Creating a New Optimized Alignment
Updated October 19, 2017
This article applies to:
- Softree Optimal
In the following example, you will create a new optimized alignment and set up the associated standards, constraints and control points.
- Open the Softree Optimal application.
- File button | Open. Select Hart Rd.dsnx. Press Open.
- Arrange your screen to look like the previous examples. You may need to arrange your visible windows by selecting the View tab | Tile Vertically
It is possible to optimize the current alignment. However, in this example, we will create a new vertical alignment so that we can compare it with our initial alignment after optimization.
- In the Alignment Properties panel, press the New button to open the Vertical Optimization Options dialogue box shown below.
Figure 1: Starting a New Alignment
A New optimized alignment copies options from the selected alignment. In this case, the Pits (see previous exercise) will be set up already. The Costs are shared by all vertical alignments (see previous exercise for details).
In the next few steps, we will examine options that control the vertical alignment optimization that have not been discussed above.
The General tab in the Vertical Optimization Options dialogue box allows you to control the station range, section spacing and vertical accuracy.
Name - Name of the alignment object here (maximum 15 characters).
Description – Optional description of the alignment here.
Station Range - This area allows you to select the range of sections to be considered.
Note: ".." in From is the beginning of the alignment, similarly a ".." in the To field is the end of the alignment.
Sections sampled - This area allows you to choose the section points to be included in the optimization. Clicking on the button will allow you to choose specific point types using the Point Type Selection dialogue and Report Point Properties. The Selected points specifies how many cross sections will be calculated.
Equal spaced sections defined by the Spacing field will be added to those defined by the Point Type Selection dialogue.
Note: The larger the number of sections, the more accurate the optimization and the longer the process will take.
Vertical Control - This section allows the user to control the vertical extents (upper and lower bounds) and accuracy of the optimization in the vertical direction.
Min. and Max. Offset - These offsets are measured relative to the current vertical alignment (L-line). If there is no vertical alignment, then the offsets are measured from ground.
Accuracy Advanced – Set this checkbox to display the accuracy slider. This control allows the user to select the horizontal and vertical accuracy (from low to high).
Note: The higher the accuracy the more accurate the optimization and the longer the process will take. However, the resolution time is more dependent on the number of sections.
Figure 2: General Options dialogue box fields.
- Enter the parameters as shown in Figure 3, below
- Change the Name to “Trial 1” and Description to “K=30”.
- In the Sections area, uncheck All and enter 5.0 in the Spacing field. Type <tab> to move to the next field – this will update the point count.
Figure 3: Optimizer General Options
5.0m is the value suggested by the accurate costing procedure (previous exercise); now you should see 192 selected cross sections to be calculated.
- We will keep the 10.0m vertical offsets.
Softree Optimal allows you to control grades and vertical curvatures.
- Click on the Standards tab.
In this first trial, we will use the default Curves [Fast] Alignment Specification. This will generate short vertical curves with no tangents between them. As the name suggests, this will solve quickly; we will examine other options later.
- Enter the parameters as shown in Figure 4 below:
- In the Curvature area enter minimum K values of 30 for both Sag and Crest.
- Press Add/Edit (note: the values appear in the Parameters list only after you do this).
Curvature (K) - This area allows you to set curvature constraints.
Linear - If selected, the alignment will be constrained to be a straight line (no vertical curve) over the selected range.
Sag, Crest. - If not Linear, the alignment will be constrained to be greater than the specified K values over the selected range.
Figure 4: Standards tab, for curve and grade constraints.
You have now applied the default grades (+/-10%, extracted from the Road Class Parameters) and K=30 (design speed of approximately 80 kph) to the entire alignment. It is possible, however, to divide the alignment into intervals and set different Grade/K constraints for each interval.
Note: ".." in From Stn. is the beginning of the alignment, similarly ".." in the To Stn. field is the end of the alignment.
Control Points Tab
- Click on the Control Pts. tab.
Control points allow you to set the elevation and/or grade at specific points along the alignment. In this example (a road re-alignment) it is important that the start and end of the alignment match the existing road. The human engineered alignment provided meets this requirement, so you only need to tell the optimizer to match the existing alignment at each end.
- Define a control point at the start of the alignment:
- Press the Add button at the bottom of the screen to add a new control point.
- Select Start of alignment and press OK.
The Elevation (361.057m) has been automatically extracted from the existing alignment.
- Check Enable Grade control.
- Then, press the Get from Alignment button to match the initial grade (-2.49%).
This will add a control point, forcing the optimized alignment to match the existing vertical alignment at station 0.0.
Figure 5: Control Points
- Similarly, define a control point at the end of the alignment (see figure above).
Note: There is a Tolerance field available for both vertical and horizontal control points. If possible, looser tolerances allow the optimizer more freedom to minimize costs. For example, a culvert may require a minimum cover depth but higher alignments are OK; alignment will never drop below Elevation – Tolerance.
Pits, Costs and Constraints
Pits and Costs have already been defined (see previous exercises) and we will not be using the Constraints in this exercise.
- Press the OK button at the bottom to exit the Vertical Optimization Options dialogue.
You will see the new alignment at the top of the list as shown in the figure below:
Figure 6: Alignment Options
Display of the Vertical Band
We have constrained the alignment vertically using control points; we have also constrained the offset from the current alignment to be less than 10.0m. You can display these constraints graphically:
- Maximize the Profile window
- Display the vertical band in the profile window:
- In the Alignment(s) list, click the button beside our new Trial 1 alignment to expand the tree.
- Select the Constraints branch.
Figure 7: Graphical display of the vertical band.
Calculation of the Optimal Vertical Alignment
Now that the options have been defined, you can calculate an optimal vertical alignment.
- Press the Process button .
Figure 8: Process Control dialogue box.
You will be prompted with the Process Control dialogue. This dialogue allows you to review the specifications you have entered for the road by selecting items in the tree control. It also gives you a choice of four actions:
- Pre-Process: this process calculates all the necessary cross-sections. It is a pre-requisite to Optimal Profile and Quick Profile, but can also be done on its own.
- Feasibility Check: check that the constraints are geometrically feasible same as above except that cross sections inside the vertical extents are calculated (pre-process) to determine the true vertical band (sections that fall off the surface model are discarded).
- Quick Profile: generate a vertical alignment as close as possible to the ground (not minimum cost, not optimal).
- Optimal Profile: generate a vertical alignment with minimum cost. Cross sections inside the vertical extents must be calculated (pre-process) first. A valid Softree Optimal license is required to use this functionality.
For larger projects, the Optimal Profile process can take a long time to complete, even the pre-process calculation of cross sections can be time consuming. To avoid wasting time, it is worth doing a Quick Feasibility test first.
- Choose only the Feasibility check action.
- Press the Process button.
Figure 9: A vertical alignment matching your specifications is possible.
Note: If a feasibility test fails, it is usually because a vertical alignment with specified grades and curvatures will not fit within the vertical band you have defined by the current alignment and the vertical extents.
- Repeat the step above, but this time choose the Optimal Profile action.
At the end of the optimization, a dialogue box appears summarizing the status of the optimization. This information can also be accessed later through the Log tab in the Vertical Optimization Options dialogue box.
Figure 10: Final log, errors and warnings will be reported here.
Optimization is a three-step process:
- Pre-process (calculation cross sections at sampled stations)
- Alignment optimization (using the settings defined above)
- Cost calculation (using the spacing set in the Re-Cost^ dialogue box)
Note: The Alignment optimization always takes longer than Cost calcuation so it is often wise to use a larger spacing (select fewer points) for this step.
You will receive a warning if the Cost calculation is using fewer points than the Alignment optimization.
- Press OK to close the log.
- Set the Compare with current check box at the top of the Alignment Properties panel.
Figure 11: Optimized Results
Note that the selected optimal alignment is blue in this example (you can change the color and line-type in the options Display tab). Notice the optimized alignment total cost is now $404,000 compared to $475,000 in the original design. This represents a cost reduction of approximately 15%.
Note: The Mass Haul graph at the bottom of the window applies to the current alignment not the new optimized alignment. Press the Set Current button to see all the properties of the new optimized alignment.
- File button | Exit. Do not save changes.