The Convert Polyline to superelevations command is designed for a conversion of a PLINE object to a superelevation line. You have to decide if the converted PLINE object will become the left or the right superelevation.
Run the command Convert Polyline to superelevation (31K4).
In the dialog box select the lane that will be converted. Choose the polyline in the longitudinal profile that represents the lane and press Enter. Repeat the same procedure to define the other lane.