This is a Great / Simple Question and an opportunity to use 4 different tools to do the same job
In the question from a user today they have two lines - one is perfectly straight line and has variable 3D elevations along it, the other is a 2D line and needs to be at a -2% cross slope from the first line but it has a variable offset in the first half of the line. The variable offset is a linear transition from ~10’ to ~5’ and then it stays at ~5’ for the remaining length.
Question was which command to use and what settings to use in that command to make it work.
There are at least 5 ways that you could do this (probably more) and each has its own nuances to take care of.
Lastly the reference line (3D) is shorter than the target line at the start and end of the line, so how to elevate the start and end of the 2D line (if needed) based on the elevations that can be computed with the -2% offset slope from the reference line. Interesting challenge …
The five options include
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Vertical Design (if you have that tool, it works well) - you have to break the target line into three pieces to make it work and then take a copy of the results and join the copy together for use in your model.
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Slope Designer - we really need to add a Slope to Offset Line function to handle this easier - but you can use this command in the Serial mode to compute the elevated offset line.
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Edit Linesting - in Vertical Mode you can create VPIs along the 2D line using the Offset Slope function of the Vertical controls
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Sideslope Command - this is pretty easy also - it uses the 3D line as the reference and a template to compute the slope to a 2D line - (the Target Line) and creates a 3D linestring for the Target Line - you have to explode the sideslope and then edit the line you created to add points to the start and end of the line and use Extend Vertical property to extend the vertical of the line to its endpoints.
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Corridor - not really necessary here because Sideslope does the same thing and you don’t have to convert the 3D line to an alignment in order to create a Corridor.
Video shows the first 4 methods = pick your preferred path depending on the tools that you have available to yourself and what you are really working with as source data.
Note the curvilinearity of the source and target lines would often dictate the best method to use to get the best / fastest result.