GenericPavementStructure subassembly can also be used as a shoulder. In the Home tab go to the Subassembly Tool Palette:

  8. In the Tool Palette's Basic or Lane tab, select the GernericPavement Structure subassembly in:

  9. Add the GernericPavementStructure subassembly to the back of the barrier kerb:

  10. Select the GernericPavementStructure subassembly and specify the follwing properties:

  11. In the Generic tab of the subassembly Tool Palette, select the LinkWidthAndSlope subassembly and add it to the Sidewalk_Out point code of the RBSidewalk subassembly:

  12. Select the LinkWidthAndSlope subassembly and modify its properties to match the following Parameters:

The Roundabout assembly should look like the image below:

  1. In Generic tab of the subassembly Tool Palette, select the LinkWidthAndSlope subassembly and add it to the P2 point code of the previous LinkWidthAndSlope subassembly:

  2. Select the LinkWidthAndSlope subassembly and modify its properties to match the following parameters:

Note that the total width of the assembly is equal to the radius of the Roundabout Outer Edge alignment:

  1. Create the Roundabout corridor. Go to the Home tab – Corridor. Specify the corridor Name, Alignment, Profile, Assembly and Target Surface. Click OK:

The Roundabout corridor will display in plan as shown in the image below:

  1. Select the Roundabout corridor in plan – right-click and select Corridor Properties:

  2. In the Surfaces tab, click on the left icon to create a corridor Top surface. Click on the plus icon to add the Top links to the surface. Set the Overhang Correction to Top Links:

  3. In the Surfaces tab, click on the left icon to create the corridor Datum surface. Click on the plus icon to add the Datum links to the surface. Set the Overhang Correction to Bottom Links:

  4. In the Boundaries tab of the Corridor Properties, right-click on the Roundabout Top Surface and Roundabout Datum Surface and select Corridor extents as outer boundary:

  5. Click OK and rebuild the corridor:

  6. The surface style will be switched to No Display for clarity. The verical alignment of Road 1 and Road 2 need to be revised to tie in with the Roundabout Top Surface. To add the top surface to the profile view, go to iDAS – Profiles – Add Surface:

  7. Select the Roundabout Top Surface and click OK:

  8. Select the profile view of Road 1 and Road 2 and press Enter. Specify the Profile Style and Label Set Style and click OK:

  9. Click No:

The top surface of the roundabout will now appear in the profile view:

  1. Update the vertical alignment of Road 1 and Road 2 to follow the Roadabout Top Surface by adding additional PVI's. Please note that the VA Auxiliary Corridor profile may be adjusted and the slope of LinkWidthAndSlope subassembly in the Auxiliary Corridor may be adjusted to suit the design requirements. When any changes are made, the corridors need to be rebuilt to reflect the changes in the profile views.

The adjusted Road 1 vertical alignment is shown in the image below:

The adjusted Road 2 vertical alignment is shown in the image below:

  1. Once all the vertical alignment adjustments have been made and the corridors have been adjusted, go to the Home tab – Profile – Create Surface Profile:

  2. Specify the Alignment and add the surfaces to the profile list as indicated in the image below. The Road 1 Top Surface , Road 2 Top Surface and the Auxiliary Corridor 1 surface can be added. Select Draw in profile view:

  3. Specify the Profile view name and Profile view style:

  4. Specify the profile styles:

  5. Specify the profile view band set:

  6. Select Create Profile View and specify the insertion point of the profile view. The same steps can be followed to create profile views from the Roundabout NW Quadrant, Roundabout SE Quadrant add the Roundabout SW Quadrant:

Note: The vertical yellow lines in the profile views indicate the start and end station of the horizontal curve which should be used as a guide to draw in the vertical alignment profile for each profile view.

  1. In the Home tab go to Profile – Profile Creation Tools:

  2. Select the profile view (Roundabout NW Quadrant) and specify the Profile style and Profile label set:

  3. In the Profile Layout Tools, select the first dropdown and select Draw Tangents:

  4. Follow the road surface profile up to the vertical line which represents the BCC of the alignment, go across to the ECC/ BCC of the reverse curve which is the next vertical line. Follow the profile of the Auxiliary Corridor Surface up the the ECC/BCC of the reverse curve, go across to the ECC of the alignment and follow the road surface profile:

The above step can be followed for the remaining profile views. Remember to create a separate profile for each profile view by repeating the follwing step:

  1. In the Home tab go to Profile – Profile Creation Tools:

  2. The vertical scale of the kerb return profile view is exagerated ten (10) times. Additional vertices may be used when following the surface profiles:

  3. Create the assembly for the roundabout bellmouth and the transition region. The transition region assembly will not have any layerworks on the right-hand side of the assembly centreline:

  4. Create the following typical assembly, called RB Bellmouth, for the roundabout bellmouth by taking into consideration the direction of the quadrant alignments:

  5. Create the following typical assembly, called RB Bellmouth Transition, for the roundabout bellmouth transition region by taking into consideration the direction of the quadrant alignments:

  6. Select the roundabout corridor in plan – right-click and select Corridor Properties:

  7. In the Parameters tab of the Corridor Properties, click on Add Baseline and specify the Baseline name and Horizontal alignment. Click OK:

  8. Specify the vertical Profile which the baseline needs to use and click OK:

  9. Right-click on the Roundabout NE Quadrant baseline and select Add Region:

  10. Specify that the RB Bellmouth assembly must be used over the corridor region and click OK:

  11. Click on the plus sign next to the Roundabout NE Quadrant baseline and specify the start and end station of the assembly:

  12. Specify the frequency to be used over the RB Bellmouth region of the corridor by selecting the ellipsis button in the Frequency field of the Corridor Properties and click OK:

  13. Specify targets by selecting the ellipsis button in the Target field of the Corridor Properties. In the Target Mapping window, click on the <None> field and choose the surface (NGL) as the surface target:

  14. Under the Width or Offset Targets, click on the <None> field of the assembly's top layer. All the layers in the assembly are linked in terms of width and slope to the top layer, therefore it is only necessary to use the top layer to target an alignment or polyline in the corridor properties:

  15. In the Set Width or Offset Target window, specify the object type as Alignments and select the relevant alignment from the list or use the green box icon to Select the alignment from model space. Once an alignment is selected, click on the Add button:

  16. The first region of the Roundabout NE Quadrant needs to target the horizontal alignment of Road 2 and the Roundabout Outer Edge alignment. After selecting these alignments, click OK:

  17. Under the Slope and Elevation Targets, click on the <None> field of the assembly's top layer. All the layers in the assembly are linked in terms of width and slope to the top layer, therefore it is only necessary to use the top layer to target an alignment or polyline in the corridor properties:

  18. In the Set Slope or Elevation Target window, specify the object type as Profiles and select the relevant alignment from the dropdown or use the green box icon to Select the alignment from model space. Once an alignment is selected, the profile which the layer needs to target can be selected from the list, click Add. Add VA Road 02 from the Road 02 alignment as an elevation target:

  19. Add the Auxiliary Corridor 1 Profile from the Roundabout Outer Edge alignment as an elevation target:

  20. Click OK to close the Set Slope Or Elevation Target window and click OK to close the Target Mapping window.

  21. In the Parameters tab of the Corridor Properties, right-click on the RB Bellmouth region of the Roundabout NE Quadrant and select Insert Region – After:

  22. Specify that the RB Bellmouth Transition assembly must be used over the corridor region and click OK:

  23. Under the Roundabout NE Quadrant baseline, specify the End Station of the assembly:

  24. Specify the frequency to be used over the RB Bellmouth Transition region of the corridor by selecting the ellipsis button in the Frequency field and click OK:

  25. Specify the targets by selecting the ellipsis button in the Target field. In the Target Mapping window, click on the <None> field and specify the surface (NGL) as the surface target:

  26. The RB Bellmouth Transistion assembly does not have any lanes, therefore no width or offset targets and slope or elevation targets need to be specified. Click OK. Right-click on the RB Bellmouth Transition region of the Roundabout NE Quadrant and select Insert Region – After:

  27. Specify that the RB Bellmouth assembly must be used over the corridor region and click OK:

  28. Under the Roundabout NE Quadrant baseline, specify the end station of the assembly:

  29. Specify the frequency to be used over the RB Bellmouth Transition region of the corridor by selecting the ellipsis button in the Frequency field and click OK:

  30. Specify the targets by selecting the ellipsis button in the Target field. In the Target Mapping window, click on the <None> field and specify the surface (NGL) as the surface target:

  31. Under the Width or Offset Targets, click on the <None> field of the assembly's top layer. All the layers in the assembly is linked in terms of width and slope to the top layer, therefore it is only necessary to use the top layer to target an alignment or polyline in the Corridor Properties:

  32. In the Set Width or Offset Target window, specify the object type as Alignments and select the relevant alignments from the list or use the green box to Select the alignment from model space. Once an alignment is selected, click on the Add button:

  33. The third region of the Roundabout NE Quadrant needs to target the horizontal alignment of Road 1 and the Roundabout Outer Edge alignment. After selecting these alignments, click OK:

  34. Under the Slope and Elevation Targets, click on the <None> field of the assembly's top layer. All the layers in the assembly is linked in terms of width and slope to the top layer, therefore it is only necessary to use the top layer to target an alignment or polyline in the Corridor Properties:

  35. In the Set Slope or Elevation Target window, specify the object type as Profiles and select the relevant alignment from the dropdown, or use the green box icon to Select the alignment from model space. Once an alignment is selected, select the profile which the layer needs to target from the list and click Add. Add the VA Road 01 from the Road 01 alignment as an elevation target:

  36. Add the Auxiliary Corridor 1 Profile from the Roundabout Outer Edge alignment as an elevation target:

  37. Click OK to close the Set Slope Or Elevations Target window and click OK to close the Target Mapping window. Click OK to close the corridor properties window and select Rebuild the corridor:

  38. The above workflow can also be used for the remaining quadrants of the roundabout, namely Roundabout NW Quadrant, Roundabout SE Quadrant and the Roundabout SW Quadrant. Each quadrant will have its own baseline as shown in the image below:

  39. The frequency of the roundabout itself can be adjusted to match the bellmouth and transition assemblies to get a smoother surface. Select the Roundabout corridor – right-click and select Corridor Properties. In the Parameters tab, click on the ellipsis button to set the Frequency of the Roundabout Outer Edge alignment baseline, use the Roundabout assembly:

  40. Set all the frequencies to 1.00m:

  41. In the Surface tab of the Corridor Properties, change the surface Style of the Roundabout Top Surface to Triangles. Click OK and Rebuild the Corridor:

  42. Select the Roundabout Top Surface – right-click and select Object Viewer:

  43. The irregularities on the surface can be viewed by selecting the Shades of Gray view style:

  44. To fix the irregularities on the surface, select the Roundabout Corridor and use the grip points to ammend the transistion region start and end station, positioning it just off the Roundabout Outer Edge alignment:

Note that if you view the Roundabout Top Surface in the Object Viewer, there is still some surface irregularities around the outer edges of the roundabout:

  1. These surface irregularities can be removed by adding manual frequencies. Select the Roundabout corridor – right-click and select Corridor Properties. In the Parameters tab, select the first region of the Roundabout NE Quadrant baseline (Region 8) and select the ellipsis button next to the Frequency:

  2. Click on the plus sign icon to add manual frequency stations:

  3. Click multiple times along the Roundabout NE Quadrant alignment and press Enter. The ideal location of these frequency points is located at corners of other triangles from other regions and the triangles should line up:

All the stations will be listed in the bottom window:

  1. The above steps can be repeated for each region within the baseline. The snap settings can be switched off to make the selection of multiple stations easier, the Triangle surface Style can be used to see where the triangles are not following the kerb: