How can I change the stationing of the horizontal alignment and keep the stationing of the vertical alignment the same relative to the horizontal alignment?
The Geometry > Horizontal Curve Set > Stationing command can be used to edit the starting station of the horizontal alignment. If you wish to maintain the distance relationship between the start of the horizontal alignment and the start of the vertical alignment, make sure that Maintain Station Difference is toggled on.
Do Not Update will leave the vertical alignment stationing as originally defined.
Synchronize Starting Stations will set the starting station of the vertical alignment to the same value as the horizontal alignment.