Roundabout Design: A Better Workflow

Size: px

Start display at page:

Download "Roundabout Design: A Better Workflow"

Amy Randall
5 years ago
Views:

1 Simon Ayers, Director Savoy Computing Services CI6620: Roundabouts have been around for many decades but have been enjoying a resurgence, particularly in the US, over the past few years. If designed well, this very simple and cost-effective traffic management concept can offer dramatic advantages over other types of intersections in terms of capacity and safety. In this class, you will learn how existing and new software technologies are being extended to bridge the gap between analysis and design, leading to better and faster roundabout solutions. The class will focus on one example of these linked technologies, running in AutoCAD Civil 3D 2012, that offers a seamless building information modeling (BIM) solution. Realistic examples will be used to illustrate the benefits for both new designs and retro-engineering of existing roundabouts. Learning Objectives At the end of this class, you will be able to: Understand how the roundabout design process is changing Optimize your roundabout design process by dynamically linking three market-leading products Create a BIM roundabout model in AutoCAD Civil 3D Perform real-time "what-if" modeling on your roundabout projects About the Speaker Simon Ayers is director and co-owner of Savoy Computing Services Ltd, U.K. He holds an honors degree in civil engineering from the University of Leeds, U.K., and has been a chartered civil engineer and member of the Institution of Civil Engineers for over 25 years. Since 1987, Simon has been involved in the design and development of engineering software, and for the past 20 years has led the development of the innovative AutoTrack suite of programs. Simon has provided advice on vehicle swept paths to the U.K. s Freight Transport Association (FTA) that led to them using AutoTrack for their industry standard booklet "Designing for Deliveries"; he also led the collaboration with the U.K. s Transport Research Laboratory (TRL) that culminated in the development of a ground breaking dynamic link between AutoTrack's respective products. simon.ayers@savoy.co.uk

How the roundabout design process is changing Roundabout design involves the balancing of three main factors, functional requirements, safety and cost. These factors are interlinked.

We need to consider ways to add capacity whilst controlling vehicle speeds.

2 How the roundabout design process is changing Roundabout design involves the balancing of three main factors, functional requirements, safety and cost. These factors are interlinked. Simply scaling up a design to handle a larger capacity is likely to lead to higher vehicle speeds and a greater risk of accidents. We need to consider ways to add capacity whilst controlling vehicle speeds. Achieving an acceptable balance between these basic factors requires a multitude of influences to be considered; vehicle speeds, vehicle paths, sightlines, surface geometry, site constraints, and many more. These requirements can be met in various ways, each of which has potential implications for the others. Typical workflow currently Currently the typical roundabout design workflow starts with a road design engineer proposing the geometry for a roundabout based upon the appropriate national guidelines. At this stage, the design team will be basing their design on past experience and simply making sure that the geometry complies with the guidelines. Sequential Process The next stage is to confirm that the proposed geometry can provide the required vehicle capacity. So, for this, a traffic engineer will measure some critical values from the drawing and create an analysis model in a tool such as ARCADY or Rodel. In an ideal world the results of the analysis would show that the 2

roundabout design was adequate but as we all know we don't live in an ideal world. In practice, the geometry will probably need some adjustment to provide capacity.

3 roundabout design was adequate but as we all know we don't live in an ideal world. In practice, the geometry will probably need some adjustment to provide capacity. Of course, in making these adjustments the road engineer has to be careful not to contravene other safety criteria such as entry path radius. This design and analysis cycle may be repeated several times. Once the roundabout geometry has been agreed we need to check that vehicles can negotiate it; that is after all why we are creating it! Design vehicles are normally specified in the guidelines, so at this point the engineer would probably use a vehicle swept path analysis program, such as AutoTrack, to check the roundabout for these vehicles. Again, if the roundabout has been designed by an experienced road engineer, the design vehicles may be able to negotiate all routes satisfactorily. If not, it's back to the drawing board to adjust the geometry, analyse and recheck the vehicle paths. Once more it's a matter of 'repeat as necessary'! Finally, once all the horizontal geometry has been confirmed, we need to create a 3D ground model so that we can design the super-elevation, surface drainage, and complete the detail design. Let s assume for that you would use AutoCAD Civil 3D for this. Even at this stage there could be a need to adjust the basic geometry... perhaps the levels don't quite work? If so, the cycle begins again. The Better Workflow A more elegant approach would be to create a model in which all the design and analysis processes share the same data so that each program can use what it needs. This sharing of data is known to us all as Building Information Modeling (BIM) and it means that data is entered once and shared wherever possible, thereby reducing the risk of errors. However, an even more elegant approach would have all the design processes not only sharing data but reacting to changes in that data so that as a shared value changes all the other calculations that use that value are automatically recalculated. If we could do this we could significantly speed up the design cycle. Dynamic Real-Time Links So, our vision of a 'better workflow' is as follows:- The road design engineer creates a roundabout using a selected national guideline document. As he adjusts the roundabout, he is warned immediately if he exceeds guideline values or if the geometry will result in excessive speeds. He then enables the capacity analysis checks and, immediately, capacity, LOS, queue and delay values are displayed on each arm. If there are problems, the engineer can adjust the geometry and optimise the capacity, whilst still monitoring vehicle speeds. 3

4 There are only a limited number of routes through a given roundabout so all the engineer has to do is select the vehicle and route he wishes to see and the optimum path is drawn. If the vehicle paths overlap or if there are other issues the engineer can adjust the geometry until the vehicle paths are satisfactory, at the same time monitoring guideline limits on geometry and speeds, as well as traffic capacity. Finally, he builds the ground model in Civil 3D making use of data extracted automatically from the roundabout design. Once created, he can investigate surface drainage, super-elevation, cut and fill and detail design. Even now, should there be a need to adjust the horizontal geometry, the Civil 3D model is rebuilt automatically based on the 2D roundabout geometry. 4

5 Optimise the design process by linking three design products If you would like to try out the workflow you will need the following software:- AutoTrack Junctions (demo available from AutoTrack Roads Pro (demo available from ARCADY 7.1 & (demo available from ARCADY - AutoTrack Link (available from needs activation) AutoCAD Civil 3D 2011 or 2012 (available from I have also provided a sample dataset for you to experiment with. The following worked example assumes you are using this dataset. First a quick reminder of the components AutoTrack Junctions The system is controlled by AutoTrack which manages the 2D roundabout geometry. It lets users adjust the geometry within defined limits and ensures that the design complies with guidance documents. It also lets users place and adjust the geometry of features such as splitter islands, pedestrian crossings. Last but not least it lets users check safety issues by calculating the fastest path radii and speeds at all critical locations, as well as all types of sightlines. ARCADY Using the new workflow we just need to invoke the ARCADY link from within AutoTrack Junctions and it creates the ARCADY model and populates it with the basic geometry automatically. Having done that, it sends the results back to AutoTrack Junctions so that the user can see the results in his CAD system. The link is dynamic and real-time so when you adjust the geometry the ARCADY values are recalculated and redisplayed instantly. This means you can see immediately how geometric changes affect the capacities. AutoTrack Roads Pro Again, in the new workflow, AutoTrack Roads Pro knows what an AutoTrack roundabout object is and can work out valid vehicle paths automatically; so all you have to do is tell it the arrival and departure leg by pointing and clicking. And because the vehicle swept path is linked to the roundabout, when the roundabout geometry changes so the paths update automatically. Preparation 1. If you need to install a version of AutoCAD or AutoCAD Civil 3D then do that first. Then install AutoTrack. Finally, install ARCADY. 5

6 Phase 1: Place the default roundabout 1. Run AutoTrack for AutoCAD Civil 3D (or whatever system you have installed). Open the sample drawing CI6620_AYERS.DWG. 2. I have drawn three polylines to represent the centerlines of two existing roads and a new link road. In Civil 3D we would normally have defined these roads using Alignments but I have drawn them as polylines here so that those of you running vanilla AutoCAD can still load and try the workflow and see that even without the Civil 3D element there is a considerable benefit in the AutoTrack ARCADY link. 3. You may wish to run XREF and unload the aerial photo ShrewsburySite.jpg for clarity. 4. Select the AutoTrack ribbon. 5. Select the New Roundabout command from the Junctions panel. 6. When the Junction Standard Explorer appears, click the [+] to expand US Junction Design Standards, followed by US Federal Highways Administration, and Roundabouts: An Informational Guide 2010, select the FHWA 2010: Urban Single Lane Roundabout and click Proceed. 7. Decline the option to make this standard the default. 8. Check that the Scale and Driving Convention are correct and click OK. Note that, if you are running Civil 3D, these settings will be copied from your Civil 3D default settings. If they are wrong or if you are running vanilla AutoCAD set the scale units to metres and the driving convention to whatever you wish. The driving convention you select will obviously affect which way round the roundabout is built! 9. You may see a scale warning if you are zoomed in or out a long way or if you have actually got your scale wrong! Only you know how to deal with this. 10. When the New Junction dialog select the Shrewsbury DTM surface and tick Project plan view onto surface. Click OK. 11. A default roundabout will appear at the cursor. Place the roundabout close to the centre of the intersection of the lines in the drawing and left click to confirm. 12. Select the arms one by one, by picking the lines in the drawing, naming them as you go, and right after the last arm has been selected to terminate the command. 13. You now have a roundabout entirely defined by the default settings in the selected standard. 14. Notice the dashed lines representing the fastest paths, one from each arm, and the fastest of the fastest paths in a different colour. 15. Adjacent to each arm is a panel with some values in it. These are the head up displays. 16. To find out what each grip is for move the cursor over it. 6

Phase 2: Adjust the roundabout 1. If necessary, adjust the number of lanes on approach roads. To do this select the roundabout and click the Edit Junction button.

7 Phase 2: Adjust the roundabout 1. If necessary, adjust the number of lanes on approach roads. To do this select the roundabout and click the Edit Junction button. For each arm that needs to be adjusted, select the Approach tab and change the Approaching Lanes and Departing Lanes. Then select the Entry tab and change Number of Lanes. Repeat for the Exit tab. 2. At the end of each arm is a double-headed arrow grip. This is the blend point. This is where the new roundabout that you are creating blends with the existing road alignments tangentially. 3. Select the Adjust Roundabout Centre Point grip at the centre of the roundabout and move it to notice how the arm geometry is recalculated and updated so that they always meet the existing alignments tangentially at the blend points. 4. You can force an arm to follow the selected alignment more closely. To do this select the roundabout, click Edit Junction, select one of the arms, e.g. Arm 1 (West), and tick the User- Defined Alignment checkbox. Now try moving the roundabout again and notice how the userdefined arm tries to follow the picked alignment. 5. Use the Road Width grip, at the end of each road, to adjust the lane widths (either to match the Google Earth image or according to the design requirements). Hold down the <CTRL> key to adjust both lanes at once. 6. Notice the warning triangles that appear if any of the changes you make exceed the requirements of the standard you have selected. As you hover over the associated grip more detail will appear. 7

8 7. Use the Central Gap Width grip to adjust the centre reservation width. 8. Use the ICD grip to adjust the ICD. Hold down the <CTRL> key to maintain the circulatory width. 9. Use the Island Radius grip to adjust the radius of the centre island. Hold down the <CTRL> key to maintain the circulatory width. 10. Use the Apron Width grip to adjust the width of the overrun area. Hold down the <CTRL> key to maintain the circulatory width. 11. Use the Circulatory Lane Width grip to adjust the circulatory lane placement. Hold down the <CTRL> key to maintain the outer circulatory lane width. 12. Use the Approach Centreline Offset grips to adjust the offset of the approach centerline from the centre of the roundabout and therefore entry deflection. 13. Use the Splitter Radius grips to adjust the radius of the definition lines where they divide as they approach the roundabout itself. 14. Use the Nearside Kerb Radius grips to adjust the radius of the nearside kerb as it approaches and meets the roundabout inscribed circle. 15. Select the Add Splitter Island command and place splitter islands. Right click to terminate the command. 16. Select the Add Pedestrian Crossing command and place crossings. Right click to terminate the command. You can divide the splitter island where the crossing meets it in Junction Properties dialog. Select the roundabout and click the Edit Junction button. Expand one of the arms with a pedestrian crossing and click on the Pedestrian Crossing tab. Select an Island Crossing Type from the list box. Phase 3: The Head-Up Displays 1. Select the roundabout and click the Edit Junction button. 2. Click on the Head-Up Display tab and notice the AutoTrack analysis values that can be displayed; fastest path radii R1-R5 and corresponding speeds V1-V5, analysis geometric values and ARCADY capacity analysis values. Tick all the fastest path radii and speeds and click Apply. 3. Close the dialog and try moving the roundabout and adjusting geometric values to see how it affects these values. 8

9 Phase 4: The ARCADY Link 1. Open the Junction Properties dialog again, select the Head Up Display tab and tick all the ARCADY values that can be displayed... RFC (or V/C ratio), LOS, Queue, Delay. 2. If you have ARCADY installed with the link then select the ARCADY tab, tick Enable ARCADY Link, click Apply and close the dialog. 3. Notice how ARCADY starts up automatically, creates an ARCADY data file and initialises it with the roundabout geometry from AutoTrack. 4. Switch to ARCADY, click the Turning button on the left and enter the number of standard vehicles per hour travelling each route through the roundabout. 5. Switch back to AutoTrack and click the Refresh Link button 6. Notice how the ARCADY values appear on the HUD s. The values are colour coded to match ARCADY to avoid confusion. 7. Move the centre of the roundabout and notice the ARCADY values changing. Phase 5: Place a vehicle 1. Locate the Swept Paths panel on the ribbon and click the AutoDrive button. 2. When the Vehicle Library Explorer appears, find a suitable vehicle and click Proceed. 3. Decline the option to set the vehicle as default. 4. Move the cursor over the roundabout and notice how the vehicle alignment changes according to the direction of traffic and the curve of the road. Left click to select a start location. 5. Move the cursor to another arm and see how the path is calculated automatically. Left click to confirm the end position. 6. Deselect the path and select the roundabout. Move the centre of the roundabout slightly and notice how the path updates when you left click to confirm. 9

10 Creating a BIM roundabout model in Civil 3D The next step is to create a 3D ground model so we can work out exactly how to build the roundabout. To help with this AutoTrack Junctions creates AutoCAD Civil 3D alignments automatically. So the next stage is to build the corridor using the alignments provided by AutoTrack. The alignments created by AutoTrack Junctions are not only created but updated as the geometry changes. So, adjusting the ICD in AutoTrack will cause the ICD alignment to be updated and then your Civil 3D ground model. That means you don t need to keep recreating the corridor every time the geometry changes slightly. This next step assumes that you have some familiarity with AutoCAD Civil 3D. If you have any problem understanding any of the steps then please me for clarification. Phase 6: Creating the 3D model 1. The alignments created by AutoTrack can be seen in the Prospector tab in Toolspace. They may be displayed in the drawing by switching on and thawing layer {Junction Name}ALIGNMENT, e.g. JTN1ALIGNMENT. The alignments are as follows:- The nearside kerb alignment, called {Junction Name} {Arm Name} Nearside Kerb, tracks the nearside kerb of the approach road around the ICD and the nearside kerb of the next exit. The offside kerb alignment, called {Junction Name} {Arm Name} Offside Kerb, tracks the offside kerb (or centreline if no centre reservation) follows the splitter to the point it intersects the ICD, around the ICD to the point at which the splitter radius of the next exit intersects the ICD, then along the splitter radius and finally the offside kerb (or centreline). The alignment alignment, called {Junction Name} {Arm Name} Alignment, tracks the arm centreline to the point it intersects the ICD, around the ICD to the point at which the centreline of the next arm intersects the ICD, then along that arm centreline. The inscribed circle alignment, called {Junction Name} Inscribed Circle, tracks the ICD. The island alignment, called {Junction Name} Island, tracks the centre island. The apron alignment, called {Junction Name} Apron, tracks the apron. 2. Create a profile on the Nearside Kerb alignment for each of the arms. 3. Create a profile on the Alignment alignment for each of the arms. 4. Create profiles for the Inscribed Circle and the Island alignments. 5. Two assemblies have already been created for you, one called LANE_UK for the approach roads and another called ROUNDABOUT_UK for the circulatory area on UK roundabouts (and other drive on the left regions) and LANE_USA and ROUNDABOUT_USA for US roundabouts (and other drive on the right regions). 10

For each arm, insert the LANE assembly on the Nearside Kerb alignment and target it to the Alignment alignment. 8.

11 LANE_UK assembly ROUNDABOUT_UK assembly 6. Now create a single corridor with baselines on the Nearside Kerb and Inscribed Circle alignments. 7. For each arm, insert the LANE assembly on the Nearside Kerb alignment and target it to the Alignment alignment. 8. For the circulatory area, insert the ROUNDABOUT assembly on the Inscribed Circle alignment and target it to the Island alignment. Corridor Region Diagram 9. Surface the roundabout and shrink wrap it to the corridor boundary. 10. Set the corridor and surface to rebuild automatically. 11

12 Performing real-time "what-if" modeling on your roundabout projects Now that you have a 3D model with all your geometry and design criteria in a single model so you can start to adjust and fine-tune your design to take account of all the issues that are significant for your particular situation. For example, you might need to look at moving the roundabout slightly to avoid buildings or to save on land acquisition costs; you might want to adjust the levels to minimize the amount of earth you need to move; or you might be looking at the effects of the increased traffic flow from a new housing estate. Whatever changes you make to any aspects of the roundabout model the effects of that change are instantly reflected in the model in all three applications, AutoTrack, ARCADY and AutoCAD Civil 3D. Phase 7: All together now! 1. Split the screen to show the 3D model in realistic isometric view in one and the roundabout model in plan in the other. 2. Adjust the roundabout geometry in the plan view and notice how everything updates...the AutoTrack and ARCADY data, the vehicle swept path and the 3D ground model. 3. Make specific adjustments to dimensions and see how it affects the geometry, the fastest paths, the capacity and the 3D model. 4. Animate the swept path through the roundabout with a tracking, fixed or drivers view camera. BIM workflow savings We have done a rough calculation and reckon that for a single edit cycle the BIM workflow is conservatively around 250 times faster than conventional methods. Just to be clear, by edit cycle we mean the adjustment of a single roundabout dimension (e.g. the ICD) and the subsequent recalculation of all the geometry, the re-analysis and the rebuilding of the 3D model. And the feedback that we are getting is that we are being very generous here and that the speed improvement is actually even more. I think the conclusion we can draw is that BIM is most definitely applicable to roundabout design! More Information Thank you for attending this Virtual Class If you enjoyed it then please recommend it to your colleagues. Feel free to me at simon.ayers@savoy.co.uk. Savoy, TRL and Autodesk, have jointly developed a website ( which looks at the use of BIM techniques in roundabout design. Here you ll find more videos, webcasts, FAQ and other useful resources. 12

Roundabout Design Using AutoCAD Civil 3D 2010 Intersection Tools

Roundabout Design Using AutoCAD Civil 3D 2010 Intersection Tools Marie-Pierre Lebel Consortech Solutions CV214-1 Learn how to leverage the new intersection design tools from AutoCAD Civil 3D 2010 for use