Create Roundabout
Icon: 
Introduction
This command is used to create a roundabout at an intersection. It works from alignments already defined, and assigns levels along the alignments based on a surface generated at the intersection from Road Strings and Kerb Return Strings.
It also changes the formation of the intersection to trim out the area under the roundabout area and to reconnect the pavement sections up through the intersection. An allowance is made to include a cross section to the internal island.
This command is suitable for many roundabout designs in typical subdivisions.
Designers can review the Vertical Grading design for the roundabout (normally the island) and adjust the vertical design as required.
The command relies upon the following being completed:
- The Roads and Kerb returns for the intersection are designed
- Two alignments have been created in the drawing
- Inner roundabout alignment - this is the central island alignment
- Outer roundabout alignment - this alignment defines the outer edge of the circulating carriageway (the outer extents of the area travelled by a vehicle moving through the roundabout)
The software will automatically assign profiles to the roundabout alignments based on the design surface, as well as trimming up the intersection with the
Auto Model command.
About the 'Roundabout' Alignments
Both alignments should be created in the same direction (either clockwise or counter-clockwise).
Alignments need to be either closed or have a small gap between the ends - the software will not create a roundabout from any alignment that doesn't appear to be closed.
For closed alignments, the software will vertically set the start and end elevations to match.
Roundabout Design Pre-Requisites
BEFORE running this command it is imperative that:
- The Roads and Kerb Returns have been designed to form an intersection, AND;
- TWO alignments exist to define the roundabout geometry:
1. An 'inner' alignment that defines the central island (normally the inner edge of the circulating carriageway - the lip of kerb)
2. An 'outer' alignment that defines the outer edge of the circulating carriageway.
An example of appropriate geometry is shown below:
The Green alignments define the Road centreline
The Red alignments define the Kerb Returns.
The intersection has been fully designed, with cross sections applied to all kerb returns and roads.
The two Blue alignments define the roundabout extents.
The inner alignment is to be used as the central island
The outer alignment is the extents of the travelled area of vehicles through the roundabout (outer edge of the circulating carriageway).
Special Note: It is important that the roundabout alignments do NOT cross the kerb return alignments (where the kerb alignments define the edge of the travelled way).
Alignment Notes:
For Civil 3D users, creating an alignment using the Fixed Curve - Circle options works well.
For non-Civil 3D users, alignments can be created from circles in the drawing.
Form Interface
The form is separated into three parts:
- Left side. This is the inputs area
- Right top section. This is a dynamic graphics window which will update as the user hovers over each input. It provides a visual description of what the input means
- Right Bottom section. Creates the Roundabout Strings and optionally trims out the Auto Model surface to incorporate the roundabout.
Details
At the command prompt "Select Roundabout to edit (alignment MUST exist)", pick the INNER alignment that defines the Roundabout. The following form is displayed:
|
Design Details |
Establish the parameters for creating the Roundabout |
|
Centre Alignment |
This is automatically populated with the name of the
alignment selected in the drawing Note: If this name does NOT match the name of the alignment that is for the inner edge of the roundabout, click on Cancel immediately and start the command again. |
 Highlight |
Click to toggle on/off a highlight over the alignment in the drawing |
| Alignment Direction | Non-editable text field advising of the direction of the selected alignment. |
|
Outer Alignment |
Use the pick list to select the alignment that describes the outer edge of the circulating carriageway for the roundabout |
| Highlight |
Click to toggle on/off a highlight over the alignment in the drawing |
|
Centre String Details |
Establishes the core parameters on the central island string - template for cross sections and the spacings between sections |
|
Template |
Pick list to select the section Template to apply. Note: The software will add/apply the code RDUM/LDUM in the cross sections and attach it horizontally and vertically to the string created from the Outer Alignment. |
|
Section Spacing |
Type in the spacing between calculated cross sections connected to the Centre Alignment. |
|
Intersection Elements |
Establish the elevations for the Centre Alignment and Outer Alignment strings by setting the intersection strings for the tee/cross road intersection |
|
Setup Elements Automatically |
This will automatically populate the Road Strings list and Ker Strings lists with all Road and Kerb Return Strings detected in the vicinity of the roundabout alignment. |
| Road Strings | Set the Roads that need to be adjusted for the roundabout to be included. Normally this requires no editing |
| Add String | Click on the Add String button and select a Road String from the drawing. It will be added to the list. |
| <List of Road Strings> |
Road Strings are listed with user controllable Start and End Chainages.
These are used to create the temporary (pre roundabout) surface for elevations. Note: Use the [backspace] button to remove the Road Name if the incorrect road string has been added |
| Kerb Strings | Set the Kerbs that need to be adjusted for the roundabout to be included. Normally this requires no editing |
| Add Kerb | Click on the Add Kerb button and select Kerb String from the drawing. It will be added to the list. |
| <List of Kerb Strings> |
Kerb strings are listed These are used to create the temporary (pre roundabout)
surface for elevations. Note: Use the [backspace] button to remove the Kerb Name if the incorrect road string has been added |
| Hover Image | This window will update
based on the hover location of the mouse on the form. |
|
Build Intersection Model |
Create the Roundabout Intersection and optionally include it in the Auto Model creation process |
|
Create Intersection Model |
Click here to create two surfaces - a Base surface and a Final Surface. The Final surface will be displayed - named RND-<Name of Inner Roundabout Alignment>-FinalModel. |
| Include Roundabout in Total Model Surface Model | Tick this ON for the roundabout to be included in the  Auto Model command. The
Total Model surface will update to incorporate the roundabout strings - kerbs and roads will trim to the outer roundabout alignment extents. |
|
Delete |
Click here to delete the Roundabout Strings and remove the string information from Auto Model (if added). |
|
OK |
Exit the form |
| Zoom Intersection | Zooms to the highlight String in the Road or Kerb String list. |
Zoom/Pan |
Click to temporarily close the form to allow zoom/pan via middle mouse. Press [Enter] or [esc] to return to the form |
| Cancel | Exit the form. |
Example output:
Outputs
Assuming that Include Roundabout in Totalmodel Surface was ticked on, run the Auto Model command to generate a surface model incorporating the roundabout:
Editing the Vertical Grading of the Roundabout
After creating the roundabout, designers can use the 
Vertical Grading Editor to adjust the cross sections or profile design.