Roundabout Design - Part 1

AUTODESK® CIVIL3D

Design of Roundabouts using Corridor Models (Part 1 of 2) Dynamic vertical modeling By Jack Strongitharm Civil 3D Technical Sales Manager UK and Ireland [email protected] August 2006

www.autodesk.co.uk/civil3D-downloads

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Contents Introduction......................................................................................3 Full Geometry Based Design...........................................................4 Step One. – Horizontal Design ........................................................5 Step 2. – Vertical Design, use of a Tilted Plane ..............................6 Step 3. – Using Corridors for Level Information, ICD.....................10 Step 4. – Centreline Vertical Profile Design...................................13 Step 5. – Using Corridors for Level Information, Centrelines.........15 Step 6. – Vertical Profile Design of the Crownlines .......................16 Step 7. – Final Roundabout Corridor Design.................................19 Step 8 – Create a Surface of the Roundabout...............................32 Step 9. – Calculation of Volumes ..................................................35 Step 10. – Dynamic Adjustments ..................................................39 Summary .......................................................................................41 Acknowledgments .........................................................................42


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Introduction Roundabout design has always been a complex process. And, because they are generally expensive to build and take a large amount of space, not that many designed. Engineers, therefore, are not well practiced in their design. However, they are becoming more popular. They do have advantages over traffic signals and maintain free-flowing movement including Heavy Goods Vehicles (HGVs). In general, roundabouts can be divided into two main categories; 1. Full geometry-based design 2. Mini roundabouts This workflow guide will approach both in two separate documents. This first workflow guide will work up a full geometry-based roundabout model using corridors. Please note: The requirements within this workflow are primarily based on Autodesk Civil 3D 2007 functionality. However it can be created in 2006 but there are extra benefits from new functionality in 2007. Also it is advisable to have a good knowledge of Civil 3D and of the subject matter. Throughout the design, the naming of all the civil objects is key to being able to bring the final design together in a logical manner.


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Full Geometry Based Design This workflow will concentrate on the vertical design for a full geometry roundabout. It is assumed that the horizontal is relatively straightforward and can be done using either Civil 3D alignment layout tools or AutoCAD drafting tools to create the geometry needed. Methods of design can vary but the main method of vertical design is the ‘Stockdale Method’ mor also known as 2/3 crown lines. This method was development by Mr R. Stockdale in the 1970s. Since then it has become main method of design in the UK. Its approach is to design an Inscribed Circle Diameter (ICD) and crown lines that intersect the ICD. Then levels and offsets can be applied to create the kerb lines, footpaths etc.

From ‘The Journal of the Institution of Highways Engineers, August/September 1978

This approach works especially well with Civil 3D, as the Assembly technology is able to create all features from a baseline, i.e. the crown line. Also the use of corridor surfaces means that you can graphically see other intersecting alignments, such as roads etc to enable a clean accurate tie in.


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Step One. – Horizontal Design Create the ICD, centreline and 2/3 crown lines horizontally using alignments For detailed guidance on this area of design refer to ‘DMRB TD 1693a’ (http://www.standardsforhighways.co.uk/dmrb/index.htm)

Below is the example that will be used, refer to drawing The alignments have been named with a suitable convention to assist in the process Civil 3D Dynamic Roundabout - Step 1.dwg to start from the beginning or move to Step 2


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Step 2. – Vertical Design, use of a Tilted Plane Refer to drawing Civil 3D Dynamic Roundabout - Step 2.dwg

To start the vertical design, we need to start from the ICD. So as a guide for levels the use of a tilted plane would give a reference for levels and ensuring drainage. It can also be used as the actual profile design.

Draw a line through the roundabout as shown below . Using the feature line toolbar, Select the ‘create from object’ and convert this line to a feature line. It is good practice to create grading features in a separate ‘Site’ from the alignments. Drape to the ground surface using ‘levels from surface’

Using the ‘quick level edit’

and uncheck ‘Insert intermediate gradient break points’

set the levels and or set a gradient such as 1% down from one side to the other


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Create a grading object from the ‘Grading’ menu

Using the grading tools offset the line both sides by -1% to the left and +1% to the right. These values depend on your requirements. As with the grading object, these values can be amended at any stage.


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Automatically created on completion will be a triangulated surface

Resultant surface from the ‘Grading Object’


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Create a profile from surface for the alignment ICD and select both the ‘EG’ Surface the grading surface ‘Tilted Plane’ Surface. Assign the ‘Tilted Plane’ Surface profile a different profile style to change colour, in this case, ‘Additional Surface1’.

This creates a dynamic Sine Curve. This acts as either a guide to design the vertical profile of the ‘ICD’ or can be used as the actual profile in the design. In this example we will use this as the actual profile in the design.

It is not necessary to draw this profile, but it will give a good understanding of what has been created by the grading ‘Tilted Plane’. EG Surface Tilted Plane Surface


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Step 3. – Using Corridors for Level Information, ICD Refer to drawing Civil 3D Dynamic Roundabout - Step 3.dwg (Grading lines are hidden for clarity) Subassemblies and Assemblies The subassembly lane type most suitable for this application is ‘Lane with outside Super’. This subassembly has the ability to widen to an alignment and also raise the edge to a profile. Also if desired you can set the pavement depths to 0 to omit any pavements you do not require.

Create an ‘Assembly’ for the ICD road

Consists of a lane to each side of the Marker. A kerb and a footpath/verge to the right of the lane We will use this assembly to create a temporary corridor. This is to create a surface that will be referenced for the actual design. When creating the corridor, use the ICD alignment, the ‘Tilted Plane’ profile, and the assembly created above.

Name the corridor ‘ICD Temporary Surface’ and set frequency to 5m (see figure below).


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From this corridor create a surface from using the ‘Top’ link codes


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To clean the workspace in the drawing change the surface style for the ‘ICD Temporary Surface’ to ‘All Off’ and also create a layer such as ‘Hidden Roads’ and change this corridor to that layer and freeze it off. In addition set this corridor in the prospector to automatic rebuild. This will rebuild to any changes to the ‘Tilted Plane’ grading object.


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Step 4. – Centreline Vertical Profile Design Refer to drawing Civil 3D Dynamic Roundabout - Step 4.dwg (Previous Corridor hidden to ‘Hidden Roads’ layer)

Create the profiles for the three centerlines . Use in addition to the ‘EG’ Surface, the ‘ICD Temporary Surface’.

Then design the new vertical profile for these centerlines and tie into the ‘ICD Surface’.

It is not necessary to create a profile on the kerb face and into the centre of the roundabout as these profiles are only used in part.


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Example profile design. The profile ties into the carriageway surface of the ICD, then extends the grade of that surface and then can continue to the desired levels.


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Step 5. – Using Corridors for Level Information, Centrelines Refer to drawing Civil 3D Dynamic Roundabout - Step 5.dwg In this section we are going to create a guide for designing the crownline profiles by using corridor surfaces. These will be used in the profile views to display where 1:40 (2.5%) would be on the Crownline profiles.

Create corridors and corridor Surfaces from the centerlines Create from an assembly with two lanes (see figure below).

Setting the pavement depths to 0 to omit them, as we do not require quantities from these corridors.

Add these corridors to the ‘Hidden Roads’ layer and turn the surface style to ‘All Off’

Now there is all the level information required to design the crown lines accurately.


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Step 6. – Vertical Profile Design of the Crownlines Refer to drawing Civil 3D Dynamic Roundabout - Step 6.dwg Now that we have all the reference surfaces we need, we’ll create the crownline profiles. When sampling for the crownline profiles, make sure to include both the ‘EG’ Surface, add the temporary corridor surfaces that it crosses. In this example for the ‘North Crownline’, we see the ‘West Temporary Surface’, the ‘ICD Surface’ and the ‘North Surface’. Use different surface styles to give a different colour for clarity.

To find the intersecting area of the crownlines and the ICD, use alignment labels to add labels that mark out the intersection of the crown lines to the ICD.

The Horizontal Geometry band also shows this area. Look for the radius of the ICD. In this case 31.35m.

Mark on the profile views, using a vertical line and then offset to the chainage values www.autodesk.co.uk/civil3D-downloads

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When designing the vertical profile ensure that between the two lines, directly follow the surface of the ICD. Then grade out accordingly. The two other surfaces show where 1:40 (2.5%) would be, so to maintain a regular grade where possible.

Example of vertical profile design www.autodesk.co.uk/civil3D-downloads

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Remaining two crownline profile designs


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Step 7. – Final Roundabout Corridor Design Refer to drawing Civil 3D Dynamic Roundabout - Step 7.dwg Treat the Roundabout as one corridor model. The corridor will be built from the crownlines with the use of the centrelines and the ICD for widening lanes and level. This method will use multiple baselines and regions. Assemblies required. You should at this point name the carriageway lanes, such as ‘Left’ and ‘Right’. As later in the exercise you will need to identify the individual subassemblies to target to alignments and profiles.

‘Crown Lines Left Edges’ (Lane on the right will act as a widening, so lane width and slope does not have to be set to a specific value.)


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‘Crown Lines Right Edges’ (a mirror of the previous detail)

ICD Roundabout (Lane at the required width and slope, kerb and footway. It is not necessary for the footway/verge strip to the right as a COGO point could be added to the resultant corridor surface later in the design)


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Create the corridor from a crownline, in this case ‘West to North Centreline’, using a frequency of 5m and set the end chainage to the intersection of the centerline and the ICD.

Location of intersection of centreline and ICD


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Set the targets Alignments = Subassembly named ‘Right’ to the ‘West Centreline’ (to widen this lane out to the alignment) Profile = Subassembly named ‘Right’ to the ‘West Centreline’ alignment and profile ‘Vertical’.


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Click on ‘OK’ to build the corridor.

Under the corridor properties, add a second region. Choose the same assembly and set the end chainage to the intersection of the ICD to the second centreline as shown above. www.autodesk.co.uk/civil3D-downloads

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Set the targets to the Alignment = Subassembly named ‘Right’ to ‘ICD’ Profile = Subassembly named ‘Right’ to ICD alignment and profile ‘Tilted Plane – Surface’

Rebuild the corridor


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Add region 3 with the end chainage running out to the end of the alignment.

Set the targets Alignment = Subassembly named ‘Right’ to ‘North Centreline’ Profile = Subassembly named ‘Right’ to ‘North Centreline’ alignment and profile ‘Vertical’


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Rebuild the corridor. This section is complete

Final corridor properties of this section.

Click on the to add a second baseline to add the second Crownline, North to South Crownline and then create this part of the corridor as above using the same assembly ‘Crown Lines Left Edges’. Targeting region 1 = ‘North Centreline’, region 2 = ICD and region 3 = ‘South Centreline’.


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Then repeat for the third crownline ‘West to South Crownline’. Using ‘Crown Lines Left Edges’ assembly. Targeting, region 1 = ‘West Centreline’, Region 2 = ICD, region 3 = ‘South Centreline’ Uncheck the previous baseline while you build each section to save time rebuilding the corridor.

Second baseline of the corridor

Third baseline of the corridor www.autodesk.co.uk/civil3D-downloads

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Corridor properties

Finally add the final baseline to create the lane, kerb and footpath/verge area on the inside of the ICD

Create using the ‘Tilted plane’ as the profile


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If you are using the ‘Tilted Plane’ surface rather than a design profile set the frequency to a regular interval and change to ‘no’ on the extra frequency interval positions such as profile geometry etc, as it will create more intervals than required.


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Recheck the remaining baselines of the corridor to ‘On’, set the target surfaces for the earthworks to ‘EG’ and rebuild.


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Final Roundabout Corridor

To tidy the arms at the ends, additional baselines maybe required to obtain a clean finish so to run a normal Corridor model up to the roundabout for each approaching arm.


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Step 8 – Create a Surface of the Roundabout Refer to drawing Civil 3D Dynamic Roundabout - Step 8.dwg Go to the corridor properties and click on the surface tab. Create a surface to the ‘Top’ link codes and give a suitable style for the display such as ‘Contours and Slope Arrows’ to understand the flow of the surface

Add a boundary to restrain the triangulation to the Daylight Feature Line. (Refer to Workflow – Corridor Surface Interactive Boundaries, www.autodesk.co.uk/civil3D-downloads for further information)


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Set the use type to an outside boundary’

Surface of the Roundabout


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3D View of the Surface


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Step 9. – Calculation of Volumes Refer to drawing Civil 3D Dynamic Roundabout - Step 9.dwg To calculate the cut and fill earthwork volumes, create another surface to the roundabout corridor. Create the surface to the ‘Datum’ link codes. Also add a boundary to the ‘Daylight Feature Lines’. This will create a surface to the underside of the paved materials, as this is the true earthworks and the paved materials of the corridor can be reported separately.

Use draw order to move the top surface to the back so to be able to choose the corridor feature lines for the boundary.

Corridor properties, set the style to ‘All Off’ as you do not need to see this surface.

Create a TIN volume surface from the ‘EG’ surface and the datum corridor surface ‘Roundabout Earthworks Datum’


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Change the surface style to ‘2D Level Banding’


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Click on the surface and properties and the analysis tab

Set to 2 Ranges and click the arrow to calculate the analysis Set Range 1 from the negative level to 0. Range 2 set level to 0 to the maximum level, see below. Also change the colours to suit, such as red for cut and green for fill.

This illustrates in green the areas in fill and red for the area in cut. The image above already shows a reasonable balance of Earthworks. www.autodesk.co.uk/civil3D-downloads

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To check the volume, either use the volume surface tools or click on the properties of the volume surface and statistics tab


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Step 10. – Dynamic Adjustments Refer to drawing Civil 3D Dynamic Roundabout - Final.dwg The roundabout is fully dynamic in its vertical design. By amending the ‘Tilted Plane’ grading object will affect the design. The changes to this surface will appear in the related profiles. Additionally if the temporary corridors are set to automatic, these also will update in the profile views.

The only changes to be made are small adjustments to the related profiles.

Above shows the grading object to be raised by 0.5m

The ICD surface has now automatically raised in the centreline profiles


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Also the ICD surface has changed on the crownlines


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Summary This method is relatively simple to produce a very complicated model using traditional engineering design methods and gives the designer more time to refine the model as the whole corridor of the roundabout is truly dynamic. Traditionally a roundabout would take upto a week to produce and a week to change. This method brings those changes to within an hour.


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Acknowledgments Many thanks to the following organisations for their input and support ACSUG (Autodesk Civil Solutions User Group) www.acsug.co.uk

LGCSB (Irish Local Government Computer Service Board) www.lgcsb.ie

Many thanks to Wigan Council for their support and providing survey datasets Wigan Council – Engineering Consultancy www.wiganmbc.gov.uk/pub/beng/


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Roundabout Design - Part 1

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