Vertical design
Vertical design is often not considered until the basic design has been sent to and approved by the planning authorities. Meaning that if the 2D geometry has to be altered due to site factors such as utility placement, drainage or construction cost which was not included in the original design, the 2D geometry would need to be reviewed and returned to the original designer.
It is common on roundabout design projects that the only information made available to construction contractors would be a 2 dimensional road profile to work from. This can be a particular issue concerning roundabouts as they contain much more complex crossfalls, curb layouts and transitions. Often, no real 3D design information is provided at all.
When a 3D ground model is produced, it is to allow for design of super-elevation, surface drainage and detailed costing’s including cut and fill to complete the detail design. The 3D design is once again often performed by a separate team to those that were involved in the original design, even if at the same organization. This is also often done without the use of the original drawings or models. Even at this stage, if levels, costs or utilities considerations are not suitable, there could be a need to adjust the basic horizontal geometry.... thus the cycle begins again.
Signage and Markings
Signage and markings are used to provide regulations, warnings, and guidance information for road users and convey important human factors messages. Although signage does not affect the geometry of the roundabout, it is a requirement in almost all locations to produce signage and marking schedules. Of course, these schedules change as the geometry is continuously altered as signs and markings are relocated due to both geometry movements and altered vehicle alignments.
Visualization
Visualization is increasingly being required during public outreach, stakeholder engagement and education programs that are now commonplace as part of the planning and design process. This is becoming very popular and is mandated in multiple locations throughout the US where roundabouts are being introduced or proposed to the public. There is also technical merit in the use of animated visualizations, a designer can consider the driver experience and analyze key design characteristics such as entry path and deflection. Reviewing designs against standards
Typically, when a design is both produced and independently reviewed by any department, this is done manually; sometimes to the extent of taking physical measurements from a paper drawing. This review is therefore reliant upon the experience of the individual, the accuracy of their measurements and any time constraints. Hence results, observations and prevailing decisions can vary greatly.
It is often the case that several people or even organizations will carry out any review, based upon individual experience.
The BIM approach
A more intelligent approach is to create one single 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, or sometimes CIM – Construction Information Modeling) and it means that data is entered once and shared wherever possible, also reducing the risk of errors.
However, an even more intelligent approach has 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 and allow almost any stage of design to be considered in any particular order.
The designer uses AutoTrack Junctions to create a roundabout model compliant with the necessary guideline document. The AutoTrack roundabout is a single, editable and intelligent object within the drawing that utilizes lines or alignments to define the approach roads; all geometry is automatically calculated. As they adjust the roundabout, the geometry is re-calculated and assessed against the design standard; the designer is warned immediately if they go outside of guideline values or if the geometry could result in excessive speeds for example.
At any time, they can enable capacity analysis checks and in real time capacity, LOS, V/C ratio (RFC), queue and delay values are displayed for each approach road. This analysis is performed by ARCADY and controlled by the original, single BIM model. If there are capacity issues, the designer or engineer can adjust the geometry to optimize the capacity whilst still monitoring vehicle speeds, etc. using the rule based design checks.
In terms of vehicle turning paths, there are only a limited number of routes through a given roundabout so all the designer has to do to analyze them is to select the vehicle and locate it on the desired entry lane and destination lane on the destination road; the required path, if possible, is calculated and the optimum path is drawn. If the vehicle paths overlap or if there are other issues the engineer can adjust the geometry until all paths are satisfactory, at the same time monitoring guideline limits on geometry and speeds, as well as traffic capacity.
Sight visibility analysis as defined in the standard is also incorporated into the model and can be displayed in the drawing alongside all other analysis. Typically, most standards have several mandated visibility checks that must be performed for each approach to the roundabout and within the circle itself.
Because signage the location of signage is mandated at roundabouts, the model will place the required standard signs at the necessary points. These signs are intelligently located and as the geometry changes, they move and rotate to face the direction of oncoming traffic. But the model also allows for them to be manually adjusted taking into account real world consideration such as a driveway or access located where a “roundabout ahead” sign should be. Most standards allow for this type of situation. Along with 2D plan symbols of each signs, 3D signage is shown at all relevant points for visual design checks.
Again, at any point the 3D ground model can be built Civil 3D by using alignments, profiles and a generic corridor that are all automatically created by the AutoTrack BIM model and then subsequently updated and rebuilt when required by any geometric changes. Once created, these can be used to investigate surface drainage, super-elevation, cut and fill, quantity take-off and other Civil 3D related attributes; as these are true, industry standard, Civil 3D corridors and thus a large amount of technical data can be gleaned from them to the extent of even being able to control the grading machine that will perform the groundwork on site. But even now, should there be a need to adjust the BIM models geometry; the linked Civil 3D entities are rebuilt automatically based on the revised geometry.
The BIM model, at any time, allows for 3D visualization of multiple vehicles interacting at roundabouts with full control of camera location, target and perspective. Of course, as the model moves into detailed 3D design stage, this is represented in the visualization. But even without the 3D surfaces, visualization often plays a key role in design checks and model assessment.
Following BIM principles, there is a central data storage model that allows for engineers to use the tools that they are familiar with. For example, the original designer may only use AutoCAD to produce the original design and the traffic engineer may use ARCADY to analyze capacity, when the 3D model is required the drawing can be opened in Civil 3D and the model extended to 3D. Even at this point, the original engineer can still open the access the model from AutoCAD and make changes as required. His changes will be reflected in the 3D model when the drawing is next opened in Civil 3D.
This central and intelligent model can be accessed by any member of the project team as and when needed and as little or as much data captured or updated as required. Access to all the separate software tools is not required to work on the model.
Performing real-time "what if" modeling on roundabout design projects
When the designer has a complete model with all geometry and design criteria in a single location, the designer may begin to adjust and fine-tune the design to take account of all the issues that are significant for each particular situation. It is rare that the first design is the optimum solution for a given roundabout project, but with traditional methods time constraints often mean that alternatives cannot be explored. 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 development.
Whatever changes you make to the model, the effects of that change are instantly reflected. Instant feedback is provided to the designer to get a feel for the design as it is edited using grips, etc. This feedback means that multiple “what if” tests can now be tried out within a few minutes each, instead of days or weeks. The increase in the number of design iterations that are now possible means that the optimum solutions can then be identified. How often have you submitted a design that was achievable within time constraints rather than the best possible solution?
Real-world benefits
Through performing calculations and listening to feedback from the transportation industry, we estimate that for a single edit cycle the BIM workflow is, conservatively, around 250 times faster than conventional methods. Just to be clear, by an edit cycle we mean the adjustment of one single roundabout dimension (such as the ICD or adding a tapered flare to one entry) and the subsequent recalculation of all necessary geometry, the re-analysis and the rebuilding of the 3D model.
The conclusion we must draw is that the application of BIM principles to the art of roundabout design allows for a much faster initial design process, leaving vastly more time available for detailed design analysis and exploration of multiple “what if” scenarios; ultimately leading to safer and more efficient roundabouts with the potential for lower construction and maintenance costs.
In summary
BIM gives you:
One single model
Instant design feedback for every change
Flexibility in design workflow
Increased intelligence
More design iterations within the same timescale
More time on projects
A better design
AutoTrack Junctions is the true BIM solution for roundabout design.
More information
Thank you for your interest in this class. Please feel free to contact any one of the three speakers using the email addresses on page 2.
Savoy Computing, Autodesk, TRL and Design Pro Software have jointly developed www.bimroundaboutdesign.com which covers the use of BIM techniques in the field of roundabout design, including videos, webcasts, FAQ’s, links and other useful resources.
Share with your friends: | 
