Junction Construction¶
Junction calculations in Gemini Terrain are performed in an external solution called Kryss3D.
We start the junction construction in Gemini Terrain by selecting which center lines should define the junction. Then we launch the Kryss3D program with the New Junction... option.
Dialog for creating a new junction
The following key information is transferred from the road bodies in Gemini Terrain:
- Design class for each reference line
- Horizontal curvature in tier table format
- Vertical curvature in tier table format
- Superelevation table separate for right/left side
This is generated based on the values for the parameter: Cross-slope. - Width extension table separate for right/left side
This is generated based on the values for the parameter: Curve extension. - Normal profile parameters
The normal profile is generated based on the parameters for the first median strip, left and right carriageway, left and right shoulder.
Figure: A = Shoulder, B = Carriageway, C = Median strip
Note
The first values that occur along the road line provide the normal profile. The slope is determined by the superelevation diagram and is the same for the median strip, carriageway, and shoulder.
The actual calculation of the junction object is performed in Kryss3D. Kryss3D calculates 3D lines for the so-called drivable area (main surfaces), i.e., up to and including the shoulder edge in the junction.
Warning
Kryss3D has the ability to change the design parameters for the links in the junction. Do not use this! Design parameters should always be changed in Gemini Terrain.
When we save and exit Kryss3D, we return to the junction dialog in Gemini Terrain. The area outside the shoulder (side surfaces), such as sidewalks, ditch values, and cutting/filling, is applied as a road body. This road body has only the right side defined and is automatically built by Gemini Terrain as standard, with the calculated line for the edge line in the junction as the center line. In a three-armed roundabout, we will get 3 such road bodies.
A very simple rule applies here:
All road parameters are adopted from the incoming road body's parameters in the joint profile position. Only values from the right side of this road body are used. These will apply all the way to the joint profile for the arm to the right. Then the values will be retrieved from the outgoing road body's road parameters in the joint profile position.
As a user, we can change all road parameters along the edge lines in the junction. We do this by selecting the edge line and changing parameters manually. A relevant example is to stop the sidewalk against the intersecting road.
When we build the junction object, the road bodies will normally coincide exactly with the junction at the joint profiles. Any changes you make for turning radii, profile distances, etc. in the junction program should not cause problems.
Summary procedure for junction design¶
Instructions
- Design roads to be included in the junction
- Create a new junction object that launches Kryss3D
- Select junction type in Kryss3D
- Edit parameters in the junction in Kryss3D
- Minimize the junction in Kryss3D
- Save and exit Kryss3D
- Build the junction and calculate masses in Gemini Terrain
- Create a mass report in Gemini Terrain
Using the road standard¶
When constructing the road bodies included in the junction, the following must be done:
Instructions
- Design class must be specified in the road design dialog.
- Road parameters for cross-section up to shoulder edge, cross-slope, and curve extension are generated from the road standard with the Generate button
Note
Warnings about errors in the alignment should be considered from a professional standpoint, but it is completely legal to ignore such warnings in Gemini Terrain.
Without using the road standard¶
It is possible to design junctions independently of the road standard to adapt data to more local considerations. An example of this is housing developments where we don't have the same requirements for driving dynamic values as with other roads. Even though the road standard is not to be the basis for the dimensioning of road and junction, we must still enter a design class.
When constructing the road bodies included in the junction, the following must be done:
Instructions
- Design class must be specified in the normal profile dialog (Kryss3D requires this)
- Road parameters for cross-section up to shoulder edge, cross-slope, and curve extension are entered manually under road parameters.
How does the junction handle roads with manual calculation method?¶
It is fully possible to create junctions from manual roads, but we need to know what is a valid normal profile in Kryss3D. Complex roads with many surfaces and slopes cannot be solved in a simple way.
The surfaces in manual roads are converted to road parameters before key information is transferred to Kryss3D. Below is a description of which surfaces in a manual road are used.
- Superelevation table separate for right/left side
This is generated based on the cross-slope. This is determined by the slope of surface -1.01 and 1.01. - Width extension table separate for right/left side
This is generated based on curve extension. This is determined by the difference between surface 1.01 and the other 1-series surfaces. - Normal profile parameters
The normal profile is generated based on the parameters for the first median strip surface (surface -0.01 and 0.01), left and right carriageway (-1.01 and 1.01), left and right shoulder (-2.01 and 2.01).
Illustration of surfaces in normal profile
Note
The first values that occur along the road line provide the normal profile. The slope is determined by the superelevation diagram and is the same for median strip, carriageway, and shoulder.
About Kryss3D¶
We refer to the help in Kryss3D for detailed information on the use of the program. Below are some of the most used functions in the program described.
Editing parameters in Kryss3D¶
We can change turning radii and line methods. This is done by right-clicking on the center line for the arm (link) and selecting the function Turning radii:
Dialog for adjusting turning radii
We can also change channelization and lane widths, island widths. This is done by right-clicking on the center line for the arm (link) and selecting the function Channelization lane widths:
Dialog for adjusting channelization and lane widths
Here you can choose to add channelization to an arm even if you selected an unchannelized junction when you created it the first time. Note that the channelization types that can be selected depend on the selected junction type. You should use the help extensively to find out about the possibilities.
The upper group of fields concerns the design of the islands and the shoulder lines directly outside the islands (inner shoulder). It is possible to change the shape of islands in this dialog, at least regarding widths and rounding radii, and distance to inner shoulder. Note that different methodologies are used for different types of islands; check the help for more information.
The lower group of fields concerns widths of lanes and outer shoulder. Note that if you change these, the junction will probably not meet the road body at the joint profile. Therefore, use these values with great caution.
It is possible to change all points in each segment profile. This is for advanced users, and one should be aware of one important thing:
The segment profiles are reset if you change channelization/lane widths, or if you change the design parameters on the roads in Gemini Terrain.
There are two obvious cases where you may want to make changes to the segment profiles:
- You want to change the shape of an island.
- You want to expand the lane width at the innermost part of the junction.
A segment profile can be changed by right-clicking on the segment profile and selecting the function Edit segment profile:
Dialog for editing segment profile
Here you can choose to edit relative or absolute values.
Relative values: If you just want to change a width of an element, while external elements adjust accordingly.
Absolute values: If you want to move one element at a time and want the other elements to remain in place. Note that negative values apply to the left side and positive values apply to the right side. By changing the sign, you can, for example, move the entire island to one side of the road.
Minimizing the junction in Kryss3D¶
Why minimize the junction?
If you do not minimize the junction, the entire road body becomes part of the junction object. This will cause the following problems:
- You cannot calculate masses for the road bodies.
- Junctions cannot be inserted elsewhere on the road bodies without lines being drawn multiple times on top of each other, and masses being calculated twice.
Therefore, always use the Minimize junction function in the junction program.
What is a joint profile?
When the junction is minimized, so-called joint profiles are created in the junction's arms where we get a transition to the road bodies.
A normal minimization will never make the arms shorter than 30 meters. We can make the junction even smaller by right-clicking on the center line for the arm (link) and selecting the function Profile distances:
Dialog for adjusting profile distances
By reducing the values for profile distances, the junction can be minimized further as long as there is room for all calculated lines in the junction. If too small a value is entered here, some of the calculated lines will disappear from the screen. This is a signal that the calculation cannot be carried out, and that the profile distance must be increased again.
Note that further minimization can be done by changing turning radii and methods.
Junctions with channelization can be reduced in the same way. The dialog with profile distances will then typically contain more options:
Dialog for profile distances in channelized junction
Note
Note that the junction in channelized approaches can never be reduced further than to the start of channelization expansion. The unchannelized stretch can be made very small. In the example above, the length of the arm will be 1+30+10+20+0.5 = 61.5 meters measured from the outer central island. The junction cannot be reduced less than this on this arm without shrinking the splitter island.
Similar principles are used on all junction types, and all types of islands.