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Curves with Tangents

Updated October 19, 2017


This article applies to:
  • Softree Optimal

In this section, we will examine the two curve types that include tangents between vertical curves.

  1. Open the Softree Optimal application.
  1. File | Open. Select Hart Rd curves.dsnx. Press Open.
  2. Maximize the Profile window, ensure the Alignment Properties panel is visible

Figure 1: Profile window with curve labels enabled showing Trial 2, 50m back to back curves.

The current alignment when you open this project is Trial 2, the 50m back to back curves vertical alignment created in the previous exercise.

Trial 3 and Trial 4 have been created for you and optimized to save you time. The process used to create these alignments is very similar to the previous exercise and you should have no problem doing this for yourself at the end of this exercise.

Curves and tangents [Slow]

  1. Set Trial 3 current, with Trial 2 in the Profile background:
    1. Select Trial 3.
    2. Press the Set Current button.
    3. Select Trial 2.

This alignment was created with the Curves and tangents [Slow] curve type. As you can see in the figure below, there are fewer curves. Also, note that the there is little elevation difference from Trial 2 (back to back curves); therefore, it is reasonable to use the quick, back to back solution as a first iteration and cost estimate.

Figure 2: Profile window showing both Trial 2 (solid line) and Trial 3 (dash dot line)

  1. Open the Standards options for Trial 3
    1. Select Trial 3 then press the Options button (or right click on Trial 3 and choose Options).
    2. Select the Standards tab.

Figure 3: Curves and tangents [Slow] options.

Note that the Min. tangent length is equal to the Min. curve length but not editable.

  1. Cancel to close Options.

Variable curves and tangents [Slowest]

  1. Set Trial 4 current, with Trial 2 in the Profile background
    1. Select Trial 4
    2. Press the Set Current button.
    3. Select Trial 2.

This alignment was created with the Variable curves and tangents [Slowest] curve type. There are fewer curves still but it is still a close match to Trial 2.

Figure 4: Profile window showing Trial 4, 100m curves and 50m tangents.

  1. Open the Standards options for Trial 4.

Figure 5: Variable curves and tangents [Slowest] options.

Note that the Min. tangent length is not equal to the Min. curve length and you can change it. Also, note the new value called Base length.

For this type of curve, Softree Optimal divides the road into segments of Base length. Curves will start or end on segment boundaries; tangents and curves will be multiples of Base length greater than or equal to the minimum values specified. In this example, the second curve starts at station 150 and ends at station 375; this curve would not be possible in Trial 2 or Trial 3.

Base length is calculated from the minimum curve and tangent lengths and your choice of Accuracy. If Base Length is too small (less than your sample spacing), you will generate a conflict:

  1. Try a very small base length:
    1. Set Min. tangent length to 20.0m.
    2. Slide the Accuracy up to high (5).
    3. Press the Conflict button that appears in the lower left of the Options dialogue box.

Figure 6: Conflict caused by curve base length shorter than sample spacing.

    1. Press OK to close the conflict log.

Note: Many conflicting constraints and specification will be detected automatically and reported in the conflict log. For example, defining a Control Pt. with a required grade greater than your Standards maximum will generate a conflict.

  1. Try entering a few different parameters and see what you get.

In summary, by making the Base length smaller (higher Accuracy), you can make the curves more granular and therefore more flexible. While this provides the best alignment solution of all the curve types, it is also the slowest.

  1. Press Cancel to exit the dialogue.

The information list has been set up to show the optimization time (Alignment process time).


Figure 7: Optimization time (Alignment process time) may be added to the information list.

  1. Select the alignments one at a time and watch Alignment process time in the list.

The times for the three optimizations, on the author’s laptop, are shown below:

Trial 2 Curves [Fast] 3.52 seconds
Trial 3 Curves and tangents [Slow] 24.79 seconds
Trial 4 Variable curves and tangents [Slowest] 54.33 Seconds

Table 1: Comparison of optimization times for different curve types.

Note that these times do not include the pre-process time which is roughly constant at 30 seconds for all three.

Note: it is possible to create a large problem that will take days to solve or that will cause the solver to run out of memory.

At this point you may want to try re-optimizing to see how long your computer takes. You may also want to experiment with some of the curve parameters we have discussed.

  1. File | Exit. Do not save changes.
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