If you work with grade 1 splines you also get the 3d route drawn, if you have already created the 3d polylines you can convert them with recreate surfaces (works with curves) setting the grade on 1 and giving the precise number of polylinea vertices.
first choosing the line type and scale and applying them to the 3dpoly, you could explode these latter, which would appear to be treated according to the type line chosen.
They would lose the attribute of polylinee3d and assume that of simple lines. to join each other could be grouped with the group command.
if you try to join them with the joint command would return 3d poly and they would reappear continuously losing the dotted. at this point instead of the joint command you could group with the group command.
